CN114728903A

CN114728903A - Compound containing imide group, curing agent containing imide group, cured epoxy resin, and electrical insulating material using same

Info

Publication number: CN114728903A
Application number: CN202080080567.8A
Authority: CN
Inventors: 谷中爱步; 中井诚; 田洼由纪
Original assignee: Unitika Ltd
Current assignee: Unitika Ltd
Priority date: 2019-12-10
Filing date: 2020-12-07
Publication date: 2022-07-08
Anticipated expiration: 2040-12-07
Also published as: TWI829983B; TW202128620A; KR20220114525A; JPWO2021117686A1; WO2021117686A1; JP2021193094A; CN114728903B; JP6960705B1

Abstract

The present invention provides a curing agent (particularly, a compound containing an imide group) for producing an electrically insulating epoxy resin cured product which sufficiently prevents local accumulation of charges under a high-temperature and high-electric field and has excellent heat resistance and dielectric properties. The present invention relates to a compound containing an imide group selected from the group consisting of a diimide dicarboxylic acid-based compound, a diimide tetracarboxylic acid-based compound and a monoimide tricarboxylic acid-based compound.

Description

Compound containing imide group, curing agent containing imide group, cured epoxy resin, and electrical insulating material using same

Technical Field

The present invention relates to an imide group-containing compound, an imide group-containing curing agent, an epoxy resin cured product, and an electrical insulating material using the same.

Background

Epoxy resins cured products made of epoxy resins and curing agents thereof are excellent in thermal properties, mechanical properties and electrical properties, and are widely used industrially, mainly for electric and electronic materials. As the curing agent for producing a cured epoxy resin, for example, a phenol curing agent, an acid anhydride curing agent, an amine curing agent, and the like are used.

In recent years, in the field of power devices represented by power modules for vehicles, there has been a demand for further increase in current, reduction in size, and increase in efficiency, and a transition to silicon carbide (SiC) semiconductors has been progressing. Since SiC semiconductors can operate at higher temperatures than conventional silicon (Si) semiconductors, semiconductor packaging materials used in SiC semiconductors are also required to have higher heat resistance than ever before (for example, patent document 1). Further, although power devices are used under high-temperature and high-electric-field conditions with the miniaturization and the increase in output, electric charges are accumulated in insulating materials under high-temperature and high-electric-field conditions, and the electric field inside semiconductors is distorted, thereby lowering the withstand voltage of semiconductor elements. Therefore, in order to improve the performance of power devices and to improve the withstand voltage at high temperatures, it is necessary to develop a material that does not cause charge accumulation at high temperatures and high electric fields.

In the field of power transmission lines, insulators made of ceramics or ceramics have been used, but since the insulators are heavy and brittle, insulators using polymers have been developed (for example, patent document 2). In recent years, insulators have been increased in voltage, and polymers used in insulators are required to be materials having dielectric properties lower than those of conventional products so as not to cause charge accumulation and high insulating properties that can be endured even when the voltage is increased.

In the field of electric vehicles, an insulating wire coating material is used for an electric wire constituting an electric device such as a motor (for example, patent document 3). In recent years, the output of motors has been increased, and the influence of partial discharge due to inverter surge has been increased. Accordingly, the wire coating material used for the motor is required to have a dielectric property lower than that of a conventional product in order to prevent the occurrence of the surge of the inverter and to have a high insulation property that can withstand the high output.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2007 and 305962

Patent document 2: japanese patent laid-open publication No. 2013-234311

Patent document 3: japanese patent laid-open No. 2012 and 224714

Disclosure of Invention

The present inventors have found that when a conventional material (particularly, an epoxy resin cured product produced using a conventional curing agent) is used as an electrical insulating material, electric charges locally accumulate at a high temperature and a high electric field, and the insulation may be broken, so that sufficient insulation cannot be obtained. For example, in the field of power devices, conventional insulating materials may locally accumulate charges due to a high-temperature and high-electric-field environment, and may damage the insulation.

The purpose of the present invention is to provide an epoxy resin cured product that sufficiently prevents local accumulation of charges under high-temperature and high-electric fields, and a curing agent (particularly, a compound containing an imide group) for producing the epoxy resin cured product.

It is another object of the present invention to provide an epoxy resin cured product that sufficiently prevents local accumulation of charges under a high-temperature and high-electric field and has excellent heat resistance and dielectric properties, and a curing agent (particularly, a compound containing an imide group) for producing the epoxy resin cured product.

In the present specification, the local accumulation of electric charges refers to a phenomenon in which electric charges generated in the interior of an electrically insulating material under a high-temperature and high-electric field are biased, and which can be observed by measuring a charge density distribution over time. The high-temperature and high-electric-field environment is, for example, a temperature of 120 ℃ or higher (particularly 130 to 150 ℃) and an electric field environment of 40 to 120kV/mm (particularly 80 to 120 kV/mm). The electrical insulation and the insulating property include such a property that local accumulation of electric charge is sufficiently prevented under a high-temperature and high-electric field.

In general, the higher dielectric constant and the dielectric loss tangent may be evaluated as being excellent or the lower dielectric constant may be evaluated as being excellent depending on the purpose, and in the present invention, the dielectric characteristics mean particularly the performance that both the dielectric constant and the dielectric loss tangent can be sufficiently reduced.

The present inventors have conducted extensive studies to solve the above problems, and as a result, have found that a cured product comprising a specific imide group-containing curing agent and an epoxy resin is excellent in all of heat resistance, dielectric properties, and insulating properties, and have completed the present invention.

That is, the gist of the present invention is as follows.

< 1 > an imide group-containing compound selected from the group consisting of diimide dicarboxylic acid-based compounds, diimide tetracarboxylic acid-based compounds and monoimide tricarboxylic acid-based compounds.

< 2 > an imide group-containing curing agent selected from < 1 > said imide group-containing compounds.

Less than 3 is more than one epoxy resin condensate which is composed of less than 2 is more than the curing agent containing imide group and epoxy resin.

< 4 > the cured epoxy resin composition according to < 3 >, wherein the epoxy resin has 2 or more epoxy groups in 1 molecule.

< 5 > the cured epoxy resin composition according to < 3 > or 4, wherein the imide group-containing curing agent has a molecular weight of 200 to 1100.

< 6 > the cured epoxy resin according to any one of < 3 > to < 5 >, wherein the imide group-containing curing agent has a functional group equivalent of 50 to 500.

< 7 > an electrically insulating material comprising the cured epoxy resin of any one of < 3 > to < 6 >.

< 8 > an encapsulating material comprising the cured epoxy resin of any one of < 3 > to < 6 >.

< 9 > the encapsulating material according to < 8 > for a power semiconductor module.

< 10 > an insulator comprising the cured epoxy resin of any one of < 3 > to < 6 >.

< 11 > the insulator according to < 10 > is used for a power transmission line.

< 12 > an electric wire coating material comprising the cured epoxy resin of any one of < 3 > to < 6 >.

< 13 > the electric wire covering material according to < 12 > for an electric vehicle.

< 14 > a printed wiring board comprising the cured epoxy resin of any one of < 3 > to < 6 >.

The present invention provides an electrically insulating cured epoxy resin which is excellent in heat resistance, dielectric properties and insulating properties and suitable for use in, for example, encapsulating materials (particularly semiconductor encapsulating materials), insulators, wire coating materials, and the like, and a curing agent (particularly, a compound containing an imide group) for producing the cured epoxy resin.

The cured product of the electrically insulating epoxy resin of the present invention has excellent insulating properties such that local accumulation of charges is sufficiently prevented particularly under a high-temperature and high-electric field.

Drawings

FIG. 1 is a graph showing changes with time in the charge density distribution of the cured epoxy resins of examples A-1, B-2 and C-1.

FIG. 2 is a graph showing the change with time in the charge density distribution of the epoxy resin cured products of comparative examples 1 to 3.

