Imide group-containing epoxy resin and curable epoxy resin composition containing same

Abstract

The present invention provides: an imide group-containing epoxy resin which has excellent fluidity and enables the achievement of a cured product that is excellent in terms of uniformity and heat resistance even under relaxed curing conditions (for example, curing temperature conditions of 200°C or lower); and a curable epoxy resin composition which uses the same. The present invention relates to an imide group-containing epoxy resin which contains a diimide dicarboxylic acid-based compound represented by a specific general formula and a bifunctional epoxy resin, wherein the diimide dicarboxylic acid-based compound and the bifunctional epoxy resin are ester-bonded to each other, and the epoxy equivalent is 1,000 or less.

Description

Imide group-containing epoxy resin and curable epoxy resin composition containing the same

[0001] The present invention relates to an imide group-containing epoxy resin having an imide skeleton and a curable epoxy resin containing the same.

[0002] Curable resins such as epoxy resins have excellent heat resistance, mechanical properties, and electrical properties, and are widely used industrially, primarily as electrical and electronic materials such as insulating materials for printed wiring boards and semiconductor encapsulation materials.

[0003] In recent years, the development of materials for electronic components has been actively pursued to accommodate the increasing demand for high-capacity, high-speed communication. For example, rising junction temperatures due to the performance improvements of semiconductor elements and increased heat generation due to improved efficiency have increased the need for higher performance epoxy resin materials, requiring higher heat resistance than ever before.

[0004] Furthermore, in the field of power semiconductors, such as automotive power modules, there is a demand for even higher current, smaller size, and higher efficiency, and a shift to silicon carbide (SiC) semiconductors is underway. Because SiC semiconductors can operate under higher temperature conditions than conventional silicon (Si) semiconductors, semiconductor encapsulation materials used for SiC semiconductors are required to have higher heat resistance than ever before.

[0005] On the other hand, methods such as cast molding and transfer molding are used to encapsulate power semiconductors and semiconductor elements, but these do not use solvents and must flow and harden at the molding temperature (200°C or lower) to exhibit sufficient performance.

[0006] For example, Patent Document 1 discloses a cured product obtained by using a compound having an imide structure in an epoxy resin.

[0007] International Publication No. 2021 / 117686 Brochure

[0008] However, the cured product of Patent Document 1 is produced using a solvent, and the curing condition is a high temperature of 300° C. When Patent Document 1 is cured at 200° C. without using a solvent, there are problems such as poor fluidity, reduced uniformity, and insufficient heat resistance.

[0009] An object of the present invention is to provide an imide group-containing epoxy resin having excellent fluidity, which can give a cured product having excellent uniformity and heat resistance even under moderate curing conditions (for example, a curing temperature of 200°C or less), and a curable epoxy resin composition using the same.

[0010] As a result of intensive research into the above-mentioned problems, the present inventors have found that the above-mentioned object can be achieved by preliminarily reacting a bifunctional epoxy resin with a specific diimidedicarboxylic acid compound, and have thus arrived at the present invention.

[0011] That is, the gist of the present invention is as follows: <1> An imide group-containing epoxy resin comprising a diimidedicarboxylic acid compound represented by general formula (1) and a bifunctional epoxy resin, wherein the diimidedicarboxylic acid compound and the bifunctional epoxy resin are ester-bonded, and the epoxy equivalent is 1,000 or less. (In formula (1), X １ and X ２ each independently represents a structure derived from an aromatic tricarboxylic acid anhydride component, an alicyclic tricarboxylic acid anhydride component, or an aliphatic tricarboxylic acid anhydride component; R １represents a structure derived from an aromatic diamine component or an alicyclic diamine component.) <2> The imide group-containing epoxy resin according to <1>, wherein the bifunctional epoxy resin is one or more epoxy resins selected from the group consisting of bisphenol A epoxy resins, naphthalene epoxy resins, biphenyl epoxy resins, and anthracene epoxy resins. <3> The imide group-containing epoxy resin according to <1> or <2>, wherein the bifunctional epoxy resin is one or more epoxy resins selected from the group consisting of naphthalene epoxy resins and biphenyl epoxy resins, and wherein the epoxy equivalent is 500 or less. <4> The imide group-containing epoxy resin according to any one of <1> to <3>, wherein the bifunctional epoxy resin is one or more epoxy resins selected from the group consisting of naphthalene epoxy resins and biphenyl epoxy resins, and wherein the epoxy equivalent is 250 to 350. <5> The imide group-containing epoxy resin according to any one of <1> to <4>, wherein the imide group-containing epoxy resin has a structure in which one molecule of the diimide dicarboxylic acid compound is bonded to each end of the diimide dicarboxylic acid compound via an ester bond. <6> A method for producing an imide group-containing epoxy resin, comprising reacting a diimide dicarboxylic acid compound with a difunctional epoxy resin in the presence of a phosphorus compound. <7> The method for producing an imide group-containing epoxy resin according to <6>, wherein the diimide dicarboxylic acid compound is blended in an amount such that the functional group equivalent of the diimide dicarboxylic acid compound is in an equivalent ratio of 0.01 to 0.6 relative to the epoxy equivalent of the difunctional epoxy resin. <8> The method for producing an imide group-containing epoxy resin according to <6> or <7>, wherein the bifunctional epoxy resin is one or more epoxy resins selected from the group consisting of naphthalene-type epoxy resins and biphenyl-type epoxy resins, and the amount of the diimidedicarboxylic acid compound is such that the functional group equivalent of the diimidedicarboxylic acid compound is in an equivalent ratio of 0.05 to 0.35 relative to the epoxy equivalent of the bifunctional epoxy resin.<9> A method for producing an imide group-containing epoxy resin according to any one of <6> to <8>, wherein the bifunctional epoxy resin is one or more epoxy resins selected from the group consisting of naphthalene-type epoxy resins and biphenyl-type epoxy resins, and the amount of the diimide dicarboxylic acid compound is such that the functional group equivalent of the diimide dicarboxylic acid compound is 0.15 to 0.25 equivalent ratio relative to the epoxy equivalent of the bifunctional epoxy resin. <10> A method for producing an imide group-containing epoxy resin according to any one of <6> to <9>, comprising producing the imide group-containing epoxy resin according to any one of <1> to <5>. <11> A curable epoxy resin composition comprising the imide group-containing epoxy resin according to any one of <1> to <5> and a curing agent. <12> A cured product of the curable epoxy resin composition according to <11>. <13> An electrical insulating material comprising the cured product according to <12>. <14> An encapsulant comprising the cured product according to <12>. <15> The encapsulant according to <14>, which is used in a power semiconductor module. <16> A printed wiring board comprising the cured product according to <12>.

[0012] According to the present invention, it is possible to provide a highly fluid imide group-containing epoxy resin having an imide skeleton, which can give a cured product with excellent uniformity and heat resistance even when the curing conditions are relaxed, and a curable epoxy resin composition using the same. The cured product obtained by curing the curable epoxy resin composition of the present invention can be suitably used for electrical insulating materials, sealing materials, and printed wiring boards.

[0013] <Imide Group-Containing Epoxy Resin> The imide group-containing epoxy resin of the present invention is a reaction product of a diimide dicarboxylic acid compound and a difunctional epoxy resin. Specifically, the imide group-containing epoxy resin of the present invention contains a diimide dicarboxylic acid compound and a difunctional epoxy resin, and the diimide dicarboxylic acid compound and the difunctional epoxy resin are ester-bonded. More specifically, the structure of the imide group-containing epoxy resin of the present invention is not particularly limited as long as it has the epoxy equivalent weight described below. For example, the imide group-containing epoxy resin of the present invention may be one structure selected from the group consisting of the following structures (A), (B), and (C), or may be a mixture of two or more structures selected from the group.

[0014] Structure (A): A structure in which one molecule of a diimidedicarboxylic acid compound is bonded to each end of the molecule via an ester bond. In Structure (A), more specifically, one of the two carboxyl groups in the diimidedicarboxylic acid compound forms an ester bond by reacting with one of the two epoxy groups in the bifunctional epoxy resin. The other carboxyl group forms an ester bond by reacting with one of the two epoxy groups in another bifunctional epoxy resin.

