Heat-resistant electric wire

Abstract

A heat-resistant electric wire including a core wire and a coating that covers the core wire. The coating is formed from a modified fluorine-containing copolymer that is obtained by irradiating a copolymer with radiation at an exposure of 250 kGy or lower at a temperature of not higher than the melting point of the copolymer. The copolymer is at least one copolymer selected from a copolymer including a tetrafluoroethylene unit and a perfluoro(alkyl vinyl ether) unit and a copolymer including a tetrafluoroethylene unit and a hexafluoropropylene unit.

Claims

1. A heat-resistant electric wire comprising a core wire and a coating that covers the core wire, the coating being formed from a modified fluorine-containing copolymer that is obtained by irradiating a copolymer with radiation at an exposure of 90 kGy or lower at a temperature of not higher than the melting point of the copolymer, wherein the copolymer including a tetrafluoroethylene unit and a perfluoro(alkyl vinyl ether) unit includes 2.0 to 12 mass % of the perfluoro(alkyl vinyl ether) unit in all the monomer units, wherein the copolymer has 191 or more functional groups per 10.sup.6 carbon atoms and the functional groups include at least one selected from the group consisting of —CF═CF.sub.2, —CF.sub.2H, —COF, —COOH, —COOCH.sub.3; —CONH.sub.2, and —CH.sub.2QH.

2. A method of producing the heat-resistant electric wire according to claim 1, comprising extrusion-molding, on a core wire, a copolymer including a tetrafluoroethylene unit and a perfluoro(alkyl vinyl ether) unit to provide a coating that covers the core wire, and irradiating the coating with radiation.

3. The production method according to claim 2, wherein the coating further contains polytetrafluoroethylene.

Description

EXAMPLES

(1) Next, the present invention will be described in detail below with reference to, but not limit to, examples.

(2) The physical properties were determined by the following methods.

(3) (Amount of Monomer Unit)

(4) The amounts of the respective monomer units were determined by .sup.19F-NMR.

(5) (Melt Flow Rate (MFR))

(6) The mass (g/10 min) of the polymer flowed out of a nozzle (inner diameter: 2 mm, length: 8 mm) per 10 minutes at 372° C. and 5 kg load was determined using a melt indexer (Yasuda Seiki Seisakusho Ltd.) in conformity with ASTM D1238.

(7) (Glass Transition Temperature)

(8) The glass transition temperature was determined by dynamic viscoelasticity measurement using DVA-220 (IT Keisoku Seigyo K.K.).

(9) A compression molded sheet having a length of 25 mm, a width of 5 mm, and a thickness of 0.2 mm was used as a sample specimen, and the measurement was performed at a temperature-increasing rate of 5° C./min and a frequency of 10 Hz. The temperature corresponding to the tan δ peak was defined as the glass transition temperature.

(10) (Melting Point)

(11) The melting point is a temperature corresponding to the maximum value on a heat-of-fusion curve obtained at a temperature-increasing rate of 10° C./min using a differential scanning calorimeter (DSC).

(12) (Number of Functional Groups)

(13) A sample was molten at 340° C. for 30 minutes, and then compression molded into a film having a thickness of 0.25 to 0.3 mm. This film was analyzed by scanning 40 times using a Fourier transform infrared (FT-IR) spectrometer (trade name: 1760X, PerkinElmer Co., Ltd.), and thereby an infrared absorption spectrum was obtained. Then, the difference spectrum was obtained between the infrared absorption spectrum and the base spectrum of a polymer that is completely fluorinated and is free from functional groups. With the absorption peak of a specific functional group appearing in this difference spectrum, the number N of the functional group per 1×10.sup.6 carbon atoms in the sample was calculated according to the following formula (A):
N=I×K/t  (A)
wherein

(14) I: absorbance

(15) K: correction coefficient

(16) t: thickness of film (mm).

