Precursor mixture for in situ polymerization thermoplastic epoxy resin, epoxy resin composition, epoxy resin composition sheet, prepreg, and in situ polymerization thermoplastic fiber reinforced plastic using these

Abstract

The present invention provides: an epoxy resin composition which has excellent heat resistance and enables the achievement of an in situ polymerization type thermoplastic fiber-reinforced plastic that is able to be produced by a hot melt process; and a precursor mixture of this epoxy resin composition.　A precursor mixture which is obtained by addition polymerization of a bifunctional epoxy resin and a bifunctional phenolic compound, and which is used for an in situ polymerization type thermoplastic epoxy resin. This precursor mixture is characterized in that: two or more kinds of bifunctional phenolic compounds are contained as essential components; the total of the bifunctional phenolic compounds relative to 1 mole of the bifunctional epoxy resin is from 0.9 to 1.1 moles; and the viscosity at 60°C is from 1 Pa·s to 50 Pa·s.

Description

[Technical Field]

[0001] The present invention relates to an in-situ polymerization type thermoplastic epoxy resin and a thermoplastic fiber-reinforced plastic (FRTP). Here, the in-situ polymerization type thermoplastic resin refers to a resin that has a low molecular weight when shipped from a factory, but can be rapidly polymerized by hot melting (heat melting) after impregnation into reinforcing fibers at the fiber-reinforced thermoplastic plastic (FRTP) manufacturing site to be converted into a high-molecular-weight thermoplastic resin. [Background technology]

[0002] Thermoplastic resins are materials that become plastic when heated and can be easily molded. However, thermoplastic resins generally have high molecular weights and high melt viscosities, so high temperatures and high pressures are required for molding. It is not easy to compound them in narrow spaces or with materials that are difficult to heat or pressurize.

[0003] To address this issue, Patent Document 1 proposes a method for producing in-situ polymerization thermoplastic epoxy resins using a difunctional epoxy resin and a difunctional curing agent. This technology uses a low-molecular-weight resin, which allows for easy impregnation and produces thermoplastic fiber-reinforced plastics with few voids. However, it also describes that crystalline compounds can be diluted to a degree that prevents crystallization, and in the only example, as shown in Table 1, as much as 90 parts of organic solvent is used for approximately 300 parts by weight of the raw materials used. While examples of crystalline epoxy resins and phenolic compounds are given, there is a need for a technology that can reduce the amount of organic solvent used while suppressing crystallization.

[0004] Non-Patent Document 1 discloses that the glass transition temperature (Tg) of a polymerized in-situ polymerized thermoplastic epoxy resin can be controlled by changing the main chain structure depending on the type of epoxy resin or phenolic compound. However, no further discussion is given here regarding materials with modified main chain structures. According to the inventors' research, using raw materials with low purity results in problems such as insufficient molecular weight or gelation occurring before on-site application. While distillation and recrystallization are industrially used to increase purity, the higher the purity, the lower the yield per hour. Recrystallization requires relatively high crystallinity. Therefore, when using highly crystalline phenolic compounds in a system containing almost no solvent, it is difficult to uniformly dissolve and stably maintain them in the epoxy resin. Because the phenolic compound precipitates before the carbon fiber impregnation process, the designed molar ratio cannot be microscopically achieved during impregnation. As a result, there is a problem that a sufficient molecular weight cannot be achieved.

[0005] On the other hand, Patent Document 2 discloses a method for producing a crystalline adduct of bisphenol A and bisphenol TMC, in which the melting point is lowered by heating and cooling a mixture of the two. This crystalline bisphenol adduct is only disclosed in terms of its melting point, and there is no mention whatsoever of its application to epoxy resins, particularly in-situ polymerized thermoplastic epoxy resins. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] WO2004 / 060981 [Patent Document 2] Japanese Patent Application Publication No. 9-059196 [Non-patent literature]

[0007] [Non-Patent Document 1] Review of Epoxy Resins: Recent Advances I, p422-p430 (Epoxy Resin Technology Association) Summary of the Invention

[0008] An object of the present invention is to provide an epoxy resin composition and a precursor mixture thereof from which an in situ polymerization type thermoplastic fiber reinforced plastic having excellent heat resistance and capable of being produced by a hot melt method can be obtained even in the absence of a solvent or in the presence of a small amount of solvent.

[0009] As a result of extensive investigations to solve the above problems, it has been found that by melting two or more types of phenolic compounds, adding an epoxy resin, rapidly cooling the mixture, and then mixing in a polymerization catalyst, it is possible to provide a B-stage epoxy resin composition that does not require curing in a subsequent step, with substantially no polymerization reaction proceeding, and further to provide an in situ polymerization type thermoplastic epoxy resin that has excellent heat resistance.

