Inverter surge-resistant insulated wire and method of producing the same

1. An inverter surge-resistant insulated wire, having at least one baked enamel layer around the outer periphery of a conductor having a rectangular cross-section, at least one extrusion-coated resin layer around the outer side thereof, and an adhesive layer having a thickness of 2 to 20 μm between the baked enamel layer and the extrusion-coated resin layer,

wherein each of the at least one extrusion-coated resin layer on the adhesive layer is formed by the same resin,

a cross-sectional shape of the baked enamel layer and the extrusion-coated resin layer in the cross-section of the inverter surge-resistant insulated wire is rectangular, and in the cross-sectional shape formed by the baked enamel layer and the extrusion-coated resin layer surrounding the conductor in a cross-sectional view, at least a pair of two sides of two pairs of two sides opposing at the upper side and the downside or at the right side and the left side with respect to the conductor each meet the conditions that a total thickness of the baked enamel layer and the extrusion-coated resin layer is 80 μm or more, a thickness of the baked enamel layer is 60 μm or less, a thickness of the extrusion-coated resin layer is 200 μm or less,

the resin of the extrusion-coated resin layer has a melting point of 300° C. or more and 370° C. or less,

the adhesive layer is a layer of a thermoplastic resin selected from the group consisting of polysulfone, polyether sulfone, polyether imide, and polyphenyl sulfone,

a film crystallinity of the extrusion-coated resin layer, which can be measured using Differential Scanning calorimetry and the following calculation formula, is 50% or more:

the film crystallinity (%)=[(the melting heat amount−the crystallization heat amount)/(the melting heat amount)]×100, and  Calculation formula:

a peak voltage of the partial discharge inception voltage of the inverter surge-resistant insulated wire is 1200 Vp or more and 3200 Vp or less.

2. The inverter surge-resistant insulated wire according to claim 1 , wherein the extrusion-coated resin layer is composed of a single layer.

3. The inverter surge-resistant insulated wire according to claim 1 , wherein a dielectric breakdown voltage after a 300° C. 168 hour heat treatment of the inverter surge-resistant insulated wire is 90% or more of the dielectric breakdown voltage before the heat treatment.

4. The inverter surge-resistant insulated wire according to claim 1 , wherein adhesive strength among coated layers of the inverter surge-resistant insulated wire is 100 g or more and less than 400 g.

5. The inverter surge-resistant insulated wire according to claim 1 , wherein the extrusion-coated resin layer is a layer formed by at least one thermoplastic resin selected from the group consisting of polyether ether ketone, modified-polyether ether ketone, thermoplastic polyimide, and aromatic polyamide.

6. The inverter surge-resistant insulated wire according to claim 1 , wherein the adhesive layer is a layer formed by at least one thermoplastic resin selected from the group consisting of polyetherimide, polyphenylsulfone, and polyethersulfone.

7. A method of producing the inverter surge-resistant insulated wire according to claim 1 comprising:

baking a varnish-made resin on the outer periphery of the baked enamel layer to form the adhesive layer; and then

extruding a thermoplastic resin for forming the extrusion-coated resin layer on the adhesive layer thereby to contact with the adhesive layer, the thermoplastic resin becoming a molten state at a higher temperature than a glass transition temperature of the resin that is used for the adhesive layer and heat-sealing the extrusion-coated resin on the baked enamel layer via the adhesive layer thereby to form the extrusion-coated resin layer.