Detailed Description

The compound containing an imide group of the present invention is useful as a curing agent (particularly, a curing agent for an epoxy resin). When the compound containing an imide group of the present invention is used as a curing agent (particularly, a curing agent for an epoxy resin), it is also referred to as "an imide group-containing curing agent". Hereinafter, the electrically insulating epoxy resin cured product of the present invention will be described in detail, but in this description, an imide group-containing compound will be described in detail as an imide group-containing curing agent.

< electrically insulating epoxy resin cured product >

The electrically insulating epoxy resin cured product of the present invention is composed of an imide group-containing curing agent and an epoxy resin.

[ curing agent containing imide group ]

Examples of the imide group-containing curing agent include imide group-containing compounds such as diimide dicarboxylic acid compounds, diimide tetracarboxylic acid compounds, and monoimide tricarboxylic acid compounds. The imide group-containing curing agent may be at least 1 imide group-containing curing agent selected from these. From the viewpoint of further improving heat resistance, dielectric characteristics and insulating properties, the imide group-containing curing agent is preferably at least 1 imide group-containing curing agent selected from the group consisting of diimide dicarboxylic acid compounds.

The molecular weight of the imide group-containing curing agent is not particularly limited, but is preferably 200 to 1100, more preferably 300 to 1000, further preferably 300 to 700, and most preferably 400 to 600 from the viewpoint of further improving heat resistance, dielectric properties, and insulating properties.

The functional group equivalent of the imide group-containing curing agent is not particularly limited, but is preferably 50 to 500, more preferably 800 to 400, even more preferably 100 to 400, and most preferably 200 to 350, from the viewpoint of further improving heat resistance, dielectric characteristics, and insulating properties. The functional group equivalent is a value calculated by dividing the molecular weight by the number of functional groups (for example, carboxyl groups) of the imide group-containing curing agent per 1 molecule.

The amount of the imide group-containing curing agent to be incorporated in the curing agent is not particularly limited, and is preferably 50% by mass or more, more preferably 80% by mass or more, further preferably 90% by mass or more, and most preferably 100% by mass, relative to the total amount of the curing agent, from the viewpoint of further improving heat resistance, dielectric properties, and insulation properties. The amount of the imide group-containing curing agent added is 100% by mass based on the total amount of the curing agents, and means that the curing agent is composed only of the imide group-containing curing agent. When 2 or more types of imide group-containing curing agents are blended, the total blending amount thereof may be within the above range.

(diimide dicarboxylic acid compound)

The diimide dicarboxylic acid compound is a compound having 2 imide groups and 2 carboxyl groups in 1 molecule. The diimide dicarboxylic acid compound has no amide group. The imide dicarboxylic acid compound can be produced by producing an amic acid compound by reacting functional groups with each other using a tricarboxylic anhydride component and a diamine component as raw material compounds, and then carrying out an imidization reaction. Here, the reaction of the functional groups with each other may be carried out in a solution or in a solid phase, and the production method is not particularly limited.

The diimide dicarboxylic acid compound using a tricarboxylic acid anhydride component and a diamine component is a compound in which 2 molecules of the tricarboxylic acid anhydride component and 1 molecule of the diamine component react to form 2 imide groups.

In the production of the diimide dicarboxylic acid compound using the tricarboxylic acid anhydride component and the diamine component, the diamine component is usually used in an amount of about 0.5 times by mole, for example, 0.1 to 0.7 times by mole, preferably 0.3 to 0.7 times by mole, more preferably 0.4 to 0.6 times by mole, and further preferably 0.45 to 0.55 times by mole, based on the tricarboxylic acid anhydride component.

The tricarboxylic acid anhydride component that can constitute the diimide dicarboxylic acid compound is not particularly limited, and for example, an aromatic tricarboxylic acid anhydride component containing an aromatic ring is preferable, and trimellitic anhydride is particularly preferable, from the viewpoint of further improving the heat resistance, dielectric properties, and insulation properties of the diimide dicarboxylic acid compound and the epoxy resin cured product obtained using the same. The tricarboxylic anhydride component constituting the diimide dicarboxylic acid compound may be used alone in 1 kind, or 2 or more kinds may be used as a mixture.

The diamine component that can constitute the diimide dicarboxylic acid compound is not particularly limited, and for example, an aromatic diamine component containing an aromatic ring is preferable from the viewpoint of further improving heat resistance, dielectric characteristics, insulating properties and solubility of the diimide dicarboxylic acid compound and an epoxy resin cured product obtained using the same, and m-xylylenediamine, p-xylylenediamine, 4' -diaminodiphenyl ether and dimer diamine are particularly preferable. The diamine component constituting the diimide dicarboxylic acid compound may be used alone in 1 kind, or may be used in a mixture of2 or more kinds.

(diimide tetracarboxylic acid compound)

The diimide tetracarboxylic acid compound is a compound having 2 imide groups and 4 carboxyl groups in 1 molecule. The amic acid compound can be produced by reacting functional groups with each other using a tetracarboxylic dianhydride component and a monoaminodicarboxylic acid component as raw material compounds, and the diimide tetracarboxylic acid compound can be produced by performing an imidization reaction. Here, the reaction of the functional groups with each other may be carried out in a solution or in a solid phase, and the production method is not particularly limited.

The diimide tetracarboxylic acid compound using a tetracarboxylic dianhydride component and a monoaminodicarboxylic acid component is a compound in which 2 molecules of the monoaminodicarboxylic acid component and 1 molecule of the tetracarboxylic dianhydride component react to form 2 imide groups.

In the production of a diimide tetracarboxylic acid compound using a tetracarboxylic dianhydride component and a monoaminodicarboxylic acid component, the monoaminodicarboxylic acid component is usually used in an amount of about 2 times by mole, for example, 1.5 to 10.0 times by mole, preferably 1.8 to 2.2 times by mole, more preferably 1.9 to 2.1 times by mole, and further preferably 1.95 to 2.05 times by mole, relative to the tetracarboxylic dianhydride component.

The tetracarboxylic dianhydride component that can constitute the diimide tetracarboxylic compound is not particularly limited, and for example, an aromatic tetracarboxylic dianhydride component containing an aromatic ring and/or an aliphatic tetracarboxylic dianhydride component not containing both an aromatic ring and an aliphatic ring is preferable, and 3,3 ', 4,4 ' -benzophenone tetracarboxylic dianhydride, 4,4 ' - (hexafluoroisopropylidene) diphthalic anhydride, and 1,2,3, 4-butane tetracarboxylic dianhydride are particularly preferable, from the viewpoint of further improving the heat resistance, dielectric properties, insulation properties, solubility, and versatility of the diimide tetracarboxylic dianhydride and the epoxy resin cured product obtained using the diimide tetracarboxylic dianhydride. The tetracarboxylic dianhydride component which can constitute the diimide tetracarboxylic acid-based compound may be used alone in 1 kind, or may be used in a mixture of2 or more kinds.

The monoaminodicarboxylic acid component that can constitute the diimide tetracarboxylic acid compound is not particularly limited, and aromatic monoaminodicarboxylic acid components containing an aromatic ring are preferable, and 2-aminoterephthalic acid, 2-aminoisophthalic acid, 4-aminoisophthalic acid, 5-aminoisophthalic acid, 3-aminophthalic acid, and 4-aminophthalic acid are particularly preferable, from the viewpoint of further improving the heat resistance, dielectric properties, insulation properties, and solubility of the diimide tetracarboxylic acid compound and the epoxy resin cured product obtained using the imide tetracarboxylic acid compound. The monoaminodicarboxylic acid component constituting the diimide tetracarboxylic acid compound may be used alone in 1 kind, or may be used in a mixture of2 or more kinds.

(Monoimide tricarboxylic acid-based compound)

The monoimide tricarboxylic acid-based compound is a compound having 1 imide group and 3 carboxyl groups in 1 molecule. The amic acid compound can be produced by reacting functional groups with each other using a tricarboxylic acid anhydride component and a monoaminodicarboxylic acid component as raw material compounds, and the monoimide tricarboxylic acid compound can be produced by performing an imidization reaction. Here, the reaction of the functional groups with each other may be carried out in a solution or in a solid phase, and the production method is not particularly limited.

