WO2019175942A1

WO2019175942A1 - Epoxy resin composition, epoxy resin film, and method for producing epoxy resin film

Info

Publication number: WO2019175942A1
Application number: PCT/JP2018/009554
Authority: WO
Inventors: 慎吾田中; 竹澤　由高; 一也木口; 智子東内; 片木　秀行
Original assignee: 日立化成株式会社
Priority date: 2018-03-12
Filing date: 2018-03-12
Publication date: 2019-09-19
Also published as: JP7342852B2; JPWO2019175942A1

Abstract

An epoxy resin composition which comprises an epoxy resin and a hardener and is capable of forming a cured object that has a liquid-crystal structure and that, when having a thickness of 30 μm, has a minimum visible-light transmittance of 50% or higher.

Description

Epoxy resin composition, epoxy resin film, and method for producing epoxy resin film

The present invention relates to an epoxy resin composition, an epoxy resin film, and a method for producing an epoxy resin film.

An epoxy resin is widely used as a material of an insulating member constituting an electronic device from the viewpoint of high withstand voltage and easy molding. In recent years, with the increase in energy density due to downsizing and higher performance of electronic devices, the amount of heat generated per unit volume tends to increase. Therefore, high thermal conductivity is also required for insulating members.

As a method for increasing the thermal conductivity of an epoxy resin used as a material for an insulating member, for example, Patent Document 1 discloses an epoxy compound having a highly oriented mesogen structure in a molecule that can form a liquid crystal structure in a cured product. It is described that it is effective to use an epoxy resin composition containing it.

JP-A-11-323162

However, the cured product of the epoxy resin composition in which the liquid crystal structure is formed has a high thermal conductivity, but the transparency tends to decrease. For this reason, the epoxy resin composition described in Patent Document 1 is used for applications that require transparency in addition to thermal conductivity (for example, in the case of using a cured epoxy resin film). There is room for improvement.

In view of the above situation, an object of the present invention is to provide an epoxy resin composition from which a cured epoxy resin product having excellent thermal conductivity and transparency can be obtained even when a film is formed. Another object of the present invention is to provide an epoxy resin film excellent in thermal conductivity and transparency and a method for producing the same.

Means for solving the above problems include the following embodiments.
<1> An epoxy resin composition comprising an epoxy resin and a curing agent, and having a liquid crystal structure and capable of forming a cured product having a minimum visible light transmittance of 50% or more measured at a thickness of 30 μm. .
<2> The epoxy resin composition according to <1>, wherein the liquid crystal structure is a nematic structure.
<3> The epoxy resin composition according to <1> or <2>, wherein the liquid crystal structure can be formed at a curing temperature of 60 ° C. or less.
<4> The epoxy resin composition according to any one of <1> to <3>, wherein the epoxy resin includes at least one of epoxy compounds represented by the following general formula (m1) or general formula (m2) object.

[In the general formulas (m1) and (m2), R ¹ to R ⁴ each independently represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. ]
<5> The epoxy resin composition according to any one of <1> to <4>, wherein the epoxy resin is in a prepolymer state.
<6> The epoxy resin composition according to any one of <1> to <5>, wherein the curing agent includes metaxylylenediamine.
<7> An epoxy resin film that is a cured film of the epoxy resin composition according to any one of <1> to <6>.
<8> The epoxy resin film according to <7>, wherein the cured film has a nematic structure.
<9> An epoxy resin film comprising a step of forming the epoxy resin composition according to any one of <1> to <6> into a film shape to obtain a molded product, and a step of curing the molded product Manufacturing method.
The manufacturing method of the epoxy resin film as described in <9> whose temperature at the time of shape | molding the <10> said epoxy resin composition in a film form is 100 degrees C or less.
<11> The method for producing an epoxy resin film according to <9> or <10>, wherein the temperature at which the molded product is cured is 60 ° C. or less.

According to the present invention, there is provided an epoxy resin composition from which an epoxy resin cured product having excellent thermal conductivity and transparency can be obtained even when formed into a film. Moreover, according to this invention, the epoxy resin film excellent in thermal conductivity and transparency and its manufacturing method are provided.

It is a photograph when the epoxy resin film produced in Example 1 is observed from the top.

Hereinafter, the present invention will be described in detail. However, the present invention is not limited to the following embodiments. In the following embodiments, the components (including element steps and the like) are not essential unless otherwise specified. The same applies to numerical values and ranges thereof, and the present invention is not limited thereto.
In the present disclosure, numerical ranges indicated using “to” include numerical values described before and after “to” as the minimum value and the maximum value, respectively.
In the numerical ranges described stepwise in the present disclosure, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of another numerical description. . Further, in the numerical ranges described in the present disclosure, the upper limit value or the lower limit value of the numerical range may be replaced with the values shown in the examples.
In the present disclosure, the content of each component in the composition is the total of the plurality of substances present in the composition unless there is a specific indication when there are a plurality of substances corresponding to each component in the composition. Mean content.
In the present disclosure, the particle size of each component in the composition is a mixture of the plurality of types of particles present in the composition unless there is a specific indication when there are a plurality of types of particles corresponding to each component in the composition. Means the value of
In the present disclosure, the “epoxy compound” means a compound having an epoxy group in the molecule, and the “epoxy resin” means a concept of capturing the epoxy compound as an aggregate.

<Epoxy resin composition>
The epoxy resin composition of the present disclosure includes an epoxy resin and a curing agent, and can form a cured product having a liquid crystal structure and a minimum visible light transmittance of 50% or more measured at a thickness of 30 μm. An epoxy resin composition.

According to the above epoxy resin composition, it is possible to obtain a cured epoxy resin that is excellent in thermal conductivity and excellent in transparency even when formed into a film.

