EPOXY RESIN, EPOXY RESIN COMPOSITION, EPOXY RESIN CURED PRODUCT, AND COMPOSITE MATERIAL

Abstract

An epoxy resin, comprising an epoxy compound having two or more mesogenic structures, and having a loss tangent of 1 or more at 35 C. before curing.

Claims

1. An epoxy resin, comprising an epoxy compound having two or more mesogenic structures, and having a loss tangent of 1 or more at 35 C. before curing.

2. The epoxy resin according to claim 1, wherein the epoxy compound has a mesogenic structure represented by the following Formula (1): ##STR00035## wherein, in Formula (1), X represents a single bond or a linking group that includes at least one divalent group selected from the following 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: ##STR00036## 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; k represents an integer from 0 to 7; 1 represents an integer from 0 to 12; m represents an integer from 0 to 8; and each n independently represents an integer from 0 to 4.

3. The epoxy resin according to claim 2, wherein the mesogenic structure represented by Formula (1) is a structure represented by the following Formula (2): ##STR00037##

4. The epoxy resin according to claim 2, wherein the epoxy compound has a structure represented by the following Formula (1-A) or Formula (1-B): ##STR00038## wherein, in Formula (1-A) and Formula (1-B), each of R.sup.1 and R.sup.2 independently represents an alkyl group having 1 to 8 carbon atoms; X represents a single bond or a linking group that includes at least one divalent group selected from 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 Z independently represents O or NH; each m independently represents an integer from 0 to 4; and each n independently represents an integer from 0 to 4.

5. The epoxy resin according to claim 4, wherein the epoxy compound has a structure represented by the following Formula (2-A) or the following Formula (2-B): ##STR00039##

6. The epoxy resin according to claim 1, wherein at least one of the two or more mesogenic structures has a structure represented by at least one of Formula (3) or Formula (4): ##STR00040## wherein, in Formula (3) and Formula (4), each of R.sup.3 to R.sup.6 independently represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms.

7. The epoxy resin according to claim 1, wherein the epoxy compound has two mesogenic structures and a divalent aromatic group that is disposed between the two mesogenic structures.

8. The epoxy resin according to claim 7, wherein the divalent aromatic group is a phenylene group or a divalent biphenyl group.

9. The epoxy resin according to claim 1, comprising a mesogenic epoxy monomer represented by the following Formula (1-m): ##STR00041## 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); 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: ##STR00042## 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; k represents an integer from 0 to 7; 1 represents an integer from 0 to 12; m represents an integer from 0 to 8; and each n independently represents an integer from 0 to 4.

10. The epoxy resin according to claim 9, wherein the mesogenic epoxy monomer comprises an epoxy compound represented by the following Formula (2-m): ##STR00043##

11. The epoxy resin according to claim 9, wherein the mesogenic epoxy monomer comprises an epoxy compound represented by the following Formula (3-m) or Formula (4-m): ##STR00044## 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 having 1 to 3 carbon atoms.

12. The epoxy resin according to claim 9, wherein a content of the mesogenic epoxy monomer is not greater than 50% of the total epoxy resin.

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

14. The epoxy resin composition according to claim 13, wherein the curing agent comprises a compound having two or more amino groups that are directly bonded to an aromatic ring.

15. The epoxy resin composition according to claim 13, wherein the curing agent comprises 3,3-diaminodiphenylsulfone.

16. An epoxy resin cured product, which is obtained by curing the epoxy resin composition according to claim 13.

17. A composite material, comprising the epoxy resin cured product according to claim 16 and a reinforcing material.

18. The composite material according to claim 17, wherein the reinforcing material comprises a carbon material.

Description

EXAMPLES

[0164] In the following, the invention is explained by referring to the Examples. However, the invention is not limited to these Examples.

Example 1

[0165] 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.

[0166] After confirming that the mesogenic epoxy monomer was dissolved and the solution became clear, 4,4-dihydroxybiphenyl was added as a specific aromatic 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 (B) (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.