[0010] That is, the present invention provides a precursor mixture for use in an in-situ polymerization type thermoplastic epoxy resin obtained by addition polymerization of a difunctional epoxy resin and a difunctional phenol compound, comprising: The precursor mixture is characterized by containing two or more bifunctional phenolic compounds as essential components, the total amount of the bifunctional phenolic compounds being 0.9 to 1.1 moles per mole of the bifunctional epoxy resin, and having a viscosity of 1 Pa·s or more and 50 Pa·s or less at 60°C.

[0011] The precursor mixture preferably does not contain a solvent, or if it does contain a solvent, the amount of the solvent is preferably 10 parts by weight or less per 100 parts by weight of the total amount of the bifunctional epoxy resin and the bifunctional phenol compound. When the precursor mixture is made to a thickness of 2 mm, the haze value in the thickness direction is preferably less than 30%.

[0012] The two or more bifunctional phenol compounds are preferably selected from the group consisting of bisphenol compounds and biphenol compounds, the proportion of the component with the largest amount in the two or more bifunctional phenol compounds is preferably 90% by weight or less, and at least one of the two or more bifunctional phenol compounds preferably has a melting point of 160° C. or higher. In addition, since the phenol compounds need to be melted at high temperatures, the vapor pressure of the bifunctional phenol compound is preferably 0.01 Pa or less at 25° C.

[0013] The present invention provides an epoxy resin composition obtained by blending a polymerization catalyst with the precursor mixture. The epoxy resin composition preferably uses 0.05 to 5.0% by weight of the polymerization catalyst relative to the total weight of the bifunctional epoxy resin and the bifunctional phenol compound, and blends the polymerization catalyst with the precursor mixture without using a solvent or using a solvent in an amount twice or less relative to the amount of the polymerization catalyst.

[0014] When the 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 or more and 150 Pa·s or less.

[0015] The present invention is an epoxy resin composition sheet obtained by forming the epoxy resin composition into a thickness of 10 μm or more and 300 μm or less.

[0016] The present invention relates to an in situ polymerization type thermoplastic epoxy resin obtained by polymerizing the above-mentioned epoxy resin composition, or to a sheet-like in situ polymerization type thermoplastic epoxy resin obtained by polymerizing the above-mentioned epoxy resin composition sheet.

[0017] The present invention relates to a prepreg obtained from the epoxy resin composition and / or the epoxy resin composition sheet and reinforcing fibers, and to an in-situ polymerization type thermoplastic fiber reinforced plastic obtained by polymerizing the prepreg.

[0018] The precursor mixture for an in situ polymerized thermoplastic epoxy resin of the present invention does not precipitate phenol compound crystals even when cooled to room temperature after mixing. Therefore, even when a large amount of organic solvent is not used for impregnating carbon fibers, specific components can be uniformly impregnated into the fibers without being filtered out, thereby making it possible to obtain an epoxy resin composition with stable polymerization quality. DETAILED DESCRIPTION OF THE INVENTION

[0019] The present invention will be described in detail below based on preferred embodiments thereof. The in situ polymerization type thermoplastic epoxy resin is obtained by addition polymerization of a bifunctional epoxy resin and a bifunctional phenol compound, and the precursor mixture (sometimes referred to as a precursor) used for the in situ polymerization type thermoplastic epoxy resin of the present invention contains two or more types of bifunctional phenol compounds as essential components. The bifunctional phenolic compound is a compound having two phenolic hydroxyl groups in one molecule, and preferably has a purity of 95% by weight or more. If the purity as a bifunctional compound is high, positional isomers may be contained. If monofunctional impurities are contained, the molecular weight after polymerization will not increase, which may result in poor mechanical properties of the produced thermoplastic resin. Therefore, it is preferable that the amount of monofunctional impurities is 2% by weight or less relative to the bifunctional phenol compound. If trifunctional or higher impurities are contained, the impurities tend to form crosslinked structures as starting points, which may increase the dispersion of the polymer and may cause gelation, resulting in loss of thermoplasticity. Therefore, the amount of trifunctional or higher impurities is preferably 1% by weight or less relative to the bifunctional phenol compound. Furthermore, even if an impurity component does not have an active group that reacts with either the epoxy resin or the phenolic hydroxyl group and does not inhibit the polymerization reaction by itself, if the amount is large, the molecular weight after polymerization may become small. Therefore, it is preferable that the amount of such an impurity component is 2% by weight or less relative to the bifunctional phenol compound.

[0020] To enhance the heat resistance of in-situ polymerization thermoplastic epoxy resins, it is desirable to adopt a rigid structure. However, this requires larger molecules, which increases the viscosity of the precursor mixture. For handling using the hot-melt method, the viscosity of the precursor mixture at 60°C should preferably be between 1 and 50 Pa·s. If the viscosity is less than 1 Pa·s, the resin components in the epoxy resin composition sheets and prepregs described below become too soft, resulting in poor handling at room temperature. Furthermore, if the viscosity exceeds 50 Pa·s, high temperatures are required for the application to substrates such as release paper and film, and for the impregnation of reinforcing fibers, which can affect storage stability. Therefore, it is preferable that the molecular weights of the two or more bifunctional phenol compounds are all not more than 500. In addition, it is preferable that the weight average molecular weight (Mw) of the mixture of two or more compounds is not more than 320.