In the present disclosure, visible light means light having a wavelength in the range of 400 nm to 700 nm. That is, the minimum value of the visible light transmittance being 50% or more means that the transmittance in the entire wavelength range of 400 nm to 700 nm is 50% or more.

The cured product obtained using the epoxy resin composition is not particularly limited as long as the minimum value of the visible light transmittance measured at a thickness of 30 μm is 50% or more, but it is 60% or more from the viewpoint of transparency. May be.

The cured product obtained by using the epoxy resin composition is not particularly limited as long as the minimum value of visible light transmittance measured at a thickness of 30 μm is 50% or more, but from the viewpoint of transparency, it is measured at a thickness of 50 μm. The minimum visible light transmittance may be 50% or more.

From the viewpoint of thermal conductivity, the liquid crystal structure of the cured product obtained by curing the epoxy resin composition is preferably a nematic or smectic structure. From the viewpoint of transparency, the liquid crystal structure is preferably a nematic structure.

From the viewpoint of workability, it is preferable that the liquid crystal structure of the cured product can be formed at a curing temperature of 60 ° C. or lower. As a method for enabling the liquid crystal structure of the cured product to be formed at a curing temperature of 60 ° C. or lower, a curing agent that can be cured at a low temperature (for example, room temperature) may be selected.

(Epoxy resin)
The epoxy resin contained in the epoxy resin composition is not particularly limited as long as it can form a liquid crystal structure in a cured product obtained by reacting with a curing agent.

Examples of the epoxy resin capable of forming a liquid crystal structure in the cured product include an epoxy resin containing an epoxy compound (hereinafter also referred to as a liquid crystalline epoxy compound) capable of forming a liquid crystal structure in the cured product. Examples of the liquid crystalline epoxy compound include an epoxy compound having a mesogenic structure. An epoxy compound having a mesogenic structure has a rigid and linear molecular structure, and therefore has a property that molecules are aligned in a cured product to form a liquid crystal structure.

Examples of the mesogen structure include a biphenyl structure, a phenylbenzoate structure, a cyclohexylbenzoate structure, an azobenzene structure, a stilbene structure, a terphenyl structure, an anthracene structure, derivatives thereof, and two or more of these mesogen structures via a bonding group. Examples include bonded structures.

When an epoxy compound having a mesogenic structure reacts with a curing agent to form a resin matrix, a higher-order structure derived from the mesogenic structure (both periodic structures) in the resin matrix (part derived from the epoxy resin and the curing agent in the cured product). Say) is formed. Here, the higher order structure (periodic structure) means a state in which molecules are aligned in the resin matrix, for example, a state in which a crystal structure or a liquid crystal structure exists in the resin matrix. The presence of such a crystal structure or liquid crystal structure can be directly confirmed by, for example, observation with a polarizing microscope under crossed Nicols or X-ray scattering. In addition, if the crystal structure or liquid crystal structure is present, the change in the storage elastic modulus of the resin with respect to temperature becomes small, so the presence of the crystal structure or liquid crystal structure is indirectly confirmed by measuring the change in the storage elastic modulus with respect to temperature. it can.

High-order structures with high regularity derived from mesogenic structures include nematic structures and smectic structures. The nematic structure is a liquid crystal structure in which the molecular long axis is oriented in a uniform direction and has only alignment order. On the other hand, the smectic structure is a liquid crystal structure having a one-dimensional positional order in addition to the orientation order and having a layer structure with a constant period. In addition, the direction of the period of the layer structure is uniform within the same periodic structure of the smectic structure. When the periodic structure is formed in the resin matrix, it is possible to suppress scattering of phonons, which are heat conductive media, and the thermal conductivity tends to be high.

Whether or not the periodic structure includes a smectic structure can also be determined by X-ray diffraction measurement. Specifically, for example, using a Cu K _alpha 1 line, tube voltage 40 kV, tube current 20 mA, in the range of 2θ is 0.5 ° ~ 30 °, the wide angle X-ray analyzer (e.g., Rigaku Corporation, "RINT2500HL") When X-ray diffraction measurement is performed using 2 and θ has a diffraction peak in the range of 1 ° to 10 °, it is determined that the periodic structure includes a smectic structure.

From the viewpoint of the thermal conductivity of the cured product, the ratio of the periodic structure of the liquid crystal structure in the cured product is preferably 60% by volume or more, and more preferably 80% by volume or more with respect to the entire resin matrix. The ratio of the liquid crystal structure to the entire resin matrix can be easily measured, for example, by observing with a polarizing microscope. Specifically, the cured product is observed with a polarizing microscope (for example, Nikon Corporation, “OPTIPHOT2-POL”), the area of the liquid crystal structure is measured, and the percentage of the entire field of view observed with the polarizing microscope is obtained. The ratio of the liquid crystal structure to the entire resin matrix can be easily measured.

When the liquid crystal structure is a smectic structure, the periodic structure of the smectic structure preferably has a period length (length of one period) of 2 nm to 4 mm. When the period length is 2 nm to 4 mm, higher thermal conductivity can be exhibited. The period length in the periodic structure is obtained by performing X-ray diffraction using a cured product of the epoxy resin composition as a measurement sample under the following conditions using a wide-angle X-ray diffractometer (for example, Rigaku Corporation, “RINT2500HL”). The diffraction angle obtained can be obtained by converting the following Bragg equation.

(Measurement condition)
・ X-ray source: Cu
・ X-ray output: 50 kV, 250 mA
・ Divergent slit (DS): 1.0 °
-Scattering slit (SS): 1.0 °
・ Reception slit (RS): 0.3mm
Scanning speed: 1.0 degree / minute Bragg's formula: 2 dsin θ = nλ
Here, d is the length of one period, θ is the diffraction angle, n is the reflection order, and λ is the X-ray wavelength (0.15406 nm).

