Foamed electrical wire and a method of producing the same

1. A foamed electrical wire, comprising:

a conductor; and

a foamed insulating layer;

wherein the foamed insulating layer comprises a resin, which is only one resin selected from the group consisting of polyphenylene sulfide, polyethylene naphthalate, polyether ether ketone and thermoplastic polyimide, and

wherein an average diameter of bubbles formed in the resin of the foamed insulating layer is 5 μm or less.

2. The foamed electrical wire according to claim 1 , wherein the effective dielectric constant of the foamed insulating layer is 2.5 or less.

3. The foamed electrical wire according to claim 1 , wherein the dielectric constant of the thermoplastic resin is 4.0 or less.

4. The foamed electrical wire according to claim 1 , wherein the thickness of the foamed resin layer is from 30 to 200 μm.

5. The foamed electrical wire according to claim 1 , wherein the average bubble diameter of the foamed insulating layer is from 0.1 to 5 μm.

6. The foamed electrical wire according to claim 1 , further comprising a non-foamed outer skin layer outside of the foamed insulating layer,

wherein the thickness of the outer skin layer is 20% or less with respect to the total of the thickness of the outer skin layer and the thickness of the foamed insulating layer.

7. The foamed electrical wire according to claim 1 , further comprising a non-foamed inner skin layer inside of the foamed insulating layer,

wherein the thickness of the inner skin layer is 20% or less with respect to the total of the thickness of the inner skin layer and the thickness of the foamed insulating layer.

8. The foamed electrical wire according to claim 1 , further comprising:

a non-foamed outer skin layer outside of the foamed insulating layer; and

a non-foamed inner skin layer inside of the foamed insulating layer;

wherein the total of the thickness of the inner skin layer and the thickness of the outer skin layer is 20% or less with respect to the total of the thickness of the inner skin layer, the thickness of the outer skin layer and the thickness of the foamed insulating layer.

9. The foamed electrical wire according to claim 8 ,

wherein the thickness of the outer skin layer is 9 μm or less; and

wherein the thickness of the inner skin layer is 1 μm or less.

10. A method of producing a foamed electrical wire, comprising a step of:

coating a conductor with an insulating layer; and

foaming the insulating;

wherein the foamed insulating layer comprises a resin, which is only one resin selected from the group consisting of polyphenylene sulfide, polyethylene naphthalate, polyether ether ketone and thermoplastic polyimide, and

wherein an average diameter of bubbles formed in the resin of the foamed insulating layer is 5 μm or less.

11. The method of producing a foamed electrical wire according to claim 10 , wherein the thickness of the foamed resin layer is from 30 to 200 μm.

12. The method of producing a foamed electrical wire according to claim 10 , wherein the average bubble diameter of the foamed insulating layer is from 0.1 to 5 μm.

13. The method of producing a foamed electrical wire according to claim 10 ,

wherein a non-foamed outer skin layer is provided outside of the foamed insulating layer;

wherein a non-foamed inner skin layer is provided inside of the foamed insulating layer; and

wherein the total of the thickness of the inner skin layer and the thickness of the outer skin layer is 20% or less with respect to the total of the thickness of the inner skin layer, the thickness of the outer skin layer and the thickness of the foamed insulating layer.

14. The method of producing a foamed electrical wire according to claim 13 , wherein the thickness of the outer skin layer is 9 μm or less; and

wherein the thickness of the inner skin layer is 1 μm or less.