[0021] The two or more bifunctional phenol compounds are preferably selected from bisphenol compounds or biphenol compounds. Examples of bisphenol compounds include bisphenol A, bisphenol F (manufactured by Nippon Steel Chemical & Material Co., Ltd.), bisphenol fluorene, biscresol fluorene (manufactured by Osaka Gas Chemicals 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.), bisphenol S, and tetramethylbisphenol S. Examples of biphenol compounds include biphenol, dimethylbiphenol, and tetramethylbiphenol. Other examples of bifunctional phenol compounds include benzenediols such as hydroquinone, methylhydroquinone, dibutylhydroquinone, resorcinol, methylresorcinol, catechol, and methylcatechol, and naphthalenediols such as naphthalenediol.

[0022] The bifunctional phenol compound is a mixture of two or more of the exemplified bifunctional phenol compounds. By mixing two or more bifunctional phenol compounds, the epoxy resin composition can be prevented from precipitating during storage at room temperature.

[0023] The content of the largest bifunctional phenol compound relative to the total amount of two or more bifunctional phenol compounds is preferably 90% by weight or less, more preferably 80% by weight or less. Of the two or more bifunctional phenol compounds, at least one bifunctional phenol compound preferably has a melting point of 160° C. or higher, more preferably 200° C. or higher. It is also desirable that all of the bifunctional phenol compounds have melting points of 150° C. or higher.

[0024] The bifunctional epoxy resin used in the epoxy resin composition of the present invention is a resin having two epoxy groups in one molecule, and its purity is preferably 95% or more. If the purity as a bifunctional compound is high, positional isomers and oligomers may be contained. If monofunctional impurities are present, the molecular weight will not increase after polymerization, which may result in poor mechanical properties of the produced thermoplastic resin. Therefore, it is preferable that the monofunctional impurities be 2% by weight or less relative to the difunctional epoxy resin. If trifunctional or higher impurities are present, the impurities tend to form crosslinked structures as starting points, which may lead to increased dispersion of the polymer and gelation, impairing thermoplasticity. Therefore, it is preferable that the amount of trifunctional or higher impurities is 1% by weight or less relative to the bifunctional epoxy resin. Furthermore, even if there are impurity components that do not have active groups that react with either the epoxy resin or the phenolic hydroxyl group and that do not inhibit the polymerization reaction by themselves, if the amount is large, the molecular weight after polymerization may become small. Therefore, it is preferable that the amount of such impurity components is 2% by weight or less relative to the bifunctional epoxy resin.

[0025] Examples of bifunctional epoxy resins include bisphenol-type epoxy resins such as bisphenol A-type epoxy resins, bisphenol F-type epoxy resins, bisphenol S-type epoxy resins, bisphenolacetophenone-type epoxy resins, diphenyl sulfide-type epoxy resins, diphenyl ether-type epoxy resins, tetramethylbisphenol F-type epoxy resins, bisphenol fluorene-type epoxy resins, and biscresol fluorene-type epoxy resins; biphenol-type epoxy resins such as tetramethylbiphenol-type epoxy resins; diphenyldicyclopentadiene-type epoxy resins; alkylene glycol-type epoxy resins; dihydroxynaphthalene-type epoxy resins; and dihydroxybenzene-type epoxy resins, but are not limited to these. The difunctional epoxy resin that can be suitably used has an epoxy equivalent weight in the range of 150 to 350 g / eq.

[0026] In the precursor mixture of the present invention, the blending ratio of the bifunctional epoxy resin and the bifunctional phenol compound is 0.9 to 1.1 moles, 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, of the total bifunctional phenol compound per mole of the bifunctional epoxy resin. If the blending ratio of the bifunctional phenol compound is within this range, the molecular weight of the resulting in-situ polymerized thermoplastic epoxy resin is sufficiently elongated, which is preferable.

[0027] The organic solvent is not an essential component of the precursor mixture. It is preferable that the amount of the organic solvent is 10 parts by weight or less, based on 100 parts by weight of the total amount of the bifunctional epoxy resin and the bifunctional phenol compound. It is more preferable that the amount of the organic solvent is 5 parts by weight or less, and it is desirable that the organic solvent is not contained at all. Furthermore, when an organic solvent is used, it is preferable that the boiling point of the organic solvent at 1 atmosphere is 200°C or less.

[0028] The mixing conditions for the precursor mixture depend on the melting point of the bifunctional phenol compound used, but it is preferable to melt the compound at 200° C. or less. Alternatively, the bifunctional phenol compound may be melted in advance at 300° C. or less, preferably 200° C. or less, and then the bifunctional epoxy resin is added, followed by rapid cooling and mixing at 150° C. or less.