Examples of the liquid crystalline epoxy compound include epoxy compounds represented by the following general formula (A).

In general formula (A), X represents a linking group containing at least one selected from the group (I) consisting of the following divalent groups. Y is independently an aliphatic hydrocarbon group having 1 to 8 carbon atoms, an aliphatic alkoxy group having 1 to 8 carbon atoms, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, a cyano group, a nitro group, or an acetyl group. Indicates. n independently represents an integer of 0 to 4.

In the group (I) consisting of a divalent group, each Y independently represents an aliphatic hydrocarbon group having 1 to 8 carbon atoms, an aliphatic alkoxy group having 1 to 8 carbon atoms, a fluorine atom, a chlorine atom, a bromine atom, An iodine atom, a cyano group, a nitro group, or an acetyl group is shown. n independently represents an integer of 0 to 4, k represents an integer of 0 to 7, m represents an integer of 0 to 8, and l represents an integer of 0 to 12.

In the group (I) consisting of the general formula (A) and the divalent group, each Y is independently preferably an aliphatic hydrocarbon group having 1 to 8 carbon atoms, and preferably a methyl group. n, k, m and l are each preferably 0 or 1 independently.

From the viewpoint of forming a liquid crystal structure in the cured product, the epoxy resin preferably contains an epoxy compound having one or more structures represented by the following general formula (M1) or general formula (M2).

In general formula (M1) and general formula (M2), R ¹ to R ⁴ each independently represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. R ¹ to R ⁴ are each independently preferably a hydrogen atom or an alkyl group having 1 to 2 carbon atoms, more preferably a hydrogen atom or a methyl group, and even more preferably a hydrogen atom. Also, it is preferable that 2 to ⁴ of R ¹ to R ⁴ are hydrogen atoms, more preferably 3 or 4 are hydrogen atoms, and more preferably that all 4 are hydrogen atoms. preferable. When any of R ¹ to R ⁴ is an alkyl group having 1 to 3 carbon atoms, at least one of R ¹ and R ⁴ is preferably an alkyl group having 1 to 3 carbon atoms.

Examples of the epoxy compound having one structure represented by the general formula (M1) or the general formula (M2) include an epoxy compound represented by the following general formula (m1) or (m2).

Specific examples of ^R 1 ~ ^{R 4} in the general formula (m1) and (m2) is the same as the specific examples of ^R 1 ~ ^{R 4} in the general formula (M1) and the general formula (M2), also the preferred ranges It is.

Examples of the epoxy compound represented by the general formula (m1) include compounds described in JP 2011-74366 A. Specifically, 4- {4- (2,3-epoxypropoxy) phenyl} cyclohexyl = 4- (2,3-epoxypropoxy) benzoate and 4- {4- (2,3-epoxypropoxy) phenyl} cyclohexyl = At least one compound selected from the group consisting of 4- (2,3-epoxypropoxy) -3-methylbenzoate.

Examples of the epoxy compound represented by the general formula (m2) include 1- (3-methyl-4-oxiranylmethoxyphenyl) -4- (oxiranylmethoxyphenyl) -1-cyclohexene.

From the viewpoint of the transparency of the cured product, the epoxy resin is preferably in a state (prepolymer) containing a liquid crystalline epoxy compound (preferably an epoxy compound having a mesogenic structure) and a multimer thereof. Liquid crystalline epoxy compounds are generally easy to crystallize and may have a lower solubility in solvents than other epoxy compounds. Here, the transparency of the cured product tends to be improved by using a prepolymer containing a multimer obtained by polymerizing a part of the liquid crystalline epoxy compound. Furthermore, crystallization of the epoxy resin before curing is suppressed, and the moldability of the epoxy resin composition tends to be improved.

The multimer of the liquid crystalline epoxy compound is not particularly limited as long as it contains a structure (preferably a mesogenic structure) derived from two or more liquid crystalline epoxy compounds in the molecule. Specifically, as a multimer of a liquid crystalline epoxy compound, a liquid crystalline epoxy compound and a compound having two or more functional groups capable of reacting with an epoxy group of the liquid crystalline epoxy compound (hereinafter also referred to as a prepolymerizing agent) The compound obtained by making it react is mentioned.

∙ The type of prepolymerizing agent is not particularly limited. From the viewpoint of forming a liquid crystal structure in the cured product, a dihydroxybenzene compound having a structure in which two hydroxyl groups are bonded to one benzene ring, a diaminobenzene compound having a structure in which two amino groups are bonded to one benzene ring, It consists of a dihydroxybiphenyl compound having a structure in which one hydroxyl group is bonded to each of two benzene rings forming a biphenyl structure, and a diaminobiphenyl compound having a structure in which one amino group is bonded to each of two benzene rings forming a biphenyl structure. It is preferably at least one selected from the group (hereinafter also referred to as a specific aromatic compound).

Examples of the dihydroxybenzene compound include catechol, resorcinol, hydroquinone, and derivatives thereof.
Examples of the diaminobenzene compound include 1,2-diaminobenzene, 1,3-diaminobenzene, 1,4-diaminobenzene, and derivatives thereof.

Dihydroxybiphenyl compounds include 2,2′-dihydroxybiphenyl, 2,3′-dihydroxybiphenyl, 2,4′-dihydroxybiphenyl, 3,3′-dihydroxybiphenyl, 3,4′-dihydroxybiphenyl, 4,4 ′ -Dihydroxybiphenyl (4,4'-biphenol), derivatives thereof and the like.
Diaminobiphenyl compounds include 2,2'-diaminobiphenyl, 2,3'-diaminobiphenyl, 2,4'-diaminobiphenyl, 3,3'-diaminobiphenyl, 3,4'-diaminobiphenyl, 4,4 ' -Diaminobiphenyl, derivatives thereof and the like.