The monoimide tricarboxylic acid-based compound using the tricarboxylic acid anhydride component and the monoaminodicarboxylic acid component is a compound in which 1 molecule of the monoaminodicarboxylic acid component reacts with 1 molecule of the tricarboxylic acid anhydride component to form 1 imide group.

In the production of the monoimide tricarboxylic acid compound using the tricarboxylic acid anhydride component and the monoaminodicarboxylic acid component, the monoaminodicarboxylic acid component is used in an amount of usually about 1 time by mole, for example, 0.5 to 5.0 times by mole, preferably 0.8 to 1.2 times by mole, more preferably 0.9 to 1.1 times by mole, and further preferably 0.95 to 1.05 times by mole, based on the tricarboxylic acid anhydride component.

The tricarboxylic acid anhydride component that can constitute the monoimide tricarboxylic acid-based compound is not particularly limited, and for example, an aromatic tricarboxylic acid anhydride component containing an aromatic ring is preferable, and trimellitic anhydride is particularly preferable, from the viewpoint of further improving the heat resistance, dielectric properties, and insulation properties of the monoimide tricarboxylic acid-based compound and an epoxy resin cured product obtained using the same. The tricarboxylic acid anhydride component constituting the monoimide tricarboxylic acid-based compound may be used alone in 1 kind, or 2 or more kinds may be used as a mixture.

The monoaminodicarboxylic acid component that can constitute the monoimide tricarboxylic acid-based compound is not particularly limited, and for example, an aromatic monoaminodicarboxylic acid component containing an aromatic ring is preferable from the viewpoint of further improving heat resistance, dielectric properties and insulation properties of the monoimide tricarboxylic acid-based compound and an epoxy resin cured product obtained using the same, and 2-aminoterephthalic acid, 2-aminoisophthalic acid, 4-aminoisophthalic acid, 5-aminoisophthalic acid, 3-aminophthalic acid and 4-aminophthalic acid are particularly preferable. The monoaminodicarboxylic acid component constituting the monoamide tricarboxylic acid-based compound may be used alone in 1 kind, or 2 or more kinds may be used as a mixture.

[ method for producing curing agent containing imide group ]

The imide group-containing curing agent can be produced in a solvent or without a solvent, and the production method is not particularly limited.

Examples of the method of producing in a solvent include a method in which a predetermined raw material (for example, a tricarboxylic acid anhydride component, a diamine component, a tetracarboxylic dianhydride component, and a monoaminodicarboxylic acid component) is added to an aprotic solvent such as N-methyl 2-pyrrolidone, stirred at 80 ℃, and then imidized.

The method of imidization is not particularly limited, and examples thereof include a thermal imidization method by heating to 250 to 300 ℃ under a nitrogen atmosphere, and a chemical imidization method by treating with a dehydrocyclization agent such as a mixture of a carboxylic acid anhydride and a tertiary amine.

Examples of the method of producing the polymer in the absence of a solvent include a method utilizing a mechanochemical effect. The method utilizing a mechanochemical effect refers to a method in which a mechanochemical effect is exhibited by utilizing mechanical energy generated when a raw material compound used in a reaction is pulverized to obtain an organic compound.

The mechanochemical effect is an effect (or phenomenon) of imparting mechanical energy (compressive force, shearing force, impact force, grinding force, or the like) to a raw material compound in a solid state under a reaction environment to pulverize the raw material compound and activate a pulverization interface formed. Thereby, a reaction of the functional groups with each other occurs. The reaction of the functional groups with each other usually takes place between 2 or more molecules of the starting compound. For example, the reaction of the functional groups with each other may occur between 2 molecules of the starting compound having different chemical structures, or may occur between 2 molecules of the starting compound having the same chemical structure. The reaction of the functional groups with one another takes place not only between the molecules of the 2 starting compounds of the defined group 1 but generally also between the molecules of the 2 starting compounds of the other groups. A new reaction of functional groups with each other can occur between the compound molecules generated by the reaction of functional groups with each other and the molecules of the starting compound. The reaction of the functional groups with each other is usually a chemical reaction, whereby a bonding group (particularly a covalent bond) is formed between 2 molecules of the raw material compound by the functional group of each molecule of the raw material compound, and another 1 molecule of the compound is generated.

The reaction environment refers to an environment in which the raw material compound is present for the reaction, that is, an environment to which mechanical energy is applied, and may be, for example, an environment in an apparatus. Being in a solid state under a reaction environment means being in a solid state under an environment to which mechanical energy is imparted (for example, under temperature and pressure within the apparatus). The raw material compound in a solid state in the reaction environment may be in a solid state at ordinary temperature (25 ℃) and normal pressure (101.325 kPa). The raw material compound in a solid state in the reaction environment may be in a solid state at the start of imparting mechanical energy. The raw material compound in a solid state in the reaction environment of the present invention may be changed to a liquid state (for example, a molten state) during the reaction (or during the treatment) due to an increase in temperature, pressure, or the like caused by the continuation of the application of mechanical energy, but is preferably continuously in a solid state during the reaction (or during the treatment) from the viewpoint of improving the reaction rate.

The details of the mechanochemical effect are not clear, but are believed to follow the following principles. When 1 or more solid raw material compounds are pulverized by applying mechanical energy, the pulverization interface is activated by the absorption of the mechanical energy. It is considered that a chemical reaction occurs between 2 molecules of the raw material compound by utilizing the surface activity of the pulverization interface. Pulverization means that mechanical energy is imparted to particles of a raw material compound, and the particles absorb the mechanical energy, whereby the particles are cracked and the surface is renewed. Surface renewal refers to the formation of the pulverization interface as a new surface. In the mechanochemical effect, the state of the new surface formed by the renewal of the surface is not particularly limited as long as the activation of the pulverization interface occurs by the pulverization, and may be in a dry state or a wet state. The wet state of the new surface formed by surface renewal is caused by the raw material compound in a liquid state, which is different from the raw material compound in a solid state.

Mechanical energy is imparted to a raw material mixture containing 1 or more raw material compounds in a solid state under a reaction environment. The state of the raw material mixture is not particularly limited as long as the raw material compound in a solid state is pulverized by imparting mechanical energy. For example, since all the raw material compounds contained in the raw material mixture are in a solid state, the raw material mixture may be in a dry state. In addition, for example, since at least 1 kind of the raw material compounds contained in the raw material mixture is in a solid state and the remaining raw material compounds are in a liquid state, the raw material mixture may be in a wet state. Specifically, for example, when the raw material mixture contains only 1 raw material compound, the 1 raw material compound is in a solid state. Further, for example, when the raw material mixture contains 2 raw material compounds, the 2 raw material compounds may 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.

In the method utilizing the mechanochemical effect, the functional group is a 1-valent group (atomic group) which can be a cause of reactivity in the molecular structure, and is used in a concept not including an unsaturated bond group such as a double bond between carbons or a triple bond between carbons (for example, a radical polymerizable group). The functional group is a group containing carbon atoms and heteroatoms. The hetero atom is 1 or more atoms selected from oxygen atom, nitrogen atom and sulfur atom, particularly oxygen atom and nitrogen atom. The functional group may further contain a hydrogen atom. The functional groups to be reacted are usually 2 functional groups, and the structures of the molecules of the starting compound having one functional group and the molecules of the starting compound having another functional group may be different from each other, or may be the same. By reacting to form 2 bonds (especially covalent bonds) of the molecules of the starting compound, 1 molecularization thereof is achieved. By the reaction of the functional groups with each other, small molecules such as water, carbon dioxide and/or alcohol may be produced as by-products, or may be produced without by-products.