[0015] Structure (B): A structure in which one molecule of a diimidedicarboxylic acid compound is bonded to each end of one molecule of a bifunctional epoxy resin via an ester bond. In Structure (B), more specifically, one of the two epoxy groups in the bifunctional epoxy resin forms an ester bond by reacting with one of the two carboxyl groups in the diimidedicarboxylic acid compound. The other epoxy group forms an ester bond by reacting with one of the two carboxyl groups in another diimidedicarboxylic acid compound.

[0016] Structure (C): Oligomer Structure In Structure (C), specifically, a diimidedicarboxylic acid compound and a bifunctional epoxy resin are repeatedly bonded via ester bonds, and the number of repeating units is usually 10 or less, particularly 5 or less, and from the viewpoint of further improving the fluidity of the imide group-containing epoxy resin and the uniformity and heat resistance of the resulting cured product, it is preferably 3 or less, more preferably 2. The lower limit of the number of repeating units is not particularly limited and may be, for example, 2.

[0017] In structures (A) to (C), when an ester bond is formed, a hydroxyl group is generated by opening the epoxy ring. Each of these hydroxyl groups may independently react with a carboxyl group of another diimidedicarboxylic acid compound to form an ester bond, or with an epoxy group of another bifunctional epoxy resin to form an ether bond, or may not react with any group at all.

[0018] The imide group-containing epoxy resin of the present invention preferably has Structure (A) from the viewpoint of further improving the fluidity of the imide group-containing epoxy resin and the uniformity and heat resistance of the resulting cured product. Specifically, from the same viewpoint as above, the imide group-containing epoxy resin of the present invention preferably contains an imide group-containing epoxy resin having Structure (A).

[0019] In this specification, "fluidity" refers to the fluidity of the imide group-containing epoxy resin and is a characteristic related to a lower viscosity at 140°C. Since the imide group-containing epoxy resin needs to flow during molding, a lower viscosity is preferable. "Uniformity" refers to the uniformity of the cured product of the imide group-containing epoxy resin and curing agent and is a characteristic related to the presence of fewer insoluble components in the cured product. Insoluble components are foreign substances that impair the transparency of the cured product and can arise from a decrease in compatibility between the imide group-containing epoxy resin and curing agent and / or the presence of unreacted imide dicarboxylic acid compounds during the cured product production process. Residual insoluble components can lead to poor curing and / or reduced physical properties, so uniform curing is desirable. "Heat resistance" refers to the heat resistance of the cured product of the imide group-containing epoxy resin and curing agent and is a characteristic related to a higher glass transition temperature of the cured product. Since the cured product must operate under high-temperature conditions, a higher glass transition temperature is preferable.

[0020] The epoxy equivalent of the imide group-containing epoxy resin of the present invention must be 1000 or less (particularly 100 to 1000), and from the viewpoint of further improving the fluidity of the imide group-containing epoxy resin and the uniformity and heat resistance of the resulting cured product, it is preferably 800 or less (particularly 150 to 800), more preferably 500 or less (particularly 200 to 500), and more preferably 250 to 350. If the epoxy equivalent exceeds 1000, the fluidity and uniformity will decrease.

[0021] In this specification, the epoxy equivalent is the molecular weight of an epoxy resin per epoxy group, and is a value measured by nuclear magnetic resonance spectroscopy.

[0022] The viscosity (140°C) of the imide group-containing epoxy resin of the present invention is usually 1000 Pa s or less, and from the viewpoint of further improving the fluidity, it is preferably 500 Pa s or less, more preferably 200 Pa s or less, even more preferably 100 Pa s or less, sufficiently preferably 10 Pa s or less, and even sufficiently preferably 5 Pa s or less. The lower limit of the viscosity is not particularly limited, and the viscosity is usually 0.01 Pa s or more, particularly 0.05 Pa s or more. From the viewpoint of further improving the fluidity and heat resistance of the cured product, it is preferably 0.5 Pa s or more, more preferably 1 Pa s or more.

[0023] In this specification, the viscosity is a value at 140° C. determined by dynamic viscoelasticity measurement.

[0024] [Diimidedicarboxylic acid compound] A diimidedicarboxylic acid compound is a compound having two imide groups and two carboxyl groups in one molecule. A diimidedicarboxylic acid compound does not have an amide group. A tricarboxylic acid anhydride component and a diamine component are used as raw materials, and functional groups are reacted to produce an amide acid compound. A diimidedicarboxylic acid compound can be produced by proceeding with an imidization reaction. Here, the reaction between functional groups may be carried out in solution or in a solid state, and the production method is not particularly limited.

[0025] A diimidedicarboxylic acid-based compound using a tricarboxylic acid anhydride component and a diamine component is a compound in which two molecules of the tricarboxylic acid anhydride component react with one molecule of the diamine component to form two imide groups, and more specifically, is a diimidedicarboxylic acid compound having a structure represented by general formula (1).

[0026]

[0027] In general formula (1), X １ and X ２ Each of X independently represents a structure derived from a tricarboxylic acid anhydride component (for example, an aromatic tricarboxylic acid anhydride component, an alicyclic tricarboxylic acid anhydride component, or an aliphatic tricarboxylic acid anhydride component) described below. １ and X ２may each independently be a residue derived from the above components. １ represents a structure derived from a diamine component (for example, an aromatic diamine component or an alicyclic diamine component) described later. １ may be a residue derived from the above moieties.

[0028] In producing a diimidedicarboxylic acid compound using a tricarboxylic acid anhydride component and a diamine component, the diamine component is usually used in an amount of about 0.5 times by molar, for example, 0.1 to 0.7 times by molar, preferably 0.3 to 0.7 times by molar, more preferably 0.4 to 0.6 times by molar, and even more preferably 0.45 to 0.55 times by molar, relative to the tricarboxylic acid anhydride component.

[0029] Tricarboxylic acid anhydride components that can constitute diimide dicarboxylic acid compounds include aromatic tricarboxylic acid anhydride components containing an aromatic ring, alicyclic tricarboxylic acid anhydride components containing an aliphatic ring but not an aromatic ring, and aliphatic tricarboxylic acid anhydride components containing neither an aromatic ring nor an alicyclic ring. The tricarboxylic acid anhydride component may contain an ether group and / or a thioether group, and / or one or more hydrogen atoms may be substituted with a halogen atom (e.g., a fluorine atom, a chlorine atom, or a bromine atom). The tricarboxylic acid anhydride component may also be an acid halide component. An acid halide component is a compound in which the OH group of the carboxyl group in the tricarboxylic acid anhydride component is substituted with a halogen atom.

[0030] Examples of aromatic tricarboxylic anhydride components include trimellitic anhydride and 1,2,4-naphthalene tricarboxylic anhydride. These may be used alone or in a mixture of two or more. The number of aromatic rings contained in one molecule of the aromatic tricarboxylic anhydride component is not particularly limited, and may be, for example, 1 to 4, and particularly 1 to 2. In particular, naphthalene rings are counted as containing two aromatic rings per molecule.

[0031] Examples of the alicyclic tricarboxylic anhydride component include 1,2,3-cyclohexanetricarboxylic anhydride and 1,2,4-cyclohexanetricarboxylic anhydride. These may be used alone or in combination of two or more. The number of alicyclic rings contained in one molecule of the alicyclic tricarboxylic anhydride component is not particularly limited and may be, for example, 1 to 4, and particularly 1 to 2.

[0032] Examples of the aliphatic tricarboxylic anhydride component include 3-carboxymethylglutaric anhydride, 1,2,4-butanetricarboxylic acid-1,2-anhydride, cis-propene-1,2,3-tricarboxylic acid-1,2-anhydride, etc. These may be used alone or in combination of two or more.

[0033] From the viewpoint of the heat resistance of the diimidedicarboxylic acid compound, the imide group-containing epoxy resin obtained using the same, and the cured product obtained using the same, the tricarboxylic acid anhydride component of the diimidedicarboxylic acid compound preferably contains an aromatic tricarboxylic acid anhydride component and / or an alicyclic tricarboxylic acid anhydride component, and more preferably contains an aromatic tricarboxylic acid anhydride component.

[0034] From the viewpoint of the solubility of the diimidedicarboxylic acid compound, it is preferable to use an alicyclic tricarboxylic acid anhydride component and / or an aliphatic tricarboxylic acid anhydride component among the above-mentioned tricarboxylic acid anhydride components as the tricarboxylic acid anhydride component of the diimidedicarboxylic acid compound. From the viewpoint of further improving the solubility of the diimidedicarboxylic acid compound, it is preferable to use only an alicyclic tricarboxylic acid anhydride component and / or an aliphatic tricarboxylic acid anhydride component among the above-mentioned tricarboxylic acid anhydride components as the tricarboxylic acid anhydride component of the diimidedicarboxylic acid compound.