Examples of the derivative of the specific aromatic compound include a compound in which a substituent such as an alkyl group having 1 to 8 carbon atoms is bonded to the benzene ring of the specific aromatic compound. A specific aromatic compound may be used individually by 1 type, and may use 2 or more types together.

Among the specific aromatic compounds, hydroquinone, 1,4-diaminobenzene, 4,4'-dihydroxybiphenyl (4,4'-biphenol), 4,4'-diaminobiphenyl and derivatives thereof are preferable. Since these compounds have a structure in which the functional group in the molecule is substituted so as to have a para-position, the multimer obtained by reacting with the liquid crystalline epoxy compound tends to have a linear structure. For this reason, it is considered that the stacking property of molecules is high, and it is easy to form a higher order structure in the cured product.

A reaction catalyst may be used when the epoxy compound and the prepolymerizing agent are reacted. The type of the reaction catalyst is not particularly limited, and an appropriate catalyst can be selected from the viewpoint of reaction rate, reaction temperature, storage stability, and the like. Specific examples include imidazole compounds, organophosphorus compounds, tertiary amines, and quaternary ammonium salts. A reaction catalyst may be used individually by 1 type, and may use 2 or more types together.

When the liquid crystalline epoxy compound is reacted with the prepolymerizing agent, the ratio of the multimer in the prepolymer, the molecular weight of the multimer, and the like can be adjusted by adjusting the blending ratio of the two.
For example, the compounding ratio may be such that the equivalent ratio of the epoxy group of the liquid crystalline epoxy compound to the functional group of the prepolymerizing agent (epoxy group / functional group) is 100/5 to 100/50. The compounding ratio may be 100/30.

When the liquid crystalline epoxy compound is an epoxy compound represented by the general formula (A), the multimer is an epoxy compound having a structure represented by the following general formula (1-A) or general formula (1-B). There may be.

In general formula (1-A) and general formula (1-B), the definitions and preferred examples of X, Y and n are the same as the definitions and preferred examples of X, Y and n in general formula (A). R ¹ and R ² each independently represents an alkyl group having 1 to 8 carbon atoms, preferably an alkyl group having 1 to 3 carbon atoms, and more preferably a methyl group. Each m independently represents an integer of 0 to 4. Z independently represents —O— or —NH—.

From the viewpoint of higher order structure formation, the epoxy compound having a structure represented by the general formula (1-A) is preferably an epoxy compound having a structure represented by the following general formula (2-A), The epoxy compound having a structure represented by the general formula (1-B) is preferably an epoxy compound having a structure represented by the following general formula (2-B).

In general formula (2-A) and general formula (2-B), the definitions and preferred examples of X, Y, n, m, R ¹ , R ² and Z are the general formula (1-A) and the general formula ( The definition and preferred examples of X, Y, n, m, R ¹ , R ² and Z in 1-B) are the same.

In the multimer of the liquid crystalline epoxy compound, the number of structures derived from the liquid crystalline epoxy compound is not particularly limited as long as it is 2 or more. From the viewpoint of reducing the viscosity during work, it is preferable that at least a part of the multimer of the liquid crystalline epoxy compound is an epoxy compound (dimer compound) containing two structures derived from the liquid crystalline epoxy compound.

Examples of the structure when the multimer of the liquid crystalline epoxy compound is a dimer compound include an epoxy compound represented by the following general formula (3-A) or (3-B).

In general formula (3-A) and general formula (3-B), the definitions and preferred examples of X, Y, n, m, R ¹ , R ² and Z are the general formula (1-A) and the general formula ( The definition and preferred examples of X, Y, n, m, R ¹ , R ² and Z in 1-B) are the same.

From the viewpoint of forming a higher order structure in the cured product, the epoxy compound having a structure represented by the general formula (3-A) is an epoxy compound having a structure represented by the following general formula (4-A). Preferably, the epoxy compound having a structure represented by the general formula (3-B) is preferably an epoxy compound having a structure represented by the following general formula (4-B).

In general formula (4-A) and general formula (4-B), the definitions and preferred examples of X, Y, n, m, R ¹ , R ² and Z are the general formula (3-A) and the general formula ( The definition and preferred examples of X, Y, n, m, R ¹ , R ² and Z in 3-B) are the same.

The epoxy resin composition may further contain an epoxy compound that does not correspond to the liquid crystalline epoxy compound as long as the liquid crystal structure is formed in the cured product. In the present disclosure, an epoxy compound that does not correspond to a liquid crystalline epoxy compound means an epoxy compound that does not form a liquid crystal structure in a cured product obtained by reacting only it with a curing agent.

Epoxy compounds that do not correspond to liquid crystal epoxy compounds include glycidyl ethers of phenol compounds such as bisphenol A, bisphenol F, bisphenol S, phenol novolak, cresol novolak, resorcinol novolak; alcohol compounds such as butanediol, polyethylene glycol, and polypropylene glycol. Glycidyl ethers; glycidyl esters of carboxylic acid compounds such as phthalic acid, isophthalic acid and tetrahydrophthalic acid; Epoxy monomers; vinylcyclohexene epoxides obtained by epoxidizing intramolecular olefin bonds, 3,4-epoxycyclohexyl Cycloaliphatic epoxy monomers such as methyl-3,4-epoxycyclohexanecarboxylate, 2- (3,4-epoxy) cyclohexyl-5,5-spiro (3,4-epoxy) cyclohexane-m-dioxane; bis (4 -Hydroxy) thioether epoxidized product: paraxylylene modified phenolic resin, metaxylylene paraxylylene modified phenolic resin, terpene modified phenolic resin, dicyclopentadiene modified phenolic resin, cyclopentadiene modified phenolic resin, polycyclic aromatic ring modified phenolic resin, naphthalene Examples thereof include glycidyl ethers such as ring-containing phenol resins; stilbene type epoxy monomers; halogenated phenol novolac type epoxy monomers (excluding liquid crystal epoxy monomers among these). These epoxy compounds may be used individually by 1 type, and may use 2 or more types together.

