COMPOSITION, AND ELECTRIC WIRE AND METHOD FOR PRODUCING SAME

Abstract

The invention provides a composition capable of providing an electric wire with small fluctuations in the wire diameter. The composition includes a modified polytetrafluoroethylene (A) having a cylinder extrusion pressure of 80 MPa or lower at a reduction ratio of 1600 and a non-fibrillatable low-molecular-weight polytetrafluoroethylene (B).

Claims

1. A composition comprising: a modified polytetrafluoroethylene (A) having a cylinder extrusion pressure of 80 MPa or lower at a reduction ratio of 1600; and a non-fibrillatable low-molecular-weight polytetrafluoroethylene (B).

2. The composition according to claim 1, wherein the modified polytetrafluoroethylene (A) comprises a particle core and a particle shell.

3. The composition according to claim 2, wherein the particle core comprises a modified polytetrafluoroethylene (i) obtainable by copolymerization with at least one selected from the group consisting of: fluoro(alkyl vinyl ethers) represented by the following formula (I):
F.sub.2C=CFO(CF.sub.2).sub.n1X.sup.1 (I) wherein X.sup.1 is a hydrogen atom or a fluorine atom; and n1 is an integer of 1 to 6; vinyl heterocycles represented by the following formula (II): ##STR00003## wherein X.sup.2 and X.sup.3 are the same as or different from each other, and are each a hydrogen atom or a fluorine atom; and Y is -CR.sup.1R.sup.2-, where R.sup.1 and R.sup.2 are the same as or different from each other, and are each a fluorine atom, a C1-C6 alkyl group, or a C1-C6 fluoroalkyl group; and fluoroolefins represented by the following formula (III):
CX.sup.4X.sup.5=CX.sup.6(CF.sub.2).sub.n2F (III) wherein X.sup.4, X.sup.5, and X.sup.6 are each a hydrogen atom or a fluorine atom, and at least one of them is a fluorine atom; and n2 is an integer of 1 to 5.

4. The composition according to claim 2, wherein the particle shell comprises a modified polytetrafluoroethylene (ii), and the modification in the modified polytetrafluoroethylene (ii) is achieved by the use of a chain-transfer agent and/or by copolymerization with a fluoro(alkyl vinyl ether) represented by the following formula (I):
F.sub.2C=CFO(CF.sub.2).sub.n1X.sup.1 (I) wherein X.sup.1 is a hydrogen atom or a fluorine atom; and n1 is an integer of 1 to 6, or a fluoroolefin represented by the following formula (III):
CX.sup.4X.sup.5=CX.sup.6(CF.sub.2).sub.n2F (III) wherein X.sup.4, X.sup.5, and X.sup.6 are each a hydrogen atom or a fluorine atom, and at least one of them is a fluorine atom; and n2 is an integer of 1 to 5.

5. The composition according to claim 1, which is an electric wire coating material.

6. An electric wire comprising: a core wire; and a coating material formed from the composition according to claim 1.

7. A method for producing an electric wire comprising: a coating step of coating a core wire with the composition according to claim 1; a first heating step of heating the coated core wire up to the first melting point of the low-molecular-weight polytetrafluoroethylene (B) or higher; a second heating step of heating the coated core wire to 150 C. to 300 C.; and a cooling step of cooling the coated core wire.

Description

EXAMPLES

[0209] The invention is described hereinbelow referring to, but not limited to, examples.

(Method of Calculating Fluctuations in Wire Diameter)

[0210] Using a laser-type wire diameter measurement device (Keyence Corp.), the outer diameter of a coated wire passing at a line speed of 7 m/min is measured once per second. Then, the average value and standard deviation of the diameters are determined.

[0211] Fluctuations in wire diameter=(standard deviation of diameters)/(average value of diameters)

(Method of Measuring Permittivity and Tan )

[0212] The permittivity and the tan were measured using a vector network analyzer (VISA) HP-8510C (Hewlett-Packard Co. (current Agilent Technologies)), and a 2.45 GHz cavity resonator and calculation software (both available from. Kanto Electronic Application and Development Inc.).

(Proportion of Particle Core to Sum of Particle Core and Particle Shell)

[0213] This proportion was calculated from the mass proportion of the amount of monomers consumed after the start of polymerization and before addition of shell-modifying monomers to the amount of monomers consumed during the whole polymerization reaction.

(Standard Specific Gravity (SSG))

[0214] The SSG was measured by water displacement in conformity with ASTM D4895-98.