The reaction of the functional groups with each other may be a reaction of all the functional groups (particularly, 1-valent functional groups) that can undergo a chemical reaction with each other, for example, a reaction of2 functional groups selected from a carboxyl group and a halide (group) thereof, an acid anhydride group, an amino group, an isocyanate group, a hydroxyl group, and the like. The 2 functional groups are not particularly limited as long as they are chemically reacted, and may be, for example, 2 functional groups having different chemical structures or 2 functional groups having the same chemical structure.

Examples of the reaction between the functional groups include a condensation reaction, an addition reaction, and a complex reaction thereof.

The condensation reaction is a reaction in which bonding or connection between molecules of the raw material compounds is achieved with the detachment of small molecules such as water, carbon dioxide, and alcohol between molecules of the raw material compounds. Examples of the condensation reaction include a reaction to form an amide group (amidation reaction), a reaction to form an imide group (imidization reaction), and a reaction to form an ester group (esterification reaction).

The addition reaction is an addition reaction between functional groups, and is a reaction in which bonding or connection between molecules of the raw material compound is achieved without detachment of small molecules between molecules of the raw material compound. Examples of the addition reaction include a reaction to form a urea group, a reaction to form a urethane group, and a reaction to open a ring of a cyclic structure (i.e., a ring-opening reaction). The ring-opening reaction is a reaction in which a part of a cyclic structure is cleaved in a raw material compound having a cyclic structure (for example, an acid anhydride group-containing compound, a cyclic amide compound, a cyclic ester compound, an epoxy compound) and a site where the cleavage is effected is bonded or linked to a functional group of another raw material compound. The ring-opening reaction generates, for example, an amide group, a carboxyl group, an ester group, and an ether group. In particular, in the ring-opening reaction of an acid anhydride group in an acid anhydride group-containing compound as a raw material compound, the acid anhydride group is opened to bond or connect with other raw material compound molecules (amino group or hydroxyl group). As a result, for example, an amide group or an ester group and a carboxyl group are simultaneously formed.

More specifically, the reaction of the functional groups with each other may be, for example, 1 or more reaction selected from the following reactions:

(A) a reaction of the acid anhydride group with the amino group to form (a1) an amide group and a carboxyl group, (a2) an imide group, (a3) an isoimide group, or (a4) a mixed group thereof;

(B) a reaction of generating an imide group by a reaction of an acid anhydride group and an isocyanate group;

(C) a reaction of generating an amide group by a reaction of a carboxyl group or a halide thereof with an amino group or an isocyanate group;

(D) a reaction of generating an ester group by a reaction of a carboxyl group or a halide thereof with a hydroxyl group;

(E) a reaction in which an isocyanate group reacts with an amino group to form a urea group;

(F) a reaction in which an isocyanate group reacts with a hydroxyl group to form a carbamate group; and

(G) the reaction of the acid anhydride group with the hydroxyl group produces an ester group and a carboxyl group.

In the production of the imide group-containing curing agent from each of the above raw material compounds, the reaction of the functional groups corresponds to the reaction of the above (a). In the method of producing in the absence of a solvent, after the method utilizing the mechanochemical effect is carried out, the imidization can be carried out by the same method as the imidization in the method of producing in a solvent.

[ epoxy resin ]

The epoxy resin used in the present invention is not particularly limited as long as it is an organic compound having 2 or more epoxy groups in 1 molecule. Specific examples of the epoxy resin include bisphenol a type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, naphthalene type epoxy resin, biphenyl type epoxy resin, dicyclopentadiene type epoxy resin, phenol novolac type epoxy resin, cresol novolac type epoxy resin, isocyanurate type epoxy resin, alicyclic epoxy resin, acrylic modified epoxy resin, polyfunctional epoxy resin, brominated epoxy resin, and phosphorus modified epoxy resin. The epoxy resins may be used alone or in combination of2 or more. The epoxy group may be a glycidyl group. The epoxy resin is available in the form of a commercially available product.

The epoxy resin has an epoxy equivalent of usually 100 to 3000, preferably 150 to 300.

[ additives ]

The cured epoxy resin of the present invention may further contain additives such as a curing accelerator, a thermosetting resin, an inorganic filler, an antioxidant, and a flame retardant.

The curing accelerator is not particularly limited, and examples thereof include imidazoles such as 2-methylimidazole, 2-ethyl-4-methylimidazole and 2-phenylimidazole; tertiary amines such as 4-dimethylaminopyridine, benzyldimethylamine, 2- (dimethylaminomethyl) phenol, 2,4, 6-tris (dimethylaminomethyl) phenol and the like; organic phosphines such as triphenylphosphine and tributylphosphine. The curing accelerator may be used alone or in combination of2 or more.

The amount of the curing accelerator is not particularly limited, and is, for example, 0.01 to 2% by mass based on the total amount of the epoxy resin solution described later, preferably 0.01 to 1% by mass, and more preferably 0.05 to 0.5% by mass, from the viewpoint of further improving the heat resistance, dielectric properties, and insulating properties of the cured epoxy resin.

The thermosetting resin is not particularly limited, and examples thereof include cyanate ester resins, isocyanate resins, maleimide resins, polyimide resins, urethane resins, and phenol resins. The thermosetting resin may be used alone, or 2 or more kinds may be used in combination.

Examples of the inorganic filler include silica, glass, alumina, talc, mica, barium sulfate, aluminum hydroxide, magnesium hydroxide, calcium carbonate, magnesium oxide, titanium oxide, silicon nitride, and boron nitride. The inorganic filler may be used alone or in combination of2 or more. The inorganic filler is preferably an inorganic filler surface-treated with a surface-treating agent such as an epoxy silane coupling agent or an aminosilane coupling agent. The inorganic filler may be used alone or in combination of2 or more.

Examples of the antioxidant include hindered phenol antioxidants, phosphorus antioxidants, and thioether antioxidants. The antioxidant may be used alone or in combination of2 or more.

The flame retardant is not particularly limited, and is preferably a non-halogen flame retardant from the viewpoint of the influence on the environment. Examples of the flame retardant include phosphorus flame retardants, nitrogen flame retardants, and silicone flame retardants. The flame retardants may be used alone or in combination of2 or more.

Method for producing cured product of electrically insulating epoxy resin

The electrically insulating epoxy resin cured product of the present invention can be produced by heating an epoxy resin solution described in detail below containing an imide group-containing curing agent and an epoxy resin.

For example, an electrically insulating epoxy resin cured product of the present invention can be produced by coating an epoxy resin solution on a substrate, and drying and curing the epoxy resin solution by heating. After curing, the cured product can be used by peeling it from the substrate. The method of applying the epoxy resin solution is not particularly limited, and examples thereof include a casting method and an immersion method. An epoxy resin cured product can be obtained in the form of a sheet, a film or the like by coating a substrate with an epoxy resin solution, drying and curing the coating, and then peeling the coating from the substrate.

In addition, for example, an electrically insulating epoxy resin cured product of the present invention can be produced by pouring an epoxy resin solution into a mold, molding, drying, and curing. The method for molding the epoxy resin solution is not particularly limited, and examples thereof include transfer molding and injection molding.

The coating film, the laminate thereof, and the molded product (i.e., molded product) thereof obtained by using the epoxy resin solution of the present invention can be completely cured by heating to react the imide group-containing curing agent with the epoxy resin. The heating temperature (curing temperature) is usually 80 to 350 ℃, preferably 130 to 300 ℃. The heating time (curing time) is usually 1 minute to 20 hours, preferably 5 minutes to 10 hours.

The epoxy resin cured product of the present invention may have any size. When the cured epoxy resin of the present invention has a form of, for example, a film, a plate, a film, a sheet or the like, the thickness of the cured epoxy resin may be usually 1 μm to 100 mm.

[ epoxy resin solution ]

The epoxy resin solution is obtained by mixing at least a curing agent containing an imide group and an epoxy resin in an organic solvent. Preferably, in the epoxy resin solution, the imide group-containing curing agent and the epoxy resin are dissolved in an organic solvent, and at least the imide group-containing curing agent, the epoxy resin and the organic solvent are uniformly mixed at a molecular level. Dissolution refers to the uniform mixing of solutes in a solvent on a molecular scale. The solution is a mixed liquid in which a solute is uniformly mixed in a solvent on a molecular scale, and the solute is dissolved in the solvent to such an extent that the solute is transparent to the naked eye at normal temperature (25 ℃) and normal pressure (101.325kPa), for example. The epoxy resin solution may further contain the above-mentioned additives.