[0029] It is desirable that the precursor mixture be completely melted at a temperature of 200°C or less. The precursor mixture is placed in a glass petri dish to a thickness of 2 mm without any bubbles, and if the haze value (turbidity) in the thickness direction is less than 30%, it is determined to have melted to a level that does not affect the polymerization reaction. The haze value is more preferably less than 20%, and even more preferably less than 10%.

[0030] The viscosity of the precursor mixture at 60°C is 1 Pa·s or more and 50 Pa·s or less. If the viscosity is less than 1 Pa·s, the thermoplastic epoxy resin precursor mixture and subsequent materials will be too soft, which may result in poor handling at around room temperature. Furthermore, if the viscosity exceeds 50 Pa·s, this may result in poor workability when blending the polymerization catalyst in the next step, or in poor storage stability due to the need for high-temperature processing. A more preferable viscosity is 3 Pa·s or more and 40 Pa·s or less, and preferably 5 Pa·s or more and 30 Pa·s or less. The precursor mixture is in a viscous liquid or solid state at room temperature.

[0031] The weight-average molecular weight of the precursor mixture, as determined by a standard polystyrene calibration curve, is preferably 300 to 500. A more preferred weight-average molecular weight is 300 to 450, and more preferably 300 to 400. By keeping the weight-average molecular weight within this range, it is easy to keep the viscosity of the precursor mixture at 60°C within a preferred range.

[0032] The precursor mixture of the present invention is blended with a polymerization catalyst to form an epoxy resin composition. While known and conventional polymerization catalysts can be used in the epoxy resin composition, phosphine compounds are preferred. Specific examples include phosphorus-based polymerization catalysts such as triphenylphosphine, tris-para-toluylphosphine, tris-ortho-toluylphosphine, and tris-para-methoxyphenylphosphine. Other polymerization catalysts include imidazole compounds, such as TBZ, 1B2MZ, and 1B2PZ. The polymerization catalyst is preferably present in an amount of 0.05% to 5.0% by weight based on the total weight of the bifunctional phenol compound and the bifunctional phenol compound. It is more preferably present in an amount of 3.0% by weight or less, even more preferably present in an amount of 2.0% by weight or less, and particularly preferably present in an amount of 1.0% by weight or less. If the amount is less than 0.05% by weight, in-situ polymerization may take a long time, resulting in reduced productivity, and the catalyst may be deactivated for some reason before the target molecular weight is reached. If the content exceeds 5.0% by weight, the curing reaction will proceed rapidly, but storage stability will be impaired, which may cause problems with process compatibility. In addition, since this component is involved in the reaction but not incorporated into the skeleton, there is a risk of impairing the physical properties after polymerization. In addition, it is simply expensive, which is economically disadvantageous.

[0033] 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 inhibit the reaction between the epoxy resin and the phenolic compound. However, hydrocarbons, ketones, and ethers are preferred due to their availability. Specific examples include toluene, xylene, acetone, methyl ethyl ketone, isobutyl ketone, cyclopentanone, cyclohexanone, and diethylene glycol dimethyl ether. However, even if the organic solvent is not involved in the reaction, if it is present in a large amount in an in-situ polymerization epoxy resin composition, it dilutes the epoxy resin and phenolic compound. Therefore, if the amount is too large, the molecular weight after polymerization may decrease. Therefore, the amount of organic solvent is preferably no more than twice the amount of the polymerization catalyst. In other words, it is preferable to use a polymerization catalyst solution containing 33% by weight or more of the polymerization catalyst as an active ingredient. Note that if the polymerization catalyst can be uniformly mixed with the bifunctional phenolic compound, an organic solvent may not be used.

[0034] The epoxy resin composition of the present invention can be stored at room temperature or refrigerated. As with the precursor mixture, the haze value in the thickness direction of the epoxy resin composition when made to a thickness of 2 mm is preferably less than 30%. The epoxy resin composition of the present invention does not necessarily contain a solvent; even if it does, a small amount may be used. Crystallization can be suppressed by blending two or more bifunctional phenolic compounds. The viscosity at 60°C is 3.0 to 150 Pa·s, preferably 4 to 100 Pa·s, and more preferably 5 to 80 Pa·s. If the viscosity is less than 3.0 Pa·s, the resin components in the epoxy resin composition sheet or prepreg described below may become too soft, potentially resulting in poor handleability at around room temperature. Furthermore, if the viscosity exceeds 150 Pa·s, high temperatures are required for the film coating process and the reinforcing fiber impregnation process, which may affect storage stability.

[0035] The in-situ polymerization epoxy resin composition of the present invention is a composition that contains two or more bifunctional phenolic compounds, a bifunctional epoxy resin, and a polymerization catalyst as essential components and can be polymerized by heating. It may also contain additives. 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. To stabilize the polymerization reaction, it is desirable to use additives that are different from the resin phase. However, to the extent that they do not affect the reaction, organic solvents, plasticizers, and compatible flame retardants may be included as dissolution aids or viscosity adjusters.