##STR00030##

[0167] It was confirmed that the epoxy resin included an epoxy compound having two mesogenic structures derived from the mesogenic epoxy monomer and a divalent aromatic group derived from 4,4-dihydroxybiphenyl (dimer compound) by liquid chromatography.

[0168] Subsequently, 50 g of the epoxy resin and 9.4 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 resin was mixed with a spatula to prepare an epoxy resin composition. After taking some of the epoxy resin composition for evaluating the interlayer adhesion (approximately 5 g), the remainder was heated 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 the fracture toughness having a size of 3.75 mm7.5 mm33 mm was prepared from the epoxy resin cured product.

Example 2

[0169] 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.

[0170] After confirming that the mesogenic epoxy monomer was dissolved and the solution became clear, 2,2-dihydroxybiphenyl was added as a specific aromatic 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 (B) (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.

##STR00031##

[0171] It was confirmed that the epoxy resin included an epoxy compound having two mesogenic structures derived from the mesogenic epoxy monomer and a divalent aromatic group derived from 2,2-dihydroxybiphenyl (dimer compound) by liquid chromatography.

[0172] Subsequently, 50 g of the epoxy resin and 9.4 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 resin was mixed with a spatula to prepare an epoxy resin composition. After taking some of the epoxy resin composition for evaluating the interlayer adhesion (approximately 5 g), the remainder was heated 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 the fracture toughness having a size of 3.75 mm7.5 mm33 mm was prepared from the epoxy resin cured product.

Example 3

[0173] 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.

[0174] After confirming that the mesogenic epoxy monomer was dissolved and the solution became clear, hydroquinone was added as a specific aromatic 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 hydroquinone (B) (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 hydroquinone to form a multimer (specific epoxy compound), was thus obtained.

##STR00032##

[0175] It was confirmed that the epoxy resin included an epoxy compound having two mesogenic structures derived from the mesogenic epoxy monomer and a divalent aromatic group derived from hydroquinone (dimer) by liquid chromatography.

[0176] Subsequently, 50 g of the epoxy resin and 5.0 g of an epoxy compound represented by the following structure (tetramethyl biphenol epoxy resin) and 11.4 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 resin was mixed with a spatula to prepare an epoxy resin composition. After taking some of the epoxy resin composition for evaluating the interlayer adhesion (approximately 5 g), the remainder was heated 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 the fracture toughness having a size of 3.75 mm7.5 mm33 mm was prepared from the epoxy resin cured product.

##STR00033##

Example 4

[0177] 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.

[0178] After confirming that the mesogenic epoxy monomer was dissolved and the solution became clear, 4,4-dihydroxybiphenyl was added as a specific aromatic 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 (B) (A:B) was 10:0.5, 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.

##STR00034##

[0179] It was confirmed that the epoxy resin included an epoxy compound having two mesogenic structures derived from the mesogenic epoxy monomer and a divalent aromatic group derived from 4,4-dihydroxybiphenyl (dimer compound) by liquid chromatography.

[0180] Subsequently, 50 g of the epoxy resin and 12.9 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 resin was mixed with a spatula to prepare an epoxy resin composition. After taking some of the epoxy resin composition for evaluating the interlayer adhesion (approximately 5 g), the remainder was heated 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 the fracture toughness having a size of 3.75 mm7.5 mm33 mm was prepared from the epoxy resin cured product.

Comparative Example 1

[0181] An epoxy resin was prepared in a similar manner to Example 1, except that hydroquinone was used instead of 4,4-dihydroxybiphenyl 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 hydroquinone (B) (A:B) was 10:1.0.

[0182] It was confirmed that the epoxy resin included an epoxy compound having two mesogenic structures derived from the mesogenic epoxy monomer and a divalent aromatic group derived from hydroquinone (dimer compound) by liquid chromatography.