The organic solvent used in the epoxy resin solution is not particularly limited as long as it can uniformly dissolve the curing agent and the epoxy resin, and a non-halogenated solvent is preferable from the viewpoint of influence on the environment. Examples of such a non-halogenated solvent include amide compounds such as N, N-dimethylformamide, N-dimethylacetamide, and N-methyl-2-pyrrolidone. These non-halogenated solvents are all useful as general-purpose solvents. The organic solvent may be used alone, or 2 or more of them may be used in combination.

The method for producing the epoxy resin solution is not particularly limited, and for example, a single dissolution method, a batch dissolution method, or the like may be used. The individual dissolution method is preferable in view of obtaining a uniform resin solution in a short time. The individual dissolution method is a method of mixing the imide group-containing curing agent and the epoxy resin separately in advance, dissolving them in an organic solvent, and then mixing them. The collective dissolution method is a method of mixing and dissolving an imide group-containing curing agent and an epoxy resin in an organic solvent at the same time. In the individual dissolution method and the collective dissolution method, the mixing temperature is not particularly limited, and may be, for example, 80 to 180 ℃, particularly 100 to 160 ℃. The heating for achieving the above mixing temperature may be, for example, reflux heating of the organic solvent.

In the epoxy resin solution, the amount of the imide group-containing curing agent to be added is preferably an amount such that the functional group equivalent of the imide group-containing curing agent is 0.5 to 1.5 equivalent, more preferably 0.7 to 1.3 equivalent, to the epoxy equivalent of the epoxy resin, from the viewpoint of further improving the heat resistance, dielectric properties and insulating properties of the resulting epoxy resin cured product. The functional group equivalent of the imide group-containing curing agent corresponds to an equivalent calculated from the content of a hydroxyl group or a carboxyl group.

The total amount of the imide group-containing curing agent and the epoxy resin to be blended in the epoxy resin solution is not particularly limited, but is preferably 30 to 90% by mass, more preferably 40 to 80% by mass, and still more preferably 50 to 70% by mass, based on the total amount of the epoxy resin solution, from the viewpoint of further improving the heat resistance, dielectric properties, and insulating properties of the resulting epoxy resin cured product.

The epoxy resin solution generally has a viscosity of 10 to 70 pas, particularly 30 to 70 pas, preferably 40 to 60 pas, and does not have a so-called gel form. The gel is not a viscous substance, but is generally in the state of a solid substance having no fluidity. Specifically, when the epoxy resin solution is mixed with a further solvent, the epoxy resin solution and the further solvent are mutually compatible with each other, and the whole is uniformly mixed at a molecular level. However, even when the gel is mixed with a further solvent, the gel remains in a lump without being dissolved in each other, and the gel cannot be uniformly mixed on a molecular level as a whole. The mixing in the case of determining compatibility can be generally carried out by mixing 100g of the solution or gel with 100g of the solvent under stirring conditions of normal temperature (25 ℃ C.), normal pressure (101.325kPa) and 100 rpm. In this case, the "further solvent" is a solvent that is compatible with the solvent contained in the solution or gel, and is, for example, a solvent represented by the same structural formula as the solvent contained in the solution or gel. The viscosity of the epoxy resin solution is a viscosity at 30 ℃ measured by a brookfield digital viscometer.

In the epoxy resin solution, the epoxy resin hardly reacts unexpectedly, and thus may have a low viscosity as described above. Therefore, a cured product can be produced with sufficient workability using an epoxy resin solution. In detail, the epoxy resin solution generally has a reactivity of 10% or less. The reaction rate is a ratio of the number of glycidyl groups reacted in the epoxy resin solution to the total number of glycidyl groups contained in the epoxy resin.

Use of cured product of electrically insulating epoxy resin

The epoxy resin cured product of the present invention is useful for all applications requiring at least one property (preferably a property including at least electrical insulation) among heat resistance, dielectric properties, and electrical insulation. In particular, the cured epoxy resin of the present invention can be preferably used as all electrical insulating materials. Examples of such an electrically insulating material include a packaging material (for example, a packaging material for a power semiconductor module), an insulator (particularly, an insulator coating material) (for example, an insulator for a power transmission line (particularly, an insulator coating material for a power transmission line)), an electric wire coating material (for example, an electric wire coating material for an electric vehicle), an insulating material for a printed wiring board, and the like.

Use of electrically insulating epoxy resin cured product as encapsulating material:

when the electrically insulating cured epoxy resin of the present invention is used as an encapsulating material, for example, after a power semiconductor module is produced, an epoxy resin solution is filled into a mold provided with the module, and the epoxy resin solution is dried and cured, whereby the cured epoxy resin of the present invention can be used as an encapsulating material for a power semiconductor module.

Use of cured electrically insulating epoxy resin as insulator coating material:

when the cured epoxy resin of the present invention is used as an insulator coating material, for example, an epoxy resin solution may be used to coat the outer peripheral portion (particularly, the outer peripheral surface) of the core of an insulator to form a layer, and the layer may be dried and cured to use the cured epoxy resin of the present invention as an insulator coating material. Examples of the core generally include glass fiber reinforced plastics such as glass fiber reinforced epoxy resin and glass fiber reinforced phenolic resin molded into various shapes such as a cylindrical shape and a columnar shape. The thickness of the cured epoxy resin as the coating material formed on the outer periphery of the core may vary depending on the size and shape (e.g., presence or absence of the umbrella portion, its shape, size, and spacing) of the polymer insulator to be obtained, but the thinnest portion is preferably 1mm or more, more preferably 2mm or more, from the viewpoint of further improving heat resistance, dielectric characteristics, insulation properties, and the like. When the electrically insulating cured epoxy resin of the present invention is used as an insulator coating material, the thickness of the coating material is usually 1 to 100mm, preferably 2 to 50 mm. When the cured epoxy resin of the present invention is used as an insulator coating material, the cured epoxy resin of the present invention is particularly useful as an insulator coating material for a power transmission line from the viewpoint of insulation properties (particularly insulation properties for further sufficiently preventing dielectric breakdown due to local accumulation of charges).

Use of cured electrically insulating epoxy resin as an electric wire coating material:

when the electrically insulating cured epoxy resin of the present invention is used as an electric wire coating material, an epoxy resin solution may be applied to the surface of a conductor and sintered (i.e., dried and cured), and thus the cured epoxy resin of the present invention may be used as an electric wire coating material. Examples of the conductor include copper and copper alloy. The coating method and the sintering method can be performed in the same manner and under the same conditions as those of the coating method and the sintering method in the conventional method for forming an electric wire coating. The coating and sintering may be repeated more than 2 times. The epoxy resin solution may be used in admixture with other resins. The thickness of the wire coating material is preferably 1 to 100 μm, and more preferably 10 to 50 μm, from the viewpoint of protecting the conductor. When the cured epoxy resin of the present invention is used as an electric wire coating material, the cured epoxy resin of the present invention is particularly useful as an electric wire coating material for electric vehicles from the viewpoint of insulation properties (in particular, insulation properties for sufficiently preventing dielectric breakdown due to local accumulation of electric charges).

Use of cured electrically insulating epoxy resin as an insulating material for printed wiring boards:

the printed wiring board usually contains an electrically insulating cured epoxy resin, and may further contain a glass cloth. When the electrically insulating cured epoxy resin of the present invention is used as an insulating material for a printed wiring board, the cured epoxy resin of the present invention can be used as an insulating material for a printed wiring board by impregnating or coating a glass cloth with an epoxy resin solution, followed by drying and curing. May be a printed wiring board. The printed wiring board may be provided with wiring (conductors) on the surface and/or inside thereof, and/or may also mount electronic components. The thickness of the printed wiring board is not particularly limited.

