JP2020158641A - Epoxy resin, epoxy resin composition, epoxy resin cured product and composite material - Google Patents

Abstract

To provide an epoxy resin and an epoxy resin composition that can form a cured product having strength and toughness in a balanced manner, and an epoxy resin cured product and a composite material obtained by using them.SOLUTION: An epoxy resin contains an unsubstituted biphenyl structure, the content of the unsubstituted biphenyl structure totalling 20 mass% or more, and an epoxy equivalent of 230 g/eq or more.SELECTED DRAWING: None

Description

The present disclosure relates to epoxy resins, epoxy resin compositions, epoxy resin cured products and composite materials.

In recent years, the replacement of metals with fiber reinforced plastics (FRP) has been progressing in fields where high levels of strength and toughness are required, such as aircraft body structural materials. Epoxy resins are used for various purposes by taking advantage of their excellent strength and heat resistance, and are also widely used as materials for FRP (see, for example, Patent Documents 1 and 2).

Japanese Unexamined Patent Publication No. 2017-82213 Special Table 2017-505844

Epoxy resin exhibits excellent strength, but there is room for improvement in toughness. However, there is generally a trade-off relationship between the strength and toughness of the epoxy resin, and it is difficult to improve the toughness while maintaining the required strength.

In view of the above circumstances, the present disclosure provides an epoxy resin and an epoxy resin composition capable of forming a cured product having an excellent balance between strength and toughness, and an epoxy resin cured product and a composite material obtained by using these. Make it an issue.

Means for solving the above problems include the following embodiments.
<1> An epoxy resin containing an unsubstituted biphenyl structure, having a content of the unsubstituted biphenyl structure of 20% by mass or more and an epoxy equivalent of 230 g / eq or more.
<2> The epoxy resin according to <1>, which comprises a 4,4'-biphenyl structure as the unsubstituted biphenyl structure.
<3> The epoxy resin according to <1> or <2>, further comprising a naphthalene structure.
<4> The epoxy resin according to any one of <1> to <3>, which has a viscosity at 100 ° C. of 50 Pa · s or less.
<5> Any one of <1> to <4>, which has a fracture toughness value of 1.1 MPa · m ^1/2 or more when made into a cured product together with 3,3'-diaminodiphenyl sulfone as a curing agent. The epoxy resin described in the section.
<6> When a cured product is prepared together with 3,3'-diaminodiphenyl sulfone as a curing agent, interference fringes due to depolarization can be seen in the observation in the cross Nicol state using a polarizing microscope. <1> to < The epoxy resin according to any one of 5>.
<7> An epoxy resin composition containing the epoxy resin according to any one of <1> to <6> and a curing agent.
<8> An epoxy resin cured product, which is a cured product of the epoxy resin composition according to <7>.
<9> A composite material containing the cured epoxy resin according to <8> and a reinforcing material.

According to the present disclosure, an epoxy resin and an epoxy resin composition capable of forming a cured product having an excellent balance between strength and toughness, and an epoxy resin cured product and a composite material obtained by using them are provided.

Hereinafter, embodiments for carrying out 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 the numerical values and their ranges, and does not limit the present invention.

In the present disclosure, the term "process" includes not only a process independent of other processes but also the process if the purpose of the process is achieved even if the process cannot be clearly distinguished from the other process. ..
The numerical range indicated by using "~" in the present disclosure includes the numerical values before and after "~" as the minimum value and the maximum value, respectively.
In the numerical range 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 range described stepwise. .. Further, in the numerical range described in the present disclosure, the upper limit value or the lower limit value of the numerical range may be replaced with the value shown in the examples.
In the present disclosure, each component may contain a plurality of applicable substances. When a plurality of substances corresponding to each component are present in the composition, the content rate or content of each component is the total content rate or content of the plurality of substances present in the composition unless otherwise specified. Means quantity.
In the present disclosure, a plurality of types of particles corresponding to each component may be contained. When a plurality of particles corresponding to each component are present in the composition, the particle size of each component means a value for a mixture of the plurality of particles present in the composition unless otherwise specified.
In the present disclosure, the term "layer" is used not only when the area where the layer exists is observed, but also when the layer is formed in the entire area or only a part of the area. included.
In the present disclosure, the term "laminated" means that layers are stacked, and two or more layers may be bonded or two or more layers may be detachable.
In the present disclosure, the "epoxy compound" means a compound having an epoxy group in the molecule. The "epoxy resin" is a concept in which a plurality of epoxy compounds are regarded as an aggregate and means a state in which the compound is not cured.

≪Epoxy resin≫
The epoxy resin of the present disclosure is an epoxy resin containing an unsubstituted biphenyl structure, the content of the unsubstituted biphenyl structure is 20% by mass or more of the whole, and the epoxy equivalent is 230 g / eq or more.

The cured product obtained by curing the epoxy resin has an excellent balance between strength and toughness. The reason is not always clear, but it is presumed as follows.

The epoxy resin of the present disclosure contains an unsubstituted biphenyl structure, and the content thereof is 20% by mass or more of the whole. The unsubstituted biphenyl structure has a property as a so-called mesogen structure, and the epoxy resin containing this property tends to have the molecules of the epoxy resin oriented in a certain direction when cured. It is considered that the structure in which these molecules are oriented imparts toughness to the cured product. Further, it is considered that when the epoxy equivalent is 230 g / eq or more, fluidity is imparted and process suitability can be improved, the molecules of the epoxy resin are more easily oriented during curing, and the cured product is imparted with better toughness. Be done.