[0035] Diamine components that can constitute diimidedicarboxylic acid compounds include aromatic diamine components containing aromatic rings and alicyclic diamine components containing aliphatic rings but no aromatic rings. The diamine component may contain an ether group and / or a thioether group, and / or one or more hydrogen atoms may be substituted with a halogen atom (e.g., a fluorine atom, a chlorine atom, or a bromine atom). The diamine component may have a side chain.

[0036] Examples of aromatic diamine components include m-phenylenediamine, p-phenylenediamine, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminobenzanilide, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, bis(4-aminophenyl)sulfone, 9,9-bis(4-aminophenyl)fluorene, metaxylenediamine, 4,4'-bis(3-aminophenoxy)biphenyl, 4,4'-bis(4-aminophenoxy)biphenylbis[4-(4-aminophenoxy)phenyl]sulfone, and analogs of the above diamines. These may be used alone or in combination of two or more. The number of aromatic rings contained in one molecule of the aromatic diamine component is not particularly limited and may be, for example, 1 to 4, particularly 1 to 2. In particular, a fluorene ring is counted as containing two aromatic rings in one molecule.

[0037] Examples of alicyclic diamine components include trans-1,4-cyclohexanediamine, 4,4'-methylenebis(cyclohexylamine), and 1,4-bis(aminomethyl)cyclohexane. These may be used alone or in combination of two or more. The number of alicyclic rings contained in one molecule of the alicyclic diamine component is not particularly limited and may be, for example, 1 to 4, and particularly 1 to 2.

[0038] From the viewpoint of the heat resistance of the diimidedicarboxylic acid compound, the imide group-containing epoxy resin obtained using the same, and the cured product obtained using the same, the diamine component of the diimidedicarboxylic acid compound preferably contains an aromatic diamine component and / or an alicyclic diamine component, and more preferably contains an aromatic diamine component.

[0039] From the viewpoint of the solubility of the diimidedicarboxylic acid compound, it is preferable to use a diamine component having an ether group, a thioether group, a sulfonyl group, a sulfonic acid group, a methyl group, a methylene group, an isopropylidene group, a phenyl group, a fluorene structure, a halogen atom (or a halogen atom-containing substituent), or a siloxane bond among the above diamine components. From the viewpoint of further improving the solubility of the diimidedicarboxylic acid compound, it is preferable to use only a diamine component having an ether group, a thioether group, a sulfonyl group, a sulfonic acid group, a methyl group, a methylene group, an isopropylidene group, a phenyl group, a fluorene structure, a halogen atom (or a halogen atom-containing substituent), or a siloxane bond among the above diamine components.

[0040] The diimidedicarboxylic acid compound can be produced in a solvent or without a solvent, but the production method is not particularly limited.

[0041] As a method for producing in a solvent, for example, predetermined raw materials (e.g., tricarboxylic acid anhydride component, diamine component, tetracarboxylic acid dianhydride component, monoaminodicarboxylic acid component) are added to an aprotic solvent such as N-methyl-2-pyrrolidone, and the mixture is stirred at 80°C, followed by imidization.

[0042] The imidization method is not particularly limited, and may be, for example, a thermal imidization method in which the imidization is carried out by heating at 250°C to 350°C (particularly 280 to 320°C) for 1 to 10 hours (particularly 1 to 3 hours) in a nitrogen atmosphere, or a chemical imidization method in which the imidization is carried out by treating with a dehydration cyclization reagent such as a mixture of a carboxylic acid anhydride and a tertiary amine.

[0043] Examples of solvent-free production methods include a method utilizing the mechanochemical effect, which is a method of obtaining an organic compound by utilizing the mechanical energy generated when the raw material compounds used in the reaction are pulverized to produce a mechanochemical effect.

[0044] The mechanochemical effect is an effect (or phenomenon) in which mechanical energy (compression, shear, impact, grinding, etc.) is applied to a raw material compound in a solid state in a reaction environment, pulverizing the raw material compound and activating the resulting pulverized interface. This causes a reaction between functional groups. A reaction between functional groups typically occurs between two or more raw material compound molecules. For example, a reaction between functional groups may occur between two raw material compound molecules with different chemical structures, or between two raw material compound molecules with the same chemical structure. A reaction between functional groups does not occur only between a specific pair of two raw material compound molecules, but typically also occurs between other pairs of two raw material compound molecules. A new reaction between functional groups may occur between a compound molecule produced by a reaction between functional groups and a raw material compound molecule. A reaction between functional groups is typically a chemical reaction in which a bonding group (particularly a covalent bond) is formed between two raw material compound molecules via the functional groups of each raw material compound molecule, producing another compound molecule.

[0045] The reaction environment refers to the environment in which the raw material compound is placed for the reaction, i.e., the environment in which mechanical energy is applied, and may be, for example, the environment inside the apparatus. Being in a solid state in the reaction environment means being in a solid state under the environment in which mechanical energy is applied (e.g., under the temperature and pressure inside the apparatus). A raw material compound in a solid state in the reaction environment may generally be in a solid state at room temperature (25°C) and normal pressure (101.325 kPa). A raw material compound in a solid state in the reaction environment may be in a solid state at the start of the application of mechanical energy. The present invention does not prevent a raw material compound in a solid state in the reaction environment from changing to a liquid state (e.g., a molten state) during the reaction (or processing) due to an increase in temperature and / or pressure accompanying the continued application of mechanical energy. However, from the viewpoint of improving the reaction rate, it is preferable that the raw material compound be in a solid state continuously during the reaction (or processing).

[0046] Although the details of the mechanochemical effect are unclear, it is believed to follow the following principle: When mechanical energy is applied to one or more solid-state raw material compounds to cause milling, the absorption of this mechanical energy activates the milled interface. It is believed that this surface activation energy at the milled interface causes a chemical reaction between two raw material compound molecules. Milling refers to the application of mechanical energy to raw material compound particles, which absorb the mechanical energy, causing cracks in the particles and renewing the surface. Surface renewal refers to the formation of a milled interface as a new surface. In the mechanochemical effect, the state of the new surface formed by surface renewal is not particularly limited as long as activation of the milled interface occurs due to milling, and it may be in a dry state or a wet state. The wet state of the new surface due to surface renewal is due to the raw material compounds being in a liquid state separate from the solid-state raw material compounds.

[0047] Mechanical energy is applied to a raw material mixture containing one or more raw material compounds that are in a solid state under a reaction environment. The state of the raw material mixture is not particularly limited as long as the application of mechanical energy causes the solid-state raw material compounds to be pulverized. For example, the raw material mixture may be in a dry state because all of the raw material compounds contained in the raw material mixture are in a solid state. Alternatively, the raw material mixture may be in a wet state because at least one raw material compound contained in the raw material mixture is in a solid state and the remaining raw material compounds are in a liquid state. Specifically, for example, when the raw material mixture contains only one raw material compound, the one raw material compound is in a solid state. Alternatively, for example, when the raw material mixture contains two raw material compounds, the two raw material compounds may both be in a solid state, or one raw material compound may be in a solid state and the other raw material compound may be in a liquid state.

[0048] This mechanochemical effect using mechanical energy is used to cause a reaction between functional groups. Specifically, a reaction occurs between the acid anhydride group of the tricarboxylic acid anhydride component and the amino group of the diamine component, producing an imide group.

[0049] In the method for producing in the absence of a solvent, after carrying out a method utilizing the mechanochemical effect, imidization may be carried out by a method similar to the imidization method in the method for producing in a solvent (particularly a thermal imidization method).

[0050] [Difunctional Epoxy Resin] A difunctional epoxy resin has a structure having two epoxy groups per molecule. If a multifunctional epoxy resin having three or more epoxy groups per molecule is used, the reaction between the epoxy resin and the diimidedicarboxylic acid compound does not proceed sufficiently, leaving unreacted material, making it impossible to produce an imide group-containing epoxy resin. As a result, the uniformity of the epoxy resin cured product using a curing agent decreases, and sufficient heat resistance cannot be obtained.