The cured epoxy resin of the present invention can be suitably used as an electrical and electronic material for other applications, for example, a mold material for a bushing transformer, a mold material for a solid insulated switchgear, an electrical penetration material for a nuclear power plant, a laminate sheet by lamination, and the like.

Examples

The present invention will be specifically described below with reference to examples, but the present invention is not limited thereto. The evaluation and measurement are performed by the following methods.

A. Evaluation and measurement

[ production method and evaluation method of imide group-containing curing agent ]

(1) Method for preparing imide group-containing curing agent

A sample 150g obtained by mixing an acid component and an amine component at the ratio shown in the table was mixed and pulverized at a rotation speed of about 9000rpm for 1 minute by using Wonder Crusher (osaka chemical co., ltd.) WC-3C, and this operation was repeated 3 times to perform mechanochemical treatment.

The treated sample was transferred to a glass vessel, and imidization was performed in an inert oven (Yamaoto science) DN411I under nitrogen atmosphere at a calcination temperature of 300 ℃ for a calcination time of2 hours.

As described below, the identification of the curing agent containing an imide group is performed by the molecular weight being the same as that of the target structure and by absorption from the imide group by infrared spectroscopy.

(2) Molecular weight of imide group-containing curing agent

The molecular weight was determined by measuring with a high performance liquid chromatography mass spectrometer (LC/MS) under the following conditions.

Sample preparation: curing agent/DMSO solution containing imide groups (200. mu.g/mL)

The device comprises the following steps: MicroTOF2-kp manufactured by Bruker Daltonics

Column: cadenza CD-C183 mm 2mm x 150mm

Mobile phase: (mobile phase A) 0.1% aqueous formic acid solution, (mobile phase B) methanol

Gradient (B Conc.): 0min (50%) -5, 7min (60%) -14.2min (60%) -17 min (100%) -21.6min (100%) -27.2min (50%) -34min (50%)

An ionization method: ESI

Detection conditions are as follows: negative mode

(3) Confirmation of the reaction

The identification was performed by measurement under the following conditions by infrared spectroscopy (IR).

Infrared spectroscopy (IR)

The device comprises the following steps: system 2000 infrared spectrometer manufactured by Perkin Elmer

The method comprises the following steps: KBr method

Cumulative number of times: 64 scans (resolution 4 cm)^-1)

1778cm for confirmation of the Presence or absence of an imide group^-1Nearby and 1714cm^-1Nearby absorption.

Very good: (reaction progress) in some cases;

x: (reaction not carried out) is not the case.

[ method for evaluating cured epoxy resin ]

(1) Reactivity

The epoxy resin cured products obtained in examples and comparative examples were subjected to transmission infrared absorption spectrum (IR) measurement under the following conditions, and the absorbance ratio of glycidyl groups was determined.

Usually 900-950 cm^-1Wave number of (2)The zones detect absorption from glycidyl groups. The absorbance was calculated by using, as a baseline, a line obtained by linearly connecting the base portions on both sides of the absorption peak detected at these wave numbers, and using, as the absorbance, the length from the intersection point when the peak of the peak was vertically connected to the baseline to the peak of the peak.

Infrared spectroscopy (IR)

The method comprises the following steps: KBr method

Cumulative number of times: 64 scans (resolution 4 cm)^-1)

Next, the details of the method for calculating the reaction rate of glycidyl groups will be described

First, IR measurement samples were prepared by mixing the epoxy resin solutions obtained in examples and comparative examples with KBr powder, and the IR measurements were performed. The absorbance α of the glycidyl group was determined by confirming that the intensity of the peak showing the highest absorbance in the obtained spectrum falls within the range of absorbance 0.8 to 1.0. Next, the sample was heat-treated in an oven at a temperature of 300 ℃ for 2 hours under a nitrogen flow to complete the curing reaction. The cured sample was subjected to IR measurement by the same method, and the absorbance α' of the wave number due to the glycidyl group was obtained. The reaction rate of the sample at this time was determined from the following equation, with the reaction rate of the glycidyl group before the curing reaction set to 0%.

Reaction rate (%) { 1- (. alpha.'/. alpha.) }. times.100

Very good: 90% -100% (optimal);

o: 80% or more and less than 90% (good);

and (delta): more than 70% and less than 80% (practically, there is no problem);

x: less than 70% (practically problematic).

(2) Glass transition temperature (Tg) (Heat resistance)

The measurement was carried out by a Differential Scanning Calorimetry (DSC) under the following conditions.

The device comprises the following steps: DSC 7 manufactured by Perkin Elmer

Temperature rise rate: 20 ℃/min

The temperature was raised from 25 ℃ to 300 ℃ and, after lowering the temperature, raised again from 25 ℃ to 300 ℃ and the onset temperature of the discontinuous change in the transition temperature from the obtained temperature-raising curve was taken as the glass transition temperature (Tg).

Use of "jER 828: bisphenol A epoxy resin manufactured by Mitsubishi chemical corporation

Very good: tg (optimally) at 190 ℃;

o: tg is more than or equal to 170 ℃ and less than 190 ℃ (good);

and (delta): tg is more than or equal to 140 ℃ and less than 170 ℃ (no problem exists in practical use);

x: tg < 140 ℃ is problematic in practice.

Use of "EOCN-1020-55: o-cresol novolac type epoxy resin manufactured by Nippon chemical Co., Ltd. "case of epoxy resin

Very good: tg (optimally) is more than or equal to 200 ℃;

o: tg is more than or equal to 180 ℃ and less than 200 ℃ (good);

and (delta): tg is more than or equal to 150 ℃ and less than 180 ℃ (no problem exists in practical use);

x: tg < 150 ℃ C (practically problematic).

(3) Insulation (measurement of Charge Density distribution)

The charge density distribution of the epoxy resin cured products obtained in examples and comparative examples was measured by a pulsed electrostatic stress for high temperature measurement (PEA) measurement system under the following conditions, and the maximum electric field in the obtained samples was evaluated. After an epoxy resin cured product sample was placed in a high voltage application unit in a state of being immersed in silicone oil, the sample was heated to 140 ℃ and, after reaching 140 ℃, the temperature was controlled to be 140 ℃ and a direct current voltage was applied 30 minutes later. In consideration of the acoustic characteristic impedance of the sample, a commercially available sheet of conductive PEEK (polyetheretherketone) was used for the anode (anode), and an aluminum plate was used for the cathode (cathode). The cured epoxy resin (sample) had a film shape and was sandwiched between an anode and a cathode. When a DC voltage was applied, a DC voltage corresponding to an average electric field of 20kV/mm was applied for 10 minutes in consideration of the thickness of the sample, and then short-circuited for 5 minutes, a pulse voltage (5ns, 200V) was applied at 1ms intervals (1kHz) during the voltage application and the short-circuit, and the obtained waveforms were added and averaged 1000 times to obtain a1 waveform. The measurement interval is 10 seconds. After the measurement of the above-mentioned 20kV/mm applied neutralization and short circuit was completed, the applied DC voltage was increased so that the average applied electric field became 40kV/mm, a series of measurements were performed in the same manner as described above, and the measurements were repeated in the order of average applied electric field corresponding to 60, 80, 100 and 120 kV/mm. The charge density distribution measured over time is shown in fig. 1 and 2. FIG. 1 is a graph showing the change with time of the charge density distribution of the epoxy resin cured products of examples A-1, B-2 and C-1 (particularly, the epoxy resin cured product using bisphenol A type epoxy resin). FIG. 2 is a graph showing the change with time in the charge density distribution of the epoxy resin cured products (particularly, the epoxy resin cured product using bisphenol A type epoxy resin) of comparative examples 1 to 3. The smaller the maximum electric field (particularly, the ratio of the maximum electric field to the applied electric field), the more excellent the insulation.