[0036] The epoxy resin composition sheet of the present invention (sometimes referred to as a composition sheet) is prepared by coating an epoxy resin composition on release-treated paper or plastic film, and optionally providing a release-treated cover film. Known and commonly used release paper, release plastic film, and cover film can be used, and are not particularly limited. The thickness of the epoxy resin composition sheet is determined by the design thickness and resin ratio of the prepreg, but is typically 10 μm or more and 300 μm or less. If the thickness is less than 10 μm, the fiber mesh will become noticeable unless the reinforcing fibers are properly defibrated. If the thickness exceeds 300 μm, it will be difficult to uniformly impregnate the reinforcing fibers. The thickness is preferably 15 μm or more and 150 μm or less, and more preferably 20 μm or more and 100 μm or less.

[0037] The reinforcing fibers used in the present invention are intended to reinforce plastics, and are not particularly limited, including carbon fibers, aramid fibers, and cellulose fibers. The fiber form is also not particularly limited, and examples include UD sheets, woven fabrics, tows, chopped fibers, nonwoven fabrics, and paper. 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.

[0038] The prepreg of the present invention is obtained from an epoxy resin composition and / or an epoxy resin composition sheet and reinforcing fibers. The volume ratio of reinforcing fiber to resin is 2:8 to 7:3, and preferably 5:5 to 7:3. If the reinforcing fiber ratio is less than 2, the amount of reinforcing fiber is so small that the strength required of the fiber-reinforced material may not be fully achieved. If it exceeds 7, there is a risk that the resin will be insufficient, resulting in an increase in voids. If voids remain during impregnation, they may become defects in the final product and may not achieve the desired strength, so it is desirable to reduce voids during impregnation. This can be achieved by heat treatment or pressure treatment. Heat treatment is generally carried out at a temperature of 50°C or higher and 100°C or lower. If the temperature is lower than 50°C, the viscosity of the resin cannot be sufficiently reduced, which may result in poor impregnation. If the temperature exceeds 100°C, a polymerization reaction may occur. The heat treatment time is usually between 5 seconds and 3 minutes. If the heat treatment time is less than 5 seconds, the viscosity may not be sufficiently reduced and impregnation may not proceed properly depending on the thickness. If the heat treatment time exceeds 3 minutes, the polymerization reaction may proceed slightly, which may result in the desired tackiness not being achieved. One way to further improve impregnation accuracy is to use thermocompression bonding with a heat press or heated roll. The pressure depends on the base material, but is between 0.01 MPa and 1 MPa. If the pressure is less than 0.01 MPa, impregnation may be insufficient, and if it exceeds 1 MPa, the reinforcing fibers may be damaged or the resin may leak out.

[0039] When the in-situ polymerization type thermoplastic epoxy resin of the present invention is used, for example, by polymerizing it under conditions of a temperature of 150 to 200°C and a pressure of 0.1 MPa or more and 1.0 MPa or less, an in-situ polymerization type thermoplastic fiber reinforced plastic can be obtained. The in situ polymerization type thermoplastic epoxy resin of the present invention preferably has a weight average molecular weight (Mw) of 35,000 to 150,000, more preferably 50,000 to 100,000, in the in situ polymerization type thermoplastic fiber reinforced plastic. The dispersion (weight average molecular weight / number average molecular weight) is preferably 1 or more and 20 or less, more preferably 2 or more and 15 or less. When the dispersion exceeds 20, gelation tends to occur easily. However, the dispersion is never less than 1. The glass transition temperature (Tg) exhibits physical properties of 100 to 130°C. [Example]

[0040] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, "parts" means parts by weight, and "%" means % by weight. The raw materials used in the following examples are as follows.

[0041] [Phenol compounds] A1: Bisphenol A (Nippon Steel Chemical & Material Co., Ltd., molecular weight 228, melting point 158°C) A2: 4,4'-(3,3,5-trimethylcyclohexylidene)bisphenol (Honshu Chemical Industry Co., Ltd., BisP-HTG, molecular weight 310, melting point 206°C) A3: 9,9-bis(4-hydroxy-3-methylphenyl)fluorene (Osaka Gas Chemicals Co., Ltd., molecular weight 378, melting point 217°C)

[0042] [Epoxy resin] B1: Bisphenol A liquid epoxy resin (Nippon Steel Chemical & Material Co., Ltd., YD-128, epoxy equivalent 188g / eq) B2: Tetramethylbisphenol F type epoxy resin (YSLV-80XY: Nippon Steel Chemical & Material Co., Ltd., YSLV-80XY, epoxy equivalent 192 g / eq) B3: Tetramethylbiphenol type epoxy resin (Mitsubishi Chemical Corporation, YX4000, epoxy equivalent 188g / eq)

[0043] [Polymerization catalyst] C1: Tris(paramethoxyphenyl)phosphine (TPAP, manufactured by Hokko Chemical Industry Co., Ltd.)

