Polyvalent carboxyl group-containing curing agent, epoxy resin composition, sheet-like composition, and epoxy resin cured product

Abstract

To provide an epoxy resin curing agent and an epoxy resin composition using the same, which use biomass-derived raw materials to produce an epoxy resin cured product that exhibits low irritancy and volatility, high adhesive strength and heat resistance, and is also decomposable. [Solution] A polyvalent carboxyl group-containing curing agent represented by the following formula (1) and an epoxy resin composition using the same. TIFF2026049845000019.tif48140 (In the formula, X is a single bond or a double bond; R 1 R is a hydrocarbon group which may contain oxygen atoms with 1 to 20 carbon atoms; 2 , R 3 (Independently, a hydrogen atom, a halogen atom, a nitrogen atom, an oxygen atom, or an organic group having 1 to 20 carbon atoms that may contain a halogen atom, or an amino group; q is independently 1 or 2, m is 2 to 8, n is 0 to 4, and m+n is 3 to 8.)

Description

[Technical Field]

[0001] This invention relates to a polyvalent carboxyl group-containing curing agent used in paints, civil engineering adhesives, flooring materials, composite materials, electrical and electronic materials, optical materials, etc., as well as epoxy resin compositions containing the same and their cured products. [Background technology]

[0002] Epoxy resins come in a variety of viscosities and melting temperatures suitable for various curing and molding methods and applications. By selecting the epoxy resin with the optimal viscosity and melting temperature, molding becomes easier, and physical properties such as heat resistance, adhesion, mechanical strength, and electrical properties can be adjusted by selecting the type of epoxy resin and curing agent, or by combining them. This is why they are widely used. On the other hand, the raw materials for plastics, including epoxy resins, are mostly obtained from fossil fuels, mainly petroleum, raising concerns about the depletion of fossil fuels and environmental problems such as global warming caused by carbon dioxide emissions from incinerating plastic waste. Therefore, there is a movement to use biomass-derived raw materials for plastics. Non-patent document 1 selects chemical products and materials from biomass-derived sugars as biomass-derived raw materials, listing bio-organic acids such as succinic acid, itaconic acid, and aspartic acid. These raw materials cannot be used as curing agents for epoxy resins as they are due to issues such as volatility and irritation to the skin and eyes, and their future applications have been awaited. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] International Publication No. 2014 / 050978 [Patent Document 2] Japanese Patent Publication No. 2016-141799 [Non-patent literature]

[0004] [Non-Patent Document 1] Industrial Bioproducts: Today and Tomorrow (Contracted by: Energetics, Columbia, Maryland; Commissioned by: Biomass Programme, Department of Energy Efficiency and Renewable Energy, U.S. DOE, Washington, D.C., July 2003) [Overview of the project] [Problems that the invention aims to solve]

[0005] In order to increase the biomass content of epoxy resins, the inventors diligently studied bio-organic acids described in Non-Patent Document 1 and investigated their use as curing agents for epoxy resins. However, succinic acid, for example, is difficult to use because it is highly irritating to the skin and eyes, and it volatilizes when heated. [Means for solving the problem]

[0006] The inventors developed an epoxy resin curing agent with reduced volatility by modifying the acid anhydride derived from biomass with a polyhydric alcohol to suppress volatility. Here, Patent Document 1 describes that a polycarboxylic acid resin (A) can be obtained by performing an addition reaction between an alcoholic hydroxyl group and an acid anhydride group using an acid anhydride (a) and a polyhydric alcohol compound (b). However, acid anhydride (a) is a six-membered ring structure acid anhydride represented by general formula (1) described in Patent Document 1, and is not a biomass-derived raw material. Even if it were produced from a biomass-derived raw material, many steps would be required. Therefore, using a five-membered ring structure acid anhydride obtained by dehydrating and cyclizing biomass-derived raw materials such as succinic acid, itaconic acid, and citraconic acid, which are easily produced from sugar fermentation, as in the present application, would lead to a reduction in manufacturing energy, etc. Such a five-membered ring structure acid anhydride was not disclosed or suggested in Patent Document 1. Furthermore, while Patent Document 2 discloses a composition comprising a polyhydric alcohol compound (A), an acid anhydride compound (B), and a thermosetting resin (C), it does not disclose or suggest biomass-derived raw materials as the acid anhydride compound (B), similar to Patent Document 1. In contrast, it has been confirmed that cured products using the curing agent developed by the present inventors have low volatility and good workability, and that practical heat resistance and adhesive properties can be obtained. Moreover, it has been confirmed that the cured products are decomposable under specific conditions.