The content of the unsubstituted biphenyl structure contained in the epoxy resin may be 20% by mass or more, preferably 25% by mass or more, and more preferably 30% by mass or more. The upper limit of the content of the unsubstituted biphenyl structure contained in the epoxy resin is not particularly limited. For example, it may be 50% by mass or less of the whole.

The epoxy equivalent of the epoxy resin may be 230 g / eq or more, preferably 240 g / eq or more, and more preferably 250 g / eq or more. The upper limit of the epoxy equivalent of the epoxy resin is not particularly limited. For example, it may be 500 g / eq or less. In the present disclosure, epoxy equivalents are measured by the perchloric acid titration method.

In the present disclosure, the "unsubstituted biphenyl structure" means a structure represented by the following formula (A). The number of unsubstituted biphenyl structures in one molecule of the epoxy compound constituting the epoxy resin may be one or two or more.

From the viewpoint of the balance between the strength and toughness of the cured product, it is more preferable that the epoxy resin contains a structure (4,4'-biphenyl structure) represented by the following formula (a) as an unsubstituted biphenyl structure.

When the epoxy resin is made into a cured product together with a cured product (preferably 3,3'-diaminodiphenyl sulfone), interference fringes due to depolarization may be observed when observing in a cross Nicol state using a polarizing microscope. preferable. It can be determined that the cured product in this case has a liquid crystal structure formed inside. The liquid crystal structure is considered to be formed by orienting the molecules of the epoxy compound during curing, which is considered to impart excellent toughness to the cured product.

The epoxy resin may contain only an epoxy compound having an unsubstituted biphenyl structure, or may contain both an epoxy compound having an unsubstituted biphenyl structure and an epoxy compound having no unsubstituted biphenyl structure. The type of epoxy compound having no unsubstituted biphenyl structure is not particularly limited and can be selected from commonly used ones.

In certain embodiments, the epoxy resin may include an epoxy compound having an aromatic ring as an epoxy compound having no unsubstituted biphenyl structure. The epoxy compound having an aromatic ring is preferably a compound in which one or more glycidyl ether groups are bonded to the aromatic ring, and is preferably a compound in which two glycidyl ether groups are bonded to the aromatic ring. Examples of the aromatic ring include a benzene ring and a naphthalene ring.

Specific examples of the epoxy compound having no unsubstituted biphenyl structure include an epoxy compound represented by the following general formula (1-a) and an epoxy compound represented by the following general formula (1-b).

In the general formula (1-a) and the general formula (1-b), Z is independently an aliphatic hydrocarbon group having 1 to 8 carbon atoms, an alkoxy group having 1 to 8 carbon atoms, a fluorine atom, a chlorine atom, and the like. Represents a bromine atom, an iodine atom, a cyano group, a nitro group, or an acetyl group. p represents an integer from 0 to 4. q represents an integer from 0 to 6.
p is preferably 0 to 2, and more preferably 0.
q is preferably 0 to 4, more preferably 0 to 2, and even more preferably 0.

Among the epoxy compounds represented by the general formula (1-a) and the epoxy compounds represented by the following general formula (1-b), the following general formulas (1-c) to (1-e) are used. The epoxy compound to be used is preferable.

In the general formulas (1-c) to (1-e), the definitions and preferable examples of Z, p, and q are the Z, p, of the general formulas (1-a) and the general formula (1-b). And q are similar to the definitions and preferred examples.

When the epoxy resin contains an epoxy compound having no unsubstituted biphenyl structure, the amount thereof may be 25% by mass or more as long as the content of the unsubstituted biphenyl structure contained in the epoxy resin is 20% by mass or more. The amount is preferably 30% by mass or more, and more preferably 30% by mass or more.

(Specific epoxy compound)
The epoxy resin may contain a polymer of an epoxy monomer having an unsubstituted biphenyl structure (hereinafter, also referred to as a specific epoxy compound).
When the epoxy resin contains a specific epoxy compound, it tends to be easy to achieve the condition that the epoxy equivalent is 230 g / eq or more while the content of the unsubstituted biphenyl structure in the entire epoxy resin is 20% by mass or more. Further, when the epoxy resin contains a specific epoxy compound, crystallization and high viscosity of the epoxy resin before curing are suppressed, and the handleability tends to be excellent.

The specific epoxy compound may be a polymer of epoxy monomers having an unsubstituted biphenyl structure or a polymer of an epoxy monomer having an unsubstituted biphenyl structure and an epoxy monomer having no unsubstituted biphenyl structure. Further, the specific epoxy compound may be a polymer (dimer) of two molecules of epoxy monomer or a polymer of three molecules of epoxy monomer.
The number of unsubstituted biphenyl structures contained in the specific epoxy compound may be one or two or more. When the specific epoxy compound has two or more unsubstituted biphenyl structures, these unsubstituted biphenyl structures may be the same as or different from each other.

The specific epoxy compound preferably has a structure in which two or more epoxy monomers are linked via a divalent group containing an aromatic ring.
When the specific epoxy compound contains a divalent group containing an aromatic ring, the divalent group may or may not contain an unsubstituted biphenyl structure.

Examples of the aromatic ring when the specific epoxy compound contains a divalent group containing an aromatic ring include a phenylene structure, a biphenyl structure, and a naphthalene structure. Examples of the phenylene structure include a structure represented by the following general formula (5A), a biphenyl structure includes a structure represented by the following general formula (5B), and a naphthalene structure is represented by the following general formula (5C). The structure to be used is mentioned.

