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

Abstract

An epoxy resin, comprising an epoxy compound A that has at least two mesogenic structures and at least one phenylene group, and an epoxy compound B that has at least two mesogenic structures and at least one divalent biphenyl group.

Claims

1. An epoxy resin composition, comprising: an epoxy resin comprising: an epoxy compound A that has at least two mesogenic structures and at least one phenylene group, an epoxy compound B that has at least two mesogenic structures and at least one divalent biphenyl group, wherein the ratio between epoxy compound A and epoxy compound B (epoxy compound A:epoxy compound B) is from 3:7 to 9:1; and a curing agent selected from the group consisting of 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-diaminobenzene, 1,4-diaminobenzene, 4,4′-diaminobenzanilide, trimethylene-bis-4-aminobenzoate, phenol, o-cresol, m-cresol, p-cresol, catechol, resorcinol, hydroquinone, 1,2,3-trihydroxybenzene, 1,2,4-trihydroxybenzene, and 1,3,5-trihydroxybenzene.

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

3. The epoxy resin according to claim 1, wherein at least one of the at least two mesogenic structures of at least one of the epoxy compound A or the epoxy compound B has a structure represented by the following Formula (3): ##STR00020## wherein, in Formula (3), each of R.sup.3 to R.sup.6 independently represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms.

4. The epoxy resin composition according to claim 1, being configured to form a smectic structure in a cured state.

5. An epoxy resin cured product comprising a cured product of the epoxy resin composition according to claim 1.

6. A reinforcing material, comprising the epoxy resin cured product according to claim 5 and a reinforcing 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. The “part” and “%” are based on mass, unless otherwise specified.

Synthesis of Epoxy Resin 1

(2) To a 500-mL three-necked flask, 50 parts by mass of (4-{4-(2,3-epoxypropoxy)phenyl}cyclohexyl=4-(2,3-epoxypropoxy)benzoate (following structure) were placed as the mesogenic epoxy monomer, and 80 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, 5.2 g of 4,4′-biphenol as a specific aromatic compound and 0.5 g of triphenylphosphine as a reaction catalyst were added, and further heated 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.). Epoxy resin 1, in which a part of the mesogenic epoxy monomer is reacted with the specific aromatic compound to be in a state of epoxy compound B, was thus obtained.

(4) ##STR00019##

Synthesis of Epoxy Resin 2

(5) Epoxy resin 2, in which a part of the mesogenic epoxy monomer is reacted with the specific aromatic compound to be in a state of epoxy compound A, was obtained in a similar manner to the synthesis of Epoxy Resin 1, except that 3.1 g of hydroquinone were used instead of 5.2 g of 4,4-biphenol.

Synthesis of Epoxy Resin 3

(6) Epoxy resin 3, in which a part of the mesogenic epoxy monomer is reacted with the specific aromatic compound to be in a state of epoxy compound A, was obtained in a similar manner to the synthesis of Epoxy Resin 1, except that 3.1 g of resorcinol were used instead of 5.2 g of 4,4-biphenol.

(7) (Pre-Treatment of Curing Agent)

(8) 160 g of 3,3-diaminodiphenylsulfone (Fujifilm Wako Pure Chemical Corporation) were pulverized with a pulverizer (Nano Jetmizer, trade name, HJ-50-B, Aishin Nano Technologies Co., Ltd.) at a pressure of 0.15 MPa and a processing rate of 240/hr, thereby obtaining 155 g of a powder having an average particle size of 8 μm. The obtained powder was used in the Examples and the Comparative Examples as described below.

Example 1

(9) 35.0 g of Epoxy Resin 1 and 15.0 g of Epoxy Resin 2 were placed in a plastic container and heated at 90° C. in a thermostatic chamber. Then, 9.5 g of 3,3′-diaminodiphenylsulfone were added thereto, and the mixture was stirred with a spatula for 1 minute. Subsequently, the mixture was stirred with a planetary centrifugal mixer at 1,600 rotations/min (rpm) for 30 minutes, thereby preparing an epoxy resin composition.

(10) The epoxy resin composition was placed in a stainless dish treated with a mold release agent, and heated at 150° C. for 4 hours to cure the epoxy resin composition. After cooling the same to room temperature (25° C.), the epoxy resin cured product was taken out from the stainless dish. A sample for evaluation of fracture toughness, having a size of 3.75 mm×7.5 mm×33 mm, and a sample for evaluating glass transition temperature, having a size of 2 mm×0.5 mm×40 mm, were prepared from the epoxy resin cured product.

Example 2

(11) An epoxy resin cured product was prepared in a similar manner to Example 1, except that 25.0 g of Epoxy Resin 1, 25.0 g of Epoxy Resin 2 and 9.6 g of 3,3′-diaminodiphenylsulfone were used. Samples for evaluation of fracture toughness and glass transition temperature were prepared in a similar manner to Example 1.

Example 3

(12) An epoxy resin cured product was prepared in a similar manner to Example 1, except that 35.0 g of Epoxy Resin 1, 15.0 g of Epoxy Resin 3 instead of Epoxy Resin 2, and 9.7 g of 3,3′-diaminodiphenylsulfone were used. Samples for evaluation of fracture toughness and glass transition temperature were prepared in a similar manner to Example 1.

Example 4

(13) An epoxy resin cured product was prepared in a similar manner to Example 1, except that 45.0 g of Epoxy Resin 1, 5.0 g of Epoxy Resin 2 and 9.5 g of 3,3′-diaminodiphenylsulfone were used. Samples for evaluation of fracture toughness and glass transition temperature were prepared in a similar manner to Example 1.