[0007] In other words, the present invention relates to the following [1] to [8]. [1] A curing agent containing a polyvalent carboxyl group, represented by the following general formula (1). [ka] (In the formula, X represents a single bond or a double bond, R 1 R represents a hydrocarbon group which may contain oxygen atoms with 1 to 20 carbon atoms. 2 , R 3 (Independently, represents a hydrogen atom, a halogen atom, a nitrogen atom, an oxygen atom, or a C1-C20 organic group which may contain a halogen atom, or an amino group. q is independently 1 or 2, m is 2-8, n is 0-4, and m+n is 3-8.) [2] The polyvalent carboxyl group-containing curing agent according to [1], wherein the carboxyl group content of the polyvalent carboxyl group-containing curing agent is 75% or more of the total of alcoholic hydroxyl groups and carboxyl groups. [3] The polyvalent carboxyl group-containing curing agent according to [1], wherein the curing agent is obtained by reacting an acid anhydride represented by general formula (2) with a polyhydric alcohol. [ka] (In the formula, X, R 2 , R 3 q is the same as in general formula (1). [4] The polyhydric carboxyl group-containing curing agent according to [3], wherein either or both of the acid anhydride and the polyhydric alcohol are derived from biomass. An epoxy resin composition containing a polycarboxyl group-containing curing agent (A) according to any one of [5][1] to [4] and an epoxy resin (B). [6] The epoxy resin composition according to [5], having a biomass content of 30% or more. [7] A sheet-like composition obtained by applying or impregnating the epoxy resin composition according to [5] to a substrate. [8] An epoxy resin cured product obtained by curing the epoxy resin composition according to [5].

Advantages of the Invention

[0008] According to the polycarboxyl group-containing curing agent of the present invention having a specific structure, an epoxy resin composition prepared by blending this with an epoxy resin has low volatility and improved workability, and moreover, its cured product exhibits high adhesive strength, heat resistance, etc., and has been found to be useful for paints, civil engineering adhesives, flooring materials, composite materials, electrical and electronic materials, optical materials, etc. Further, since the curing agent is made using biomass-derived raw materials, an epoxy resin composition with a high biomass content can be obtained. Furthermore, since it also has the property of being decomposable by a specific reagent, easy peeling after adhesion and the extraction and reuse of expensive materials such as carbon fibers and IC chips contained in the cured product are possible, and it is a material that can contribute to de-oiling and carbon neutrality.

Brief Description of the Drawings

[0009] [Figure 1] Figure 1 shows a gel permeation chromatography (GPC) chart of the polycarboxyl group-containing curing agent according to Example 1.

Modes for Carrying Out the Invention

[0010] The details of the present invention are shown below. The polycarboxyl group-containing curing agent (A) of the present invention is a curing agent represented by the general formula (1), and the epoxy resin composition of the present invention contains the polycarboxyl group-containing curing agent (A) and an epoxy resin (B). Also, as described later, in the epoxy resin composition of the present invention, a curing agent other than the polycarboxyl group-containing curing agent (A) may be used in combination, or a curing accelerator or the like may be used. Further, a thermosetting resin or a thermoplastic resin other than the epoxy resin (B) may be used in combination. Further, a filler, a film material serving as a base material, a fiber material used to enhance strength, a cloth material, etc. may be used. Further, various additives may be blended.

[0011] The polycarboxyl group-containing curing agent (A) is a compound having the structure shown in the following general formula (1), and can be easily synthesized by reacting an acid anhydride of the following general formula (2) with a polyhydric alcohol. That is, in a preferred embodiment, the polycarboxyl group-containing curing agent (A) is a compound (esterification reactant) obtained by reacting an acid anhydride of the following general formula (2) with a polyhydric alcohol. However, the synthesis method is not limited as long as it is a compound having the structure shown in the general formula (1).

[0012]

Chemical formula

[0013]

Chemical formula

[0014] R in general formula (1) 1 R is a polyhydric alcohol residue and, as mentioned above, is a hydrocarbon group that may contain oxygen atoms with 1 to 20 carbon atoms. That is, R 1 The polyhydric alcohol is the remainder of the polyhydric alcohol shown below, excluding the -OH group. Here, in general formula (1), m+n is 3 to 8, so polyhydric alcohols with three to eight functionalities are used. By using such polyhydric alcohols with three to eight functionalities, low viscosity and high adhesive strength can be expected, as well as high heat resistance. Therefore, the blend of polyhydric alcohols with three to eight functionalities can be appropriately adjusted depending on the application. Although there are no restrictions on such polyhydric alcohols, specific examples include trimethylolethane, trimethylolpropane, dimethylolpropane, pentaerythritol, dipentaerythritol, tripentaerythritol, sorbitol, maltitol, and glycerol. It is desirable that there are three or more alcoholic hydroxyl groups in one molecule. Of these, pentaerythritol and dipentaerythritol are preferred, and pentaerythritol is more preferred, from the viewpoint of versatility and balance in providing low viscosity, high adhesive strength, and high heat resistance.

[0015] Furthermore, from the viewpoint of carbon neutrality, it is desirable to utilize biomass raw materials as polyhydric alcohols. The preferred content of biomass raw materials is that the higher the amount, the better. Preferably, the biomass content (described later) is 50% or more, more preferably 80% or more, even more preferably 90% or more, and most preferably 100%. Two or more types of polyhydric alcohols may be used in combination. By using such biomass raw materials as polyhydric alcohols, it is possible to obtain a curing agent derived from biomass raw materials that was previously unknown. That is, it is possible to obtain a curing agent represented by formula (1) with some or all of its components derived from biomass raw materials. This is a preferred embodiment because it is possible to aim for compositions containing these, including not only epoxy resins but also curing agents, and cured products thereof, with a high biomass content (up to 100%).

