Insulated wire having a layer containing bubbles, electrical equipment, and method of producing insulated wire having a layer containing bubbles

1. An insulated wire, comprising:

an insulating film made from a thermosetting resin disposed on a conductor directly or via an insulating layer interposed therebetween,

wherein the insulating film made from a thermosetting resin is a layer containing bubbles prepared by baking a varnish of thermosetting resin, and

wherein a layer containing no bubbles is formed as an upper or lower layer of the layer containing bubbles, and

wherein the insulating layer containing bubbles made from a thermosetting resin has bubbles of an average size of 10 μm or less, an insulating layer containing no bubbles with a thickness of 1 μm or greater is disposed as an upper layer and/or a lower layer of the insulating layer containing bubbles, and the insulating layer containing bubbles made from a thermosetting resin is laminated in one or more layers.

2. The insulated wire as described according to claim 1 ,

wherein the insulated wire has a combination of the layer containing bubbles and the layer containing no bubbles with a thickness of 1 μm or more as an upper layer and/or a lower layer of the layer containing bubbles, and

wherein the layer containing bubbles is laminated in two or more layers.

3. The insulated wire according to claim 1 ,

wherein the varnish of the thermosetting resin contains a solvent for the thermosetting resin, a bubble forming agent, and a solvent having a boiling point higher than that of the solvent for the thermosetting resin as a mixed solvent.

4. The insulated wire according to claim 1 ,

wherein the thermosetting resin is a polyamideimide resin.

5. The insulated wire according to claim 1 ,

wherein the thermosetting resin layer containing bubbles contains a thermoplastic resin.

6. An electrical/electronic equipment using the insulated wire according to claim 1 , in a coil of a transformer incorporated into the electrical/electronic equipment and/or a motor coil of a rotor.

7. A method of producing an insulated wire, comprising the steps of:

applying a varnish of thermosetting resin on a conductor directly or via an insulating layer interposed therebetween;

baking the varnish of thermosetting resin to generate bubbles during the baking step for this varnish of a thermosetting resin so that the insulated wire has a layer containing bubbles made from the thermosetting resin as an insulating layer,

wherein the insulating layer containing bubbles has bubbles of an average size of 10 μm or less, an insulating layer containing no bubbles with a thickness of 1 μm or greater is disposed as an upper layer and/or a lower layer of the insulating layer containing bubbles, and the insulating layer containing bubbles made from the thermosetting resin is laminated in one or more layers.

8. The method of producing an insulated wire according to claim 7 ,

wherein the varnish of thermosetting resin contains a mixed solvent containing a high boiling solvent for bubble formation and a solvent for the thermosetting resin and the high boiling solvent for bubble formation has a boiling point higher than that of the solvent for the thermosetting resin,

wherein the high boiling solvent takes the role as both a bubble nucleating agent and a foaming agent when one kind of the high boiling solvent is added to the varnish of a thermosetting resin, and

wherein a high boiling solvent acting as the foaming agent and a high boiling solvent acting as the bubble nucleating agent are high boiling solvents different from each other when two or more kinds of the high boiling solvents are used and added to the varnish.

9. The method of producing an insulated wire according to claim 7 ,

wherein the varnish of thermosetting resin is a varnish of thermosetting resin prepared by using a mixed solvent composed of at least three kinds of solvents each having a boiling point of 160° C. or higher.