[0051] Examples of bifunctional epoxy resins include bisphenol A epoxy resins, bisphenol F epoxy resins, bisphenol S epoxy resins, naphthalene epoxy resins, bisphenyl epoxy resins, and anthracene epoxy resins. Among them, from the viewpoint of further improving the fluidity of the imide group-containing epoxy resin and the uniformity and heat resistance of the resulting cured product, bisphenol A epoxy resins, naphthalene epoxy resins, bisphenyl epoxy resins, and anthracene epoxy resins are preferred, bisphenol A epoxy resins, naphthalene epoxy resins, and bisphenyl epoxy resins are more preferred, naphthalene epoxy resins and bisphenyl epoxy resins are even more preferred, and naphthalene epoxy resins are particularly preferred. The epoxy resins may be used alone or in combination of two or more.

[0052] The bisphenol A type epoxy resin is a compound having a bisphenol A skeleton and two epoxy groups in one molecule, and may be, for example, an epoxy resin represented by the general formula (E1). (In formula (E1), n ​​is an integer of 0 to 3. Each hydrogen atom bonded to a carbon atom constituting the benzene ring may be independently substituted with a methyl group.)

[0053] The naphthalene type epoxy resin is, for example, a compound having a naphthalene skeleton and two epoxy groups in one molecule, and may be an epoxy resin represented by general formula (E2). (In formula (E2), n is an integer of 0 to 3. Each hydrogen atom bonded to a carbon atom constituting the naphthalene ring may be independently substituted with a methyl group.)

[0054] The anthracene-type epoxy resin is a compound having an anthracene skeleton and two epoxy groups in one molecule, and may be, for example, an epoxy resin represented by general formula (E3). (In formula (E3), n is an integer of 0 to 3. Each hydrogen atom bonded to a carbon atom constituting the anthracene ring may be independently substituted with a methyl group.)

[0055] The biphenyl type epoxy resin is, for example, a compound having a biphenyl skeleton and two epoxy groups in one molecule, and may be an epoxy resin represented by general formula (E4). (In formula (E4), n is an integer of 0 to 3. Each hydrogen atom bonded to a carbon atom constituting the benzene ring may be independently substituted with a methyl group.)

[0056] The difunctional epoxy resin is commercially available or can be produced by a known method.

[0057] The epoxy equivalent of the bifunctional epoxy resin is not particularly limited and may be, for example, 100 to 1,000 g / eq. From the viewpoint of further improving the fluidity of the imide group-containing epoxy resin and the uniformity and heat resistance of the resulting cured product, it is preferably 100 to 500 g / eq, more preferably 100 to 300 g / eq, and even more preferably 150 to 250 g / eq.

[0058] <Method for producing imide group-containing epoxy resin> The method for producing the imide group-containing epoxy resin of the present invention is not particularly limited, and examples thereof include a method of heating and mixing under a nitrogen atmosphere. Specifically, a diimidedicarboxylic acid compound is heated and mixed with a bifunctional epoxy resin in the presence of a phosphorus compound to react them. Such a treatment for producing an imide group-containing epoxy resin can also be considered as a pretreatment of the epoxy resin, which is carried out before the epoxy resin is reacted with a cured product.

[0059] The heating temperature during mixing is not particularly limited and may be, for example, 100 to 250°C. From the viewpoint of further improving the fluidity of the imide group-containing epoxy resin and the uniformity and heat resistance of the resulting cured product, the heating temperature is preferably 130 to 200°C, and particularly preferably 150 to 200°C.

[0060] The reaction time (mixing time) is not particularly limited and may be 0.1 to 10 hours, but from the viewpoint of further improving the fluidity of the imide group-containing epoxy resin and the uniformity and heat resistance of the resulting cured product, it is preferably 0.5 to 5 hours, more preferably 0.5 to 2 hours.

[0061] In the imide group-containing epoxy resin, the amount of the diimide dicarboxylic acid compound is not particularly limited, and may be, for example, an amount such that the functional group equivalent of the diimide dicarboxylic acid compound is 0.01 to 0.6 equivalents relative to the epoxy equivalent of the bifunctional epoxy resin. From the viewpoint of further improving the flowability of the imide group-containing epoxy resin and the uniformity and heat resistance of the resulting cured product, the amount of the diimide dicarboxylic acid compound is preferably 0.05 to 0.5 equivalents, preferably 0.05 to 0.35 equivalents, and more preferably 0.15 to 0.25 equivalents relative to the epoxy equivalent of the bifunctional epoxy resin. The functional group equivalent of the diimide dicarboxylic acid compound corresponds to the equivalent calculated from the carboxyl group content. Specifically, in the present invention, since both the diimide dicarboxylic acid compound and the bifunctional epoxy resin are bifunctional, the functional group equivalent of the diimide dicarboxylic acid compound corresponds to the molar amount of the diimide dicarboxylic acid compound per mole of the bifunctional epoxy resin. When two or more diimidedicarboxylic acid compounds are used, the total amount of these compounds may be the above-mentioned blending amount.

[0062] Because the phosphorus-based compound acts as a catalyst, its amount is preferably 0.1 to 1 part by mass, more preferably 0.1 to 0.5 parts by mass, and even more preferably 0.2 to 0.5 parts by mass, per 100 parts by mass of the total amount of the diimidedicarboxylic acid compound and bifunctional functional group. When two or more phosphorus-based compounds are used, the total amount of these compounds should be within the above range. When a catalyst other than a phosphorus-based compound is used as a catalyst, gelation occurs during synthesis of the imide group-containing epoxy resin, resulting in an increase in viscosity. This reduces the compatibility between the imide group-containing epoxy resin and the curing agent during production of the cured product, causing these components to behave as insoluble components, resulting in a decrease in the uniformity (transparency) of the cured product.

[0063] The phosphorus-based compound is not particularly limited, and examples thereof include organic phosphines such as aromatic organic phosphines (e.g., triphenylphosphine, tri(o-tolyl)phosphine, tri(m-tolyl)phosphine, tri(p-tolyl)phosphine, tris(4-methoxyphenyl)phosphine, diphenylcyclohexylphosphine), alicyclic organic phosphines (e.g., tricyclohexylphosphine), and aliphatic organic phosphines (e.g., tributylphosphine (particularly tri-tert-butylphosphine), tri-n-octylphosphine); aromatic phosphonium salts (e.g., tetraphenylphosphonium bromide, n-butyltriphenylphosphonium bromide); Examples of the phosphorus-based compound include phosphonium salts such as methyltriphenylphosphonium bromide, methyltriphenylphosphonium bromide, ethyltriphenylphosphonium bromide, (methoxymethyl)triphenylphosphonium chloride, benzyltriphenylphosphonium chloride, tetraphenylphosphonium tetraphenylborate, tetraphenylphosphonium tetra-p-tolylborate, triphenylborane-triphenylphosphine, tri-tert-butylphosphonium tetraphenylborate, and aliphatic phosphonium salts (e.g., tetrabutylphosphonium bromide). Phosphorus-based compounds may be used alone or in combination of two or more. Phosphorus-based compounds are commercially available.

[0064] From the viewpoint of further improving the fluidity of the imide group-containing epoxy resin and the uniformity and heat resistance of the resulting cured product, the phosphorus-based compound is preferably an organic phosphine, more preferably an aromatic organic phosphine, and even more preferably triphenylphosphine.

[0065] <Curable Epoxy Resin Composition> The curable epoxy resin composition of the present invention comprises a mixture of at least an imide group-containing epoxy resin and a curing agent.

[0066] Examples of the curing agent include imidazoles, dicyandiamides, phenol-based curing agents, thiol-based curing agents, amine-based curing agents, acid anhydride-based curing agents, cyanate-based curing agents, and active ester-based curing agents. Among these, imidazoles, acid anhydride-based curing agents, and amine-based curing agents are preferred. One of the above curing agents may be used alone, or two or more may be used in combination.

[0067] Examples of imidazoles include 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-heptadecylimidazole, 2-undecylimidazole, 1,2-dimethylimidazole, 4-methyl-2-phenylimidazole, N-benzyl-2-methylimidazole, 2-phenyl-1-benzyl-1H-imidazole, 1-(2-cyanoethyl)-2-undecylimidazole, Examples include 1-(2-cyanoethyl)-2-ethyl-4-methylimidazole, 1-(2-cyanoethyl)-2-phenylimidazole, 1-cyanoethyl-2-methylimidazole, 2,4-diamino-6-[2-methylimidazolyl-(1)]ethyl-s-triazine, 4,5-di(hydroxymethyl)-2-phenyl-1H-imidazole, and 4-methyl-2-phenyl-5-hydroxymethyl-1H-imidazole.