[0044] [Reinforced fiber] I1: PAN-based carbon fiber (Toray Industries, Inc., T700SC-12K-60E)

[0045] Example 1 A separable flask equipped with a stirrer, thermocouple, nitrogen inlet, and nitrogen outlet was charged with 150 parts of A1 and 50 parts of A2. The mixture was heated without solvent, stirring to a temperature sufficient to prevent powder from flying around. A1 began to melt when the internal temperature exceeded 150°C. At 180°C, A2 melted and became homogeneous. 317 parts of B1 (40°C) were added and mixed while the system was cooled. The mixture was further cooled to 50°C with stirring, yielding a homogeneous liquid precursor mixture. The appearance of the resulting precursor mixture was evaluated as good, and its viscosity at 60°C was measured using a CV-1s (Toa Kogyo Co., Ltd.) and found to be 2 Pa·s. 100 parts of the precursor mixture was weighed out, and 2 parts of a 50% C1 catalyst solution that had been dissolved in cyclohexanone was added and mixed to obtain an epoxy resin composition. The appearance of the obtained epoxy resin composition was evaluated as good, and its viscosity at 60°C was measured using an Anton Paar MCR102 and found to be 5 Pa·s. The appearance was evaluated visually. If insoluble matter precipitated in the sample, it was marked with an X. The sample was placed in a petri dish to a thickness of 2 mm, and if the haze value was 30% or more, it was marked with a △, and if the haze value was less than 30%, it was marked with an ◯.

[0046] The obtained epoxy resin composition was applied to a thickness of 50 μm onto a silicone-coated release paper using a bar coater preheated to 80° C. A polyethylene cover film was then placed on top to protect the paper, thereby obtaining an epoxy resin composition sheet. The peelability of the obtained epoxy resin composition sheet was evaluated and rated as good. The releasability of the composition sheet was evaluated under conditions of 23°C x 50% RH based on the presence or absence of resin transfer to the cover film peeled from the epoxy resin composition sheet and the presence or absence of defects in the sheet itself, such as cracks. If there was no resin transfer or sheet defects, the releasability was evaluated as ◯, and if there was resin transfer or sheet defects, the releasability was evaluated as ×.

[0047] Next, the cover film was peeled off from the obtained epoxy resin composition sheet, and carbon fiber (I1) was attached to the peeled resin surface so as to give a strand density of 15 strands per 10 cm. Pressure was applied using a hot press preheated to 90°C so that the surface pressure became 0.5 MPa, and after 1 minute the sheet was removed and air-cooled to obtain an epoxy resin prepreg with Rc=33%. The peelability of the obtained prepreg was evaluated and rated as good. The prepreg releasability was evaluated based on whether or not there was any transfer of resin to the release paper peeled from the prepreg at 23°C and 50% RH. If there was no transfer of resin, the releasability was evaluated as ◯, and if there was transfer of resin, the releasability was evaluated as ×. The tackiness of the obtained prepreg was evaluated and rated as good. Tackiness was evaluated by determining whether prepregs could be peeled off without disturbing the fibers when lightly overlapped at 23°C and 50% RH, and whether they exhibited adhesive strength that prevented separation after lightly pressing with a roller. "Lightly overlapped" refers to adhesion using only the weight of the prepregs, while "lightly pressed with a roller" refers to adhesion using a 500g roller. Tackiness was evaluated as "good" when the prepregs were peeled off without disturbing the fibers when lightly overlapped, and exhibited adhesive strength that prevented separation after lightly pressing with a roller. Tackiness was evaluated as "poor" when the adhesive strength was too strong even when lightly overlapped, or when the adhesive strength did not increase even when lightly pressed with a roller.

[0048] The release paper was peeled off from the prepreg at 23°C and 50% RH. Four layers of prepreg were laminated in a 0 / 90 / 90 / 0 ratio, and the resulting laminate was polymerized at a pressure of 0.5 MPa and 160°C for 1 hour to obtain a laminate. The weight average molecular weight (Mw) of the in-situ polymerization type thermoplastic epoxy resin in the obtained laminate was 76000. The method for measuring Mw is as follows. Analysis was performed using a Tosoh Corporation HLC-8320 GPC. The columns consisted of a TSKguardcolumn HXL, a TSKgel GMHXL, a TSKgel GMHXL, and a TSKgel G2000HXL connected in series, and the column oven was set to 40°C. The eluent was tetrahydrofuran, and the detector was an RI detector. The flow rates were 1 mL / min on the sample side and 0.5 mL / min on the reference side. Approximately 0.1 g of laminate 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 subjected to analysis. Molecular weights were calculated using a standard polystyrene calibration curve, and elution times were corrected using cyclohexanone. The glass transition temperature (Tg) of the thermoplastic fiber reinforced plastic was 100° C. The method for measuring Tg is as follows. In accordance with JIS K 7121, measurements were performed using a differential scanning calorimeter (Hitachi High-Tech Science Corporation, EXSTAR6000 DSC6200) at a temperature increase rate of 10°C / min, and the temperature was expressed as DSC Tmg (the midpoint temperature of the transition curve between the tangent line between the glassy state and the rubbery state).