(17) For reference, Table 2 shows the absorption frequencies, molar absorption coefficients, and correction coefficients of the functional groups mentioned herein. The molar absorption coefficients are determined from the FT-IR measurement data of a low-molecular-weight model compound.

(18) TABLE-US-00002 TABLE 2 Absorption Molar absorption frequency coefficient Correction Functional group (cm.sup.−1) (l/cm/mol) coefficient Model compound —COF 1883 600 388 C.sub.7F.sub.15COF —COOH free 1815 530 439 H(CF.sub.2).sub.6COOH —COOH bonded 1779 530 439 H(CF.sub.2).sub.6COOH —COOCH.sub.3 1795 680 342 C.sub.7F.sub.15COOCH.sub.3 —CONH.sub.2 3436 506 460 C.sub.7H.sub.15CONH.sub.2 —CH.sub.2OH, —OH 3648 104 2236 C.sub.7H.sub.15CH.sub.2OH —CF.sub.2H 3020 8.8 26485 H(CF.sub.2CF.sub.2).sub.3CH.sub.2OH —CF═CF.sub.2 1795 635 366 CF.sub.2═CF.sub.2
(Crack Resistance: Winding Crack Test on Electric Wire)

(19) Ten 20-cm-long electric wires were cut out of the resulting coated electric wire. These wires were used as electric wires (specimens) for a crack test. These specimens each in a straight state were heated at 260° C. for 96 hours.

(20) Each specimen was taken out and cooled at room temperature, and then wound around an electric wire having the same diameter as the specimen. This workpiece was used as a sample. This sample was again heated at 260° C. for 1 hour. Then, the sample was taken out and cooled at room temperature, and the electric wire was straightened. The number of electric wires with cracking was counted visually and using a magnifier. If just a single crack was present in a single electric wire, this electric wire was evaluated as cracked. When the number of cracked electric wires was 1 or less among the 10 wires, this case was evaluated as good. When the number was 2 or more, this case was evaluated as poor.

(21) (Heat Resistance: Dimensional Change Test on Electric Wire)

(22) A 20-mm portion from the tip of the resulting coated electric wire was exposed and the remaining portion was covered with aluminum foil. This workpiece was used as a measurement sample. This sample was hung on a fence and heated in an electric furnace at a predetermined temperature of 310° C. for 60 minutes. Then, the sample was taken out of the electric furnace and cooled down to room temperature. The dimensional change of the electric wire due to melt deformation was checked. The evaluation method was as follows. Four outer diameters of the hung electric wire at the position 0.5 mm from the lower tip were measured before and after the heating. Electric wires satisfying (average outer diameter after heating)/(average outer diameter before heating)=1.04 or higher were defined as having a dimensional change. Alternatively, if visual observation found that the coating sagged to be longer than the conductor or the coating formed a thread-like stream, such electric wires were evaluated as having a dimensional change of the coating. In the tables, the evaluation “observed” means that the dimensional change was present, while the evaluation “not observed” means that the dimensional change was absent.

(23) (Heat Resistance: Melt-Deformation Test on Electric Wire (Sagging))

(24) A 20-mm portion from the tip of the resulting coated electric wire was exposed and the remaining portion was covered with aluminum foil. This workpiece was used as a measurement sample. This sample was hung on a fence and heated in an electric furnace from 300° C. to 390° C. in 10° C. increments. The sample was maintained at each temperature stage for 20 minutes. Then, the sample was taken out and the sagging thereof due to melt deformation was observed in the same manner as mentioned above. The temperature at which the dimensional change or the sagging was observed was defined as the melt deformation starting temperature (° C.) of the coating.