When the epoxy resin composition includes a liquid crystal epoxy compound and an epoxy compound that does not correspond to the liquid crystal epoxy compound, the content of the epoxy compound that does not correspond to the liquid crystal epoxy compound is 1 on the mass basis. In some cases, it is preferably 0.3 or less, more preferably 0.2 or less, and even more preferably 0.1 or less.

From the viewpoint of moldability, the content of the epoxy resin contained in the epoxy resin composition is preferably 50% by volume or less and more preferably 35% by volume or less in the total solid content of the epoxy resin composition. 15% by volume or less is particularly preferable. The volume-based content of the epoxy resin relative to the total solid content is a value determined by the following formula.

Content (% by volume) of epoxy resin with respect to the total solid content = {(Aw / Ad) / ((Aw / Ad) + (Bw / Bd) + (Cw / Cd))} × 100
Here, each variable is as follows.
Aw: mass composition ratio of epoxy resin (mass%)
Bw: mass composition ratio (% by mass) of curing agent
Cw: mass composition ratio (% by mass) of other optional components (excluding solvent)
Ad: Specific gravity of epoxy resin Bd: Specific gravity of curing agent Cd: Specific gravity of other optional components (excluding solvent)

(Curing agent)
The curing agent contained in the epoxy resin composition is not particularly limited as long as it is a compound capable of causing a curing reaction with the epoxy resin. Specific examples of the curing agent include amine curing agents, acid anhydride curing agents, phenol curing agents, polymercaptan curing agents, polyaminoamide curing agents, isocyanate curing agents, and blocked isocyanate curing agents. These curing agents may be used alone or in combination of two or more.

From the viewpoint of the transparency of the cured product, the curing agent is preferably an amine curing agent or a phenol curing agent, and more preferably an amine curing agent. Among the amine curing agents, a compound having an aromatic ring and two amino groups (aromatic diamine) is preferable, and a compound in which two amino groups are bonded to each aromatic ring via a methylene group is more preferable. A compound (metaxylylenediamine) in which two amino groups bonded through a methylene group are in the meta position is more preferable.

The content of the curing agent in the epoxy resin composition can be appropriately set in consideration of the kind of the curing agent to be blended and the physical properties of the liquid crystalline epoxy monomer.

Specifically, the equivalent number (chemical equivalent) of the functional group of the curing agent is preferably 0.005 to 5 equivalents relative to 1 equivalent of the epoxy group in the liquid crystalline epoxy monomer, and 0.01 to 3 equivalents. Equivalents are more preferable, and 0.5 to 1.5 equivalents are even more preferable. When the number of equivalents of the functional group of the curing agent is 0.005 equivalents or more with respect to 1 equivalent of the epoxy group, the curing rate of the liquid crystalline epoxy monomer tends to be further improved. Moreover, it exists in the tendency which can control hardening reaction more appropriately that the equivalent number of the functional group of a hardening | curing agent is 5 equivalent or less with respect to 1 equivalent of an epoxy group.

The chemical equivalent in the present disclosure represents, for example, when a phenol curing agent is used as the curing agent, the number of equivalents of the hydroxyl group of the phenol curing agent relative to 1 equivalent of the epoxy group, and an amine curing agent is used as the curing agent. Represents the number of equivalents of active hydrogen of the amine curing agent with respect to 1 equivalent of epoxy group.

(Filler)
The epoxy resin composition may contain a filler. As the filler, ceramic particles can be used from the viewpoints of thermal conductivity and insulation. Examples of the ceramic particles include alumina particles, silica particles, magnesium oxide particles, boron nitride particles, aluminum nitride particles, and silicon nitride particles. The filler preferably includes at least one selected from the group consisting of alumina particles, boron nitride particles, aluminum nitride particles, and magnesium oxide particles, and more preferably includes alumina particles. The alumina particles preferably include alumina particles with high crystallinity, and more preferably include α-alumina particles.

The volume average particle diameter of the filler is preferably 0.01 μm to 1 μm from the viewpoint of thermal conductivity, and more preferably 0.01 μm to 0.1 μm from the viewpoint of transparency.

Here, the volume average particle diameter of the filler is measured using a laser diffraction method. The measurement by the laser diffraction method can be performed using a laser diffraction scattering particle size distribution measuring device (for example, LS230 manufactured by Beckman Coulter, Inc.). The volume average particle diameter of the filler in the epoxy resin composition or its cured product is measured using a laser diffraction scattering particle size distribution measuring device after extracting the filler from the epoxy resin composition or its cured product.

Specifically, the filler is extracted from the epoxy resin composition or a cured product thereof using an organic solvent, nitric acid, aqua regia, etc., and sufficiently dispersed with an ultrasonic disperser to prepare a dispersion. With respect to this dispersion, a volume cumulative distribution curve is measured by a laser diffraction scattering particle size distribution measuring apparatus. When the volume cumulative distribution curve is drawn from the small diameter side, the volume average particle diameter of the filler contained in the epoxy resin composition or the cured product thereof is obtained by determining the particle diameter (D50) that becomes 50% cumulative as the volume average particle diameter. The diameter is measured.

When a film-like cured product is obtained using an epoxy resin composition, the filler content in the total solid content of the epoxy resin composition is preferably 20% by mass or less, and preferably 15% by mass or less. More preferably, it is more preferably 10% by mass or less.