In the general formula (5A), the general formula (5B), and the general formula (5C), * represents a bond position with an adjacent atom. Examples of adjacent atoms include oxygen atoms and nitrogen atoms. R ¹ and R ² each independently represent an alkyl group having 1 to 8 carbon atoms. Each of m independently represents an integer of 0 to 4. p represents an integer from 0 to 6.

R ¹ and R ² are each independently preferably an alkyl group having 1 to 3 carbon atoms, and more preferably a methyl group.

m is preferably an integer of 0 to 2, more preferably an integer of 0 to 1, and even more preferably 0, respectively. p is preferably an integer of 0 to 2, and more preferably an integer of 0 to 1.

Among the structures represented by the general formula (5A), the structure represented by the following general formula (5a) is preferable, and among the structures represented by the general formula (5B), the structure represented by the following general formula (5b) is preferable. The structure is preferred. Among the structures represented by the general formula (5C), the structures represented by the following general formulas (5c-1) and general formula (5c-2) are preferable. It is considered that the specific epoxy compound having such a structure has high molecular stacking property and is more likely to form a liquid crystal structure.

Formula (5a), in the general formula (5b), the general formula (5c-1), and the general formula ^(5c-2), defined and preferred examples of R ^{1, R} 2, m, and p have the general formula ( 5A), the general formula (5B), and is the same as the definitions and preferable examples of ^R 1, ^{R 2} and m, and p in the general formula (5C). * Represents the bond position with an adjacent atom.

The specific epoxy compound may be an epoxy compound having a structure represented by the following general formula (1-A), general formula (1-B), or general formula (1-C).

In the general formula (1-A), the general formula (1-B), and the general formula (1-C), the definitions and preferable examples of X, Y and n are the X, Y and n of the general formula (1). Similar to the definition and preferred examples. ^{Further, the} definition and preferred examples of R ^{1, R} 2, m, and p, ^{R 1, R} 2, m, and the definition of p in the general formula (5A), the general formula (5B), and the general formula (5C) And similar to the preferred example. Z independently represents -O- or -NH-. * Represents a binding site with an adjacent atom.

The specific epoxy compound may have at least one structure selected from the group consisting of the following general formulas (1-a') and (1-b'). When the specific epoxy compound has at least one structure selected from the group consisting of (1-a') and (1-b'), the elastic modulus tends to be further improved.

In the general formula (1-a') and the general formula (1-b'), the definitions and preferable examples of Z, p, q are Z, p of the general formula (1-a) and the general formula (1-b). , Q are similar to the definitions and preferred examples. * Represents a binding site with an adjacent atom.

Among the structures represented by the general formula (1-a'), the structures represented by the general formula (1-c') and the general formula (1-d') are preferable, and the general formula (1-b') is used. Among the structures represented, the structure represented by the general formula (1-e') is preferable.

In general formulas (1-c') to general formulas (1-e'), definitions and preferred examples of Z, p, and q are Z, in general formulas (1-c) to general formulas (1-e). Similar to the definitions and preferred examples of p and q. * Represents a binding site with an adjacent atom.

The specific epoxy compound may be a reaction product of an epoxy monomer and a compound having a functional group capable of reacting with an epoxy group.

Examples of the functional group capable of reacting with the epoxy group include a hydroxyl group, an amino group, an isocyanate group and the like. The number of functional groups capable of reacting with the epoxy group in the compound having a functional group capable of reacting with the epoxy group may be one or two or more, and is preferably two. Further, the functional group may or may not be directly linked to the aromatic ring, and may be linked to the aromatic ring via an alkylene oxide chain such as an ethylene oxide chain or a propylene oxide chain, or an alkyl chain.

From the viewpoint of forming a liquid crystal structure in the cured product, the compound having a functional group capable of reacting with an epoxy group is a dihydroxybenzene compound having a structure in which two hydroxyl groups are bonded to one benzene ring, and two to one benzene ring. A diaminobenzene compound having a structure in which two amino groups are bonded, a dihydroxybiphenyl compound having a structure in which one hydroxyl group is bonded to each of two benzene rings forming a biphenyl structure, and one in each of two benzene rings forming a biphenyl structure. It consists of a diaminobiphenyl compound having a structure in which an amino group is bonded, a dihydroxynaphthalene compound having a structure in which two hydroxyl groups are bonded to one naphthalene ring, and a diaminonaphthalene compound having a structure in which two amino groups are bonded to one naphthalene ring. 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.

Examples of the dihydroxybiphenyl compound include 2,2'-dihydroxybiphenyl, 2,3'-dihydroxybiphenyl, 2,4'-dihydroxybiphenyl, 3,3'-dihydroxybiphenyl, 3,4'-dihydroxybiphenyl, 4,4'. -Dihydroxybiphenyl, derivatives thereof and the like can be mentioned.

Examples of the diaminobiphenyl compound 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 dihydroxynaphthalene compound include 1,2-dihydroxynaphthalene, 1,3-dihydroxynaphthalene, 1,4-dihydroxynaphthalene, 1,5-dihydroxynaphthalene, 1,6-dihydroxynaphthalene, 1,7-dihydroxynaphthalene, 1, Examples thereof include 8-dihydroxynaphthalene, 2,3-dihydroxynaphthalene, 2,6-dihydroxynaphthalene, 2,7-dihydroxynaphthalene, and derivatives thereof.

