There is provided an electric wire having a conductor total cross-sectional area of 2 mm.sup.2 or less and high reliability. The electric wire includes: a twisted wire conductor (2) including a plurality of strand conductors (21 to 27) twisted together with each other and having a total cross-sectional area of the plurality of strand conductors of 2 mm.sup.2 or less; and a covering member (3) made from a resin material having a flexural modulus of 0.6 GPa or more and covering the twisted wire conductor so that an inner wall thereof is in contact with an outer peripheral surface of the twisted wire conductor, wherein the twisted wire conductor (2) has, on an outer peripheral surface thereof, recesses having a maximum depth of 5% or less of a maximum diameter of the twisted wire conductor in a cross section perpendicular to a length direction of the twisted wire conductor and containing boundaries of the plurality of strand conductors.

An insulated electrically conductive element (1) for the aerospace field has an elongate electrically conductive element surrounded by at least two layers, said two layers being an electrically insulating layer (4) surrounding the elongate electrically conductive element (2) and a first semiconductor layer (5) surrounding said electrically insulating layer (4), at least one of the layers having at least one fluoropolymer.

The present invention is concerned with a dielectric material comprising a fluoropolymer, wherein at least part of the crystalline region of the fluoropolymer is in the β-phase. The dielectric material of the present invention may show relaxor-like ferroelectricity. The present invention also relates to a novel method of producing such a material, and the use of such a material in a high energy density capacitor. The method comprises layering sheets of PVDF on one another and applying pressure to the multilayer under a temperature which is preferably within 40° C. of the temperature of fusion. Further, the film is preferably quenched.

There is provided a copolymer containing tetrafluoroethylene unit and perfluoro(propyl vinyl ether) unit, wherein the copolymer has a content of perfluoro(propyl vinyl ether) unit of 2.7 to 4.9% by mass with respect to the whole of the monomer units, a melt flow rate at 372° C. of 0.7 to 1.4 g/10 min, and the number of functional groups of 20 or less per 10.sup.6 main-chain carbon atoms.

There is provided a fluorine-containing copolymer comprising tetrafluoroethylene unit, hexafluoropropylene unit, and a perfluoro(ethyl vinyl ether) unit, wherein the copolymer has a content of the hexafluoropropylene unit of 10.5 to 11.6% by mass with respect to the whole of the monomer units, a content of the perfluoro(ethyl vinyl ether) unit of 1.2 to 2.4% by mass with respect to the whole of the monomer units, a melt flow rate at 372° C. of 28.0 to 40.0 g/10 min, and a total number of —CF.sub.2H, carbonyl group-containing terminal groups, —CF═CF.sub.2 and —CH.sub.2OH of 25 or less per 10.sup.6 main-chain carbon atoms.

There is provided a fluorine-containing copolymer comprising tetrafluoroethylene unit, hexafluoropropylene unit and a fluoro(alkyl vinyl ether) unit, wherein the copolymer has a content of the hexafluoropropylene unit of 7.5 to 10.3% by mass with respect to the whole of the monomer units, a content of the fluoro(alkyl vinyl ether) unit of 0.8 to 2.9% by mass with respect to the whole of the monomer units, a melt flow rate at 372° C. of 0.7 to 9.5 g/10 min, and a number of functional groups of 90 or less per 10.sup.6 main-chain carbon atoms.

There is provided a copolymer containing tetrafluoroethylene unit and perfluoro(propyl vinyl ether) unit, wherein the copolymer has a content of perfluoro(propyl vinyl ether) unit of 2.51 to 2.92 mol % with respect to the whole of the monomer units, a melt flow rate at 372° C. of 19.0 to 33.0 g/10 min, and the number of functional groups of 50 or less per 10.sup.6 main-chain carbon atoms.

There is provided a copolymer containing tetrafluoroethylene unit and perfluoro(propyl vinyl ether) unit, wherein the copolymer has a content of perfluoro(propyl vinyl ether) unit of 4.4 to 6.0% by mass with respect to the whole of the monomer units, a melt flow rate at 372° C. of 7.5 to 11.0 g/10 min, and the number of functional groups of 40 or less per 106 main-chain carbon atoms.

There is provided a fluorine-containing copolymer comprising tetrafluoroethylene unit, hexafluoropropylene unit and a fluoro(alkyl vinyl ether) unit, wherein the copolymer has a content of the hexafluoropropylene unit of 7.0 to 9.4% by mass with respect to the whole of the monomer units, a content of the fluoro(alkyl vinyl ether) unit of 1.3 to 2.9% by mass with respect to the whole of the monomer units, a melt flow rate at 372° C. of 15 to 40 g/10 min, and the number of functional groups of 90 or less per 10.sup.6 main-chain carbon atoms.

There is provided a fluorine-containing copolymer containing tetrafluoroethylene unit, hexafluoropropylene unit, and perfluoro(propyl vinyl ether) unit, wherein the copolymer has a content of hexafluoropropylene unit of 6.0 to 7.6% by mass with respect to the whole of the monomer units, a content of perfluoro(propyl vinyl ether) unit of 1.2 to 1.9% by mass with respect to the whole of the monomer units, and a melt flow rate at 372° C. of 2.8 to 4.4 g/10 min.