Epoxy resin, epoxy resin composition, epoxy resin cured product, and composite material

Abstract

An epoxy resin, comprising an epoxy compound having at least two mesogenic structures and at least one divalent biphenyl group.

Claims

1. An epoxy resin, comprising an epoxy compound having at least two mesogenic structures and at least one divalent biphenyl group, wherein the at least two mesogenic structures are mesogenic structures represented by the following Formula (3): ##STR00032## wherein, in Formula (3), each of R.sup.3 to R.sup.6 independently represents a hydrogen atom.

2. The epoxy resin according to claim 1, wherein the epoxy compound has a structure in which the divalent biphenyl group is disposed between the at least two mesogenic structures.

3. The epoxy resin according to claim 1, further comprising a mesogenic epoxy monomer represented by the following Formula (1-m): ##STR00033## wherein, in Formula (1-m), X represents a single bond or a linking group that includes at least one divalent group selected from the following Group (A): ##STR00034## wherein, in Group (A), each Y independently represents 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, a bromine atom, an iodine atom, a cyano group, a nitro group or an acetyl group; each n independently represents an integer from 0 to 4; k represents an integer from 0 to 7; m represents an integer from 0 to 8; and 1 represents an integer from 0 to 12.

4. The epoxy resin according to claim 3, wherein the mesogenic epoxy monomer represented by Formula (1-m) includes a mesogenic epoxy monomer represented by the following Formula (2-m): ##STR00035## wherein, in Formula (1-m), X represents a single bond or a linking group that includes at least one divalent group selected from the Group (A); each Y independently represents 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, a bromine atom, an iodine atom, a cyano group, a nitro group or an acetyl group; and each n independently represents an integer from 0 to 4.

5. The epoxy resin according to claim 3, wherein the mesogenic epoxy monomer represented by Formula (1-m) includes a mesogenic epoxy monomer represented by the following Formula (3-m) or Formula (4-m): ##STR00036## wherein, in Formula (3-m) and Formula (4-m), each of R.sup.3 to R.sup.6 independently represents a hydrogen atom or an alkyl group of 1 to 3 carbon atoms.

6. The epoxy resin according to claim 3, wherein the mesogenic epoxy monomer is included in an amount of 50% or less with respect to a total amount of the epoxy resin.

7. An epoxy resin composition, comprising the epoxy resin according to claim 1, and a curing agent.

8. The epoxy resin composition according to claim 7, which is configured to form a smectic structure in a cured state.

9. The epoxy resin composition according to claim 7, wherein the curing agent includes a compound having two or more amino groups that are directly bonded to an aromatic ring.

10. The epoxy resin composition according to claim 7, wherein the curing agent is 3,3′-diaminodiphenylsulfone.

11. An epoxy resin cured product, comprising a cured product of the epoxy resin composition according to claim 7.

12. A composite material, comprising the epoxy resin cured product according to claim 11 and a reinforcing material.

13. The composite material according to claim 12, wherein the reinforcing material includes a carbon material.

Description

EXAMPLES

(1) In the following, the invention is explained by referring to the Examples. However, the invention is not limited to these Examples.

Example 1

(2) To a 500-mL three-necked flask, 50 parts by mass of a mesogenic epoxy monomer having a structure described below were placed, and 100 parts by mass of propyleneglycol monomethyl ether were added. A cooling tube and a nitrogen inlet tube were attached to the flask, and a stirring blade was attached so as to be immersed in the solvent. Then, the flask was immersed in an oil bath at 120° C. and subjected to stirring.

(3) After confirming that the mesogenic epoxy monomer was dissolved and the solution became clear, 4,4′-dihydroxybiphenyl was added as a specific biphenyl compound, such that the ratio of the equivalent amount of epoxy group of the mesogenic epoxy monomer (A) to the equivalent amount of hydroxy group of 4,4′-dihydroxybiphenyl (A:B) was 10:2.5, and 0.5 g of triphenylphosphine were added as a reaction catalyst. The heating of the mixture was continued in an oil bath at 120° C. for 3 hours. Thereafter, propyleneglycol monomethyl ether was evaporated under reduced pressure, and the residue was cooled to room temperature (25° C.). An epoxy resin, in which a part of the mesogenic epoxy monomer is reacted with 4,4′-dihydroxybiphenyl to form a multimer (specific epoxy compound), was thus obtained.