Examples of the diaminonaphthalene compound include 1,2-diaminonaphthalene, 1,3-diaminonaphthalene, 1,4-diaminonaphthalene, 1,5-diaminonaphthalene, 1,6-diaminonaphthalene, 1,7-diaminonaphthalene, 1, Examples thereof include 8-diaminonaphthalene, 2,3-diaminonaphthalene, 2,6-diaminonaphthalene, 2,7-diaminonaphthalene, and derivatives thereof.

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 or naphthalene ring of the specific aromatic compound. As the specific aromatic compound, one kind may be used alone, or two or more kinds may be used in combination.

The functional group equivalent of a compound having a functional group capable of reacting with an epoxy group is not particularly limited. From the viewpoint of reaction efficiency, the functional group equivalent (equivalent to active hydrogen when the functional group is an amino group) of a compound having a functional group capable of reacting with an epoxy group is 65 g / eq to 200 g / eq. Is more preferable, and it is more preferably 70 g / eq to 150 g / eq, and even more preferably 75 g / eq to 100 g / eq.

The method for synthesizing a specific epoxy compound by reacting an epoxy monomer with a compound having a functional group capable of reacting with an epoxy group is not particularly limited. Specifically, for example, a specific epoxy compound is obtained by dissolving an epoxy monomer, a compound having a functional group capable of reacting with an epoxy group, and a reaction catalyst used as necessary in a solvent and stirring while heating. Can be synthesized.

Alternatively, for example, a specific epoxy compound is obtained by mixing an epoxy monomer, a compound having a functional group capable of reacting with an epoxy group, and a reaction catalyst used as necessary without using a solvent and stirring while heating. Can be synthesized.

The solvent is not particularly limited as long as it can dissolve the epoxy monomer and a compound having a functional group capable of reacting with the epoxy group, and can heat the compound to a temperature required for the reaction. Specific examples thereof include cyclohexanone, cyclopentanone, ethyl lactate, propylene glycol monomethyl ether, N-methylpyrrolidone, methyl cellosolve, ethyl cellosolve, propylene glycol monopropyl ether and the like.

The amount of the solvent is not particularly limited as long as the epoxy monomer, the compound having a functional group capable of reacting with the epoxy group, and the reaction catalyst used as needed can be dissolved at the reaction temperature. Although the solubility varies depending on the type of raw material before the reaction, the type of solvent, etc., for example, when the charged solid content concentration is 20% by mass to 60% by mass, the viscosity of the solution after the reaction is in a preferable range. There is a tendency.

The type of reaction catalyst is not particularly limited, and an appropriate one can be selected from the viewpoints of reaction rate, reaction temperature, storage stability and the like. Specific examples thereof include imidazole compounds, organic phosphorus compounds, tertiary amines, and quaternary ammonium salts. One type of reaction catalyst may be used alone, or two or more types may be used in combination.

From the viewpoint of heat resistance of the cured product, an organic phosphorus compound is preferable as the reaction catalyst. Preferred examples of the organic phosphorus compound are an organic phosphine compound, a compound having an intramolecular polarization obtained by adding a compound having a π bond such as maleic anhydride, a quinone compound, a diazophenylmethane, and a phenol resin to the organic phosphine compound, and an organic compound. Examples thereof include a complex of a phosphine compound and an organic boron compound. Of these, a compound obtained by adding an organic phosphine compound and a quinone compound is preferable.

Specifically, as the organic phosphine compound, triphenylphosphine, diphenyl (p-tril) phosphine, tris (alkylphenyl) phosphine, tris (alkoxyphenyl) phosphine, tris (alkylalkoxyphenyl) phosphine, tris (dialkylphenyl) phosphine, Tris (trialkylphenyl) phosphine, tris (tetraalkylphenyl) phosphine, tris (dialkoxyphenyl) phosphine, tris (trialkoxyphenyl) phosphine, tris (tetraalkoxyphenyl) phosphine, trialkylphosphine, dialkylarylphosphine, alkyldiaryl Examples include phosphine.

Specifically, as the quinone compound, 1,4-benzoquinone, 2,5-turquinone, 1,4-naphthoquinone, 2,3-dimethylbenzoquinone, 2,6-dimethylbenzoquinone, 2,3-dimethoxy-5-methyl- Examples thereof include 1,4-benzoquinone, 2,3-dimethoxy-1,4-benzoquinone and phenyl-1,4-benzoquinone.

Specific examples of the organic boron compound include tetraphenyl borate, tetra-p-tolyl borate, and tetra-n-butyl borate.

The amount of the reaction catalyst is not particularly limited. From the viewpoint of reaction rate and storage stability, it is preferably 0.1 part by mass to 1.5 parts by mass with respect to 100 parts by mass of the total mass of the epoxy monomer and the compound having a functional group capable of reacting with the epoxy group. , 0.2 parts by mass to 1 part by mass, more preferably.

The specific epoxy compound can be synthesized using a reaction vessel such as a flask for a small amount of scale and a synthesis pot for a large amount of scale. The specific synthesis method is as follows, for example. First, the epoxy monomer is put into a reaction vessel, a solvent is added if necessary, and the epoxy monomer is heated to the reaction temperature by an oil bath or a heat medium to dissolve the epoxy monomer. A compound having a functional group capable of reacting with an epoxy group is added thereto, and then a reaction catalyst is added as needed to initiate the reaction. Then, if necessary, the solvent is distilled off under reduced pressure to obtain a specific epoxy compound.