[0016] Examples of specific polyhydric alcohol structural formulas are shown below, but are not limited to these. In the structural formulas below, the polyhydric alcohol residue R 1 Examples of compounds with 3 to 15 carbon atoms are given. In addition, polyhydric alcohols with fewer than three functionalities or more than eight functionalities may be used in combination, but it is preferable that those with fewer than three functionalities or more than eight functionalities constitute 30% by mass or less of the raw material polyhydric alcohol. [ka]

[0017] The polyvalent carboxyl group-containing curing agent (A) may have a structure that includes alcoholic hydroxyl groups in addition to carboxyl groups. The carboxyl group content is preferably 75% or more of the total content of carboxyl groups and alcoholic hydroxyl groups, more preferably 85% or more, and 100% is particularly preferred for applications that require increased heat resistance. Here, the content can be determined by checking the Area% of each peak in the GPC measurement, multiplying the number of alcoholic hydroxyl groups and carboxyl groups in each peak by the peak area percentage (Area%), calculating the content related to the total number of terminal groups, and then determining the percentage of that content from the number of carboxyl groups present.

[0018] A generalized method for finding this is as follows: For example, when the acid anhydride is reacted with a tetrafunctional polyhydric alcohol, a tetrafunctional carboxyl group-containing curing agent is obtained. In this case, depending on the molar ratio, carboxyl groups and alcoholic hydroxyl groups may be present as terminal functional groups. The reaction product in which all alcoholic hydroxyl groups react with the acid anhydride has the largest molecular weight and has four carboxyl groups at its ends. Also, the reaction product in which three alcoholic hydroxyl groups react with the acid anhydride has a molecular weight that is smaller by the amount of one acid anhydride, and the terminal functional groups of this reaction product are three carboxyl groups and one alcoholic hydroxyl group. Similarly, reaction products in which two alcoholic hydroxyl groups react with the acid anhydride, and reaction products in which one alcoholic hydroxyl group reacts with the acid anhydride are obtained, and the peak area ratios related to each reaction product are checked. The content of carboxyl groups in the total number of functional groups can be calculated by multiplying each peak area ratio by the number of carboxyl groups and the number of alcoholic hydroxyl groups. An example of such a calculation is shown below. In other words, for each peak, starting from the reactant with the largest molecular weight, if Peak 1 (Alcoholic hydroxyl group A / Carboxyl group C = 0 / 4 (number)) (84 Area%), Peak 2 (A / C = 1 / 3 (number)) (10 Area%), Peak 3 (A / C = 2 / 2 (number)) (5 ​​Area%), and Peak 4 (A / C = 3 / 1 (number)) (1 Area%), the total content of alcoholic hydroxyl group A and the total content of carboxyl group C can be calculated as follows, and the carboxyl group content (%) can be calculated from these results. Alcoholic hydroxyl group A: 0 × 84 Area% + 1 × 10 Area% + 2 × 5 Area% + 3 × 1 Area% = 0.23. Carboxyl group C: 4 × 84 Area% + 3 × 10 Area% + 2 × 5 Area% + 1 × 1 Area% = 3.77 Carboxyl group content (%) = 3.77 / (3.77 + 0.23) = 94.25

[0019] R in general formula (1) 2 , R 3R independently represents a hydrogen atom, a halogen atom, a C1-C20 organic group which may contain a nitrogen atom, an oxygen atom, or a halogen atom, i.e., a chain hydrocarbon which may contain such atoms, an organic group such as a phenyl group, a naphthyl group, a vinyl group, or an aryl group, or an amino group. If it is a vinyl group or an aryl group, copolymerization with vinyl resins is possible, and if it is an amino group, it can contribute to the curing reaction with epoxy groups. 2 , R 3 This does not form a ring structure in which the two are joined together.

[0020] Examples of acid anhydrides represented by general formula (2) include five-membered ring acid anhydrides such as itaconic anhydride, citraconic anhydride, succinic anhydride, maleic anhydride, and aspartic anhydride. From the viewpoint of carbon neutrality, it is desirable to utilize biomass raw materials. The acid anhydride is a compound in which biomass raw materials are readily available, and the more biomass raw material it contains, the better. Preferably, the biomass content (described later) is 50% or more, more preferably 80% or more, even more preferably 90% or more, and most preferably 100%. Two or more types of acid anhydrides may be used in combination. By using such biomass raw materials for the acid anhydride, it is possible to aim for compositions containing not only epoxy resin but also curing agents, and cured products thereof, that have a high biomass content (up to 100%), as described above, thus making this a preferred embodiment. Examples of specific structural formulas are shown below, but the invention is not limited to these. Two or more types of these five-membered ring acid anhydrides may be used in combination.