(4) ##STR00028##

(5) Subsequently, 50 g of the epoxy resin and 9.1 g of 3,3′-diaminodiphenylsulfone as a curing agent were placed in a stainless dish, and heated on a hot plate at 180° C. After the resin in the stainless dish was melted, the heating was continued at 180° C. for 1 hour. After cooling to room temperature (25° C.), the resin was taken out from the stainless dish and heated in a thermostat chamber at 230° C. for 1 hour to complete the curing, thereby obtaining an epoxy resin cured product. A sample for evaluating fracture toughness having a size of 3.75 mm×7.5 mm×33 mm was prepared from the epoxy resin cured product.

Example 2

(6) To a 500-mL three-necked flask, 50 parts by mass of a mesogenic epoxy monomer having a structure described below were placed, and 100 parts by mass of propyleneglycol monomethyl ether were added. A cooling tube and a nitrogen inlet tube were attached to the flask, and a stirring blade was attached so as to be immersed in the solvent. Then, the flask was immersed in an oil bath at 120° C. and subjected to stirring.

(7) After confirming that the mesogenic epoxy monomer was dissolved and the solution became clear, 2,2′-dihydroxybiphenyl was added as a specific biphenyl compound, such that the ratio of the equivalent amount of epoxy group of the mesogenic epoxy monomer (A) to the equivalent amount of hydroxy group of 2,2′-dihydroxybiphenyl (A:B) was 10:2.5, and 0.5 g of triphenylphosphine were added as a reaction catalyst. The heating of the mixture was continued in an oil bath at 120° C. for 3 hours. Thereafter, propyleneglycol monomethyl ether was evaporated under reduced pressure, and the residue was cooled to room temperature (25° C.). An epoxy resin, in which a part of the mesogenic epoxy monomer is reacted with 2,2′-dihydroxybiphenyl to form a multimer (specific epoxy compound), was thus obtained.

(8) ##STR00029##

(9) Subsequently, 50 g of the epoxy resin and 9.1 g of 3,3′-diaminodiphenylsulfone as a curing agent were placed in a stainless dish, and heated on a hot plate at 180° C. After the resin in the stainless dish was melted, the heating was continued at 180° C. for 1 hour. After cooling to room temperature (25° C.), the resin was taken out from the stainless dish and heated in a thermostat chamber at 230° C. for 1 hour to complete the curing, thereby obtaining an epoxy resin cured product. A sample was prepared from the epoxy resin cured product in a similar manner to Example 1.

Example 3

(10) To a 500-mL three-necked flask, 50 parts by mass of a mesogenic epoxy monomer having a structure described below were placed, and 100 parts by mass of propyleneglycol monomethyl ether were added. A cooling tube and a nitrogen inlet tube were attached to the flask, and a stirring blade was attached so as to be immersed in the solvent. Then, the flask was immersed in an oil bath at 120° C. and subjected to stirring.

(11) After confirming that the mesogenic epoxy monomer was dissolved and the solution became clear, 4,4′-dihydroxybiphenyl was added as a specific biphenyl compound, such that the ratio of the equivalent amount of epoxy group of the mesogenic epoxy monomer (A) to the equivalent amount of hydroxy group of 4,4′-dihydroxybiphenyl (A:B) was 10:2.5, and 0.5 g of triphenylphosphine were added as a reaction catalyst. The heating of the mixture was continued in an oil bath at 120° C. for 3 hours. Thereafter, propyleneglycol monomethyl ether was evaporated under reduced pressure, and the residue was cooled to room temperature (25° C.). An epoxy resin, in which a part of the mesogenic epoxy monomer is reacted with 4,4′-dihydroxybiphenyl to form a multimer (specific epoxy compound), was thus obtained.

(12) ##STR00030##

(13) Subsequently, 50 g of the epoxy resin and 9.1 g of 3,3′-diaminodiphenylsulfone as a curing agent were placed in a stainless dish, and heated on a hot plate at 180° C. After the resin in the stainless dish was melted, the heating was continued at 180° C. for 1 hour. After cooling to room temperature (25° C.), the resin was taken out from the stainless dish and heated in a thermostat chamber at 230° C. for 1 hour to complete the curing, thereby obtaining an epoxy resin cured product. A sample was prepared from the epoxy resin cured product in a similar manner to Example 1.

Comparative Example 1

(14) An epoxy resin cured product was prepared in a similar manner to Example 1, except that 50 g of biphenyl-type epoxy resin (YL6121H, Mitsubishi Chemical Corporation) and 19.3 g of 3,3′-diaminodiphenylsulfone as a curing agent were used. A sample was prepared from the epoxy resin cured product in a similar manner to Example 1.