Example 1

(25) A tetrafluoroethylene (TFE)/perfluoro(propyl vinyl ether) (PPVE) copolymer (polymer composition: TFE/PPVE=94.1/5.9 (mass %), MFR: 21 g/10 min, melting point: 303° C., glass transition temperature: 93° C., number of functional groups: 191 (per 10.sup.6 carbon atoms) (specifically, CH.sub.2OH: 150, COF: 17, COOH: 24, other functional groups: 0)) used as a coating material was extrusion-molded through an extrusion-molding device at 380° C. to cover a 1.00-mm-diameter copper conductor with the coating thickness as mentioned below. Thereby, a coated electric wire was obtained.

(26) The conditions of extrusion-molding the coating and of covering the electric wire are as follows.

(27) a) Core conductor: 1.00-mm-diameter soft steel line

(28) b) Coating thickness: 600 μm (for dimensional change and melt deformation tests), 280 μm (for winding crack test)

(29) c) Coated electric wire diameter: 2.2 mm

(30) d) Electric wire pulling rate: 20 m/min (600 μm), 30 m/min (280 μm)

(31) e) Cone length: 30 mm

(32) f) Extrusion conditions:

(33) single-screw extrusion-molding device, cylinder shaft diameter=30 mm, L/D=22

(34) die (inner diameter)/tip (outer diameter)=16.0 mm/10.5 mm

(35) temperature setting of extruder: barrel portion C-1 (320° C.), barrel portion C-2 (360° C.), barrel portion C-3 (370° C.), lamp portion H (380° C.), die portion D-1 (380° C.), and die portion D-2 (380° C.); core wire pre-heating temperature: 80° C.

(36) The resulting coated electric wire was cut into a length of 20 cm. The cut wire was contained in an electron beam irradiation container of an electron beam irradiator (NHV Corp.), and then nitrogen gas was put into the container so that the container was under nitrogen atmosphere. The temperature inside the container was adjusted to 25° C. After the temperature was stabilized, the front and back sides of the coated electric wire were irradiated with 20 kGy of electron beams at an electron beam accelerating voltage of 3000 kV and an exposure intensity of 20 kGy/5 min. The coated electric wire after the irradiation was subjected to the winding crack test and the heat resistance tests. Table 3 shows the results.

(37) The heat resistance tests proved that the electric wire was not dimensionally changed even at a temperature of not lower than the melting point, and the coating did not sag due to melt flowing.

(38) In conventional techniques, the coating may be deformed due to melt flowing or may be peeled off so that the performance of the electric wire may be impaired around the melting point. Still, the present invention enables production of a heat-resistant electric wire that is not easily heat-flowed or -deformed even at a temperature of not lower than the melting point of the material copolymer by irradiating the copolymer with radiation at a temperature of not higher than the melting point.

Examples 2 to 5

(39) The winding crack test and the heat resistance tests were performed on the coated electric wire after the irradiation in the same manner as in Example 1 except that the electron beam irradiation was performed at an irradiation temperature and an exposure shown in Table 3.

(40) Table 3 shows the results.

Comparative Example 1

(41) The winding crack test and the heat resistance tests were performed on the resulting electric wire in the same manner as in Example 1 except that no electron beam irradiation was performed. Table 3 shows the results.

Examples 6 and 7 and Comparative Example 3

(42) A TFE/PPVE copolymer (polymer composition: TFE/PPVE=93.9/6.1 (mass %), F content: 75.7 mass %, MFR: 25 g/10 min, terminals stabilized by fluorine gas, melting point: 304° C., glass transition temperature: 93° C., number of functional groups: 5 (per 10.sup.6 carbon atoms) (specifically, CH.sub.2OH: 0, COF: 5, COOH: 0, other functional groups: 0)) was used as a coating material, and the winding crack test and the heat resistance tests were performed on the coated electric wire after the irradiation in the same manner as in Example 1 except that the electron beam irradiation was performed at an irradiation temperature and an exposure shown in Table 4. Table 4 shows the results.

Comparative Example 2

(43) The winding crack test and the heat resistance tests were performed on the resulting electric wire in the same manner as in Example 6 except that no electron beam irradiation was performed. Table 4 shows the results.