[0021] [ka]

[0022] In order to obtain the polyvalent carboxyl group-containing curing agent (A) of the present invention, it is preferable to carry out the reaction by blending the acid anhydride of general formula (2) with the alcoholic hydroxyl groups of the polyhydric alcohol in an equimolar amount or less. If the amount of acid anhydride of general formula (2) blended is greater than equimolar to the alcoholic hydroxyl groups, the acid anhydride of general formula (2) will remain and will volatilize due to heating during curing, which can lead to problems such as voids in the cured product and compromise the safety of the worker, so this is undesirable.

[0023] When an acid anhydride of general formula (2) is reacted with the alcoholic hydroxyl groups of a polyhydric alcohol in less than equimolar amounts, the alcoholic hydroxyl groups of the starting polyhydric alcohol remain. Retaining the alcoholic hydroxyl groups is preferable because it allows for effects such as improving the properties of the cured product, particularly adhesion, viscosity adjustment, and rate adjustment of the curing reaction. On the other hand, reacting in this manner reduces the number of carboxyl groups in each molecule that react with the epoxy group. Therefore, when reacted with an epoxy resin, the crosslinking density of the cured product may decrease, potentially reducing its heat resistance, such as the glass transition temperature. The reaction between the alcoholic hydroxyl groups and the acid anhydride can be adjusted according to the application. However, as mentioned above, regarding the carboxyl group content, it is preferable that the carboxyl group content be 75% or more, more preferably 85% or more, and 100% if heat resistance is important, relative to the total content of carboxyl groups and alcoholic hydroxyl groups in the polyhydric carboxyl group-containing curing agent (A).

[0024] The reaction conditions between an acid anhydride and a polyhydric alcohol are not limited, but vary depending on the properties of the acid anhydride of general formula (2) used as a starting material. Specifically, when using an acid anhydride of general formula (2) with a high melting point, it is preferable to carry out the reaction at a temperature above the melting point of the acid anhydride. However, if it is volatile, the reaction may be carried out at a low temperature, or by using a non-reactive solvent and washing away the volatile acid anhydride with the solvent during the reaction. Alternatively, the starting material may be dissolved in a non-reactive solvent before the reaction.

[0025] For example, since itaconic anhydride has a melting point of 68°C, it is preferable to heat it to at least 68°C or higher to carry out the reaction with polyhydric alcohols. On the other hand, since citraconic anhydride has a melting point of 7°C, the reaction can be carried out at room temperature or higher. Catalysts, polymerization inhibitors, etc., may be added as needed to carry out the reaction.

[0026] The polyvalent carboxyl group-containing curing agent (A), which uses the acid anhydride of general formula (2) as a raw material, can synthesize a curing agent with lower viscosity than that which uses methylated hexahydrophthalic anhydride, an epoxy resin curing agent, as a raw material. As an epoxy resin composition, it also has low viscosity and good workability for epoxy resin curing operations such as impregnation and casting.

[0027] The epoxy resin composition of the present invention contains the polyvalent carboxyl group-containing curing agent (A) and the epoxy resin (B). Here, as a curing agent for epoxy resin (B), a known and publicly available curing agent other than the polyvalent carboxyl group-containing curing agent (A) can also be used in combination. Examples of known and publicly available curing agents include amine-based curing agents, acid anhydride curing agents, phenol-based curing agents, and activated ester curing agents.

[0028] Any known epoxy resin (B) can be used. For example, bisphenol-type epoxy resins obtained by epoxidizing bisphenol A, bisphenol F, bisphenol S, bisphenol fluorene, biphenol, and their alkyl-substituted derivatives; novolac-type epoxy resins obtained by epoxidizing novolac resins obtained by reacting alkyl-substituted phenols such as phenol and cresol with aldehydes; aralkyl-type epoxy resins obtained by epoxidizing aralkyl resins obtained by reacting bisphenols, phenols with benzenedimethanol, bischloromethylbenzene, bischloromethylbiphenyl, etc.; amine-type epoxy resins obtained by epoxidizing para-aminophenol, diaminodiphenylmethane, etc.; crystalline epoxy resins with melting points; ester-type epoxy resins obtained by epoxidizing carboxyl group-containing compounds such as dimer acid; phosphorus-containing epoxy resins; alcohol-type epoxy resins obtained by epoxidizing alcohols such as propylene glycol, methylolpropane, and pentaerythritol; and alicyclic epoxy resins obtained by epoxidizing alicyclic compounds containing limonene, cyclohexene, and dicyclopentadiene structures, but are not limited to these. In particular, the biomass content can be increased by using biomass-derived epoxy resins such as isosorbide-type epoxy resins, cardanol-type epoxy resins, linseed oil epoxy resins, bishydroxymethylfuran epoxy resins, and natural rubber epoxy resins. Furthermore, the biomass content can be increased even further by using epichlorohydrin derived from glycerol, which is used in the epoxidation process.

