In-situ polymerization type thermoplastic epoxy resin precursor mixture, epoxy resin composition, epoxy resin composition sheet, prepreg, and in-situ polymerization type thermoplastic fiber reinforced plastic using the same

Abstract

This invention provides an epoxy resin composition and its precursor mixture that yields in-situ polymerizable thermoplastic fiber-reinforced plastics with excellent heat resistance and can be produced by hot melt processing. A precursor mixture is used to obtain an in-situ polymerizable thermoplastic epoxy resin by addition polymerization of a difunctional epoxy resin and a difunctional phenolic compound. The precursor mixture is characterized by containing two or more difunctional phenolic compounds as essential components, with the total amount of difunctional phenolic compounds being 0.9 to 1.1 moles relative to 1 mole of the difunctional epoxy resin, and a viscosity of 1 Pa·s to 50 Pa·s at 60°C.

Description

Technical Field

[0001] This invention relates to in-situ polymerizable thermoplastic epoxy resins and thermoplastic fiber-reinforced plastics. Here, in-situ polymerizable thermoplastic resins refer to resins that are low molecular weight when shipped from the factory, but can be converted into high molecular weight thermoplastic resins by rapidly polymerizing them through hot melting (heating and melting) after being impregnated with reinforcing fibers at the fiber-reinforced thermoplastic (FRTP) manufacturing site. Background Technology

[0002] Thermoplastic resins are materials that become plastic 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. Combining them with materials that are difficult to heat and pressurize in confined spaces is not easy.

[0003] To address this issue, 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. According to this technology, since a low molecular weight resin is used, impregnation is easy, and thermoplastic fiber-reinforced plastics with fewer pores can be provided. However, on the other hand, it describes crystalline compounds that can be diluted to the point where crystallization does not occur. In the sole embodiment, an organic solvent of approximately 90 parts by weight relative to about 300 parts of the raw materials shown in Table 1 is used. Epoxy resins and phenolic compounds are also examples of crystalline compounds, but a technique to suppress crystallization while reducing the amount of organic solvent is desired.

[0004] Non-patent literature 1 discloses a method for controlling the glass transition temperature (Tg) of in-situ polymerizable thermoplastic epoxy resins by altering the backbone of the main chain according to the type of epoxy resin and phenolic compound. However, this involves materials whose backbone of the main chain is altered, and no further research has been conducted.

[0005] According to the research of the inventors, problems arise when using raw materials with low purity, such as no increase in molecular weight or gelation before on-site construction. Industrially, methods to improve purity include distillation or recrystallization; however, distillation suffers from the problem that increasing purity leads to a decrease in yield per unit time, and recrystallization requires high crystallinity. Therefore, when using highly crystalline phenolic compounds in a system with almost no solvent, it is difficult to achieve uniform dissolution and stable retention in epoxy resin. Since the phenolic compounds precipitate before the impregnation process with carbon fibers, the designed molar ratio cannot be achieved microscopically during impregnation. As a result, sometimes insufficient molecular weight is not achieved.

[0006] On the other hand, Patent Document 2 discloses a method for lowering the melting point of a crystalline adduct of bisphenol A and bisphenol TMC by heating and cooling a mixture of the two. Only the melting point of this bisphenol crystalline adduct is disclosed; there is no mention of its application in epoxy resins, particularly in-situ polymerized thermoplastic epoxy resins.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: WO2004 / 060981

[0010] Patent Document 2: Japanese Patent Application Publication No. 9-059196

[0011] Non-patent literature

[0012] Non-Patent Literature 1: Review of Recent Advances in Epoxy Resins I, pp. 422-430 (Epoxy Resin Technology Association) Summary of the Invention

[0013] The objective of this invention is to provide an epoxy resin composition and its precursor mixture that can produce in-situ polymerizable thermoplastic fiber-reinforced plastics with excellent heat resistance and can be produced by hot melt method, even without solvent or with a small amount of solvent.

[0014] In-depth research was conducted to address the aforementioned issues, and it was found that by melting two or more phenolic compounds, adding epoxy resin and rapidly cooling it, and then mixing a polymerization catalyst, a B-stage epoxy resin composition that undergoes virtually no polymerization reaction and does not require curing in subsequent processes can be provided. This results in the provision of an in-situ polymerized thermoplastic epoxy resin with excellent heat resistance.

[0015] That is, the present invention is a precursor mixture, characterized in that it is a precursor mixture for in-situ polymerizable thermoplastic epoxy resin obtained by addition polymerization of a difunctional epoxy resin and a difunctional phenolic compound.

[0016] It contains two or more difunctional phenolic compounds as essential components. The total amount of difunctional phenolic compounds is 0.9 to 1.1 moles relative to 1 mole of difunctional epoxy resin, and the viscosity at 60°C is 1 Pa·s to 50 Pa·s.

[0017] The precursor mixture described above is preferably solvent-free, or if it contains solvent, the solvent content is 10 parts by weight or less relative to 100 parts by weight of the total amount of the difunctional epoxy resin and the difunctional phenolic compound. The haze value in the thickness direction when the precursor mixture is prepared to a thickness of 2 mm is preferably less than 30%.