(Other ingredients)
An epoxy resin composition may contain components other than an epoxy resin, a hardening | curing agent, and a filler as needed. Examples of such components include a curing accelerator, a solvent, a coupling agent, a dispersant, an elastomer, and a release agent.

When using a phenol curing agent as the curing agent, it is preferable to use a curing accelerator in combination. By using a curing accelerator in combination, the epoxy resin composition can be further sufficiently cured. The kind in particular of hardening accelerator is not restrict | limited, You may select from the hardening accelerator normally used. Examples of the curing accelerator include imidazole compounds, phosphine compounds, and borate salt compounds.

Solvents include acetone, isobutyl alcohol, isopropyl alcohol, isopentyl alcohol, ethyl ether, ethylene glycol monoethyl ether, xylene, cresol, chlorobenzene, isobutyl acetate, isopropyl acetate, isopentyl acetate, ethyl acetate, methyl acetate, cyclohexanol, cyclohexanone 1,4-dioxane, dichloromethane, styrene, tetrachloroethylene, tetrahydrafuran, toluene, normal hexane, 1-butanol, 2-butanol, methanol, methyl isobutyl ketone, methyl ethyl ketone, methylcyclohexanol, methylcyclohexanone, chloroform, carbon tetrachloride , 1,2-dichloroethane, and other organic solvents that are generally used in the manufacturing technology of various chemical products. It can be.

(Use of epoxy resin composition, etc.)
The epoxy resin composition of the present disclosure is excellent in thermal conductivity and transparency when cured. Therefore, the epoxy resin composition of the present embodiment is suitable for a heat dissipation material of various exothermic electronic components (for example, an IC (Integrated Circuit) chip or a printed wiring board), a molding material of an illumination device, and the like. Can be used.

<Epoxy resin film>
The epoxy resin film of the present disclosure is a film-like cured product of the above-described epoxy resin composition. The epoxy resin film of the present disclosure is excellent in thermal conductivity and excellent in transparency because a liquid crystal structure is formed inside by curing the above-described epoxy resin composition.

The thickness of the epoxy resin film is not particularly limited and can be selected according to the application. From the viewpoint of ensuring sufficient transparency, the thickness of the epoxy resin film may be 500 μm or less, preferably 200 μm or less, and more preferably 100 μm or less. From the viewpoint of ensuring sufficient strength, the thickness of the epoxy resin film may be 5 μm or more, preferably 10 μm or more, and more preferably 20 μm or more.

When the thickness of the epoxy resin film is not constant, the thickness is measured at five randomly selected thicknesses of the epoxy resin film, and the value is given as an arithmetic average value (average thickness). The thickness can be measured using a micrometer or the like.

The visible light transmittance of the epoxy resin film is not particularly limited, but the minimum value of the visible light transmittance measured for the obtained epoxy resin film is preferably 50% or more, and more preferably 60% or more. The visible light transmittance of the epoxy resin film can be measured by the method described above.

From the viewpoint of thermal conductivity, the epoxy resin film preferably has a nematic structure or a smectic structure as a liquid crystal structure. When a smectic structure is formed inside the epoxy resin film, the periodic structure of the smectic structure preferably has a period length of 2 nm to 4 nm. When the period length is 2 nm to 4 nm, higher thermal conductivity can be exhibited. The periodic length of the smectic structure can be measured by the method described above. When a nematic structure is formed as a liquid crystal structure, the state of the nematic liquid crystal structure can be observed by observing with a polarizing microscope (for example, Nikon Corporation, “OPTIPHOT2-POL”).

<Method for producing epoxy resin film>
The manufacturing method of the epoxy resin film of this indication has the process of shape | molding the epoxy resin composition mentioned above in a film form, and obtaining the molded article, and the process of hardening the said molded article.

The epoxy resin film produced by the above method is excellent in thermal conductivity and transparency.
The conditions for molding the epoxy resin composition into a film are not particularly limited, but it is preferably performed at a temperature of 100 ° C. or lower. The conditions for curing the film-like molded product are not particularly limited, but it is preferably performed at a temperature of 60 ° C. or lower. The curing time is not particularly limited, but for example, 1 hour to 96 hours is preferable, and 2 hours to 48 hours is more preferable.

In the above method, if necessary, the molded product may be further heat treated (hereinafter also referred to as “post-curing”). By performing post-curing, the crosslinking density tends to be further improved. The heat treatment may be performed only once or two or more times.

The heating device used for post-curing is not particularly limited, and a commonly used heating device can be used. The post-curing temperature is not particularly limited, and is preferably 60 ° C. to 100 ° C., and more preferably 80 ° C. to 100 ° C. The post-curing time is not particularly limited, and is preferably 10 minutes to 600 minutes, and more preferably 60 minutes to 300 minutes.

The thickness of the epoxy resin film produced by the above method is not particularly limited, and can be selected according to the use. From the viewpoint of ensuring sufficient transparency, the thickness of the epoxy resin film may be 500 μm or less, preferably 200 μm or less, and more preferably 100 μm or less. From the viewpoint of ensuring sufficient strength, the thickness of the epoxy resin film may be 5 μm or more, preferably 10 μm or more, and more preferably 20 μm or more.

The visible light transmittance of the epoxy resin film produced by the above method is not particularly limited, but the minimum value of the visible light transmittance measured for the obtained epoxy resin film is preferably 50% or more, and 60% or more. More preferably. The visible light transmittance of the epoxy resin film can be measured by the method described above.