[0029] Here, in this invention, biomass degree is defined as follows: That is, biomass degree is determined by the measurement of naturally occurring radiocarbons (which are measured according to the standard ASTM D 6866). 14This can be confirmed from the bio-based carbon content based on the concentration of C). In the case of natural raw materials, the radioactive carbon content is 100%, and in the case of petroleum oil-based materials, it is 0%. If the biomass content is confirmed at the raw material stage but it is a reactant, it can be easily calculated from the proportion of the raw material in the reactant. The epoxy resin composition of the present invention preferably has a biomass content of 30% or more, and more preferably 40% or more. By using biomass-derived raw materials in the epoxy resin and curing agent, the biomass content can be increased, and an epoxy resin composition with a high biomass content can be obtained. By increasing the biomass content using biomass-derived raw materials in this way, it is possible to reduce manufacturing energy and other factors, contribute to carbon neutrality, and also contribute to sustainable product development, making this a preferred embodiment.

[0030] The epoxy resin composition of the present invention may also contain thermosetting resins or thermoplastic resins other than epoxy resin (B). Examples of thermosetting resins other than epoxy resin (B) include, but are not limited to, phenolic resins, polyurethanes, imide resins, vinyl resins, methacrylic resins, acrylic resins, acid-terminated polyester resins, urea resins, melamine resins, diallyl phthalate resins, and silicon resins.

[0031] Examples of thermoplastic resins other than epoxy resin (B) include, but are not limited to, polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, ABS resin, polystyrene, methacrylic resin, polyvinyl alcohol, cellulose-based plastics, thermoplastic elastomers, polyamide resins, polyacetal, polycarbonate, phenoxy resin, polyphenylene ether, thermoplastic polyester resin, fluororesin, polyphenylene sulfide, polyetherimide, polyetherketone, polyamideimide, and polyimide.

[0032] The epoxy resin composition of the present invention may be blended with fillers, fiber materials, cloth materials, etc., for purposes such as increasing the strength of the cured product or imparting flame retardancy.

[0033] Examples of fillers include barium sulfate, titanium dioxide, zinc oxide, calcium carbonate, silica, talc, clay, kaolin, glass flakes, glass beads, graphite, aluminum oxide, aluminum hydroxide, magnesium hydroxide, alumina, boehmite, polystyrene beads, polyethylene beads, polypropylene beads, and polytetrafluoroethane beads.

[0034] Examples of fiber materials and cloth materials include carbon fiber, glass cloth, and aramid fiber.

[0035] Various additives can also be used, including anti-settling agents, adhesion promoters, internal release agents, throttling agents, leveling agents, and antioxidants.

[0036] Next, the sheet-like composition and the epoxy resin cured product of the present invention will be described. The sheet-like composition of the present invention is obtained by applying or impregnating a substrate with the epoxy resin composition described above.

[0037] While there are no limitations on the substrate, examples of embodiments include coating plastic sheets such as polyethylene terephthalate or metal foils such as copper foil with the epoxy resin composition, or impregnating glass yarn, carbon fiber, or their cloth materials with the epoxy resin composition. Furthermore, known methods can be used for coating or impregnation, and are not limited. For example, methods such as spray coating, die coating, flow coating, and curtain coating can be used to apply the epoxy resin composition to the substrate. Impregnation can be carried out by methods such as dipping, pressure impregnation, vacuum impregnation, immersion (dipping), and coating.

[0038] By heating and curing the epoxy resin composition of the present invention, a cured epoxy resin product of the present invention can be obtained. This cured product can be obtained by molding the epoxy resin composition by methods such as casting, compression molding, transfer molding, and press molding. The conditions for this process are typically a temperature of 80 to 300°C and a pressure of 0.1 to 1000 kgf / cm². 2 The duration will range from 1 minute to 10 hours.

[0039] The epoxy resin cured product of the present invention allows for the decomposition of the resin matrix under specific conditions, enabling easy peeling by decomposing the adhesive surface. Furthermore, metals, substrates, fillers, electronic components, etc., contained within the cured product can be separated and recovered, making reuse possible.

[0040] One dismantling method involves decomposing the resin by high-temperature heating, but the recovered metals, substrates, fillers, and electronic components are also exposed to high temperatures, leading to degradation and limiting their reuse applications. The epoxy resin cured product of the present invention can be easily dismantled by immersion in an amine compound, allowing the recovered materials to be reused in a wide range of applications.

[0041] The ester skeleton is known to readily react with amine compounds, decomposing through amidation. While any amine compound can be decomposed, alkylamines are preferred as the decomposition solution, and considering the working environment and the acceleration of decomposition by heating, a boiling point of 100°C or higher is preferred. Specifically, examples include, but are not limited to, amylamine, hexylamine, ethylhexylamine, hebutylamine, 2-hexyldecane-1-amine, octylamine, and undecaneamine. Furthermore, low-boiling point amine compounds may be used in combination, or other solvents, swelling agents, surfactants, and other additives may be used in combination.

[0042] Decomposition can be carried out by immersion, but heating may be applied or the decomposition solution may be made to flow by stirring or other means to accelerate the process. [Examples]

[0043] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to these examples.