Comparative Example 2

(15) An epoxy resin cured product was prepared in a similar manner to Example 1, except that 50 g of bisphenol A epoxy resin (EPIKOTE 828XA, Mitsubishi Chemical Corporation) and 15.1 g of 3,3′-diaminodiphenylsulfone as a curing agent were used. A sample was prepared from the epoxy resin cured product in a similar manner to Example 1.

Comparative Example 3

(16) An epoxy resin cured product was prepared in a similar manner to Example 1, except that 50 g of a mesogenic epoxy monomer having a structure described below and 13.8 g of 3,3′-diaminodiphenylsulfone as a curing agent were used. A sample was prepared from the epoxy resin cured product in a similar manner to Example 1.

(17) ##STR00031##

Comparative Example 4

(18) An epoxy resin was prepared in a similar manner to Example 1, except that the mesogenic epoxy monomer was allowed to react with hydroquinone, instead of 4,4′-dihydroxybiphenyl.

(19) An epoxy resin cured product was prepared in a similar manner to Example 1, except that 50 g of the obtained epoxy resin and 9.7 g of 3,3′-diaminodiphenylsulfone as a curing agent were used. A sample was prepared from the epoxy resin cured product in a similar manner to Example 1.

(20) [Evaluation of Viscosity Behavior]

(21) The viscosity behavior of the epoxy resin was evaluated by measuring the dynamic shear viscosity (Pa.Math.s).

(22) The dynamic shear viscosity (Pa.Math.s) was measured with a rheometer (MCR-301 from Anton-Paar GmbH) in an oscillation mode, according to JIS K 7244-10:2005. The measurement was conducted using a parallel plate with a diameter of 12 mm at a frequency of 1 Hz, a gap of 0.2 mm, and a torsion of 2%.

(23) In the measurement, after melting the epoxy resin by heating at 150° C. for over 3 minutes, the temperature of the epoxy resin was decreased from 150° C. to 30° C. at a rate of 2° C./min (temperature decrease step), and then the temperature of the epoxy resin was increased from 30° C. to 150° C. at a rate of 2° C./min (temperature increase step), and a dynamic shear viscosity at 70° C. at the temperature increase step was measured. The results are shown in Table 1.

(24) [Measurement of Fracture Toughness]

(25) As an index for the fracture toughness of the epoxy resin cured product, the fracture toughness (MPa.Math.m.sup.1/2) of the sample was calculated based on the result of three-point bending test based on ASTM D5045, using a tester (Instron 5948, Instron). The results are shown in Table 1.

(26) [Existence or Non-Existence of Smectic Structure]

(27) In order to determine whether or not a smectic structure is formed in the epoxy resin cured product, an X-ray diffraction measurement was performed using CuKα 1 line, under a tube voltage of 50 kV, a tube current of 30 mA, a scan rate of 1°/min and a measurement range 2θ=2° to 30° using an X-ray diffractometer (Rigaku Corporation). The existence or non-existence of a smectic structure was determined by the following criteria. The results are shown in Table 1.

(28) YES: diffraction peak is observed in a range of 2θ=2° to 10°, and a smectic structure is formed.

(29) NO: diffraction peak is not observed in a range of 2θ=2° to 10°, and a smectic structure is not formed.

(30) TABLE-US-00001 TABLE 1 Epoxy resin Cured product Crystal Viscosity Fracture precipitation at 70° C. toughness Formation of at 70° C. [Pa .Math. s] [MPa .Math. m.sup.1/2] smectic structure Example 1 NO 34 2.1 YES Example 2 NO 20 1.8 YES Example 3 NO 2,390 1.8 YES Comparative YES 55,000 0.9 NO Example 1 Comparative NO 2 0.7 NO Example 2 Comparative YES 696,000 1.6 YES Example 3 Comparative NO 926 1.6 YES Example 4

(31) As shown in Table 1, the epoxy resins of the Examples, including a specific epoxy compound having a mesogenic structure and a biphenyl group, exhibited a low viscosity at 70° C., indicating favorable handleability. Further, the cured products obtained from the epoxy resins exhibited favorable fracture toughness.

(32) The epoxy resins of Comparative Examples 1 and 3, including an epoxy compound that has a mesogenic structure but not in the form of a specific epoxy compound, were in a crystalline state at 70° C. and the viscosity was high. Further, the cured products obtained from the epoxy resins exhibited lower fracture toughness than the Examples.

(33) In Comparative Example 2, in which an epoxy compound not having a mesogenic structure was used, the viscosity at 70° C. was low but the fracture toughness of the cured product was lower than the Examples.

(34) In Comparative Example 4, in which an epoxy compound having a phenylene group but not having a biphenyl group was used, the viscosity at 70° C. was low but the fracture toughness of the cured product was lower than the Examples.