The reaction temperature is not particularly limited as long as the reaction between the epoxy group of the epoxy monomer and the functional group capable of reacting with the epoxy group proceeds. The reaction temperature is, for example, preferably in the range of 100 ° C. to 180 ° C., and more preferably in the range of 100 ° C. to 170 ° C. By setting the reaction temperature to 100 ° C. or higher, the time until the reaction is completed tends to be shortened. On the other hand, by setting the reaction temperature to 180 ° C. or lower, the possibility of gelation tends to be reduced.

When synthesizing a specific epoxy compound, the blending ratio of the epoxy monomer as a raw material and the compound having a functional group capable of reacting with the epoxy group is not particularly limited. For example, the compounding ratio in which the ratio (A: B) of the equivalent number of epoxy groups (A) to the equivalent number of functional groups capable of reacting with the epoxy group (A: B) is in the range of 10:10 to 10: 0.01. May be. From the viewpoint of toughness and heat resistance of the cured product, a blending ratio in which A: B is in the range of 10: 5 to 10: 0.1 is preferable.

The structure of the specific epoxy compound obtained by the synthesis includes, for example, the molecular weight of the specific epoxy compound estimated to be obtained by the reaction of the epoxy monomer used in the synthesis with a compound having a functional group capable of reacting with the epoxy group. It can be determined by collating with the molecular weight of the target compound determined by liquid chromatography performed using a liquid chromatograph equipped with a UV and mass spectrum detector.

For liquid chromatography, for example, "LaChrom II C18" manufactured by Hitachi, Ltd. is used as an analytical column, and the mixing ratio (volume basis) of the eluent is adjusted to acetonitrile / tetrahydrofuran / 10 mmol / l acetate by using the gradient method. The measurement is carried out by continuously changing from ammonium ammonium aqueous solution = 20/5/75 to acetonitrile / tetrahydrofuran = 80/20 (20 minutes from the start) and then to acetonitrile / tetrahydrofuran = 50/50 (35 minutes from the start). The flow velocity is 1.0 ml / min. The UV spectrum detector detects the absorbance at a wavelength of 280 nm, and the mass spectrum detector detects the ionization voltage as 2700 V.

The epoxy resin preferably contains both a specific epoxy compound and an epoxy monomer (prepolymer). When both the specific epoxy compound and the epoxy monomer are present in the epoxy resin in an appropriate ratio, the handleability before curing tends to be better. In addition, the crosslink density at the time of curing can be made higher, and a cured epoxy resin product having better heat resistance tends to be obtained. The ratio of the specific epoxy compound to the epoxy monomer present in the epoxy resin can be adjusted by the compounding ratio of the epoxy monomer and the compound having a functional group capable of reacting with the epoxy group and other reaction conditions.

The content of the epoxy monomer contained in the epoxy resin is preferably 50% or less of the total epoxy resin. Epoxy resins having an epoxy monomer content of 50% or less tend to have a lower viscosity when the temperature rises than epoxy resins having an epoxy monomer content of more than 50%, and tend to be excellent in handleability. The reason is not clear, but when the epoxy monomer content is 50% or less of the total epoxy resin, crystals are crystallized at a temperature lower than the melting temperature of the epoxy resin as compared with the case where the epoxy monomer content exceeds 50%. It is presumed that this is because the precipitation of epoxy is more suppressed.

In the present disclosure, the content of the epoxy monomer in the epoxy resin can be calculated from, for example, a chart obtained by a liquid chromatograph.
More specifically, it is determined as the ratio (%) of the area of the peak derived from the mesogen epoxy monomer to the total area of the peaks derived from all the components constituting the epoxy resin in the chart obtained by the liquid chromatograph. Specifically, the absorbance of the epoxy resin to be measured at a wavelength of 280 nm is detected, and the total area of all the detected peaks and the area of the peak corresponding to the epoxy monomer are calculated by the following formula.

Percentage of peak areas derived from epoxy monomer (%) = (area of peaks derived from epoxy monomer / total area of peaks derived from all components constituting the epoxy resin) × 100

Liquid chromatography is performed with a sample concentration of 0.5% by mass, tetrahydrofuran being used as the mobile phase, and a flow rate of 1.0 ml / min. The measurement can be performed using, for example, a high performance liquid chromatograph "L6000" manufactured by Hitachi, Ltd. and a data analysis device "C-R4A" manufactured by Shimadzu Corporation. As the column, for example, "G2000HXL" and "G3000HXL", which are GPC columns manufactured by Tosoh Corporation, can be used.

From the viewpoint of improving handleability, the content of the epoxy monomer is preferably 50% or less, more preferably 49% or less, and further preferably 48% or less of the entire epoxy resin.

From the viewpoint of reducing the intrinsic viscosity (viscosity at the time of melting), the content of the epoxy monomer is preferably 35% or more, more preferably 37% or more, and 40% or more of the entire epoxy resin. Is even more preferable.

[Weight average molecular weight]
The weight average molecular weight (Mw) of the epoxy resin is not particularly limited. From the viewpoint of reducing the viscosity, the weight average molecular weight (Mw) of the epoxy resin is preferably 500 to 3000, more preferably 700 to 2500, and even more preferably 800 to 2000.