[0068] Examples of acid anhydride curing agents include 4-methylcyclohexane-1,2-dicarboxylic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, methylnadic anhydride, hydrogenated methylnadic anhydride, trialkyltetrahydrophthalic anhydride, methylcyclohexenetetracarboxylic dianhydride, phthalic anhydride, trimellitic anhydride, pyromellitic anhydride, benzophenonetetracarboxylic dianhydride, ethylene glycol bisanhydrotrimellitate, glycerin bis(anhydrotrimellitate) monoacetate, and dodecenyl succinic anhydride.

[0069] Examples of amine-based curing agents include aliphatic polyamines (e.g., diethylenetriamine, triethylenetetramine, tetraethylenepentamine, m-xylenediamine, trimethylhexamethylenediamine, 2-methylpentamethylenediamine, diethylaminopropylamine), alicyclic polyamines (e.g., isophoronediamine, 1,3-bisaminomethylcyclohexane, bis(4-aminocyclohexyl)methane, norbornenediamine, 1,2-diaminocyclohexane), and aromatic polyamines (e.g., 4,4-diaminodiphenylmethane, metaphenylenediamine, diaminodiphenylsulfone).

[0070] The amount of these curing agents to be blended varies depending on the type of curing agent. Curing agents are classified as type A curing agents and type B curing agents, and the blending amounts are as follows:

[0071] The Class A curing agent is a curing agent belonging to the dicyandiamide and imidazole classes. The amount of Class A to be blended is preferably 1 to 10 parts by mass, more preferably 1 to 3 parts by mass, per 100 parts by mass of the imide group-containing epoxy resin. The Class A curing agent may be used alone or in combination of two or more types. When two or more types are used in combination, it is preferable that the total amount be within the above range.

[0072] The Class B curing agents are curing agents belonging to the following groups: phenol-based curing agents, thiol-based curing agents, amine-based curing agents, acid anhydride-based curing agents, cyanate-based curing agents, and active ester-based curing agents. The amount of Class B curing agents added is preferably an equivalent ratio of 0.1 to 1.0, more preferably 0.1 to 0.5, relative to the epoxy equivalent of the imide group-containing epoxy resin. The Class B curing agents may be used alone or in combination of two or more. When two or more types are used in combination, it is preferable that the total amount added be within the above range.

[0073] The type A curing agent and the type B curing agent may be used in combination. When used in combination, it is sufficient to use one or more types of each of the type A curing agent and the type B curing agent. For example, one type of type A curing agent and one type of type B curing agent may be used, or one type of type A curing agent and two types of type B curing agents may be used, or two types of type A curing agents and one type B curing agent may be used. When used in combination, for example, the amount of the type A curing agent is 0.1 parts by mass or more per 100 parts by mass of the imide group-containing epoxy resin, and the amount of the type B curing agent is 0.5 or more equivalents relative to the epoxy equivalent of the imide group-containing epoxy resin. When used in combination, the type A curing agent is preferably used in an amount of 0.1 to 1.0 parts by mass, more preferably 0.1 to 0.5 parts by mass, per 100 parts by mass of the imide group-containing epoxy resin. In this case, when two or more types of type A curing agents are used, it is preferable that the total amount thereof be within the above range. When used in combination, the amount of the Type B curing agent is preferably 0.5 to 1.5 equivalent ratio, more preferably 0.7 to 1.3 equivalent ratio, relative to the epoxy equivalent of the imide group-containing epoxy resin. In this case, when two or more Type B curing agents are used, it is preferable that the total amount thereof be in the above range.

[0074] Other additives such as curing accelerators, inorganic fillers, antioxidants, flame retardants, organic solvents, etc. may be added to the curable epoxy resin composition of the present invention, as long as the effects of the present invention are not impaired.

[0075] Examples of the curing accelerator include tertiary amines such as 4-dimethylaminopyridine, benzyldimethylamine, 2-(dimethylaminomethyl)phenol, and 2,4,6-tris(dimethylaminomethyl)phenol; and organic phosphines such as triphenylphosphine and tributylphosphine. One of the above curing accelerators may be used alone, or two or more may be used in combination. When a curing accelerator is used, its amount is preferably 0.01 to 2.0% by mass relative to the curable epoxy resin composition. Because this improves the heat resistance and dielectric properties of the resulting cured product, a content of 0.01 to 1% by mass is preferred, and a content of 0.05 to 0.5% by mass is more preferred.

[0076] Examples of inorganic fillers include silica, barium sulfate, alumina, aluminum nitride, boron nitride, silicon nitride, glass powder, glass frit, glass fiber, carbon fiber, and inorganic ion exchangers. One of the above inorganic fillers may be used alone, or two or more may be used in combination. When using an inorganic filler, the average particle size of the inorganic filler is preferably 50 nm to 4 μm, and more preferably 100 nm to 3 μm, as this provides better coatability and processability.

[0077] Examples of the antioxidant include hindered phenol-based antioxidants, phosphorus-based antioxidants, and thioether-based antioxidants. One of the antioxidants may be used alone, or two or more of them may be used in combination.

[0078] Examples of the flame retardant include non-halogen flame retardants, phosphorus-based flame retardants, nitrogen-based flame retardants, and silicone-based flame retardants. Among these, non-halogen flame retardants are preferred from the viewpoint of environmental impact. The flame retardants may be used alone or in combination of two or more.

[0079] The organic solvent is an organic solvent capable of dissolving the imide group-containing epoxy resin and the curing agent, and examples of such organic solvents include cyclohexanone, γ-butyrolactone, dimethylacetamide, dimethylformamide, and N-methyl-2-pyrrolidone.

[0080] The curable epoxy resin composition of the present invention preferably does not contain a solvent (particularly an organic solvent). This is because the curable epoxy resin composition of the present invention can have excellent fluidity even without a solvent due to the excellent fluidity of the imide group-containing epoxy resin. The content of the solvent (particularly an organic solvent) is not particularly limited, and is, for example, 10% by mass or less, preferably 5% by mass or less, more preferably 1% by mass or less, even more preferably 0.1% by mass or less, and particularly preferably 0% by mass or less, relative to the total amount of the curable epoxy resin composition.

[0081] The content of the solvent (particularly the organic solvent) can be calculated from the mass of the curable epoxy resin composition before and after heat treatment (i.e., drying treatment) at 80 to 250°C for 1 minute to 20 hours. Specifically, the content of the solvent (particularly the organic solvent) can be calculated based on the formula: {(X-Y) / X} x 100 (%), where X g is the mass before the drying treatment and Y g is the mass after the drying treatment.

[0082] The method for producing the curable epoxy resin composition of the present invention is not particularly limited, but examples thereof include a method in which the imide group-containing epoxy resin, the curing agent, and other additives, which are added as needed, are mixed using a mixer such as a Homodisper, a universal mixer, a Banbury mixer, or a kneader.

[0083] <Cured Product> The present invention also provides a cured product. The cured product of the present invention is a cured product of the curable epoxy resin composition of the present invention described above. By heating the curable epoxy resin composition of the present invention, the imide group-containing epoxy resin and the curing agent are reacted to obtain a cured product. The heating temperature (curing temperature) is preferably 80 to 350°C, more preferably 130 to 220°C, and even more preferably 130 to 200°C. The heating time (curing time) is preferably 1 minute to 24 hours, more preferably 5 minutes to 10 hours, and even more preferably 1 to 5 hours.

[0084] <Uses of Cured Product> The cured product of the present invention has excellent heat resistance, uniformity, and mechanical properties, and therefore can be suitably used as an electrical insulating material. Specifically, the cured product of the present invention can be suitably used as an electrical insulating material in sealing materials (e.g., sealing materials for power semiconductor modules), printed wiring boards, molding materials (e.g., molding materials for bushing transformers, molding materials for solid insulating switchgears), electrical penetrations for nuclear power plants, build-up laminates, powder coatings, and the like. In particular, the cured product of the present invention can be more suitably used as sealing materials and printed wiring boards.

[0085] When the cured product of the present invention is used as an insulating material for an encapsulant, for example, after a power semiconductor module is produced, the curable epoxy resin composition of the present invention can be filled into a mold in which the module is set, and then cured.