The device comprises the following steps: high voltage applying unit

Sample size: the length is 50mm, the width is 50mm, the thickness is 100 mu m-150 mu m

An external electric field: 20. 40, 60, 80, 100, 120kV/mm

Measuring temperature: 140 deg.C

Use "jER 828: bisphenol A epoxy resin manufactured by Mitsubishi chemical corporation

Very good: the ratio of the maximum electric field to the applied electric field in the sample is at most 1.1 or less (optimal);

o: the ratio of the maximum electric field to the applied electric field in the sample is at most greater than 1.1 and 1.3 or less (good);

and (delta): the ratio of the maximum electric field to the applied electric field in the sample is at most greater than 1.3 and 1.5 or less (practically no problem);

x: the ratio of the maximum electric field to the applied electric field in the sample is at most greater than 1.5 (practically problematic).

Very good: the ratio of the maximum electric field to the applied electric field in the sample is at most 1.2 or less (optimal);

o: the ratio of the maximum electric field to the applied electric field in the sample is at most greater than 1.2 and 1.4 or less (good);

and (delta): the ratio of the maximum electric field to the applied electric field in the sample is at most 1.4 and 1.6 or less (practically, there is no problem);

x: the ratio of the maximum electric field to the applied electric field in the sample is at most greater than 1.6 (practically problematic).

(4) Dielectric Properties (dielectric constant, dielectric loss tangent)

The measurement was carried out by an impedance analyzer under the following conditions, and the evaluation was carried out.

Impedance analyzer

The device comprises the following steps: e4991ARF impedance/material analyzer sample size manufactured by Agilent Technologies co: length 20mm, width 20mm, thickness 150 μm

Frequency: 1GHz

Measuring temperature: 23 deg.C

And (3) test environment: 23 ℃ plus or minus 1 ℃ and 50% RH plus or minus 5% RH

Very good: the dielectric constant is less than or equal to 2.6 (optimal);

o: 2.6 < dielectric constant less than or equal to 3.0 (good);

and (delta): the dielectric constant is more than 3.0 and less than or equal to 3.3 (no problem exists in practical use);

x: 3.3 < dielectric constant (practically problematic).

Very good: the dielectric loss tangent is less than or equal to 0.0175 (optimal);

o: the dielectric loss tangent is more than 0.0175 and less than or equal to 0.020 (good);

and (delta): the dielectric loss tangent is more than 0.020 and less than or equal to 0.030 (no problem exists in practical use);

x: 0.030 < dielectric loss tangent (practically problematic).

Very good: the dielectric constant is less than or equal to 2.8 (optimal);

o: the dielectric constant is more than 2.8 and less than or equal to 3.2 (good);

and (delta): the dielectric constant is more than 3.2 and less than or equal to 3.4 (no problem exists in practical use);

x: dielectric constant 3.4 < dielectric constant (practically problematic).

Very good: the medium loss tangent is less than or equal to 0.0195 (optimal);

o: the dielectric loss tangent is more than 0.0195 and less than or equal to 0.030 (good);

and (delta): the dielectric loss tangent is more than 0.030 and less than or equal to 0.042 (no problem exists in practical use);

x: 0.042 < dielectric loss tangent (practically problematic).

(5) Comprehensive evaluation

The heat resistance, dielectric characteristics and insulation properties were evaluated comprehensively.

Very good: all the evaluation results were [.

O: of all the evaluation results, the lowest evaluation result was ∘.

And (delta): of all the evaluation results, the lowest evaluation result was Δ.

X: among all the evaluation results, the lowest evaluation result was x.

[ evaluation method of epoxy resin solution ]

(1) Viscosity of epoxy resin solution

The epoxy resin solutions obtained in examples and comparative examples were measured for viscosity (Pa · s) at 30 ℃ using a Brookfield digital viscometer (Toyobo industries TVB-15M).

(2) Solubility of imide group-containing curing agent contained in epoxy resin solution

The presence or absence of a dissolved residual component (residue) in the epoxy resin solutions obtained in the examples and comparative examples was visually observed.

Very good (soluble): no dissolution residue exists; the mixture was completely dissolved within 10 minutes at 150 ℃.

O (solubility): no dissolution residue exists; the mixture was completely dissolved (time required for dissolution) at 150 ℃ for more than 10 minutes.

X (no solubility): there is a dissolution residue; there was a dissolution residue in the obtained epoxy resin solution.

B. Starting materials

(1) Imide group-containing curing agent

[ preparation of diimide dicarboxylic acid ]

Synthesis example A-1

The diimide dicarboxylic acid was produced based on the "method for producing an imide group-containing curing agent" described above. The detailed procedure is as follows.

Granular trimellitic anhydride 521 parts by mass and 4, 4' -diaminodiphenyl ether 479 parts by mass were added to a pulverization tank, and mixed and pulverized.

Thereafter, the mixture was transferred to a glass vessel, and imidization was performed at 300 ℃ for 2 hours in a nitrogen atmosphere in an inert oven to prepare a curing agent containing an imide group.

[ preparation of diimide tetracarboxylic acid ]

Synthesis example B-1

The diimide tetracarboxylic acid was produced based on the "method for producing an imide group-containing curing agent" described above. The detailed procedure is as follows.

To a pulverization tank, 471 parts by mass of granular 3,3 ', 4, 4' -benzophenonetetracarboxylic dianhydride and 529 parts by mass of 2-aminoterephthalic acid were added, and mixed and pulverized.

Synthesis example B-2

An imide group-containing curing agent was obtained in the same manner as in Synthesis example B-1, except that the acid dianhydride composition and the monoamine composition were changed.

[ preparation of Monoimide tricarboxylic acid ]

Synthesis example C-1

The monoimide tricarboxylic acid was prepared based on the "method for preparing an imide group-containing curing agent" described above. The detailed procedure is as follows.

515 parts by mass of granular trimellitic anhydride and 485 parts by mass of 2-aminoterephthalic acid were added to a pulverization tank, and mixed and pulverized.

(2) Epoxy resin

jER 828: bisphenol A epoxy resin having an epoxy equivalent of 184 to 194g/eq, manufactured by Mitsubishi chemical corporation

EOCN-1020-55: o-cresol novolac type epoxy resin having an epoxy equivalent of 195g/eq, manufactured by Nippon Chemicals Ltd

(3) Curing agents other than imide-based curing agents

Phenolite TD-2131: a novolak-type phenol resin manufactured by DIC corporation, a curing agent containing no imide group; the curing agent has the following structural formula.

HN-2200: alicyclic acid anhydrides and imide group-free curing agents available from Hitachi chemical Co., Ltd; the curing agent has the following structural formula.

jERcure 113: modified alicyclic amine manufactured by Mitsubishi chemical corporation, and a curing agent containing no imide group.

Example A-1

60 parts by mass of a sample obtained by mixing the imide group-containing curing agent obtained in Synthesis example A-1 and the epoxy resin (JeR828) at a ratio of 1.0/1.1 (equivalent ratio) was mixed with 0.2 parts by mass of a curing accelerator (2-ethyl-4-methylimidazole, manufactured by Tokyo chemical industry Co., Ltd.) and 39.8 parts by mass of Dimethylformamide (DMF) at room temperature (i.e., 20 ℃ C.), and heated under reflux at 150 ℃ for 0.5 hour to obtain an epoxy resin solution.

The epoxy resin solution obtained in this example had a viscosity of 50Pa · s and very good workability.

The obtained epoxy resin solution was applied to an aluminum substrate in a thickness of 300. mu.m, and the resulting coating film was dried in an inert oven under a nitrogen atmosphere at 180 ℃ for 2 hours, and then dried at 300 ℃ for 2 hours to carry out desolvation and curing reaction. The aluminum substrate was removed from the obtained sample with the aluminum substrate to obtain an epoxy resin cured product. The average thickness of the epoxy resin cured product (epoxy resin cured product using epoxy resin "jER 828") was 112 μm. In the present specification, the average thickness is an average of thicknesses at arbitrary 10 points.