In the present disclosure, the number average molecular weight (Mn) and the weight average molecular weight (Mw) are values obtained by liquid chromatography.
Liquid chromatography is performed with a sample concentration of 0.5% by mass, tetrahydrofuran being used as the mobile phase, and a flow rate of 1.0 ml / min. A calibration curve is prepared using a polystyrene standard sample, and Mn and Mw are measured using polystyrene-equivalent values.
The measurement can be performed using, for example, a high performance liquid chromatograph "L6000" manufactured by Hitachi, Ltd. and a data analysis device "C-R4A" manufactured by Shimadzu Corporation. As the column, for example, "G2000HXL" and "G3000HXL", which are GPC columns manufactured by Tosoh Corporation, can be used.

〔viscosity〕
The viscosity of the epoxy resin is not particularly limited and can be selected according to the application of the epoxy resin. From the viewpoint of handleability, the viscosity of the epoxy resin at 100 ° C. is preferably 50 Pa · s or less, more preferably 20 Pa · s or less, and further preferably 10 Pa · s or less.
The viscosity of the epoxy resin at 100 ° C. is measured by the method described in Examples.

The epoxy resin preferably has a fracture toughness value of 1.1 (MPa · m ^1/2 ) or more when it is made into a cured product together with a curing agent (preferably 3,3'-diaminodiphenyl sulfone).

≪Epoxy resin composition and cured epoxy resin≫
The epoxy resin composition of the present disclosure contains the epoxy resin of the present disclosure and a curing agent. The epoxy resin cured product of the present disclosure is a cured product of the epoxy resin composition of the present disclosure.

<Hardener>
The curing agent 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, phenol curing agents, acid anhydride curing agents, polypeptide curing agents, polyaminoamide curing agents, isocyanate curing agents, blocked isocyanate curing agents and the like. As the curing agent, one type may be used alone or two or more types may be used in combination.

From the viewpoint of forming a higher-order structure in the cured product of the epoxy resin composition, the curing agent is preferably an amine curing agent or a phenol curing agent, and more preferably an amine curing agent. As the amine curing agent, an amine curing agent having an aromatic ring and an amino group is preferable, an amine curing agent in which an amino group is directly bonded to the aromatic ring is more preferable, and two amino groups directly bonded to the aromatic ring are used. The amine curing agent having the above is more preferable. Examples of the aromatic ring include a benzene ring and a naphthalene ring.

Specifically, as the amine curing agent, 3,3'-diaminodiphenylsulfone, 4,4′-diaminodiphenylsulfone, 4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenylether, 4,4′-diamino− 3,3'-dimethoxybiphenyl, 4,4'-diaminophenylbenzoate, 1,5-diaminonaphthalene, 1,3-diaminonaphthalene, 1,4-diaminonaphthalene, 1,8-diaminonaphthalene, 1,3-diamino Benzene, 1,4-diaminobenzene, 4,4'-diaminobenzanilide, trimethylene-bis-4-aminobenzoate and the like can be mentioned.

From the viewpoint of forming a liquid crystal structure in the cured product of the epoxy resin composition, 3,3'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 1,3-diaminobenzene, 1,4-diaminobenzene, 4,4'-Diaminobenzanilide, 1,5-diaminonaphthalene, 4,4'-diaminodiphenylmethane and trimethylene-bis-4-aminobenzoate are preferable, and from the viewpoint of obtaining a cured product having low water absorption and high toughness. 3,3'-diaminodiphenyl sulfone is more preferred.

Examples of the phenol curing agent include a low-molecular-weight phenol compound and a phenol novolac resin obtained by connecting low-molecular-weight phenol compounds with a methylene chain or the like to form a novolak. Examples of the low molecular weight phenol compound include monofunctional phenol compounds such as phenol, o-cresol, m-cresol and p-cresol, bifunctional phenol compounds such as catechol, resorcinol and hydroquinone, 1,2,3-trihydroxybenzene and 1 , 2,4-Trihydroxybenzene, 1,3,5-trihydroxybenzene and other trifunctional phenolic compounds and the like.

The content of the curing agent in the epoxy resin composition is not particularly limited. From the viewpoint of the efficiency of the curing reaction, the equivalent number of functional groups of the curing agent contained in the epoxy resin composition (active hydrogen in the case of an amine curing agent, the equivalent number of hydroxyl groups in the case of a phenol curing agent) and the epoxy resin. The ratio of the epoxy group to the equivalent number of the epoxy group (the number of equivalents of the functional group / the number of equivalents of the epoxy group) is preferably an amount of 0.3 to 3.0, and an amount of 0.5 to 2.0. More preferably.

<Other ingredients>
The epoxy resin composition may contain other components other than the epoxy resin and the curing agent, if necessary. For example, it may contain a curing catalyst, a filler and the like. Specific examples of the curing catalyst include compounds exemplified as reaction catalysts that can be used in the synthesis of specific epoxy compounds.

[Use of epoxy resin composition and cured epoxy resin]
The use of the epoxy resin composition and the cured epoxy resin is not particularly limited, and for example, it can be suitably used for producing a fiber reinforced composite material (FRP) used for aircraft, spacecraft and the like.
In addition, the epoxy resin composition of the present disclosure can also be suitably used in a production method in which steps such as localizing thermoplastic resin particles in the surface region of a prepreg are omitted in the production of a fiber-reinforced composite material.