[0044] The physical properties in the examples and comparative examples were measured by the following method. Here, unless otherwise specified, "parts" refers to parts by mass.

[0045] (Acid value and carboxyl group equivalent) Approximately 1 g of the sample was accurately weighed, dissolved in a solvent, and its acid value was measured using a potentiometric titrator (COM-1700, manufactured by Hiranuma Sangyo Co., Ltd.) with a 0.1 N KOH solution. The carboxyl group equivalent was calculated from the obtained acid value.

[0046] (Molecular weight measurement by GPC) A Tosoh Corporation HLC-8420GPC column was used, equipped with columns (Tosoh Corporation products: TSKgelG4000HXL, TSKgelG3000HXL, TSKgelG2000HXL) in series, and the column temperature was set to 40°C. Tetrahydrofuran (THF) was used as the eluent at a flow rate of 1 mL / min, and a differential refractive index detector was used.

[0047] (Carboxyl group content) The total number of functional groups was determined from the peak area ratio of each peak in the GPC chart and the number of carboxyl groups and alcoholic hydroxyl groups in each peak, and the ratio of carboxyl groups was calculated. For example, when pentaerythritol, which has four alcoholic hydroxyl groups, is used as the polyhydric alcohol, a tetrafunctional carboxyl group-containing curing agent is obtained. Depending on the molar ratio, carboxyl groups and alcoholic hydroxyl groups may be present as terminal functional groups. The reaction product in which all alcoholic hydroxyl groups react with the acid anhydride has the largest molecular weight and is a reaction product with four carboxyl groups at the end. The reaction product in which three alcoholic hydroxyl groups react with the acid anhydride has a molecular weight that is smaller by the amount of one acid anhydride, and the terminal functional groups of that reaction product are three carboxyl groups and one alcoholic hydroxyl group. Similarly, reaction products in which two alcoholic hydroxyl groups react with the acid anhydride and reaction products in which one alcoholic hydroxyl group reacts with the acid anhydride are obtained, and the peak area ratio of each reaction product is confirmed. The percentage of carboxyl groups in the total number of functional groups was calculated by multiplying the peak area ratio by the number of carboxyl groups and the number of alcoholic hydroxyl groups.

[0048] (ICI viscosity) The viscosity (ICI viscosity) at 80°C or 100°C was measured using a CONE PLATE VISCOMETER CV-1S.

[0049] (Glass transition temperature) The glass transition temperature of the cured material was measured by heating it at a rate of 10°C / min using a Hitachi High-Tech Science DSC7000X. The values ​​are shown as Tgm.

[0050] (Adhesive strength) An epoxy resin composition was applied to 35-micron thick copper foil (3EC) manufactured by Mitsui Mining & Smelting Co., Ltd. and sandblasted mild steel plates from Nippon Test Panel Co., Ltd., and dried. The two samples were stacked and cured under vacuum pressure at 130°C for 15 minutes and 170°C for 70 minutes at 2 MPa. The 90-degree peel strength of 10 mm wide copper foil samples was measured using a Shimadzu EZTest EZ-s compact benchtop testing machine.

[0051] (disassembly) The hardened material pieces were immersed in hexylamine and stirred at 145°C for 24 hours. Those that were successfully decomposed are indicated with a "○", and those that were not are indicated with a "×".

[0052] (Epoxy resin used (B)) • YD-128: Manufactured by Nippon Steel Chemical & Material, bisphenol A type liquid epoxy resin, epoxy equivalent 186.5 g / eq, viscosity 13000 mPa·s at 25°C. • Isosorbide-type epoxy resin obtained in Synthesis Example 1 below (Hardening agent used) BRG-555: Manufactured by Aica Kogyo Co., Ltd., phenol novolac resin, phenol group equivalent 105 g / eq, softening point 69°C Ricacid MH: Manufactured by Shin-Nippon Rika Co., Ltd., acid anhydride curing agent, acid anhydride equivalent 166.2 g / eq, dynamic viscosity 53 mPa·s (25℃) (Curing accelerator used) 2E4MZ: Manufactured by Shikoku Chemicals Co., Ltd., 2-ethyl-4-methylimidazole

[0053] Synthesis Example 1 An apparatus was prepared in a four-necked glass flask equipped with a thermometer, stirrer, gas inlet tube, and reflux condenser. 73.07 parts of isosorbide and 555 parts of epichlorohydrin produced from biomass-derived glycerol were charged into the flask, and the mixture was stirred and heated while introducing nitrogen gas. The temperature was maintained at 63°C to allow dissolution. 9.00 parts of 49.5% sodium hydroxide aqueous solution were added dropwise over 2 hours. Subsequently, the pressure was slowly reduced to approximately 14.8 kPa, and 88.00 parts of 49.5% sodium hydroxide aqueous solution were added dropwise over 3 hours. The water in the sodium hydroxide aqueous solution and the reaction product water were removed from the system by azeotrope with the epichlorohydrin, and the epichlorohydrin was returned to the system while the reaction continued. After the dropwise addition was complete, the generated sodium chloride was removed by filtration, and unreacted epichlorohydrin was removed from the filtrate by heating under reduced pressure. The final conditions were 150°C and 0.66 kPa. The obtained isosorbide-type epoxy resin had an epoxy equivalent of 157.3 g / eq and a viscosity of 990 mP·s at 25°C. Radiocarbon content was measured by ASTM D 6866. 14 The bio-based carbon content, based on the concentration of C), was 100%.