[0049] Example 2 100 parts of A1 and 100 parts of A2 were charged into an apparatus similar to that used in Example 1, and the contents were heated to melt while stirring to prevent powder from flying around. A1 began to melt when the internal temperature exceeded 150°C, and A2 melted and became homogeneous at 190°C. 295 parts of B1 at 40°C were added and mixed while the system was cooled. The mixture was further cooled to 50°C while stirring, yielding a homogeneous precursor mixture. Using the obtained precursor mixture, an epoxy resin composition, an epoxy resin composition sheet, a prepreg, and a laminate were obtained in the same manner as in Example 1. The obtained laminate was measured in the same manner as in Example 1.

[0050] Example 3 50 parts of A1 and 150 parts of A2 were charged into an apparatus similar to that used in Example 1, and the contents were heated to melt while stirring to prevent powder from flying around. A1 began to melt when the internal temperature exceeded 150°C, and A2 melted and became homogeneous at 200°C. 272 ​​parts of B1 at 40°C were added and mixed while the system was cooled. The mixture was further cooled to 50°C while stirring, yielding a homogeneous precursor mixture. Using the obtained precursor mixture, an epoxy resin composition, an epoxy resin composition sheet, a prepreg, and a laminate were obtained in the same manner as in Example 1. The obtained laminate was measured in the same manner as in Example 1.

[0051] Example 4 100 parts of A1 and 100 parts of A2 were charged into an apparatus similar to that used in Example 1, and the contents were heated to melt while stirring to a degree that prevented powder from flying around. A1 began to melt when the internal temperature exceeded 150°C, and A2 melted and became homogeneous at around 190°C. 301 parts of B2 at room temperature were then added and mixed, and the system was cooled. Further stirring was continued to confirm that B2 had melted, and the system was cooled to 50°C, yielding a homogeneous liquid precursor mixture. Using the obtained precursor mixture, an epoxy resin composition, an epoxy resin composition sheet, a prepreg, and a laminate were obtained in the same manner as in Example 1. The obtained laminate was measured in the same manner as in Example 1.

[0052] Example 5 100 parts of A1 and 100 parts of A2 were charged into an apparatus similar to that used in Example 1, and the contents were heated to melt while stirring to prevent powder from flying around. A1 began to melt when the internal temperature exceeded 150°C, and A2 melted and became homogeneous at around 190°C. 294 parts of B3 (room temperature) were then added and mixed while the system was cooled. Further stirring was continued to confirm that B3 had melted, and the system was cooled to 50°C, yielding a homogeneous liquid precursor mixture. Using the obtained precursor mixture, an epoxy resin composition, an epoxy resin composition sheet, a prepreg, and a laminate were obtained in the same manner as in Example 1. The obtained laminate was measured in the same manner as in Example 1.

[0053] Example 6 In a similar apparatus to that used in Example 1, 150 parts of A1, 25 parts of A2, and 25 parts of A3 were charged and heated until the contents were melted while stirring to prevent powder from flying around. A1 began to melt when the internal temperature exceeded 150°C, and A2 and A3 melted and became homogeneous at around 190°C. Then, 69 parts of B1 and 228 parts of B3 were added at room temperature and mixed while the system was cooled. After further stirring to confirm that B1 and B3 had melted, the system was cooled to 50°C, yielding a homogeneous liquid precursor mixture. Using the obtained precursor mixture, an epoxy resin composition, an epoxy resin composition sheet, a prepreg, and a laminate were obtained in the same manner as in Example 1. The obtained laminate was measured in the same manner as in Example 1.

[0054] Comparative Example 1 200 parts of A1 were charged into an apparatus similar to that used in Example 1, and the temperature was raised until the contents were melted while stirring to a degree that prevented powder from flying around. A1 began to melt when the internal temperature exceeded 155°C, and became homogeneous at around 160°C. 340 parts of B1 at 40°C were then added and mixed while the system was cooled. Initially, a homogeneous liquid mixture was obtained, but precipitation occurred during the cooling process to 50°C, resulting in a cloudy precursor mixture. Using the obtained precursor mixture, an epoxy resin composition, an epoxy resin composition sheet, a prepreg, and a laminate were obtained in the same manner as in Example 1. The obtained laminate was measured in the same manner as in Example 1.

[0055] Comparative Example 2 200 parts of A2 were charged into the same apparatus as in Example 1, and the temperature was raised while stirring to a degree that prevented powder from flying around. An attempt was made to raise the temperature until the contents melted, but they did not melt even when the internal temperature reached 200°C. 250 parts of B1 at 40°C were added thereto, and the system was cooled while mixing. Further cooling to 50°C with stirring yielded a cloudy precursor mixture. Using the obtained precursor mixture, an epoxy resin composition, an epoxy resin composition sheet, a prepreg, and a laminate were obtained in the same manner as in Example 1. The obtained laminate was measured in the same manner as in Example 1.