≪Composite material≫
The composite material of the present disclosure includes the epoxy resin cured product of the present disclosure and a reinforcing material.
The material of the reinforcing material contained in the composite material is not particularly limited and can be selected according to the application of the composite material and the like. Specific examples of the reinforcing material include carbon materials, glass, aromatic polyamide-based resins (for example, Kevlar (registered trademark)), ultra-high molecular weight polyethylene, alumina, boron nitride, aluminum nitride, mica, and silicon. The shape of the reinforcing material is not particularly limited, and examples thereof include fibrous form and particulate form (filler). From the viewpoint of the strength of the composite material, the reinforcing material is preferably a carbon material, and more preferably carbon fiber. The reinforcing material contained in the composite material may be one kind or two or more kinds.

The form of the composite material is not particularly limited. For example, it may have a structure in which at least one cured product-containing layer containing an epoxy resin cured product and at least one reinforcing material-containing layer containing a reinforcing material are laminated.

Next, the embodiments of the present disclosure will be specifically described with reference to Examples, but the present invention is not limited to these Examples. Details of the materials used are as follows.

Epoxy monomer 1 ... In the following general formula (M1), a mixture of an epoxy monomer in which R ¹ is an all hydrogen atom and an epoxy monomer in which R ¹ is an all methyl group (mass ratio 1: 1, epoxy equivalent: 175 g / eq, Content of unsubstituted biphenyl structure: 24.3% by mass) Mitsubishi Chemical Co., Ltd.)

Epoxy monomer 2 ... Epoxy monomer in which q is 0 in the general formula (1-e) (epoxy equivalent: 143 g / eq, content of unsubstituted biphenyl structure: 0% by mass, DIC Corporation)
Specific aromatic compound 1 ... 4,4'-dihydroxybiphenyl (hydroxyl equivalent: 93 g / eq, content of unsubstituted biphenyl structure: 81.7% by mass, Honshu Chemical Industry Co., Ltd.)
Specified aromatic compound 2 ... 1,5-dihydroxynaphthalene (hydroxyl equivalent: 80 g / eq, content of unsubstituted biphenyl structure: 0% by mass, Sugai Chemical Co., Ltd.)
Reaction catalyst: Tetrabutylphosphonium and lauryl acid salt (molecular weight: 212.42)
Synthetic solvent: Cyclohexanone (molecular weight: 98.15, boiling point: 155 ° C)

[Example 1]
125 g (100 parts by mass) of epoxy monomer 1 was weighed into a 500 mL three-necked flask, and 200 g of a synthetic solvent was added thereto. A cooling tube and a nitrogen introduction tube were installed in the three-necked flask, and stirring blades were attached so as to be immersed in the synthetic solvent. The three-necked flask was immersed in an oil bath at 160 ° C., and stirring was started. After confirming that the epoxy monomer 1 was dissolved after a few minutes to form a transparent solution, 13.3 g (20 parts by mass) of the specific aromatic compound 1 was added (equivalent number of epoxy groups / equivalent number of phenolic hydroxyl groups). = 10/2), and 1.25 g of a reaction catalyst was further added, and heating was continued at an oil bath temperature of 160 ° C. After continuing heating for 3 hours, the synthetic solvent was distilled off from the reaction solution under reduced pressure, and the residue was cooled to room temperature so that the epoxy monomer 1 did not react with the multimer produced by reacting with the specific aromatic compound 1. An epoxy resin (prepolyma) containing the epoxy monomer 1 was obtained.

[Examples 2 and 3]
In the same manner as in Example 1 except that the amount of the specific aromatic compound 1 was changed to 30 parts by mass and 40 parts by mass, respectively, the epoxy monomer 1 was produced by reacting with the specific aromatic compound 1, and the multimer was not produced. An epoxy resin (prepolymer) containing the reaction epoxy monomer 1 was obtained.

[Comparative Example 1]
An epoxy resin was prepared in which the epoxy monomer 1 was not reacted with the specific aromatic compound.

[Comparative Examples 2, 3, 4]
The epoxy monomer 1 reacts with the specific aromatic compound 2 in the same manner as in Example 1 except that the specific aromatic compound 1 is changed to 20 parts by mass, 30 parts by mass, and 40 parts by mass, respectively. An epoxy resin (prepolyma) containing the resulting multimer and the unreacted epoxy monomer 1 was obtained.

[Example 4]
80.9 g (60 parts by mass) of epoxy monomer 1 and 44.1 g (40 parts by mass) of epoxy monomer 2 were weighed into a 500 mL three-necked flask, and 200 g of a synthetic solvent was added thereto. A cooling tube and a nitrogen introduction tube were installed in the three-necked flask, and stirring blades were attached so as to be immersed in the synthetic solvent. The three-necked flask was immersed in an oil bath at 160 ° C., and stirring was started. After confirming that the epoxy monomers 1 and 2 were dissolved after a few minutes to form a transparent solution, 14.3 g (20 parts by mass) of the specific aromatic compound 1 was added (equivalent number of epoxy groups / phenolic hydroxyl group). Equivalent number = 10/2), 1.25 g of a reaction catalyst was further added, and heating was continued at an oil bath temperature of 160 ° C. After continuing heating for 3 hours, the synthetic solvent was distilled off from the reaction solution under reduced pressure, and the residue was cooled to room temperature to generate a multimer in which epoxy monomers 1 and 2 reacted with the specific aromatic compound 1 and not yet. An epoxy resin (prepolymer) containing the reaction epoxy monomers 1 and 2 was obtained.