[0018] The two or more difunctional phenolic compounds mentioned above are preferably selected from bisphenol compounds and biphenol compounds, the ratio of the most abundant component among the two or more difunctional phenolic compounds is preferably 90% by weight or less, and at least one of the two or more difunctional phenolic compounds preferably has a melting point of 160°C or more. In addition, since it is necessary to melt the phenolic compounds at high temperature, the vapor pressure of the difunctional phenolic compounds at 25°C is preferably 0.01 Pa or less.

[0019] The present invention relates to an epoxy resin composition prepared by incorporating a polymerization catalyst into the aforementioned precursor mixture. Preferably, the epoxy resin composition uses 0.05 to 5.0% by weight of the polymerization catalyst relative to the total amount of the difunctional epoxy resin and the difunctional phenolic compound, without using a solvent, or using a solvent in an amount less than twice that of the polymerization catalyst, incorporating the polymerization catalyst into the precursor mixture.

[0020] When the above epoxy resin composition is made to a thickness of 2 mm, the haze value in the thickness direction is preferably less than 30%, and the viscosity at 60°C is preferably 3 Pa·s to 150 Pa·s.

[0021] The present invention relates to epoxy resin composition sheets with a thickness of 10 μm to 300 μm, which are made by forming the above epoxy resin composition.

[0022] The present invention relates to an in-situ polymerized thermoplastic epoxy resin formed by polymerizing the above-mentioned epoxy resin composition, or a sheet-like in-situ polymerized thermoplastic epoxy resin formed by polymerizing the above-mentioned epoxy resin composition into sheets.

[0023] The present invention is a prepreg obtained from the above-mentioned epoxy resin composition and / or the above-mentioned epoxy resin composition sheet and reinforcing fibers, which is an in-situ polymerized thermoplastic fiber-reinforced plastic obtained by polymerizing the prepreg.

[0024] The precursor mixture for in-situ polymerized thermoplastic epoxy resin of the present invention does not precipitate phenolic compounds even when cooled to room temperature after mixing. Therefore, even when impregnating carbon fibers, a large amount of organic solvent is not used, and specific components can be uniformly impregnated without being filtered out by the fibers, thereby obtaining epoxy resin compositions with stable polymerization quality. Detailed Implementation

[0025] The present invention will now be described in detail according to its preferred embodiments.

[0026] In-situ polymerizable thermoplastic epoxy resins are obtained by addition polymerization of difunctional epoxy resins and difunctional phenolic compounds. The precursor mixture (sometimes referred to as precursor) used in the in-situ polymerizable thermoplastic epoxy resins of the present invention contains two or more difunctional phenolic compounds as essential components.

[0027] A difunctional phenolic compound is a compound having two phenolic hydroxyl groups in one 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.

[0028] When monofunctional impurities are present, the mechanical properties of the resulting thermoplastic resin may deteriorate because the molecular weight does not increase after polymerization. Therefore, monofunctional impurities are preferably 2% by weight or less, compared to difunctional phenolic compounds.

[0029] In cases where impurities with three or more functionalities 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, compared to difunctional phenolic compounds, impurities with three or more functionalities are preferably 1% by weight or less.

[0030] It should be noted that if the amount of impurity components that do not have active groups that react with epoxy resins and phenolic hydroxyl groups, and which do not hinder the polymerization reaction as monomers, increases, the molecular weight of the polymerized product may also decrease. Therefore, it is preferable to have 2% or less by weight relative to difunctional phenolic compounds.

[0031] To improve the heat resistance of in-situ polymerized thermoplastic epoxy resins, a rigid structure is preferred. However, to achieve a rigid structure, the molecules themselves become larger, thus increasing the viscosity of the precursor mixture. For hot-melt processing, the viscosity of the precursor mixture at 60°C is preferably 1 Pa·s to 50 Pa·s. When the viscosity is less than 1 Pa·s, the resin component in the epoxy resin composition sheets and prepregs described later becomes too soft, thus reducing its processability near room temperature. Furthermore, when the viscosity exceeds 50 Pa·s, the processes of coating onto release paper, release film, and other substrates, as well as impregnating reinforcing fibers, require high temperatures, which can affect storage stability.

[0032] Therefore, the molecular weight of each of the two or more difunctional phenolic compounds is preferably 500 or less. Furthermore, the weight-average molecular weight (Mw) of the mixture of the two or more compounds is preferably 320 or less.

[0033] Two or more difunctional phenolic compounds are preferably selected from bisphenol compounds or biphenol compounds. Examples of bisphenol compounds include bisphenol A, bisphenol F (all manufactured by Nippon Steel Chemicals & Materials Co., Ltd.), bisphenol fluorene, biscresol fluorene (all 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 (all manufactured by Honshu Chemical Industry Co., Ltd.), bisphenol S, and tetramethylbisphenol S. Examples of biphenol compounds include biphenol, dimethylbiphenol, and tetramethylbiphenol. Other difunctional phenolic compounds include hydroquinone, methyl hydroquinone, butyl hydroquinone, resorcinol, methyl resorcinol, catechol, methyl catechol and other hydroquinones, naphthol and other naphthols.