[0086] Furthermore, for example, when the cured product of the present invention is used as an insulating material for printed wiring boards, a solvent is often used. In this case, the curable epoxy resin composition of the present invention can be used by impregnating or coating a glass cloth with a solution of the curable epoxy resin composition and then curing the resulting mixture. The solution of the curable epoxy resin composition of the present invention is the same as the solution of the curable epoxy resin composition when the cured product of the present invention is used as an insulating material for encapsulants. The insulating material for printed wiring boards refers to an insulating material that constitutes a printed wiring board.

[0087] The curable epoxy resin composition of the present invention can also be used for applications other than electrical insulating materials. Specifically, the curable epoxy resin composition of the present invention can be used for adhesives and CFRP.

[0088] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0089] A. Raw Materials The raw materials used in the Examples and Comparative Examples are as follows: (A) Bifunctional Epoxy Resins Bisphenol A type epoxy resin: manufactured by Tokyo Chemical Industry Co., Ltd., epoxy equivalent 170 g / eq Naphthalene type epoxy resin: manufactured by DIC Corporation, "HP-4032D", epoxy equivalent 141 g / eq Anthracene type epoxy resin: manufactured by Mitsubishi Chemical Corporation, "YX8800", epoxy equivalent 180 g / eq Biphenyl type epoxy resin: manufactured by Mitsubishi Chemical Corporation, "YX4000H", epoxy equivalent 191 g / eq

[0090] (B) Multifunctional epoxy resin Cresol novolac epoxy resin: "N-660" manufactured by DIC Corporation, epoxy equivalent 209 g / eq

[0091] (C) Diimidedicarboxylic Acid Compounds - Diimidedicarboxylic Acid X 52.3 parts by mass of 4,4'-diaminodiphenyl ether and 100 parts by mass of trimellitic anhydride were mixed and crushed three times using a Wonder Crusher WC-3C manufactured by Osaka Chemical Co., Ltd. at a rotation speed of 9000 rpm for one minute, to perform a mechanochemical treatment. The treated sample was transferred to a glass container and subjected to an imidization reaction at 300°C for two hours in a nitrogen atmosphere using an inert oven DN411I manufactured by Yamato Scientific Co., Ltd., to obtain diimidedicarboxylic acid X. Diimidedicarboxylic acid X is １ H-NMR analysis revealed that the product was a trimer composed of trimellitic acid-4,4'-diaminodiphenyl ether-trimellitic acid. Mass spectrometry revealed that the diimidedicarboxylic acid X had a number-average molecular weight of 549 and was solid at room temperature.

[0092] Diimidedicarboxylic acid Y Diimidedicarboxylic acid Y was obtained in the same manner as diimidedicarboxylic acid X, except that 52.3 parts by mass of 4,4'-diaminodiphenyl ether was used instead of 107.2 parts by mass of 2,2-bis[4-(4-aminophenoxy)phenyl]propane. １ H-NMR analysis revealed that the product was a trimer composed of 2,2-bis[4-(4-aminophenoxy)phenyl]propane trimellitic acid and trimellitic acid. Mass spectrometry revealed that the diimidedicarboxylic acid Y had a number-average molecular weight of 759 and was solid at room temperature.

[0093] Diimidedicarboxylic acid Z was obtained in the same manner as in diimidedicarboxylic acid X, except that 52.3 parts by mass of 4,4'-diaminodiphenyl ether was used instead of 29.8 parts by mass of trans-1,4-cyclohexanediamine. １ H-NMR analysis revealed that the diimidedicarboxylic acid Z was a trimer composed of trimellitic acid-trans-1,4-cyclohexanediamine-trimellitic acid. Mass spectrometry revealed that the diimidedicarboxylic acid Z had a number-average molecular weight of 462 and was solid at room temperature.

[0094] (D) Phosphorus compounds Triphenylphosphine: manufactured by Tokyo Chemical Industry Co., Ltd. (E) Other catalysts N,N-dimethylbenzylamine: manufactured by Tokyo Chemical Industry Co., Ltd.

[0095] (F) Curing agent 2-ethyl-4-methylimidazole: manufactured by Tokyo Chemical Industry Co., Ltd. 4-methylcyclohexane-1,2-dicarboxylic anhydride: manufactured by Tokyo Chemical Industry Co., Ltd. 4,4-diaminodiphenylmethane: manufactured by Tokyo Chemical Industry Co., Ltd.

[0096] B. Evaluation Methods The compounds (imide group-containing epoxy resins) and cured products obtained in the examples and comparative examples were evaluated as follows.

[0097] [Method for evaluating imide group-containing epoxy resins] (1) Confirmation of esterification reaction The imide group-containing epoxy resins obtained in the examples and comparative examples were measured and identified by infrared spectroscopy (IR) under the following conditions.

[0098] <Measurement conditions> Apparatus: Nicolet iS5 FT-IR, iD7 ATR accessory manufactured by Thermo Fisher Scientific Method: ATR method Number of scans: 64 (resolution 4 cm-1) 1680 cm originating from the carboxyl group of diimidedicarboxylic acid compounds －１ The presence or absence of absorption near the peak was confirmed. <Evaluation criteria> ⊚: The esterification reaction proceeded sufficiently; the peak derived from the carboxyl group disappeared; ×: The esterification reaction did not proceed sufficiently; the peak derived from the carboxyl group remained.

[0099] (2) Epoxy Equivalent The imide group-containing epoxy resins obtained in the Examples and Comparative Examples were measured by nuclear magnetic resonance (NMR) under the following conditions, and the epoxy equivalent was calculated. The imide group-containing epoxy resins obtained in the Examples and Comparative Examples were measured using a high-resolution nuclear magnetic resonance spectrometer (JNM-ECA500 NMR manufactured by JEOL Ltd.) １ The resin composition was determined from the peak intensity of each copolymer component by H-NMR analysis (resolution: 500 MHz, solvent: deuterated dimethyl sulfoxide, temperature: 25° C.).

[0100] <Measurement conditions> Apparatus: JNM-ECA500 NMR manufactured by JEOL Ltd. Resolution: 500 MHz Solvent: Deuterated dimethyl sulfoxide Temperature: 25°C Method: Internal standard method (sodium 3-(trimethylsilyl)propionate-2,2,3,3-d4 (TSP-d4); purity 99.8%) The epoxy equivalent was calculated from the peak intensity of the internal standard and each component. <Evaluation criteria> ◎: 250≦epoxy equivalent≦350 (best); ○: 200≦epoxy equivalent<250 or 350<epoxy equivalent≦500 (good); △: epoxy equivalent<200 or 500<epoxy equivalent≦1000 (no practical problem); ×: epoxy equivalent>1000 (problematic in practical use).

[0101] (3) Evaluation of Flowability (Viscosity Measurement) The imide group-containing epoxy resins obtained in the Examples and Comparative Examples were subjected to dynamic viscoelasticity measurement under the following conditions, and the viscosity was calculated.

[0102] <Measurement conditions> Apparatus: ARESG2 rheometer manufactured by TA Instruments Measurement temperature range: 25 to 200°C Heating rate: 5°C / min Angular frequency: 10 rad / s Viscosity was calculated at 140°C. <Evaluation criteria> ◎: Viscosity ≦ 10 Pa s (best); ○: 10 Pa s < viscosity ≦ 100 Pa s (good); △: 100 Pa s < viscosity ≦ 1000 Pa s (no practical problem); ×: 1000 Pa s < viscosity (problematic in practical use).

[0103] [Method for evaluating cured products] (1) Evaluation of uniformity (transparency) The presence or absence of insoluble components in the cured products obtained in the examples and comparative examples was visually confirmed, and the uniformity was judged. Insoluble components inhibit the uniformity and transparency of the cured products.

[0104] <Evaluation criteria> ◎ (uniform): no insoluble components, completely transparent state. △ (almost uniform): some insoluble components present, but transparent state. × (ununiform): insoluble components present, and opaque state.

[0105] (2) Glass Transition Temperature (Heat Resistance) of Cured Products The cured products obtained in the Examples and Comparative Examples were measured using a differential scanning calorimeter (DSC) under the following conditions: <Measurement Conditions> Apparatus: Perkin-Elmer DSC 6000 Heating Rate: 10°C / min The temperature was raised from 25°C to 300°C, and the starting temperature of a discontinuous change resulting from the transition temperature in the obtained temperature rise curve was taken as the glass transition temperature.

[0106] <Evaluation criteria> ⊚: Tg≧200°C (best); ◯: 200°C>Tg≧180°C (good); Δ: 180°C>Tg≧150°C (no practical problem); ×: 150°C>Tg (poor) (problems in practical use).