From the viewpoint of thermal conductivity, the epoxy resin film produced by the above method preferably has a nematic structure or a smectic structure as a liquid crystal structure. When a smectic structure is formed inside the epoxy resin film, the periodic structure of the smectic structure preferably has a period length of 2 nm to 4 nm. When the period length is 2 nm to 4 nm, higher thermal conductivity can be exhibited. The periodic length of the smectic structure can be measured by the method described above. When a nematic structure is formed as a liquid crystal structure, the state of the nematic liquid crystal structure can be observed by observing with a polarizing microscope (for example, Nikon Corporation, “OPTIPHOT2-POL”).

Hereinafter, the present invention will be specifically described by way of examples. However, the present invention is not limited to these examples. Unless otherwise specified, “part” and “%” are based on mass.

Example 1
Liquid crystalline epoxy compound (4- {4- (2,3-epoxypropoxy) phenyl} cyclohexyl = 4- (2,3-epoxypropoxy) benzoate, the following structure, hereinafter also referred to as “resin 1”) and prepolymerization 4,4-biphenol (44BP) as an agent and a prepolymer (hereinafter also referred to as “resin 2”) obtained by reacting in advance at a molar ratio (liquid crystalline epoxy compound / prepolymerizing agent) of 10 / 2.5. ) And a curing agent (metaxylylenediamine) were added to prepare an epoxy resin composition. The blending amount of the curing agent with respect to the prepolymer was adjusted so that the ratio of the number of equivalents of active hydrogen in the curing agent to the number of equivalents of epoxy group in the prepolymer (epoxy group: active hydrogen) was 1: 1.

The prepared epoxy resin composition was melt-kneaded at 90 ° C. for 10 minutes using an oil bath. Next, while melting at 100 ° C., a film having a thickness of 30 μm was coated on a 70 μm-thick substrate made of PET film to obtain a film-like molded product. Thereafter, the molded product was cured at 60 ° C. for 120 minutes to obtain an epoxy resin film.

FIG. 1 shows a photograph of the epoxy resin film produced in Example 1 observed from above. As shown in FIG. 1, the lattice pattern of the base material was visible from above the epoxy resin film.

The presence or absence of a smectic structure in the epoxy resin film was examined using a wide-angle X-ray diffractometer (Rigaku Corporation, “RINT2500HL”). The results are shown in Table 1.
The presence or absence of a nematic liquid crystal structure in the epoxy resin film was examined using a polarizing microscope (Nikon Corporation, “OPTIPHOT2-POL”). The results are shown in Table 1.

The visible light transmittance (%) in the range of 400 nm to 700 nm of the epoxy resin film was measured using a spectrophotometer (Hitachi Ltd., “U4100”). Table 1 shows the minimum values of the measured visible light transmittance.

By measuring the thermal diffusivity of the epoxy resin film using a thermal diffusivity measuring device (Bethel, “TA3”), the measurement result is multiplied by the density measured by the Archimedes method and the specific heat measured by the DSC method. The thermal conductivity (W / m · K) in the in-plane direction of the epoxy resin film was determined. The results are shown in Table 1.

(Example 2)
An epoxy was prepared in the same manner as in Example 1 except that the prepolymerizing agent was changed from 4,4-biphenol to hydroquinone (HQ) to prepare a prepolymer (hereinafter also referred to as “resin 3”). A resin composition was prepared to produce an epoxy resin film. Then, in the same manner as in Example 1, the visible light transmittance and the thermal conductivity were obtained.

The liquid crystalline epoxy compound and the prepolymerizing agent were obtained by reacting at a molar ratio (liquid crystalline epoxy compound / prepolymerizing agent) of 10 / 2.5. The blending amount of the curing agent with respect to the resin 3 was adjusted so that the ratio of the number of equivalents of active hydrogen of the curing agent to the number of equivalents of epoxy group in the resin 3 (epoxy group: active hydrogen) was 1: 1.

(Example 3)
In Example 1, the liquid crystalline epoxy compound was changed from Resin 1 to 1- (3-Methyl-4-oxiranylmethoxyphenyl) -4- (oxiranylmethoxyphenyl) -1-cyclohexene, the following structure, hereinafter “resin 4 The epoxy resin composition was prepared in the same manner as in Example 1 except that a prepolymer (hereinafter also referred to as “resin 5”) was prepared. Then, in the same manner as in Example 1, the visible light transmittance and the thermal conductivity were obtained.

The liquid crystalline epoxy compound and the prepolymerizing agent were obtained by reacting at a molar ratio (liquid crystalline epoxy compound / prepolymerizing agent) of 10 / 2.5. The blending amount of the curing agent with respect to the resin 5 was adjusted such that the ratio of the number of equivalents of active hydrogen in the curing agent to the number of equivalents of epoxy group in the resin 5 (epoxy group: active hydrogen) was 1: 1.

Example 4
In Example 2, an epoxy resin composition was prepared in the same manner as in Example 2 except that the liquid crystalline epoxy compound was changed from the resin 1 to the resin 4 to prepare a prepolymer (hereinafter also referred to as “resin 6”). An epoxy resin film was prepared. Then, in the same manner as in Example 1, the visible light transmittance and the thermal conductivity were obtained.

The liquid crystalline epoxy compound and the prepolymerizing agent were obtained by reacting at a molar ratio (liquid crystalline epoxy compound / prepolymerizing agent) of 10 / 2.5. The blending amount of the curing agent with respect to the resin 6 was adjusted such that the ratio of the number of equivalents of active hydrogen in the curing agent to the number of equivalents of epoxy group in the resin 6 (epoxy group: active hydrogen) was 1: 1.

(Example 5)
In Example 1, a solvent (tetrahydrofuran, THF) was further added to prepare an epoxy resin composition. The prepared epoxy resin composition was stirred for 30 minutes at room temperature (25 ° C., the same applies below) using a mix roller. Thereafter, it was formed into a film at room temperature. Further, an epoxy resin film was obtained by curing at 60 ° C. for 60 minutes. Then, in the same manner as in Example 1, the visible light transmittance and the thermal conductivity were obtained.