[0034] Difunctional phenolic compounds are mixtures obtained by mixing two or more difunctional phenolic compounds as exemplified. By mixing two or more difunctional phenolic compounds, the precipitation of difunctional phenolic compounds during room temperature storage can be suppressed as an epoxy resin composition.

[0035] The content of the most abundant difunctional phenolic compound is preferably 90% by weight or less, more preferably 80% by weight or less, relative to the total amount of two or more difunctional phenolic compounds.

[0036] The melting point of at least one of the two or more difunctional phenolic compounds is preferably 160°C or higher, more preferably 200°C or higher. Furthermore, the melting point of all the difunctional phenolic compounds is preferably 150°C or higher.

[0037] The difunctional epoxy resin used in the epoxy resin composition of the present invention is a resin having two epoxy groups per molecule, and its purity is preferably 95% or higher. Furthermore, if the purity of the difunctional compound is high, it may also contain positional isomers or oligomers.

[0038] In the presence of monofunctional impurities, the mechanical properties of the resulting thermoplastic resin may deteriorate because the molecular weight does not increase after polymerization. Therefore, compared to difunctional epoxy resins, monofunctional impurities are preferably 2% by weight or less.

[0039] In the presence of trifunctional or higher impurities, cross-linking structures can easily form starting from these impurities, leading not only to increased polymer dispersion but also to the potential for gelation and impaired thermoplasticity. Therefore, compared to difunctional epoxy resins, trifunctional or higher impurities are preferably 1% by weight or less.

[0040] It should be noted that if the amount of impurity components that do not have active groups that react with epoxy resin and phenolic hydroxyl groups and do not hinder the polymerization reaction is increased, the molecular weight of the polymerized product may also decrease. Therefore, it is preferable to have an amount of 2% by weight or less relative to difunctional epoxy resins.

[0041] Examples of difunctional epoxy resins include, but are not limited to, 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, tetramethylbisphenol F type epoxy resin, bisphenol fluorene type epoxy resin, biscresol fluorene type epoxy resin, biphenol type epoxy resin, tetramethylbiphenyl type epoxy resin, diphenyldicyclopentadiene type epoxy resin, alkylene glycol type epoxy resin, dihydroxynaphthalene type epoxy resin, and dihydroxybenzene type epoxy resin.

[0042] Difunctional epoxy resins are preferably epoxy resins with an epoxy equivalent in the range of 150 to 350 g / eq.

[0043] In the precursor mixture of the present invention, the proportion of difunctional epoxy resin to difunctional phenolic compound is 0.9 to 1.1 moles of the total amount of difunctional phenolic compound relative to 1 mole of difunctional epoxy resin, preferably 0.95 to 1.05 moles, more preferably 0.96 to 1.04 moles, and even more preferably 0.97 to 1.03 moles. If the proportion of difunctional phenolic compound is within this range, the molecular weight of the resulting in-situ polymerized thermoplastic epoxy resin is sufficiently increased, and therefore preferred.

[0044] 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 the difunctional epoxy resin and the difunctional phenolic compound. More preferably, it is 5 parts by weight or less, and preferably, it is not present. Furthermore, when using an organic solvent, the boiling point of the organic solvent at 1 atmosphere is preferably 200°C or less.

[0045] The mixing conditions of the precursor mixture depend on the melting point of the difunctional phenolic compound used, but it is preferred to melt it below 200°C. Alternatively, the difunctional phenolic compound can be added to the difunctional epoxy resin while it is melted below 300°C, preferably below 200°C, and then rapidly cooled and mixed below 150°C.

[0046] Preferably, the precursor mixture is completely melted at a temperature below 200°C. In a bubble-free state, the precursor mixture is placed into a glass petri dish to a thickness of 2 mm. If the haze (turbidity) in the thickness direction is less than 30%, it is considered melted to a level that does not affect the polymerization reaction. More preferably, the haze value is less than 20%, and even more preferably less than 10%.

[0047] The viscosity of the precursor mixture at 60°C is 1 Pa·s to 50 Pa·s. When the viscosity is less than 1 Pa·s, the precursor mixture of the thermoplastic epoxy resin and subsequent materials become too soft, thus potentially worsening processability near room temperature. Furthermore, when the viscosity exceeds 50 Pa·s, workability may deteriorate when incorporating a polymerization catalyst in the next process, and storage stability may worsen due to the need for high-temperature processing. A more preferred viscosity is 3 Pa·s to 40 Pa·s, and more preferably 5 Pa·s to 30 Pa·s. It should be noted that the precursor mixture is in a viscous liquid or solid state at room temperature.