[0107] [Overall evaluation] A comprehensive evaluation was made based on the evaluation results of the fluidity of the imide group-containing epoxy resin and the uniformity and heat resistance of the cured product. <Evaluation criteria> ◎: All evaluation results were ◎. ○: Of all evaluation results, the lowest evaluation result was ○. △: Of all evaluation results, the lowest evaluation result was △. ×: Of all evaluation results, the lowest evaluation result was ×.

[0108] Example 1 (Imide Group-Containing Epoxy Resin A) 100 parts by mass of naphthalene-type epoxy resin, 19 parts by mass of diimidedicarboxylic acid X, and 0.3 parts by mass of triphenylphosphine were charged into a reaction vessel equipped with a heating mechanism and a stirring mechanism. The mixture was then heated to 150°C with stirring and reacted for 1 hour at normal pressure under a nitrogen stream to obtain imide group-containing epoxy resin A. When the imide group-containing epoxy resin A was confirmed by IR, the esterification reaction had progressed sufficiently. Furthermore, １ H-NMR revealed that the epoxy equivalent of imide group-containing epoxy resin A was 216, and it was a viscous solid at room temperature. From these results and the amounts charged, it was confirmed that imide group-containing epoxy resin A has a structure in which one molecule of a diimidedicarboxylic acid compound is bonded to each end of the molecule via an ester bond.

[0109] (Cured Product) The obtained imide group-containing epoxy resin A and a curing agent were mixed to obtain the composition shown in Table 1, and the mixture was heated at 200° C. in a nitrogen atmosphere to carry out a curing reaction for 3 hours to obtain a cured product.

[0110] Example 2 (Imide Group-Containing Epoxy Resin B) An imide group-containing epoxy resin B was obtained in the same manner as in Example 1, except that 19 parts by mass of diimidedicarboxylic acid X was used instead of 39 parts by mass. When the imide group-containing epoxy resin B was confirmed by IR, the esterification reaction had progressed sufficiently. １ H-NMR revealed that imide group-containing epoxy resin B had an epoxy equivalent of 309 and was solid at room temperature. From these results and the amounts charged, it was confirmed that imide group-containing epoxy resin B had a structure in which one molecule of a diimidedicarboxylic acid compound was bonded to each end of the molecule via an ester bond.

[0111] Using the obtained imide group-containing epoxy resin B, a cured product was prepared in the same manner as in Example 1, except that the blending amounts were changed so as to obtain the composition shown in Table 1.

[0112] Examples 3 to 5 (Imide Group-Containing Epoxy Resin C) Imide group-containing epoxy resin C was obtained in the same manner as in Example 1, except that 19 parts by mass of diimidedicarboxylic acid X was used instead of 58 parts by mass. When the imide group-containing epoxy resin C was confirmed by IR, the esterification reaction had progressed sufficiently. １ H-NMR revealed that the epoxy equivalent of imide group-containing epoxy resin C was 400, and it was a solid at room temperature. From these results and the amounts charged, it was confirmed that imide group-containing epoxy resin C had a structure in which one molecule of a diimidedicarboxylic acid compound was bonded to each end of the molecule via an ester bond.

[0113] Using the obtained imide group-containing epoxy resin C, a cured product was prepared in the same manner as in Example 1, except that the blending amounts were changed so as to obtain the composition shown in Table 1.

[0114] Example 6 (Imide Group-Containing Epoxy Resin D) An imide group-containing epoxy resin D was obtained in the same manner as in Example 1, except that 19 parts by mass of diimidedicarboxylic acid X was replaced with 78 parts by mass, and 0.3 parts by mass of triphenylphosphine was replaced with 0.4 parts by mass. When the imide group-containing epoxy resin D was confirmed by IR, the esterification reaction had progressed sufficiently. １ H-NMR revealed that the epoxy equivalent of imide group-containing epoxy resin D was 543, and it was a solid at room temperature. From these results and the amounts charged, it was confirmed that imide group-containing epoxy resin D has a structure in which one molecule of a diimidedicarboxylic acid compound is bonded to each end of the molecule via an ester bond.

[0115] Using the obtained imide group-containing epoxy resin D, a cured product was prepared in the same manner as in Example 1, except that the blending amounts were changed so as to obtain the composition shown in Table 1.

[0116] Example 7 (Imide Group-Containing Epoxy Resin E) An imide group-containing epoxy resin E was obtained in the same manner as in Example 1, except that the naphthalene type epoxy resin was replaced with a bisphenol A type epoxy resin and 19 parts by mass of diimidedicarboxylic acid X was replaced with 48 parts by mass. When the imide group-containing epoxy resin E was confirmed by IR, the esterification reaction had progressed sufficiently. １ H-NMR revealed that the epoxy equivalent of imide group-containing epoxy resin E was 441, and it was a solid at room temperature. From these results and the amounts charged, it was confirmed that imide group-containing epoxy resin E had a structure in which one molecule of a diimidedicarboxylic acid compound was bonded to each end of the molecule via an ester bond.

[0117] Using the obtained imide group-containing epoxy resin E, a cured product was prepared in the same manner as in Example 1, except that the blending amounts were changed so as to obtain the composition shown in Table 1.

[0118] Example 8 (Imide Group-Containing Epoxy Resin F) Imide group-containing epoxy resin F was obtained in the same manner as in Example 1, except that the naphthalene type epoxy resin was replaced with an anthracene type epoxy resin and 19 parts by mass of diimidedicarboxylic acid X was replaced with 46 parts by mass. When the imide group-containing epoxy resin F was confirmed by IR, the esterification reaction had progressed sufficiently. １ H-NMR revealed that the epoxy equivalent of imide group-containing epoxy resin E was 375, and it was a solid at room temperature. From these results and the amounts charged, it was confirmed that imide group-containing epoxy resin F had a structure in which one molecule of a diimidedicarboxylic acid compound was bonded to each end of the molecule via an ester bond.

[0119] Using the obtained imide group-containing epoxy resin F, a cured product was prepared in the same manner as in Example 1, except that the blending amounts were changed so as to obtain the composition shown in Table 1.

[0120] Example 9 (Imide Group-Containing Epoxy Resin G) An imide group-containing epoxy resin G was obtained in the same manner as in Example 1, except that the naphthalene type epoxy resin was replaced with a biphenyl type epoxy resin and 19 parts by mass of diimidedicarboxylic acid X was replaced with 43 parts by mass. When the imide group-containing epoxy resin G was confirmed by IR, the esterification reaction had progressed sufficiently. １ H-NMR revealed that imide group-containing epoxy resin G had an epoxy equivalent of 412 and was solid at room temperature. From these results and the amounts charged, it was confirmed that imide group-containing epoxy resin G had a structure in which one molecule of a diimidedicarboxylic acid compound was bonded to each end of the molecule via an ester bond.

[0121] Using the obtained imide group-containing epoxy resin G, a cured product was prepared in the same manner as in Example 1, except that the blending amounts were changed so as to obtain the composition shown in Table 1.

[0122] Example 10 (Imide Group-Containing Epoxy Resin H) An imide group-containing epoxy resin H was obtained in the same manner as in Example 1, except that 81 parts by mass of diimide dicarboxylic acid Y was used instead of 19 parts by mass of diimide dicarboxylic acid X, and 0.4 parts by mass of triphenylphosphine was used instead of 0.3 parts by mass. When the imide group-containing epoxy resin H was confirmed by IR, the esterification reaction had progressed sufficiently. １ H-NMR analysis revealed that the epoxy equivalent of imide group-containing epoxy resin H was 450, and the resin was solid at room temperature. From these results and the amounts charged, it was confirmed that imide group-containing epoxy resin H had a structure in which one molecule of a diimidedicarboxylic acid compound was bonded to each end of the molecule via an ester bond.

[0123] Using the obtained imide group-containing epoxy resin H, a cured product was prepared in the same manner as in Example 1, except that the blending amounts were changed so as to obtain the composition shown in Table 1.

[0124] Example 11 (Imide Group-Containing Epoxy Resin I) An imide group-containing epoxy resin I was obtained in the same manner as in Example 1, except that 19 parts by mass of diimide dicarboxylic acid X was used instead of 49 parts by mass of diimide dicarboxylic acid Z. When the imide group-containing epoxy resin I was confirmed by IR, the esterification reaction had progressed sufficiently. １ H-NMR analysis revealed that the epoxy equivalent of imide group-containing epoxy resin I was 380, and the resin was solid at room temperature. From these results and the amounts charged, it was confirmed that imide group-containing epoxy resin I had a structure in which one molecule of a diimidedicarboxylic acid compound was bonded to each end of the molecule via an ester bond.

