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

1. An epoxy resin comprising a reaction product between an epoxy compound and a compound having a naphthalene structure and a functional group that is reactive with an epoxy group,

wherein the epoxy compound includes a structure of the following Formula (M-2) or (M-3):

wherein, in Formulae (M-2) and (M-3), 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; and * represents a bonding site to an adjacent atom; and

wherein the compound having a naphthalene structure and a functional group that is reactive with an epoxy group includes a dihydroxynaphthalene compound.

2. The epoxy resin according to claim 1 , wherein the dihydroxynaphthalene compound includes at least one selected from the group consisting of 1,5-dihydroxynaphthalene and 2,6-dihydroxynaphthalene.

3. The epoxy resin according to claim 1 , wherein the reaction product includes a compound represented by the following General Formula (a):

wherein, in General Formula (a), each of R 1 , R 2 and R 3 independently represents a monovalent group, wherein at least one of the monovalent groups represented by R 1 , R 2 and R 3 has a mesogenic structure, and at least one of the monovalent groups represented by R 1 , R 2 and R 3 has an epoxy group; and each Z independently represents —O— or —NH—.

4. The epoxy resin according to claim 3 ,

wherein the epoxy compound comprises a first epoxy compound, a second epoxy compound and a third epoxy compound,

wherein, in General Formula (a),

R 1 is a monovalent group having a structure derived from the first epoxy compound,

R 2 is a monovalent group having a structure derived from the second epoxy compound and the compound having a naphthalene structure and a functional group that is reactive with an epoxy group, and

R 3 is a monovalent group having a structure derived from the third epoxy compound,

wherein the first epoxy compound, the second epoxy compound and the third epoxy compound may be the same as or different from each other, and

wherein at least one of the first epoxy compound, the second epoxy compound or the third epoxy compound has a mesogenic structure.

5. The epoxy resin according to claim 1 , wherein, in an 80-minute continuous measurement of dynamic shear viscosity at a temperature of 80° C. using a viscoelastometer with a gap between a parallel plate and a stage of 0.05 mm, a frequency of 0.5 Hz and a strain of 8000%, a value of η′2/η′1 is 3 or less, the value of η′2/η′1 being obtained from an initial dynamic shear viscosity η′1 (Pa·s) and a maximum value of dynamic shear viscosity η′2 (Pa·s) obtained during the measurement.

6. The epoxy resin according to claim 5 , wherein the initial dynamic shear viscosity η′1 is 200 Pa·s or less.

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

8. An epoxy resin cured product, which is a cured product of the epoxy resin composition according to claim 7 .

9. A composite material comprising the epoxy resin cured product according to claim 8 and a reinforcing material.