[0183] Subsequently, 50 g of the epoxy resin and 12.1 g of 3,3-diaminodiphenylsulfone as a curing agent were placed in a stainless dish, and an epoxy resin composition and an epoxy resin cured product were prepared in a similar manner to Example 1. Samples were prepared from the epoxy resin cured product in a similar manner to Example 1.

Comparative Example 2

[0184] An epoxy resin was prepared in a similar manner to Example 1, except that resorcinol was used instead of 4,4-dihydroxybiphenyl 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 resorcinol (B) (A:B) was 10:2.0.

[0185] It was confirmed that the epoxy resin included an epoxy compound having two mesogenic structures derived from the mesogenic epoxy monomer and a divalent aromatic group derived from resorcinol (dimer compound) by liquid chromatography.

[0186] Subsequently, 50 g of the epoxy resin and 10.57 g of 3,3-diaminodiphenylsulfone as a curing agent were placed in a stainless dish, and an epoxy resin composition and an epoxy resin cured product were prepared in a similar manner to Example 1. Samples were prepared from the epoxy resin cured product in a similar manner to Example 1.

Comparative Example 3

[0187] An epoxy resin was prepared in a similar manner to Example 1, except that resorcinol was used instead of 4,4-dihydroxybiphenyl 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 resorcinol (B) (A:B) was 10:3.0.

[0188] It was confirmed that the epoxy resin included an epoxy compound having two mesogenic structures derived from the mesogenic epoxy monomer and a divalent aromatic group derived from resorcinol (dimer compound) by liquid chromatography.

[0189] Subsequently, 50 g of the epoxy resin and 9.0 g of 3,3-diaminodiphenylsulfone as a curing agent were placed in a stainless dish, and an epoxy resin composition and an epoxy resin cured product were prepared in a similar manner to Example 1. Samples were prepared from the epoxy resin cured product in a similar manner to Example 1.

Comparative Example 4

[0190] An epoxy resin was prepared in a similar manner to Comparative Example 2, except that hydroquinone was used instead of resorcinol 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 hydroquinone (B) (A:B) was 10:2.0.

[0191] It was confirmed that the epoxy resin included an epoxy compound having two mesogenic structures derived from the mesogenic epoxy monomer and a divalent aromatic group derived from hydroquinone (dimer compound) by liquid chromatography.

[0192] Subsequently, 50 g of the epoxy resin and 10.57 g of 3,3-diaminodiphenylsulfone as a curing agent were placed in a stainless dish, and an epoxy resin composition and an epoxy resin cured product were prepared in a similar manner to Example 1. Samples were prepared from the epoxy resin cured product in a similar manner to Example 1.

Comparative Example 5

[0193] An epoxy resin was prepared in a similar manner to Comparative Example 3, except that hydroquinone was used instead of resorcinol 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 hydroquinone (B) (A:B) was 10:3.0.

[0194] It was confirmed that the epoxy resin included an epoxy compound having two mesogenic structures derived from the mesogenic epoxy monomer and a divalent aromatic group derived from hydroquinone (dimer compound) by liquid chromatography.

[0195] Subsequently, 50 g of the epoxy resin and 9.0 g of 3,3-diaminodiphenylsulfone as a curing agent were placed in a stainless dish, and an epoxy resin composition and an epoxy resin cured product were prepared in a similar manner to Example 1. Samples were prepared from the epoxy resin cured product in a similar manner to Example 1.

[0196] <Measurement of Loss Tangent>

[0197] The loss tangent at 35 C. of the epoxy resin was measured with a rheometer (MCR-301, Anton-Paar GbmH) in an oscillation mode. The measurement was performed by using parallel plate with a diameter of 12 mm, under the conditions of frequency: 1 Hz, gap: 0.2 mm, distortion: 2%.