(Example 6)
In Example 2, an epoxy resin composition was prepared by further adding a solvent (THF). The prepared epoxy resin composition was stirred for 30 minutes at room temperature using a mix roller. Thereafter, it was formed into a film at room temperature. Further, an epoxy resin film was obtained by curing at 60 ° C. for 60 minutes. Then, in the same manner as in Example 1, the visible light transmittance and the thermal conductivity were obtained.

(Example 7)
In Example 3, an epoxy resin composition was prepared by further adding a solvent (THF). The prepared epoxy resin composition was stirred for 30 minutes at room temperature using a mix roller. Thereafter, it was formed into a film at room temperature. Further, an epoxy resin film was obtained by curing at 60 ° C. for 60 minutes. Then, in the same manner as in Example 1, the visible light transmittance and the thermal conductivity were obtained.

(Example 8)
In Example 4, an epoxy resin composition was prepared by further adding a solvent (THF). The prepared epoxy resin composition was stirred for 30 minutes at room temperature using a mix roller. Thereafter, it was formed into a film at room temperature. Further, an epoxy resin film was obtained by curing at 60 ° C. for 60 minutes. Then, in the same manner as in Example 1, the visible light transmittance and the thermal conductivity were obtained.

(Comparative Example 1)
In Example 1, instead of the resin 2, a bisphenol A type epoxy resin (Mitsubishi Chemical Corporation, “jER828”, hereinafter also referred to as “resin 7”) is used as an epoxy compound that does not correspond to the liquid crystalline epoxy compound. Then, an epoxy resin composition was prepared in the same manner as in Example 1 to produce an epoxy resin film. Then, in the same manner as in Example 1, the visible light transmittance and the thermal conductivity were obtained.

The blending amount of the curing agent with respect to the resin 7 was adjusted so that the ratio of the number of equivalents of active hydrogen of the curing agent to the number of equivalents of epoxy group in the resin 7 (epoxy group: active hydrogen) was 1: 1.

(Comparative Example 2)
In Example 1, except that Resin 1 was used instead of Resin 2, an epoxy resin composition was prepared in the same manner as in Example 1 to produce an epoxy resin film. Then, in the same manner as in Example 1, the visible light transmittance and the thermal conductivity were obtained.

The blending amount of the curing agent with respect to the resin 1 was adjusted so that the ratio of the number of equivalents of active hydrogen of the curing agent to the number of equivalents of epoxy group in the resin 1 (epoxy group: active hydrogen) was 1: 1.

(Comparative Example 3)
In Example 1, an epoxy resin composition was prepared in the same manner as in Example 1 except that the resin 4 was used instead of the resin 2, and an epoxy resin film was produced. Then, in the same manner as in Example 1, the visible light transmittance and the thermal conductivity were obtained.

The compounding amount of the curing agent with respect to the resin 4 was adjusted so that the ratio of the number of equivalents of active hydrogen of the curing agent to the number of equivalents of epoxy group in the resin 4 (epoxy group: active hydrogen) was 1: 1.

(Comparative Example 4)
In Example 5, an epoxy resin composition was prepared in the same manner as in Example 1 except that Resin 1 was used instead of Resin 2 to prepare an epoxy resin film. Then, in the same manner as in Example 1, the visible light transmittance and the thermal conductivity were obtained.

In Table 1, “-” in the column of prepolymerizing agent indicates that no prepolymerizing agent is used, and “-” in the column of solvent indicates that no solvent is used.

As shown in Table 1, the epoxy resin films produced in Examples 1 to 8 showed high thermal conductivity and excellent transparency.
Although the epoxy resin film produced in Comparative Example 1 that did not use a liquid crystalline epoxy compound was excellent in transparency, the thermal conductivity was lower than that in Examples. This is considered because the liquid crystal structure is not formed in the cured product.
Although the epoxy resin films prepared in Comparative Examples 2 to 4 in which the liquid crystalline epoxy compound was not reacted with the prepolymerizing agent were excellent in thermal conductivity, the transparency was lower than that in Examples.

Claims

An epoxy resin composition comprising an epoxy resin and a curing agent, and having a liquid crystal structure and capable of forming a cured product having a minimum visible light transmittance of 50% or more measured at a thickness of 30 μm.
The epoxy resin composition according to claim 1, wherein the liquid crystal structure is a nematic structure.
The epoxy resin composition according to claim 1, wherein the liquid crystal structure can be formed at a curing temperature of 60 ° C. or less.
The epoxy resin composition according to any one of claims 1 to 3, wherein the epoxy resin contains at least one of epoxy compounds represented by the following general formula (m1) or general formula (m2).

[In the general formulas (m1) and (m2), R 1 to R 4 each independently represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. ]
The epoxy resin composition according to any one of claims 1 to 4, wherein the epoxy resin is in a prepolymer state.
The epoxy resin composition according to any one of claims 1 to 5, wherein the curing agent contains metaxylylenediamine.
An epoxy resin film, which is a film-like cured product of the epoxy resin composition according to any one of claims 1 to 6.
The epoxy resin film according to claim 7, wherein the cured film has a nematic structure.
A method for producing an epoxy resin film, comprising: a step of forming the epoxy resin composition according to any one of claims 1 to 6 into a film to obtain a molded product; and a step of curing the molded product. .
The method for producing an epoxy resin film according to claim 9, wherein the temperature at which the epoxy resin composition is formed into a film is 100 ° C or lower.
The manufacturing method of the epoxy resin film of Claim 9 or Claim 10 whose temperature at the time of hardening | curing the said molding is 60 degrees C or less.