[0054] Example 1 An apparatus was prepared using a four-necked glass flask equipped with a thermometer, stirrer, gas inlet tube, and reflux condenser, and air was introduced through the gas inlet tube. 30.37 parts of biomass-derived pentaerythritol, 103.29 parts of biomass-derived itaconic anhydride, and 0.1291 parts of 2,6-di-t-butyl-4-methylphenol as a polymerization inhibitor were charged and heated. After the itaconic anhydride melted at approximately 70°C, the reaction was carried out at 100°C while stirring. After confirming the change in acid value and achieving a stable value close to the theoretical value, a polyvalent carboxyl group-containing curing agent with the structure shown below as the main component was obtained after 3 hours. The obtained resin was pale yellow, semi-solid, odorless, and did not sublimate. The GPC chart is shown in Figure 1. The carboxyl group equivalent was 168.7 g / eq, and the carboxyl group content was 90.6% of the total functional groups (carboxyl groups and alcoholic hydroxyl groups) including alcoholic hydroxyl groups. The ICI viscosity could not be measured at 80°C due to high viscosity, but the viscosity at 100°C was 19.5 Pa·s. The biomass content was 99.9%. [ka]

[0055] Example 2 In the same apparatus as in Example 1, nitrogen gas was introduced through a gas inlet tube, and 38.55 parts of pentaerythritol and 126.94 parts of biomass-derived citraconic anhydride (instead of itaconic anhydride) were reacted at 130°C for 3 hours without a polymerization inhibitor. The resulting resin was pale yellow, highly viscous, odorless, and non-sublimable. The carboxyl group equivalent was 150.7 g / eq, the carboxyl group content was 100% of the total functional groups (carboxyl groups and alcoholic hydroxyl groups), and the ICI viscosity (80°C) was 5.7 Pa·s. The biomass content was 100.0%. [ka]

[0056] Example 3 In the same apparatus as in Example 1, nitrogen gas was introduced through a gas inlet tube, and 24.28 parts of pentaerythritol and 99.96 parts of biomass-derived succinic anhydride (instead of itaconic anhydride) were reacted at 110°C for 4 hours without a polymerization inhibitor. The resulting resin was a pale yellow semi-solid, odorless, and did not sublimate. The carboxyl group equivalent was 131.5 g / eq, and the carboxyl group content was 100% of the total functional groups (carboxyl groups and alcoholic hydroxyl groups) including alcoholic hydroxyl groups. The ICI viscosity could not be measured at 80°C due to high viscosity, but the viscosity at 100°C was 15.2 Pa·s. The biomass content was 100.0%. [ka]

[0057] Example 4 In the same apparatus as in Example 1, nitrogen gas was introduced through a gas inlet tube, and 24.28 parts of pentaerythritol and 99.96 parts of biomass-derived allyl succinic anhydride (instead of itaconic anhydride) were reacted at 110°C for 4 hours without a polymerization inhibitor. The resulting resin was pale yellow, highly viscous, odorless, and non-sublimable. The carboxyl group equivalent was 172.2 g / eq, the carboxyl group content was 100% of the total functional groups (carboxyl groups and alcoholic hydroxyl groups), and the ICI viscosity (80°C) was 3.7 Pa·s. The biomass content was 100.0%. [ka]

[0058] Example 5 In the same apparatus as in Example 1, nitrogen gas was introduced through a gas inlet tube, and 30.18 parts of biomass-derived dipentaerythritol was added instead of pentaerythritol, and 99.81 parts of allyl succinic anhydride were added instead of itaconic anhydride. No polymerization inhibitor was added, and 0.1 g of triphenylphosphine was added as a catalyst. The reaction was carried out at 130°C for 3 hours. The resulting resin was pale yellow, highly viscous, odorless, and did not sublimate. The carboxyl group equivalent was 181.4 g / eq, the carboxyl group content was 100% of the total functional groups (carboxyl groups and alcoholic hydroxyl groups) including alcoholic hydroxyl groups, and the ICI viscosity (80°C) was 13.5 Pa·s. The biomass content was 100.0%. [ka]

[0059] Comparative Example 1 In the same apparatus as in Example 1, nitrogen gas was introduced through a gas inlet tube, and 33.00 parts of pentaerythritol and 162.88 parts of ricacid MH-T (4-methylhexahydrophthalic anhydride, manufactured by Shin-Nippon Rika Co., Ltd.) were reacted at 110°C for 3 hours without a polymerization inhibitor. The resulting resin was a pale yellow solid resin that did not sublimate and was odorless. The carboxyl group equivalent was 200.0 g / eq, the carboxyl group content was 100% of the total functional groups (carboxyl groups and alcoholic hydroxyl groups) including alcoholic hydroxyl groups, the softening point was above 140°C, and it did not melt below 100°C, so viscosity could not be measured. The biomass content was 16.8%. [ka]

[0060] The results for each compound (curing agent) obtained in Examples 1 to 5 and Comparative Example 1 are summarized in Table 1.