(Average Primary Particle Size)

[0215] The average primary particle size was determined as follows. First, a calibration curve was drawn with respect to the transmittance of incident light at a wavelength of 550 nm against the unit length of an aqueous dispersion in which the polymer concentration was adjusted to 0.22 mass % and the average primary particle size determined by measuring the Feret diameters on a transmission electron microscopic image. Then, the transmittance of the target aqueous dispersion was measured and the average primary particle size was determined based on the calibration curve.

(Apparent Density)

[0216] The apparent density was measured in conformity with JIS K6892.

(Average Secondary Particle Size)

[0217] The average secondary particle size was defined as the value corresponding to 50% of the cumulative volume in the particle size distribution determined using a laser diffraction particle size distribution analyzer at a pressure of 0.1 MPa and a measurement time of 3 seconds without cascade impaction.

Production Example 1

[0218] Based on Example 4 of WO 2006/054612, a PTFE fine powder (powder of high-molecular-weight PTFE modified with perfluoropropyl vinyl ether (PPVE) and hexafluoropropylene (HFP) (proportion of particle core to the sum of particle core and particle shell: 90%, average primary particle size: 0.25 m, standard specific gravity (SSG): 2.175, first melting point: 338 C., apparent density: 0.48 g/ml, powder average particle size (average secondary particle size): 500 m, cylinder extrusion pressure at RR of 1600: 36 MPa; hereinafter, this powder is referred to as PTFE-H)) was obtained.

[0219] The modified amount of the resulting PTFE-H was determined by the method disclosed in WO 2006/054612, i.e., nuclear magnetic resonance spectroscopy. The spectroscopy showed the PPVE content was 0.10 mass % and the HFP content was 0.03 mass %0.

Production Example 2

[0220] Based on Comparative Example 1 of WO 2009/020187, a PTFE micro powder (powder of low-molecular-weight PTFE which is TFE homopolymer, average primary particle size: 0.18 m, melt viscosity at 380 C.: 1.710.sup.4 Pa.Math.s, first melting point: 329 C., apparent density: 0.36 g/ml, powder average particle size (average secondary particle size) 4.5 m; hereinafter, this powder is referred to as PTFE-L) was obtained.

Example 1

[0221] PTFE-H and PTFE-L were mixed by dry blending such that the proportion of PTFE-H was 92 mass %, the proportion of PTFE-L was 8 mass %, and the sum of the masses was 4 kg. A hydrocarbon solvent (Isopar G) was added thereto as an extrusion aid in an amount corresponding to 19 mass % (938 g). The mixture was aged, and then preformed. A preformer had a cylinder diameter of 100 mm and included a 16-mm mandrel. The powder mixture (containing the extrusion aid) was put into the cylinder and pressurized, so that a preformed article having an outer diameter of 100 mm and an inner diameter of 16 mm was produced.

[0222] This preformed article was put into an 80-ton electric paste wire molding device. The extruding mold used had an inner diameter of 3.0 mm. The core wire used was a silver-plated copper-clad steel wire with a wire diameter of 0.913 mm (AWG 19). The line speed was set to 7 m/min. Extrusion was then started and the extrusion pressure in a stable state was 35 MPa. The extruded workpiece was passed through a 140 C. dry capstan for 30 m, a 220 C. drying furnace for 8 m, and four continuous heating furnaces (a 320 C. first heating furnace, a 332 C. second heating furnace, a 340 C. third heating furnace, and a 250 C. fourth heating furnace) for 8 m. Thereby, a coated wire having an outer diameter of 2.96 mm was produced. The fluctuations in the wire diameter was calculated to be 0.20%. The permittivity and the tan 5 were respectively measured to be 1.84 and 0.00008.

Production Example 3

[0223] Based on the method of Production Example 1 in WO 2012/086710, a PTFE fine powder (common modified PTFE powder of high-molecular-weight PTFE modified with perfluoropropyl vinyl ether (PPVE), including neither particle core nor particle shell (average primary particle size: 0.18 m, standard specific gravity (SSG) : 2.158, PPVE content: 0.15 mass %, first melting point: 336 C., apparent density: 0.45 g/ml, powder average particle size (average secondary particle size): 490 m, cylinder extrusion pressure at RR of 1600: 85 MPa; hereinafter, this powder is referred to as PTFE-H2)) was obtained.

Comparative Example 1

[0224] A coated wire was produced in the same manner as in Example 1 except that PTFE-H2 obtained in Production Example 3 was used instead of PTFE-H used in Example 1. The extrusion pressure was instable and rose to about 86 MPa. The product was dried and heated as in Example 1. The fluctuations in the wire diameter was then calculated to be 1% or higher. The permittivity and the tan 6 were respectively measured to be 1.90 and 0.00013.