[0048] The weight-average molecular weight of the precursor mixture based on the standard polystyrene calibration line is preferably 300 to 500. More preferably, it is 300 to 450, and most preferably 300 to 400. By keeping the weight-average molecular weight within this range, it is easy to achieve a preferred viscosity range for the precursor mixture at 60°C.

[0049] The precursor mixture of the present invention is combined with a polymerization catalyst to prepare an epoxy resin composition. The polymerization catalyst used in the epoxy resin composition can be any known and conventional polymerization catalyst, but is preferably a phosphine compound. Specifically, examples include phosphorus-based polymerization catalysts such as triphenylphosphine, tri-p-toluylphosphine, tri-o-toluylphosphine, and tri-p-methoxyphenylphosphine. Other polymerization catalysts include imidazole compounds, specifically TBZ, 1B2MZ, and 1B2PZ. The polymerization catalyst is preferably 0.05% to 5.0% by weight relative to the total amount of the difunctional phenolic compound and the difunctional phenolic compound. More preferably, it is 3.0% by weight or less, further preferably 2.0% by weight or less, and particularly preferably 1.0% by weight or less. When the amount is less than 0.05% by weight, the in-situ polymerization process is time-consuming, thus potentially reducing productivity. Furthermore, the catalyst may become deactivated for some reason before reaching the target molecular weight. When the content exceeds 5.0% by weight, the curing reaction proceeds rapidly. On the other hand, it may impair storage stability and cause problems with process suitability. Since it is a component that participates in the reaction but is not incorporated into the backbone, it is not only likely to impair the physical properties after polymerization, but also economically disadvantageous due to its high cost.

[0050] The polymerization catalyst is dissolved in an organic solvent as needed and then added to the precursor mixture. The organic solvent used is not particularly limited as long as it does not hinder the reaction between the epoxy resin and the phenolic compound, but hydrocarbons, ketones, and ethers are preferred for ease of preparation. Specifically, examples include toluene, xylene, acetone, methyl ethyl ketone, isobutyl ketone, cyclopentanone, cyclohexanone, and diethylene glycol dimethyl ether. However, even if the organic solvent does not participate in the reaction, if it is included in large quantities in the in-situ polymerizable epoxy resin composition, the epoxy resin and phenolic compound will be diluted. Therefore, if the amount increases, the molecular weight after polymerization may decrease. Thus, the amount of organic solvent is preferably less than twice the amount of the polymerization catalyst. In other words, it is preferable to use a polymerization catalyst solution in which the polymerization catalyst, as the active ingredient, accounts for 33% by weight or more. It should be noted that if the polymerization catalyst can be uniformly mixed with the difunctional phenolic compound, the organic solvent may not be used.

[0051] The epoxy resin composition of the present invention can be stored at room temperature or under refrigeration. Similar to the precursor mixture, it is preferable that the haze value in the thickness direction when the epoxy resin composition is made to a thickness of 2 mm be less than 30%. The epoxy resin composition of the present invention does not necessarily contain a solvent; even if it does, it can be in small amounts, and crystallization can be suppressed by combining two or more difunctional phenolic compounds. The viscosity at 60°C is 3.0–150 Pa·s, preferably 4 Pa·s–100 Pa·s, and more preferably 5 Pa·s–80 Pa·s. When the viscosity is less than 3.0 Pa·s, the resin component in the epoxy resin composition sheet or prepreg described later becomes too soft, and therefore the processability near room temperature may deteriorate. Furthermore, when the viscosity exceeds 150 Pa·s, the storage stability may be affected because the coating process and the impregnation process with reinforcing fibers need to be carried out at high temperatures.

[0052] The in-situ polymerizable epoxy resin composition of the present invention refers to a composition containing two or more difunctional phenolic compounds, a difunctional epoxy resin, and a polymerization catalyst as essential components, and which can be polymerized by heating. Additives may be included. Examples of additives include fillers such as fumed silica, flame retardants such as aluminum hydroxide and red phosphorus, and modifiers such as core-shell rubber. From the viewpoint of stabilizing the polymerization reaction, additives different from the resin phase are preferred; however, within the range that does not affect the reaction, organic solvents, plasticizers, and compatible flame retardants may be included as solubilizers, viscosity adjusters, etc.

[0053] The epoxy resin composition sheet (sometimes referred to as the composition sheet) of the present invention is made by coating an epoxy resin composition onto a release-treated paper or plastic film, and may include a release-treated cover film as needed. Commonly known films can be used for the release paper, release plastic film, and cover film; there are no particular limitations. The thickness of the epoxy resin composition sheet is determined by the designed thickness of the prepreg and the resin ratio, but is typically 10 μm to 300 μm. If the thickness is less than 10 μm, the fiber mesh becomes noticeable if the reinforcing fibers are not smoothly unraveled; if the thickness exceeds 300 μm, it is difficult to uniformly impregnate the reinforcing fibers. Preferably, the thickness is 15 μm to 150 μm, more preferably 20 μm to 100 μm.