[0056] [Table 1]

[0057] In Example 1, when the epoxy resin was directly added to a molten mixture of BPA (A1) and BisP-HTG (A2) and the system was cooled, crystallization did not occur and a uniform resin mixture was obtained. Similar results were obtained in Examples 2 and 3, in which the ratio of BPA to BisP-HTG was changed. As shown in Examples 4 and 5, it was found that similar results could be obtained even when the type of epoxy resin was changed. In Comparative Example 1, in which BPA was used alone, reprecipitation of crystals was observed during cooling, resulting in cloudiness. This is thought to be due to the influence of a small amount of seed crystals remaining in the flask. However, this phenomenon was not observed in Examples 1 to 6, demonstrating that the quality of the molten state was stabilized by adding a phenolic compound. Regarding the precursor mixture, the reprecipitation of BPA due to shearing was thought to be the cause, but the viscosity measurement at 60°C was unstable, so the results were deemed unmeasurable. Comparative Example 2, which used BisP-HTG alone, did not melt even when heated to 200°C, and could not be melted even when epoxy resin was added. This laminate and resin plate showed insufficient polymerization compared to other materials. This is thought to be because when a rigid phenolic compound with a high melting point is used alone, the phenolic compound does not melt even at the curing temperature, which adversely affects the polymerization reaction. That is, by using a phenolic compound in combination, the melting temperature can be effectively lowered, and a phenolic compound having a rigid molecular structure can be used in a thermoplastic epoxy resin composition. From the above, even rigid phenolic compounds with high melting points can be incorporated into the skeleton of in-situ polymerized thermoplastic epoxy resins by melt-mixing with other phenolic compounds, significantly reducing the use of organic solvents, thereby improving heat resistance. Furthermore, by using multiple phenolic compounds, crystalline precipitation in the resin mixture can be suppressed, thereby increasing the degree of polymerization of the laminate. Furthermore, it was shown that the peelability and tackiness of epoxy resin composition sheets and prepregs can be adjusted with good productivity without aging treatment or other processes. [Industrial Applicability]

[0058] The precursor mixture of the present invention can be used for epoxy resin compositions (sheets), and can be particularly suitably used for in situ polymerization type thermoplastic epoxy resins, prepregs, thermoplastic fiber reinforced plastics, and the like.

Claims

1. A precursor mixture for use in an in-situ polymerized thermoplastic epoxy resin obtained by addition polymerization of a difunctional epoxy resin and a difunctional phenol compound, comprising: A precursor mixture comprising two types of bifunctional phenol compounds as essential components, the two types of bifunctional phenol compounds being selected from bisphenol compounds, the first bisphenol compound having a melting point of 200°C or higher, the second bisphenol compound having a melting point of 150°C or higher but lower than 200°C, the total amount of the bifunctional phenol compounds per mole of the bifunctional epoxy resin being 0.9 to 1.1 moles, and the viscosity at 60°C being 1 Pa s or higher but 50 Pa s or lower.

2. 2. The precursor mixture according to claim 1, which does not contain a solvent, or if it contains a solvent, the amount of the solvent is 10 parts by weight or less per 100 parts by weight of the total amount of the bifunctional epoxy resin and the bifunctional phenol compound.

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

4. An epoxy resin composition obtained by blending the precursor mixture according to claim 1 with a polymerization catalyst, so that the precursor mixture and the polymerization catalyst are mutually compatible.

5. 5. The epoxy resin composition according to claim 4, wherein the polymerization catalyst is blended into the precursor mixture in an amount of 0.05 to 5.0% by weight based on the total weight of the bifunctional epoxy resin and the bifunctional phenol compound, and no solvent is used, or a solvent is used in an amount twice or less relative to the amount of the polymerization catalyst.

6. 5. The epoxy resin composition according to claim 4, which has a haze value of less than 30% in the thickness direction when made into a thickness of 2 mm.

7. 5. The epoxy resin composition according to claim 4, which has a viscosity at 60°C of 3 Pa·s or more and 150 Pa·s or less.

8. A thermoplastic epoxy resin obtained by polymerizing the epoxy resin composition according to claim 4.

9. An epoxy resin composition sheet comprising the epoxy resin composition according to claim 4 and having a thickness of 10 μm or more and 300 μm or less.

10. A sheet-like in-situ polymerization type thermoplastic epoxy resin obtained by polymerizing the epoxy resin composition sheet according to claim 9.

11. A prepreg obtained from the epoxy resin composition according to claim 4 and / or the epoxy resin composition sheet according to claim 9, and reinforcing fibers.

12. An in-situ polymerized thermoplastic fiber reinforced plastic obtained by polymerizing the prepreg according to claim 11.

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