Examples 8 to 10

(44) A TFE/PPVE copolymer (polymer composition: TFE/PPVE=93.4/6.6 (mass %), F content: 74.6 mass %, MFR: 64 g/10 min, melting point: 284° C., glass transition temperature: 90° C., number of functional groups: 497 (per 10.sup.6 carbon atoms) (specifically, CH.sub.2OH: 304, COF: 17, COOH: 152, CF.sub.2H: 24, other functional groups: 0)) was used as a coating, and the winding crack test and the heat resistance tests were performed on the coated electric wire after the irradiation in the same manner as in Example 1 except that the electron beam irradiation was performed at an irradiation temperature and an exposure shown in Table 5. Table 5 shows the results.

Comparative Example 4

(45) The winding crack test and the heat resistance tests were performed on the resulting electric wire in the same manner as in Example 8 except that no electron beam irradiation was performed. Table 5 shows the results.

Examples 11 and 12

(46) A TFE/PPVE/HFP copolymer (polymer composition: TFE/PPVE/HFP=87.9/1.0/11.1 (mass %), F content: 75.9 mass %, MFR: 24 g/10 min, melting point: 257° C., glass transition temperature: 85° C., number of functional groups: 116 (per 10.sup.6 carbon atoms) (specifically, CH.sub.2OH: 0, COF: 6, COOH: 10, CF.sub.2H: 100, other functional groups: 0)) was used as a coating, and the winding crack test and the heat resistance tests were performed on the coated electric wire after the irradiation in the same manner as in Example 1 except that the electron beam irradiation was performed at an irradiation temperature and an exposure shown in Table 6. Table 6 shows the results.

Comparative Example 5

(47) The winding crack test and the heat resistance tests were performed on the resulting electric wire in the same manner as in Example 11 except that no electron beam irradiation was performed. Table 6 shows the results.

(48) TABLE-US-00003 TABLE 3 Heat resistance tests Irradiation Melt deformation temperature Exposure Winding Dimensional starting temperature (° C.) (kGy) crack test change of coating (° C.) Comparative — Not Good Not 300 or lower Example 1 irradiated observed Example 1 25 20 Good Observed 370 or higher Example 2 80 40 Good Observed 370 or higher Example 3 200 20 Good Observed 370 or higher Example 4 245 20 Good Observed 370 or higher Example 5 245 40 Good Observed 380 or higher

(49) TABLE-US-00004 TABLE 4 Heat resistance tests Irradiation Melt deformation temperature Exposure Winding Dimensional starting temperature (° C.) (kGy) crack test change of coating (° C.) Comparative — Not Good Not 300 or lower Example 2 irradiated observed Example 6 245 20 Good Observed 320 or higher Example 7 245 40 Good Observed 340 or higher Comparative 245 300 Poor Not 300 or lower Example 3 observed

(50) TABLE-US-00005 TABLE 5 Heat resistance tests Irradiation Melt deformation temperature Exposure Winding Dimensional starting temperature (° C.) (kGy) crack test change of coating (° C.) Comparative — Not Poor Not 300 or lower Example 4 irradiated observed Example 8 150 20 Good Observed 360 or higher Example 9 245 20 Good Observed 380 or higher Example 10 245 40 Good Observed 380 or higher

(51) TABLE-US-00006 TABLE 6 Heat resistance tests Irradiation Melt deformation temperature Exposure Winding Dimensional starting temperature (° C.) (kGy) crack test change of coating (° C.) Comparative — Not Poor Not 300 or lower Example 5 irradiated observed Example 11 180 130 Good Observed 320 or higher Example 12 245 150 Good Observed 320 or higher

INDUSTRIAL APPLICABILITY

(52) Since being excellent in heat resistance and crack resistance, the heat-resistant electric wire of the present invention is suitably used as an electric wire to be used in vehicles such as automobiles, aircraft, and military vehicles.