[0054] The reinforcing fibers used in this invention are carbon fibers, aramid fibers, cellulose fibers, or other fibers used to reinforce plastics, and are not particularly limited in type. Furthermore, the fiber morphology can include UD sheets, woven fabrics, tows, chopped fibers, nonwoven fabrics, paper, etc., formed by processing fibers, and is not particularly limited in type. However, from the viewpoint of impregnation, the thickness of each fiber bundle is 1 mm or less, preferably 0.5 mm or less, and more preferably 0.2 mm or less.

[0055] The prepreg of the present invention is obtained from epoxy resin composition and / or epoxy resin composition sheets and reinforcing fibers.

[0056] The ratio of reinforcing fiber to resin, by volume, is 2:8 to 7:3, preferably 5:5 to 7:3. When the ratio of reinforcing fiber is less than 2, the amount of reinforcing fiber decreases, which may not be sufficient to meet the strength requirements of the fiber-reinforced material. When it exceeds 7, there may be insufficient resin and more voids.

[0057] If voids remain during impregnation, they become defects in the final product and may prevent it from exhibiting the desired strength. Therefore, it is preferable to reduce voids during impregnation. Methods for this include heat treatment and pressure treatment.

[0058] Heat treatment is typically performed between 50°C and 100°C. Below 50°C, the resin viscosity cannot be sufficiently reduced, potentially resulting in poor impregnation. Above 100°C, polymerization may occur. The heat treatment time is typically 5 seconds to 3 minutes. Less than 5 seconds may result in insufficient viscosity reduction and impregnation, depending on the thickness. More than 3 minutes may lead to slight polymerization, potentially resulting in unsatisfactory viscosity.

[0059] As a method to further improve impregnation accuracy, hot pressing using hot presses, hot rollers, etc., can be cited. The pressure also depends on the substrate, but is between 0.01 MPa and 1 MPa. If the pressure is less than 0.01 MPa, impregnation may become insufficient, and if it exceeds 1 MPa, the reinforcing fibers may be damaged and the resin may flow out.

[0060] When using the in-situ polymerizable thermoplastic epoxy resin of the present invention, for example by polymerizing at a temperature of 150 to 200°C and a pressure of 0.1 MPa to 1.0 MPa, an in-situ polymerizable thermoplastic fiber-reinforced plastic can be obtained.

[0061] For the in-situ polymerized thermoplastic epoxy resin of the present invention, in the in-situ polymerized thermoplastic fiber-reinforced plastic, the weight-average molecular weight (Mw) is preferably 35,000 to 150,000, more preferably 50,000 to 100,000. The dispersion (polymer average molecular weight / number average molecular weight) is preferably 1 to 20, more preferably 2 to 15. When the dispersion exceeds 20, there is a tendency for easy gelation. It should be noted that the dispersion is not less than 1. In addition, the glass transition temperature (Tg) represents the physical properties at 100 to 130°C.

[0062] Example

[0063] The present invention will now be described in detail by way of examples, but the present invention is not limited to these examples in any way. Unless otherwise stated, “parts” means parts by weight and “%” means % by weight. It should be noted that the raw materials used in the following examples are as follows.

[0064] [Phenolic compounds]

[0065] A1: Bisphenol A (manufactured by Nippon Steel Chemicals & Materials Co., Ltd., molecular weight 228, melting point 158°C)

[0066] A2: 4,4'-(3,3,5-trimethylcyclohexyl)bisphenol (manufactured by Honshu Chemical Industry Co., Ltd., BisP-HTG, molecular weight 310, melting point 206℃)

[0067] A3: 9,9-Bis(4-hydroxy-3-methylphenyl)fluorene (manufactured by Osaka Gas Chemical Co., Ltd., molecular weight 378, melting point 217℃)

[0068] [Epoxy Resin]

[0069] B1: Bisphenol A type liquid epoxy resin (manufactured by Nippon Steel Chemicals & Materials Co., Ltd., YD-128, epoxy equivalent 188g / eq)

[0070] B2: Tetramethylbisphenol F type epoxy resin (YSLV-80XY: manufactured by Nippon Steel Chemical & Materials Co., Ltd., YSLV-80XY, epoxy equivalent 192g / eq)

[0071] B3: Tetramethylbiphenol type epoxy resin (manufactured by Mitsubishi Chemical Corporation, YX4000, epoxy equivalent 188g / eq)

[0072] [Polymerization catalyst]

[0073] C1: Tris(p-methoxyphenyl)phosphine (manufactured by Hokuko Chemical Industry Co., Ltd., TPAP)

[0074] [Reinforced Fibers]

[0075] I1: PAN-based carbon fiber (manufactured by Toray Industries, Inc., T700SC-12K-60E)

[0076] Example 1

[0077] 150 parts of A1 and 50 parts of A2 were added to a separable flask equipped with a stirrer, thermocouple, nitrogen inlet, and nitrogen outlet. Without using a solvent, the mixture was stirred while heating to a level that prevented powder from flying. A1 began to melt from near 150°C, and A2 melted and became homogeneous at 180°C. Then, 317 parts of B1 (at 40°C) were added and mixed, while the system was cooled. Further cooling to 50°C while stirring yielded a homogeneous liquid precursor mixture. The appearance of the resulting precursor mixture was evaluated, and the result was 0. The viscosity at 60°C was measured using a CV-1s instrument manufactured by Toa Kogyo Co., Ltd., and the result was 2 Pa·s.