[Examples 5 and 6]
Epoxy monomers 1 and 2 were produced by reacting with the specific aromatic compound 1 in the same manner as in Example 4 except that the amounts of the specific aromatic compound 1 were changed to 30 parts by mass and 40 parts by mass, respectively. , An epoxy resin (prepolyma) containing unreacted epoxy monomers 1 and 2 was obtained.

[Comparative Example 5]
In the same manner as in Example 1 except that the epoxy monomer 1 was changed to 100 parts by mass of the epoxy monomer 2, the multimer produced by the reaction of the epoxy monomer 2 with the specific aromatic compound 1 and the unreacted epoxy monomer 2 An epoxy resin (prepolymer) containing and was obtained.

[Comparative Example 6]
Similar to Comparative Example 5 except that the specific aromatic compound 1 was changed to 20 parts by mass of the specific aromatic compound 2, the epoxy monomer 2 was produced by reacting with the specific aromatic compound 2, and the multimer was not produced. An epoxy resin (prepolyma) containing the reaction epoxy monomer 2 was obtained.

[Resin measurement]
Table 1 shows the content (% by mass) of the unsubstituted biphenyl structure of the epoxy resin prepared in Examples and Comparative Examples and the epoxy equivalent (measured by the perchloric acid titration method).

[Viscosity at 100 ° C]
The viscosity of the melted epoxy resin was measured on a hot plate set at 100 ° C. The measurement was carried out by attaching a cone (No. 5, angle 1.8 °, cone diameter 9.53 mm) to a cone plate type viscometer (CAP2000 manufactured by Brookfield), and setting the measurement condition to 50 rpm. .. Since the epoxy resin of Comparative Example 1 was a solid (not melted) at 100 ° C., no measurement was performed. The results are shown in Table 1.

[Preparation of cured epoxy resin]
The epoxy resin (100 parts by mass) obtained in Examples and Comparative Examples and a stainless steel petri dish were weighed, heated to 180 ° C. to melt, and stirred. 3,3'-Diaminodiphenyl sulfone was added thereto as a curing agent, and the mixture was stirred in a molten state. The obtained mixture was cooled to room temperature (25 ° C.) and heat-treated at 150 ° C. for 4 hours in a constant temperature bath to obtain a cured epoxy resin.

[Measurement of flexural modulus]
The obtained cured epoxy resin was cut into a rectangular parallelepiped having a size of 2.0 mm × 5.0 mm × 40 mm to prepare a test piece for evaluation of flexural modulus and bending strength. Using this test piece, a bending test was performed with a Tensilon universal material tester (Instron 5948, Instron) under the conditions of a distance between fulcrums of 32 mm and a crosshead speed of 1 mm / min. Using the measurement results, a bending stress-displacement curve was created from the formula (A), and the maximum stress was taken as the bending strength. Next, the bending strain is calculated from the equation (B), and the flexural modulus (GPa) is calculated by the equation (C) using the bending stress when the bending strain is 0.25% and the bending stress when the bending strain is 0.45%. ) Was calculated. The results are shown in Table 1.

[Measurement of fracture toughness value]
The fracture toughness value was measured as an index of the toughness of the cured epoxy resin. The cured epoxy resin obtained in Examples and Comparative Examples was cut into a rectangular parallelepiped having a size of 3.75 mm × 7.5 mm × 33 mm to prepare a test piece for evaluating fracture toughness. Using this test piece, a three-point bending measurement was performed based on ASTM D5045 to calculate a fracture toughness value (MPa · m ^1/2 ). Instron 5948 (Instron) was used as the evaluation device. The results are shown in Table 1.

[Presence / absence of liquid crystal structure]
The surface of the cured epoxy resin was polished, and it was investigated whether or not interference fringes due to depolarization were observed (a liquid crystal structure was formed) in the observation in a cross Nicol state using a polarizing microscope. The results are shown in Table 1.

As shown in Table 1, the epoxy resin cured using the epoxy resin of the example containing the unsubstituted biphenyl structure, the content of which is 20% by mass of the whole, and the epoxy equivalent is 230 g / eq or more. The product had an excellent balance of strength and toughness as compared with the epoxy resin cured product prepared by using the epoxy resin of the example of Comparative Example which did not satisfy at least one of these conditions.

Claims (9)

An epoxy resin containing an unsubstituted biphenyl structure, having a content of the unsubstituted biphenyl structure of 20% by mass or more and an epoxy equivalent of 230 g / eq or more. The epoxy resin according to claim 1, which comprises a 4,4'-biphenyl structure as the unsubstituted biphenyl structure. The epoxy resin according to claim 1 or 2, further comprising a naphthalene structure. The epoxy resin according to any one of claims 1 to 3, wherein the viscosity at 100 ° C. is 50 Pa · s or less. The invention according to any one of claims 1 to 4, wherein the fracture toughness value is 1.1 MPa · m ^1/2 or more when a cured product is prepared together with 3,3'-diaminodiphenyl sulfone as a curing agent. Epoxy resin. According to claims 1 to 5, when a cured product is prepared together with 3,3'-diaminodiphenyl sulfone as a curing agent, interference fringes due to depolarization are observed in the observation in a cross Nicol state using a polarizing microscope. The epoxy resin according to any one item. An epoxy resin composition containing the epoxy resin according to any one of claims 1 to 6 and a curing agent. An epoxy resin cured product, which is a cured product of the epoxy resin composition according to claim 7. A composite material containing the cured epoxy resin according to claim 8 and a reinforcing material.