[0125] Using the obtained imide group-containing epoxy resin I, a cured product was prepared in the same manner as in Example 1, except that the blending amounts were changed so as to obtain the composition shown in Table 1.

[0126] Comparative Example 1 (Imide Group-Containing Epoxy Resin J) An imide group-containing epoxy resin J was obtained in the same manner as in Example 1, except that 19 parts by mass of diimidedicarboxylic acid X was replaced with 58 parts by mass, and triphenylphosphine was used instead of N,N-dimethylbenzylamine. IR analysis of the imide group-containing epoxy resin J revealed that the esterification reaction had progressed sufficiently. １ H-NMR revealed that imide group-containing epoxy resin J had an epoxy equivalent of 1500 and was solid at room temperature. These results confirmed that imide group-containing epoxy resin J had a polymer structure in which diimidedicarboxylic acid compounds and bifunctional epoxy resins were repeatedly bonded via ester bonds.

[0127] Using the obtained imide group-containing epoxy resin J, a cured product was prepared in the same manner as in Example 1, except that the blending amounts were changed so as to obtain the composition shown in Table 1.

[0128] Comparative Example 2 (Imide Group-Containing Epoxy Resin K) Imide group-containing epoxy resin K was obtained in the same manner as in Example 1, except that the naphthalene type epoxy resin was replaced with a cresol novolac type epoxy resin and 19 parts by mass of diimidedicarboxylic acid X was replaced with 39 parts by mass. When the imide group-containing epoxy resin K was examined by IR, it was found that the esterification reaction had not progressed sufficiently, and some unreacted material remained. These results confirmed that the imide group-containing epoxy resin K was a simple mixture of a diimidedicarboxylic acid compound and a multifunctional epoxy resin.

[0129] Using the obtained imide group-containing epoxy resin K, a cured product was prepared in the same manner as in Example 1, except that the blending amounts were changed so as to obtain the composition shown in Table 1.

[0130] Comparative Example 3: 100 parts by mass of bisphenol A epoxy resin and 163 parts by mass of diimidedicarboxylic acid X were mixed at room temperature to obtain a mixture. When the mixture was examined by IR, it was found that the esterification reaction had not progressed sufficiently. These results confirmed that the mixture was indeed a simple mixture of a diimidedicarboxylic acid compound and a bifunctional epoxy resin.

[0131] Using the obtained mixture, a cured product was prepared in the same manner as in Example 1, except that the blending amounts were changed so as to obtain the composition shown in Table 1.

[0132] The composition of the imide group-containing epoxy resin and the evaluation results of the resulting cured product are shown in Table 1.

[0133]

[0134] The symbols in the table are as follows: -: Not blended. *: Value relative to the epoxy equivalent of the bifunctional epoxy resin. **: Not measured. ***: The acid anhydride and amine curing agent were charged at an equivalent ratio of 1 / 0.25 relative to the imide group-containing epoxy resin. On the other hand, imidazole was charged in parts by mass, regardless of the equivalent ratio.

[0135] In Examples 1 to 11, all of the resins contained a bifunctional epoxy resin and a diimidedicarboxylic acid compound, which were bonded by ester bonds and had an epoxy equivalent of 1,000 or less, resulting in imide group-containing epoxy resins with excellent fluidity. In particular, the use of a bifunctional epoxy resin and a phosphorus-based compound as a catalyst allowed for control of fluidity. Furthermore, all of the cured products were homogenized, and the use of an imidedicarboxylic acid compound resulted in excellent heat resistance.

[0136] In Comparative Example 1, the catalyst was changed from a phosphorus-based compound to a tertiary amine, and synthesis was performed. As a result, gelation occurred during synthesis of the imide group-containing epoxy resin, and the viscosity increased. This reduced the compatibility between the imide group-containing epoxy resin and the curing agent, and these components behaved as insoluble components, resulting in a decrease in the uniformity (transparency) of the cured product.

[0137] In Comparative Example 2, the bifunctional epoxy resin was replaced with a multifunctional epoxy resin to synthesize an imide group-containing epoxy resin. As a result, the reaction between the epoxy resin and diimidedicarboxylic acid did not proceed sufficiently, and some unreacted material remained. As a result, the uniformity of the cured product was poor.

[0138] In Comparative Example 3, the raw materials were simply mixed and cured, so the imide group-containing epoxy resin was not obtained, the viscosity was high, and the uniformity of the cured product was poor. Sufficient heat resistance was not achieved.

[0139] The imide group-containing epoxy resin of the present invention and cured products using the same are useful as electrical insulating materials such as sealants, printed wiring boards, molding materials, electrical penetration panels for nuclear power plants, and build-up laminates.

Claims

1. An imide group-containing epoxy resin comprising a diimide dicarboxylic acid compound represented by general formula (1) and a difunctional epoxy resin, wherein the diimide dicarboxylic acid compound and the difunctional epoxy resin are ester-bonded, and the epoxy equivalent is 1,000 or less. (In formula (1), X １ and X ２ each independently represents a structure derived from an aromatic tricarboxylic anhydride component, an alicyclic tricarboxylic anhydride component, or an aliphatic tricarboxylic anhydride component; R １ represents a structure derived from an aromatic diamine component or an alicyclic diamine component.

2. The imide group-containing epoxy resin according to claim 1, wherein the bifunctional epoxy resin is one or more epoxy resins selected from the group consisting of bisphenol A type epoxy resins, naphthalene type epoxy resins, biphenyl type epoxy resins, and anthracene type epoxy resins.

3. The imide group-containing epoxy resin according to claim 1, wherein the bifunctional epoxy resin is one or more epoxy resins selected from the group consisting of naphthalene type epoxy resins and biphenyl type epoxy resins, and the epoxy equivalent is 500 or less.

4. The imide group-containing epoxy resin according to claim 1, wherein the bifunctional epoxy resin is one or more epoxy resins selected from the group consisting of naphthalene type epoxy resins and biphenyl type epoxy resins, and the epoxy equivalent is 250 to 350.

5. The imide group-containing epoxy resin according to claim 1, wherein the imide group-containing epoxy resin has a structure in which one molecule of the diimide dicarboxylic acid compound is bonded to each end of the molecule of the difunctional epoxy resin via an ester bond.

6. A method for producing an imide group-containing epoxy resin, comprising reacting a diimidedicarboxylic acid compound with a bifunctional epoxy resin in the presence of a phosphorus compound.

7. The method for producing an imide group-containing epoxy resin according to claim 6, wherein the diimide dicarboxylic acid compound is blended in an amount such that the functional group equivalent of the diimide dicarboxylic acid compound is in an equivalent ratio of 0.01 to 0.6 relative to the epoxy equivalent of the bifunctional epoxy resin.

8. The method for producing an imide group-containing epoxy resin according to claim 6, wherein the bifunctional epoxy resin is one or more epoxy resins selected from the group consisting of naphthalene type epoxy resins and biphenyl type epoxy resins, and the amount of the diimide dicarboxylic acid compound is such that the functional group equivalent of the diimide dicarboxylic acid compound is 0.05 to 0.35 equivalent ratio to the epoxy equivalent of the bifunctional epoxy resin.

9. The method for producing an imide group-containing epoxy resin according to claim 6, wherein the bifunctional epoxy resin is one or more epoxy resins selected from the group consisting of naphthalene type epoxy resins and biphenyl type epoxy resins, and the amount of the diimide dicarboxylic acid compound is such that the functional group equivalent of the diimide dicarboxylic acid compound is 0.15 to 0.25 equivalent ratio to the epoxy equivalent of the bifunctional epoxy resin.

10. A method for producing the imide group-containing epoxy resin according to claim 6, which comprises producing the imide group-containing epoxy resin according to any one of claims 1 to 5.

11. A curable epoxy resin composition comprising the imide group-containing epoxy resin according to any one of claims 1 to 5 and a curing agent.

12. A cured product of the curable epoxy resin composition according to claim 11.

13. An electrical insulating material comprising the cured product according to claim 12.

14. A sealing material comprising the cured product according to claim 12.

15. The encapsulant according to claim 14, which is used in a power semiconductor module.

16. A printed wiring board comprising the cured product according to claim 12.

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