[0078] 100 parts of the precursor mixture were measured, and 2 parts of a 50% C1 catalyst solution, pre-dissolved in cyclohexanone, were added and mixed to obtain an epoxy resin composition. The appearance of the obtained epoxy resin composition was evaluated, and the result was 0. The viscosity at 60°C was measured using an MCR102 (Anton Pareto Pharma Inc.), and the result was 5 Pa·s.

[0079] The appearance is evaluated visually. The presence of insoluble matter in the sample is evaluated as ×. The sample is taken into a petri dish with a thickness of 2 mm. If the haze value is 30% or more, it is evaluated as △. If the haze value is less than 30%, it is evaluated as 0.

[0080] Using a rod coater preheated at 80°C, the obtained epoxy resin composition was coated onto silicone-coated release paper to a thickness of 50 μm. A polyethylene cover film was then applied for protection, resulting in an epoxy resin composition sheet.

[0081] The peelability of the obtained epoxy resin composition sheet was evaluated, and the result was 0.

[0082] It should be noted that the peelability of the composition sheet is evaluated by checking for resin transfer to the cover film peeling off from the epoxy resin composition sheet at 23°C and 50% RH, as well as for defects such as cracks in the sheet itself. If there is no resin transfer or sheet defect, the peelability is rated as 0; if there is resin transfer or sheet defect, the peelability is rated as ×.

[0083] Next, the cover film is peeled off from the obtained epoxy resin composition sheet. On the peeled resin surface, carbon fibers (I1) are bonded at a linear density of 15 strands per 10 cm. Pressure is applied using a hot press preheated to 90°C with a surface pressure of 0.5 MPa. After 1 minute, the material is removed and air-cooled to obtain an epoxy resin prepreg with Rc = 33%.

[0084] The peelability of the obtained prepreg was evaluated, and the result was 0.

[0085] It should be noted that the peelability of the prepreg is evaluated by whether there is resin transfer to the release paper peeled from the prepreg at 23°C and 50% RH. If there is no resin transfer, the peelability is rated as 0; if there is resin transfer, the peelability is rated as ×.

[0086] In addition, the viscosity of the obtained prepreg was evaluated, and the result was 0.

[0087] It should be noted that tackiness is evaluated by assessing whether the prepregs can be peeled off without disturbing the fibers when gently overlapped at 23°C and 50% RH, and whether they exhibit adhesion that prevents them from detaching after gentle roller pressing. "Gentle overlap" refers to bonding using only the weight of the prepregs themselves, and "gentle roller pressing" refers to bonding the prepregs using a 500g roller. If the prepregs can be peeled off without disturbing the fibers when gently overlapped and exhibit adhesion that prevents them from detaching after gentle roller pressing, the tackiness is rated as 0. If the prepregs bond extremely firmly when gently overlapped, or if they do not bond even with gentle roller pressing, the tackiness is rated as ×.

[0088] The release paper of the prepreg is peeled off at 23°C and 50% RH. The prepreg is then laminated in a 4-layer configuration of 0 / 90 / 90 / 0, and the resulting laminate is polymerized at a pressing pressure of 0.5 MPa and 160°C for 1 hour to obtain a laminated board.

[0089] For the resulting laminate, the weight-average molecular weight (Mw) of the in-situ polymerized thermoplastic epoxy resin is 76,000. It should be noted that the method for determining Mw is as follows.

[0090] Analysis was performed using an HLC-8320GPC manufactured by Tosoh Corporation. A series of columns (TSKguardcolumn HXL, TSKgel GMHXL, TSKgel GMHXL, and TSKgel G2000HXL) were connected in series, and the column oven was set to 40°C. Tetrahydrofuran was used as the eluent, and an RI detector was employed. The flow rate was set to 1 mL / min for the sample side and 0.5 mL / min for the reference side. Approximately 0.1 g of the laminated plate was weighed and 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 weights were converted using standard polystyrene calibration lines, and dissolution time was corrected using cyclohexanone.

[0091] In addition, the glass transition temperature (Tg) of thermoplastic fiber-reinforced plastics is 100°C. It should be noted that the method for determining Tg is as follows.

[0092] According to JIS K 7121, the measurement was performed using a differential scanning calorimeter (manufactured by Hitachi High-Tech Science Company, EXSTAR6000 DSC6200) at a heating rate of 10 °C / min, and the result was expressed as the temperature of DSC·Tmg (the intermediate temperature of the variation curve relative to the tangent of the glass and rubber states).