An epoxy resin solution and an epoxy resin cured product were prepared in the same manner as in the example, except that "EOCN-1020-55" (o-cresol novolac type epoxy resin manufactured by japan chemical) was used as the epoxy resin instead of "jER 828". The epoxy resin solution had a viscosity of 50 pas and very good workability. The average thickness of the epoxy resin cured product (epoxy resin cured product using epoxy resin "EOCN-1020-55") was 103 μm.

Examples B-1, B-2 and C-1 and comparative example 1

An epoxy resin solution and an epoxy resin cured product were prepared in the same manner as in example A-1, except that the imide group-containing curing agent obtained in Synthesis examples B-1, B-2 or C-1 or the curing agent "PHONOLITE TD-2131" was used. The imide group-containing curing agents used in the examples were the curing agents obtained in the synthesis examples having the same numbers as those of the examples.

The reactivity of glycidyl groups in the epoxy resins contained in the epoxy resin solutions obtained in examples B-1, B-2 and C-1 and comparative example 1 was 10% or less, respectively.

The epoxy resin solutions obtained in examples B-1, B-2 and C-1 and comparative example 1 all had viscosities of 30 to 70 pas and very good workability.

The average thickness of the cured epoxy resin was as follows.

Average thickness of epoxy resin cured product using epoxy resin "jER 828":

116 μm (example B-1), 115 μm (example B-2), 122 μm (example C-1), 112 μm (comparative example 1).

Average thickness of epoxy resin cured product using epoxy resin "EOCN-1020-55":

120 μm (example B-1), 104 μm (example B-2), 114 μm (example C-1), 106 μm (comparative example 1).

Comparative example 2

An alicyclic acid anhydride curing agent HN-2200, an epoxy resin (JeR828) and a curing accelerator (2,4, 6-tris (dimethylaminomethyl) phenol, manufactured by Mitsubishi chemical corporation) were mixed at a ratio of 100/80/1 (weight ratio) at room temperature (i.e., 20 ℃ C.) to obtain an epoxy resin solution.

The epoxy resin solution obtained in this comparative example had a viscosity of 50Pa · s and very good workability.

The obtained epoxy resin solution was applied to an aluminum substrate in a thickness of 300. mu.m, and the resulting coating film was dried in an inert oven under nitrogen at 120 ℃ for 5 hours and then at 150 ℃ for 15 hours to effect curing reaction. The aluminum substrate was removed from the obtained sample with the aluminum substrate to obtain a cured epoxy resin. The average thickness of the epoxy resin cured product (epoxy resin cured product using epoxy resin "jER 828") was 133 μm.

An epoxy resin solution and an epoxy resin cured product were prepared by the same method as that described above in this comparative example, except that "EOCN-1020-55" (o-cresol novolac type epoxy resin, manufactured by Nippon chemical Co., Ltd.) was used instead of "jER 828" as the epoxy resin. The epoxy resin solution had a viscosity of 40 pas and very good workability. The average thickness of the epoxy resin cured product (epoxy resin cured product using epoxy resin "EOCN-1020-55") was 140. mu.m.

Comparative example 3

The modified alicyclic amine curing agent jERcure113 and the epoxy resin (jER828) were mixed at a ratio of 100/10 (weight ratio) at room temperature (i.e., 20 ℃ C.) to obtain an epoxy resin solution.

The epoxy resin solution obtained in this comparative example had a viscosity of 50 pas and very good workability.

The obtained epoxy resin solution was applied to an aluminum substrate in a thickness of 300. mu.m, and the resulting coating film was dried in an inert oven under nitrogen at 80 ℃ for 1 hour and then at 150 ℃ for 3 hours to effect curing reaction. The aluminum substrate was removed from the obtained sample with the aluminum substrate to obtain a cured epoxy resin. The average thickness of the epoxy resin cured product (epoxy resin cured product using epoxy resin "jER 828") was 139 μm.

An epoxy resin solution and an epoxy resin cured product were prepared in the same manner as in the comparative example, except that "EOCN-1020-55" (o-cresol novolac type epoxy resin manufactured by japan chemical) was used as the epoxy resin instead of "jER 828". The epoxy resin solution had a viscosity of 40 pas and very good workability. The average thickness of the epoxy resin cured product (epoxy resin cured product using epoxy resin "EOCN-1020-55") was 123. mu.m.

The characteristic values of the curing agent and the characteristic values of the cured epoxy resin in examples and comparative examples are shown in tables 1 to 4.

The cured epoxy resins of examples A-1 to C-1 satisfy the requirements of the present invention, and therefore all of the physical properties of heat resistance, dielectric properties and insulation properties are excellent.

In these examples, only in example a-1 using the diimide dicarboxylic acid-based compound, all the evaluation results of the heat resistance, the dielectric characteristics and the insulating property were excellent.

The epoxy resin cured products of comparative examples 1 to 3 had poor properties in at least one of heat resistance, dielectric properties and insulating properties because they used a curing agent containing no imide group.

In particular, the following matters are known from the ratio of the maximum electric field/the applied electric field in each of the cured epoxy resins of examples and comparative examples and from the graphs of changes in the charge density distribution with time in fig. 1 and 2.

The cured epoxy resins of examples A-1, B-2 and C-1 were sufficiently prevented from local accumulation of charges under a high-temperature and high-electric field;

local accumulation of charge occurs in the epoxy resin cured products of comparative examples 1 to 3 under a high temperature and high electric field.

The phenomenon of local accumulation of charges, which is apparent from a time-dependent change map of the charge density distribution, is described in detail as follows:

referring to FIG. 1, the epoxy resin cured products of examples A-1, B-2 and C-1 showed approximately the same charge density distribution between the anode and the cathode.

Referring to FIG. 2, the cured epoxy resins of comparative examples 1 to 3 exhibited local accumulation of charges (i.e., localized charge) between the anode and the cathode (particularly, in the vicinity of the cathode). In fig. 2, a portion where local accumulation of electric charge often occurs is shown surrounded by a solid line (an elliptical shape).

Industrial applicability

The epoxy resin cured product of the present invention has very excellent heat resistance, dielectric properties and insulating properties. Therefore, the cured epoxy resin of the present invention is suitable for use as an encapsulating material for a power semiconductor module (particularly, a semiconductor encapsulating material), a casting material for a bushing transformer, a casting material for a solid insulated switchgear, an insulator for a power transmission line, an electric wire covering material for an electric vehicle, an electrical penetration material for a nuclear power plant, an insulating material for a printed wiring board, an electrical electronic material such as a laminate sheet, and the like.

Claims

1. A compound containing an imide group selected from the group consisting of a diimide dicarboxylic acid-based compound, a diimide tetracarboxylic acid-based compound and a monoimide tricarboxylic acid-based compound.

2. A curing agent containing an imide group selected from the imide group-containing compounds described in claim 1.

3. An epoxy resin cured product comprising the imide group-containing curing agent according to claim 2 and an epoxy resin.

4. The cured epoxy resin according to claim 3, wherein the epoxy resin has 2 or more epoxy groups in 1 molecule.

5. The cured epoxy resin according to claim 3 or 4, wherein the imide group-containing curing agent has a molecular weight of 200 to 1100.

6. The cured epoxy resin according to any one of claims 3 to 5, wherein the imide group-containing curing agent has a functional group equivalent of 50 to 500.

7. An electrical insulating material comprising the cured epoxy resin according to any one of claims 3 to 6.

8. An encapsulating material comprising the cured epoxy resin according to any one of claims 3 to 6.

9. The packaging material of claim 8, for use in a power semiconductor module.

10. An insulator comprising the cured epoxy resin according to any one of claims 3 to 6.

11. The insulator of claim 10, for use in a power transmission line.

12. An electric wire coating material comprising the cured epoxy resin according to any one of claims 3 to 6.

13. The electric wire covering material according to claim 12, used for an electric vehicle.

14. A printed wiring board comprising the cured epoxy resin according to any one of claims 3 to 6.