[0198] The measurement was performed by conducting a process of melting the epoxy resin at 150 C. for 3 minutes, a process of decreasing the temperature of the epoxy resin from 150 C. to 30 at a rate of 2 C./minute, and a process of increasing the temperature of the epoxy resin from 30 C. to 150 C. at a rate of 2 C./minute, in this order. In the process of increasing the temperature, the loss tangent at 35 C. of the epoxy resin was measured. The results are shown in Table 1.

[0199] <Evaluation of Interlayer Adhesion>

[0200] The adhesion between the sheets prepared from the epoxy resin composition was evaluated by the following method.

[0201] A stainless plate was sufficiently heated on a hot plate at 150 C., and a PET film was placed on the stainless plate and fixed. Subsequently, several grams of the epoxy resin composition were placed on the PET film and melted. The temperature of the hot plate was lowered to 100 C., and retained at 100 C. for 5 minutes. The epoxy resin composition was spread over the PET film using an applicator that had been heated to 100 C., with a gap of 100 m, thereby preparing a resin sheet.

[0202] The sheet was cut into two pieces with a size of 2 cm6 cm, respectively, and the pieces were attached to each other so as to overlap at an area of 2 cm4 cm, on a hot plate at 50 C. by hand press. Thereafter, a weight (200 g) was attached at the lower edge of one of the pieces, and the state of the pieces while applying shear load for 1 minute was evaluated by the following criteria. The results are shown in Table 1.

[0203] A: the pieces are favorably attached even after 1 minute.

[0204] B: the pieces are initially favorably attached, but cause shear separation within 1 minute.

[0205] C: the pieces are initially favorably attached, but cause shear separation by application of shear load.

[0206] D: the pieces do not attach to each other.

[0207] <Evaluation of Toughness>

[0208] As an index for the toughness of the epoxy resin cured product, a three-point bending test according to ASTM D5045 was performed using Instron 5948 (Instron), and the fracture toughness (MPa.Math.m.sup.1/2) was calculated from the result of the test. The results are shown in Table 1.

[0209] <Existence or Non-Existence of Smectic Structure>

[0210] In order to determine whether or not a smectic structure was formed in the epoxy resin cured product, an X-ray diffraction measurement was performed using CuK 1 line, under a tube voltage of 50 kV, a tube current of 300 mA, a scan rate of 1/min and a measurement range 20=2 to 30 using an X-ray diffractometer (Rigaku Corporation).

[0211] When a diffraction peak is observed in a range of 2=2 to 10, it was determined that a smectic structure is formed in the epoxy resin cured product (YES) and when a diffraction peak is not observed in a range of 2=2 to 10, it was determined that a smectic structure is no formed in the epoxy resin cured product (NO).

TABLE-US-00001 TABLE 1 Epoxy resin Epoxy resin cured product Epoxy resin composition Fracture toughness Loss tangent at 35 C. Interlayer adhesion (MPa .Math. m.sup.1/2) Smectic structure Example 1 5.1 A 2.1 YES Example 2 1.6 C 1.8 YES Example 3 12.7 A 1.6 YES Example 4 2.1 B 1.6 YES Comparative 0.2 D 1.5 YES Example 1 Comparative 0.7 D 1.5 YES Example 2 Comparative 0.8 D 1.6 YES Example 3 Comparative 0.6 D 1.5 YES Example 4 Comparative 0.8 D 1.4 YES Example 5

[0212] As shown in Table 1, the sheet prepared from the epoxy resin composition of the Examples, which includes an epoxy resin having a loss tangent of 1 or more at 35 C. before curing, exhibits a favorable interlayer adhesion as compared with the epoxy resin composition of the Comparative Examples, which includes an epoxy resin having a loss tangent of less than 1 at 35 C. before curing. Further, the epoxy resin cured product of the Examples includes a smectic structure and exhibits favorable fracture toughness.

[0213] The disclosure of Japanese Patent Application No. 2018-026891 is herein incorporated by reference.

[0214] All publications, patent applications, and technical standards mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent application, or technical standard was specifically and individually indicated to be incorporated by reference.