[0093] Example 2

[0094] In the same apparatus as in Example 1, 100 parts of A1 and 100 parts of A2 were added, and the mixture was heated until it melted while stirring to prevent the powder from flying. A1 began to melt from an internal temperature exceeding 150°C, and A2 melted and became homogeneous at 190°C. Therefore, 295 parts of B1 at 40°C were added and mixed, while the system was cooled. Then, while stirring, the mixture was cooled to 50°C to obtain a homogeneous precursor mixture.

[0095] Using the obtained precursor mixture, the same procedures as in Example 1 were performed to obtain an epoxy resin composition, epoxy resin composition sheets, prepregs, and laminates. The determinations of the obtained laminates were performed in the same manner as in Example 1.

[0096] Example 3

[0097] In the same apparatus as in Example 1, 50 parts of A1 and 150 parts of A2 were added, and the mixture was heated until it melted while stirring to prevent the powder from flying. A1 began to melt from an internal temperature exceeding 150°C, and A2 melted and became homogeneous at 200°C. Therefore, 272 parts of B1 at 40°C were added and mixed, while the system was cooled. Then, while stirring, the mixture was cooled to 50°C to obtain a homogeneous precursor mixture.

[0098] Using the obtained precursor mixture, the same procedures as in Example 1 were performed to obtain an epoxy resin composition, epoxy resin composition sheets, prepregs, and laminates. The determinations of the obtained laminates were performed in the same manner as in Example 1.

[0099] Example 4

[0100] In the same apparatus as in Example 1, 100 parts of A1 and 100 parts of A2 were added, and the mixture was heated until it melted while stirring to prevent the powder from flying. A1 melted from an internal temperature exceeding 150°C, and A2 melted and became homogeneous at around 190°C. Therefore, 301 parts of room temperature B2 were added and mixed, while the system was cooled. Stirring was then continued to confirm the melting of B2, and the mixture was cooled to 50°C to obtain a homogeneous liquid precursor mixture.

[0101] Using the obtained precursor mixture, the same procedures as in Example 1 were performed to obtain an epoxy resin composition, epoxy resin composition sheets, prepregs, and laminates. The determinations of the obtained laminates were performed in the same manner as in Example 1.

[0102] Example 5

[0103] In the same apparatus as in Example 1, 100 parts of A1 and 100 parts of A2 were added, and the mixture was heated until it melted while stirring to prevent the powder from flying. A1 melted from an internal temperature exceeding 150°C, and A2 melted and became homogeneous at around 190°C. Therefore, 294 parts of room temperature B3 were added and mixed, while the system was cooled. Stirring was then continued to confirm the melting of B3, and the mixture was cooled to 50°C to obtain a homogeneous liquid precursor mixture.

[0104] Using the obtained precursor mixture, the same procedures as in Example 1 were performed to obtain an epoxy resin composition, epoxy resin composition sheets, prepregs, and laminates. The determinations of the obtained laminates were performed in the same manner as in Example 1.

[0105] Example 6

[0106] In the same apparatus as in Example 1, 150 parts of A1, 25 parts of A2, and 25 parts of A3 were added, and the mixture was heated until it melted while stirring to prevent the powder from flying. A1 melted from an internal temperature exceeding 150°C, and A2 and A3 melted and became homogeneous at around 190°C. Therefore, 69 parts of room temperature B1 and 228 parts of B3 were added and mixed, while the system was cooled. Stirring was then continued to confirm the melting of B1 and B3, and the mixture was cooled to 50°C to obtain a homogeneous liquid precursor mixture.

[0107] Using the obtained precursor mixture, the same procedures as in Example 1 were performed to obtain an epoxy resin composition, epoxy resin composition sheets, prepregs, and laminates. The determinations of the obtained laminates were performed in the same manner as in Example 1.

[0108] Comparative Example 1

[0109] In the same apparatus as in Example 1, 200 parts of Al were added and heated until the contents melted while stirring to prevent powder from flying. The Al melted from an internal temperature exceeding 155°C and became homogeneous at around 160°C. Therefore, 340 parts of B1 at 40°C were added and mixed, and the system was cooled. Initially, a homogeneous liquid mixture was obtained, but precipitation occurred during cooling to 50°C, resulting in a cloudy precursor mixture.

[0110] Using the obtained precursor mixture, the same procedures as in Example 1 were performed to obtain an epoxy resin composition, epoxy resin composition sheets, prepregs, and laminates. The determinations of the obtained laminates were performed in the same manner as in Example 1.

[0111] Comparative Example 2

[0112] In the same apparatus as in Example 1, 200 parts of A2 were added and heated while stirring to a level that prevented the powder from flying around. The temperature was raised to the point where the contents could be melted, but it did not melt even when the internal temperature reached 200°C. 250 parts of B1 at 40°C were then added and mixed while the system was cooled. Subsequently, a cloudy precursor mixture was obtained by cooling to 50°C while stirring.

[0113] Using the obtained precursor mixture, the same procedures as in Example 1 were performed to obtain an epoxy resin composition, epoxy resin composition sheets, prepregs, and laminates. The determinations of the obtained laminates were performed in the same manner as in Example 1.

