Insulated wire and coil

1. An insulated wire, comprising:

a conductor; and

an insulating covering layer comprising a first insulation layer formed around the conductor and a second insulation layer formed around the first insulation layer,

wherein a storage elastic modulus of the second insulation layer at 300° C. is not less than 300 MPa, and a relative permittivity of the insulating covering layer is not more than 3.0,

wherein the second insulation layer comprises a resin containing at least one of a polyimide resin, a polyamide-imide resin, and a polyester imide resin,

wherein the second insulation layer consists of polyimide,

wherein the polyimide of the second insulation layer consists of aromatic tetracarboxylic dianhydrides and aromatic diamines,

wherein the aromatic tetracarboxylic dianhydrides consist of pyromellitic dianhydride (PMDA) and 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), and

wherein the aromatic diamines consist of 4,4′-bis(4-aminophenoxy)biphenyl (BAPB) and 4,4′-diaminodiphenyl ether (ODA).

2. The insulated wire according to claim 1 , wherein the storage elastic modulus of the second insulation layer at 350° C. is not less than 1 MPa.

3. The insulated wire according to claim 1 , wherein a dielectric loss tangent of the insulating covering layer is not less than 5% and not more than 20%.

4. The insulated wire according to claim 1 , wherein the first insulation layer comprises a resin comprising an imide group in a molecule thereof.

5. The insulated wire according to claim 1 , further comprising:

a lubricant layer having lubricity on the second insulation layer.

6. The insulated wire according to claim 1 , wherein the first insulation layer comprises an additive that improves adhesion with the conductor.

7. A coil comprising the insulated wire according to claim 1 .

8. The insulated wire according to claim 1 , wherein the first insulation layer comprises an insulating coating material in which at least one of polyimide resin, polyamide-imide resin, and polyester-imide resin is dissolved in an organic solvent.

9. The insulated wire according to claim 1 , wherein the first insulation layer comprises an insulating coating material in which a polyimide resin formed by mixing a tetracarboxylic dianhydride comprising pyromellitic dianhydride (PMDA) with a diamine compound comprising 4,4′-diaminodiphenyl ether (ODA) at equimolar amounts is dissolved in an organic solvent.

10. The insulated wire according to claim 9 , wherein the organic solvent comprises N-methyl-2-pyrrolidone.

11. The insulated wire according to claim 1 , wherein the first insulation layer comprises an insulating coating material in which a polyamide-imide resin formed by mixing a tricarboxylic acid anhydride comprising trimellitic anhydride (TMA) with an isocyanate comprising 4,4′-diphenylmethane diisocyanate (MDI) at equimolar amounts is dissolved in an organic solvent.

12. The insulated wire according to claim 1 , wherein the first insulation layer comprises an insulating coating material that comprises a polyester-imide resin modified with tris(2-hydroxyethyl) isocyanurate.

13. The insulated wire according to claim 1 , wherein the polyimide of the second insulation layer is obtained by a reaction of the aromatic tetracarboxylic dianhydrides with the aromatic diamines.

14. The insulated wire according to claim 1 , wherein the first insulation layer of the insulating covering layer is disposed on a surface of the second insulation layer of the insulating covering layer.

15. The insulated wire according to claim 1 , wherein the first insulation layer of the insulating covering layer comprises a polyimide resin insulating coating material.

16. The insulated wire according to claim 1 , wherein an outer surface of the conductor abuts an inner surface of the first insulation layer of the insulating covering layer, and

wherein an outer surface of the first insulation layer of the insulating covering layer abuts an inner surface of the second insulation layer of the insulating covering layer.