Example 5

(14) An epoxy resin cured product was prepared in a similar manner to Example 1, except that 16.7 g of Epoxy Resin 1, 23.3 g of Epoxy Resin 2 and 9.7 g of 3,3′-diaminodiphenylsulfone were used. Samples for evaluation of fracture toughness and glass transition temperature were prepared in a similar manner to Example 1.

Comparative Example 1

(15) An epoxy resin cured product was prepared in a similar manner to Example 1, except that 50.0 g of Epoxy Resin 1 and 9.4 g of 3,3′-diaminodiphenylsulfone were used. Samples for evaluation of fracture toughness and glass transition temperature were prepared in a similar manner to Example 1.

Comparative Example 2

(16) An epoxy resin cured product was prepared in a similar manner to Example 1, except that 50.0 g of Epoxy Resin 2 and 9.8 g of 3,3′-diaminodiphenylsulfone were used. Samples for evaluation of fracture toughness and glass transition temperature were prepared in a similar manner to Example 1.

(17) <Measurement of Dynamic Shear Viscosity of Epoxy Resin Composition>

(18) The dynamic shear viscosity (Pa.Math.s), measured with application of a high degree of shear stress, was used as an indicator of the viscosity stability of the epoxy resin composition. Specifically, the dynamic shear viscosity was measured with a parallel plate vibratory rheometer (MCR-301 from Anton-Paar GmbH) at a frequency of 1 Hz and a strain of 1000%.

(19) In the measurement, the epoxy resin composition was placed on a stage heated at 90° C. to melt, and a parallel plate with a diameter of 12 mm was allowed to descend to create a gap of 0.2 mm. Subsequently, the temperature of the stage was adjusted to 80° C. and the measurement was started. The temperature was increased to 90° C. in the first 5 minutes, and retained at 90° C. The viscosity (initial viscosity) 10 minutes after the beginning of the measurement (5 minutes after the beginning of retention at 90° C.) and the viscosity 2 hours after the beginning of the measurement (1 hour and 55 minutes after the beginning of retention at 90° C.) were measured, respectively. The increase rate in viscosity was calculated by the following formula.
Increase rate in viscosity=viscosity 2 h after/initial viscosity

(20) [Measurement of Fracture Toughness]

(21) 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 Instron 5948 (Instron).

(22) [Measurement of Dynamic Viscoelasticity]

(23) As an index for the heat resistance of the epoxy resin cured product, the glass transition temperature (Tg) was used. The glass transition temperature of the sample was calculated from the result of the measurement of dynamic viscoelasticity at a tensile mode. The measurement was conducted at a frequency of 10 Hz, a temperature elevation rate of 5° C./min, and a torsion of 0.1%. The temperature corresponding to the maximum value of tan δ, in the obtained temperature-tan δ diagram, was regarded as the glass transition temperature. The measurement was conducted using RSA-G2 (TA Instruments).

(24) [X-Ray Diffraction Measurement]

(25) In order to determine whether or not a higher-order structure (smectic structure) was formed in the epoxy resin cured product, an X-ray diffraction measurement was performed using CuKα1 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). When a diffraction peak is observed in a range of 2θ=2° to 10°, it was determined that a smectic structure is formed in the epoxy resin cured product.

(26) The initial viscosity, the viscosity 2 hours after and the increase rate in viscosity of the epoxy resin compositions of Examples 1 to 5 and Comparative Examples 1 and 2 are shown in Table 1. Further, the fracture toughness, the glass transition temperature (Tg) and the existence or non-existence of smectic structure of the epoxy resin composition cured products of Examples 1 to 5 and Comparative Examples 1 and 2 are shown in Table 1. In Table 1, YES indicates that a smectic structure exists in the epoxy resin cured product.

(27) TABLE-US-00001 TABLE 1 Comparative Comparative Unit Example 1 Example 2 Example 3 Example 4 Example 5 Example 1 Example 2 Epoxy resin Viscosity Pa .Math. s 8.9 9.6 15.9 10.0 10.6 8.1 >80 composition (initial) Viscosity Pa .Math. s 10.6 12.6 17.4 19.5 12.9 148.0 >500 (2 h after) Increase rate — 1.19 1.31 1.10 1.96 1.22 18.27 — in viscosity Epoxy resin 3:7 5:5 3:7 1:9 6.6:3.4 0:10 10:0 A:Epoxy resin B Cured Fracture  Mpa .Math. m.sup.1/2 2.00 2.05 1.85 2.03 1.81 1.92 1.56 product toughness Tg ° C. 168 168 167 169 169 170 170 Smecrtic — YES YES YES YES YES YES YES structure

(28) As shown in Table 1, the epoxy resin compositions of Examples 1 to 5, including both epoxy resin A (Epoxy Resin 2) and epoxy resin B (Epoxy Resin 1), exhibited a sufficiently low initial viscosity upon application of shear stress of as great as 1000%, and a suppressed increase in viscosity over 2 hours, indicating favorable viscosity stability. Further, the epoxy resin compositions of Examples 1 to 5 exhibited favorable fracture toughness and heat resistance.

(29) The epoxy resin compositions of Comparative Example 1, including epoxy resin B but not including epoxy resin A, exhibited an increase rate in viscosity of more than 16 times as high as the initial viscosity, even though the initial viscosity was low. Further, it was difficult to regulate the thickness of a coating formed with the epoxy resin composition without a solvent.

(30) The epoxy resin compositions of Comparative Example 2, including epoxy resin A but not including epoxy resin B, exhibited a significant increase in viscosity from the initial viscosity. Further, it was difficult to perform a coating process with the epoxy resin composition from the viewpoint of regulating the thickness of a coating or the fluidity.