[0114] [Table 1]

[0115]

[0116] In Example 1, by directly adding epoxy resin to a molten mixture of BPA (A1) and BisP-HTG (A2) and directly cooling the system, no crystallization occurred, and a homogeneous resin mixture was obtained. The same results were obtained in Examples 2 and 3, where the ratio of BPA to BisP-HTG was varied. As shown in Examples 4 and 5, it is evident that the same results are obtained even when the type of epoxy resin is changed.

[0117] In Comparative Example 1, which used elemental BPA, recrystallization and turbidity were observed upon cooling. While this was attributed to the slight residual seed crystals in the flask, no such phenomenon was observed in Examples 1 through 6, indicating that the quality of the molten state was stable by using a mixture of phenolic compounds. It should be noted that the recrystallization of BPA in the precursor mixture is thought to be affected by shear, but due to the instability of viscosity measurements at 60°C, the results could not be determined.

[0118] In Comparative Example 2, which used elemental BisP-HTG, the material did not melt even when heated to 200°C, nor did it melt even when epoxy resin was added. This laminate and resin board exhibited insufficient polymerization compared to other materials. The reason for this is likely that if a rigid phenolic compound with a high melting point is used alone, it will not melt even at the curing temperature, negatively impacting the polymerization reaction.

[0119] That is, by using phenolic compounds in combination, their melting temperature can be effectively reduced, and phenolic compounds with rigid molecular structures can be used as thermoplastic epoxy resin compositions.

[0120] In summary, even rigid phenolic compounds with high melting points can significantly reduce the use of organic solvents by melt-mixing them with other phenolic compounds, while simultaneously improving heat resistance when introduced into the skeleton of in-situ polymerizable thermoplastic epoxy resins. Furthermore, by using multiple phenolic compounds as a resin mixture, crystallization can be suppressed, thereby increasing the degree of polymerization of the laminate. Moreover, regarding epoxy resin composition sheets and prepregs, peelability and tackiness can be well adjusted in terms of productivity even after aging treatments are performed.

[0121] Industrial availability

[0122] The precursor mixture of the present invention can be used in epoxy resin compositions (sheets), and is particularly suitable for in-situ polymerized thermoplastic epoxy resins, prepregs and thermoplastic fiber-reinforced plastics.

Claims

1. A precursor mixture, characterized in that it is A precursor mixture for in-situ polymerizable thermoplastic epoxy resins obtained by addition polymerization of difunctional epoxy resins and difunctional phenolic compounds. The precursor mixture contains two or more difunctional phenolic compounds as essential components. The total amount of difunctional phenolic compounds is 0.9–1.1 moles relative to 1 mole of difunctional epoxy resin. The viscosity of the precursor mixture containing difunctional epoxy resin and difunctional phenolic compounds at 60°C is 1 Pa·s–50 Pa·s. The two or more difunctional phenolic compounds are selected from bisphenol compounds and biphenol compounds. At least one of the two or more difunctional phenolic compounds has a melting point of 160°C or higher. All difunctional phenolic compounds have a melting point above 150°C.

2. The precursor mixture according to claim 1, wherein, It contains no solvent, or if it contains solvent, the solvent content is less than 10 parts by weight relative to 100 parts by weight of the total amount of the difunctional epoxy resin and the difunctional phenolic compound.

3. The precursor mixture according to claim 1, wherein, When the thickness is 2mm, the haze value in the thickness direction is less than 30%.

4. The precursor mixture according to claim 1, wherein, The percentage of the most abundant component among the two or more difunctional phenolic compounds is less than 90% by weight.

5. An epoxy resin composition, which is formed by combining a polymerization catalyst in a precursor mixture according to any one of claims 1 to 4 and making them mutually compatible.

6. The epoxy resin composition according to claim 5, wherein, The polymerization catalyst is incorporated into the precursor mixture using 0.05 to 5.0% by weight of polymerization catalyst relative to the total amount of difunctional epoxy resin and difunctional phenolic compound, without solvent, or with a solvent amount less than twice that of polymerization catalyst.

7. The epoxy resin composition according to claim 5, wherein, When the thickness is 2mm, the haze value in the thickness direction is less than 30%.

8. The epoxy resin composition according to claim 5, wherein, The viscosity at 60℃ is 3 Pa·s to 150 Pa·s.

9. A thermoplastic epoxy resin, obtained by polymerizing the epoxy resin composition according to any one of claims 5 to 8.

10. An epoxy resin composition sheet, which is made by forming the epoxy resin composition according to any one of claims 5 to 8 into a thickness of 10 μm to 300 μm.

11. A sheet-like in-situ polymerizable thermoplastic epoxy resin, obtained by polymerizing the epoxy resin composition of claim 10 into sheets.

12. A prepreg obtained from an epoxy resin composition according to any one of claims 5 to 8 and / or an epoxy resin composition sheet according to claim 10 and reinforcing fibers.

13. An in-situ polymerized thermoplastic fiber-reinforced plastic obtained by polymerizing the prepreg as described in claim 12.

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