Thermally conductive material and thermally conductive sheet molded from the thermally conductive material
Disclosed is a thermally conductive material having excellent heat conductivity and insulating properties and having flame retardancy while retaining flexibility and toughness. More specifically, there is provided a thermally conductive material comprising: a hydrogenated copolymer (1) and/or a modified hydrogenated copolymer (2) in which each has a specific structure and is contained in a specific amount; and zinc oxide (3) comprising a core part and acicular crystal parts extending from the core part in four axial directions. The thermally conductive material optionally further comprises a paraffin oil (4), a flame retardant (5), or a filler (6) having a thermal conductivity of 10 to 400 W/m·K (the zinc oxide (3) is excluded).
1. A thermally conductive material comprising:
a hydrogenated copolymer (1) satisfying the following conditions (a) to (d) which is produced by hydrogenating a copolymer of a conjugated diene and a vinyl aromatic; and/or a modified hydrogenated copolymer (2) having at least one functional group and satisfying the following conditions (a) to (d), which is produced by hydrogenating a copolymer of a conjugated diene and a vinyl aromatic;
a zinc oxide (3) comprising a core part and acicular crystal parts extending from the core in four different axial directions; and
a paraffin oil (4),
wherein the thermally conductive material does not comprise a flame retardant (5), and satisfies the following conditions (A) to (C):
(a) the content of a vinyl aromatic unit is greater than 45 mass % and 90 mass % or less,
(b) the content of a vinyl aromatic polymer block is 40 mass % or less,
(c) the weight-average molecular weight is 5×10 4 to 100×10 4 , and
(d) the degree of hydrogenation of double bonds based on the conjugated diene is 10% or more, and
based on 100 mass % of the thermally conductive material,
(A) the total content of the hydrogenated copolymer (1), the modified hydrogenated copolymer (2), and the paraffin oil (4), [(1)+(2)+(4)], is 10 mass % or more and 24 mass % or less,
(B) the content of the zinc oxide (3) is 76 mass % or more and 90 mass % or less, and
(C) the ratio of a mass of the paraffin oil (4) to the total mass of the hydrogenated copolymer (1) and the modified hydrogenated copolymer (2), [(4)/{(1)+(2)}], is greater than 0 and 2 or less.
2. The thermally conductive material according to claim 1 , wherein the modified hydrogenated copolymer (2) has at least one functional group selected from a hydroxy group, an epoxy group, an amino group, a silanol group, and an alkoxysilane group.
3. The thermally conductive material according to claim 1 , wherein the content of the vinyl aromatic polymer block in the hydrogenated copolymer (1) and/or the modified hydrogenated copolymer (2) is 10 to 40 mass %.
4. The thermally conductive material according to claim 1 , wherein the content of the vinyl aromatic polymer block in the hydrogenated copolymer (1) and/or the modified hydrogenated copolymer (2) is less than 10 mass %.
5. The thermally conductive material according to claim 1 , wherein the hydrogenated copolymer (1) and/or the modified hydrogenated copolymer (2) has at least one structure selected from the following general formulas:
B; (i)
B-A; (ii)
B-A-B; (iii)
(B-A) m -Z; and (iv)
(B-A) n -Z-A p , (v)
(wherein B represents a random copolymer block of the conjugated diene and the vinyl aromatic, and A represents the vinyl aromatic polymer block, m is an integer of 2 or more, and each of n and p is an integer of 1 or more, Z represents a coupling agent residue).
6. The thermally conductive material according to claim 1 , wherein the modified hydrogenated copolymer (2) has at least one functional group selected from the following formulas (a) to (n):
(wherein R1 to R4 independently represent hydrogen or a hydrocarbon group having a carbon number of 1 to 24, or a hydrocarbon group having a carbon number of 1 to 24 which has a functional group selected from a hydroxy group, an epoxy group, an amino group, a silanol group, and an alkoxysilane group, R5 represents a hydrocarbon chain having a carbon number of 1 to 48 or a hydrocarbon chain having a carbon number of 1 to 48 which has a functional group selected from a hydroxy group, an epoxy group, an amino group, a silanol group, and an alkoxysilane group, Elements such as oxygen, nitrogen, and silicon may bind to the hydrocarbon groups of R1 to R4 and the hydrocarbon chain of R5 in which a binding way that such elements do not take a form of a hydroxy group, an epoxy group, a silanol group, or an alkoxysilane group, R6 represents hydrogen or an alkyl group having a carbon number of 1 to 8).
7. The thermally conductive material according to claim 1 , wherein the modified hydrogenated copolymer (2) is obtained by allowing addition reaction to take place between a modifier containing a functional group and a living end of an unhydrogenated copolymer obtained with an organolithium compound as a polymerization catalyst and then hydrogenating the modified unhydrogenated copolymer (2) obtained.
8. The thermally conductive material according to claim 1 , wherein the content of the zinc oxide (3) is 65 mass % or more and 90 mass % or less based on 100 mass % of the thermally conductive material.
9. A thermally conductive sheet having a thickness of 30 μm to 1 mm, which is obtained by molding from the thermally conductive material claim 1 .
10. A thermally conductive sheet having a thickness of greater than 1 mm to 3 cm or less, which is obtained by molding from the thermally conductive material of claim 1 .