[0061] [Table 1]

[0062] As can be seen from Table 1, viscosity could not be measured even at 100°C in Comparative Example 1, but it could be measured in all of the curing agents in Examples 1 to 5. Furthermore, the curing agents in Examples 1 to 5 have a biomass content of almost 100%.

[0063] Examples 6-15, Comparative Examples 2-5 According to the formulations shown in Table 2, the curing agents from Examples 1-5 and Comparative Example 1 were blended with epoxy resin (B) to prepare epoxy resin compositions. The epoxy resin compositions, dissolved in a solvent, were then applied to copper foil and mild steel plates, and the solvent was removed by heating and drying. Curing was performed using a vacuum press, and the 90-degree peel strength was measured. Additionally, the epoxy resin composition was heated and melted, poured into a mold, and heated at 130°C for 2.5 hours, 150°C for 2 hours, and 180°C for 3 hours to obtain cured pieces approximately 2 mm thick. The physical properties (glass transition temperature, decomposability) of the obtained cured pieces were evaluated. The biomass content of the mixture was also calculated.

[0064] [Table 2]

[0065] [Table 3]

[0066] The polyvalent carboxyl group-containing curing agent (A) of the present invention has low viscosity and does not sublimate, making it useful as a curing agent for epoxy resins. The cured product obtained by curing an epoxy resin composition containing epoxy resin (B) has heat resistance and adhesive properties comparable to conventional epoxy resin cured products, and can also be decomposed by immersion in hexylamine or by heating and stirring. This allows for easy removal after use as an adhesive, reuse of reinforcing materials such as carbon fiber, and reuse of IC chips, etc.

[0067] Furthermore, it is possible to select biomass-derived materials for the raw materials, such as polyhydric alcohols and acid anhydrides represented by general formula (2), which can contribute to reducing petroleum emissions and carbon dioxide emissions. When both the polyhydric alcohols and acid anhydrides represented by general formula (2) are biomass-derived raw materials, the curing agents in Examples 1-5 are almost 100% biomass-derived, and in Examples 6-10 in Table 2, epoxy resin cured products with a biomass content of about 40-50% are obtained. In the polyhydric carboxyl group-containing curing agent of Comparative Example 1, 16% can be biomass-derived, but in the cured product of Comparative Example 2, it is only about 8%. In Examples 11-15 in Table 3, the epoxy resin is also 100% biomass-derived, so the composition can have a biomass content of almost 100%. In Comparative Example 5, the biomass content is 53%, and in order to achieve a high biomass content, the curing agent also needs to be biomass-derived as in the present invention. [Industrial applicability]

[0068] This epoxy resin curing agent and epoxy resin composition, containing polyvalent carboxyl groups, can be used in existing applications as an epoxy resin curing product, and the dismantling of the curing product can also be useful for recycling valuable materials such as carbon fiber.

Claims

1. A polyvalent carboxyl group-containing curing agent represented by the following general formula (1). 【Chemistry 1】 (In the formula, X represents a single bond or a double bond, R １ R represents a hydrocarbon group which may contain oxygen atoms with 1 to 20 carbon atoms. ２ , R ３ (Independently, represents a hydrogen atom, a halogen atom, a nitrogen atom, an oxygen atom, or a C1-C20 organic group which may contain a halogen atom, or an amino group. q is independently 1 or 2, m is 2-8, n is 0-4, and m+n is 3-8.)

2. The polyvalent carboxyl group-containing curing agent according to claim 1, wherein the carboxyl group content of the polyvalent carboxyl group-containing curing agent is 75% or more of the total amount of alcoholic hydroxyl groups and carboxyl groups.

3. The polyvalent carboxyl group-containing curing agent according to claim 1, wherein the curing agent is obtained by reacting an acid anhydride represented by general formula (2) with a polyhydric alcohol. 【Chemistry 2】 (In the formula, X, R ２ , R ３ q is the same as in general formula (1).

4. The polyvalent carboxyl group-containing curing agent according to claim 3, wherein either or both of the acid anhydride and the polyhydric alcohol are derived from biomass.

5. An epoxy resin composition comprising a polyvalent carboxyl group-containing curing agent (A) according to any one of claims 1 to 4 and an epoxy resin (B).

6. The epoxy resin composition according to claim 5, wherein the biomass content is 30% or more.

7. A sheet-like composition obtained by applying or impregnating a substrate with the epoxy resin composition described in claim 5.

8. An epoxy resin cured product obtained by curing the epoxy resin composition according to claim 5.

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