JPH1067904A - Heat resistant insulating composition and electric cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a heat resistant insulating composition having an excellent mechanical strength and also a markedly improved heat resistance especially in view of an electric characteristic even in a non-crosslinking state by adding a relatively small amount of a blending agent, and an electric cable equipped with a coating layer consisting of the composition. SOLUTION: This heat resistant insulating composition is obtained by mixing 2-10 pt.wt. tetrafluoroethylene micro powder to 100 pts.wt. copolymer consisting mainly of ethylene and tetrafluoroethylene. As the tetrafluoroethylene micro powder, low molecular weight polytetrafluoroethylene fine particles having <=50μm mean particle diameter are used. This electric cable is equipped with a coating layer consisting of the above heat resistant insulating composition.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a heat-resistant insulating composition having excellent mechanical strength and, in an uncrosslinked state, having significantly improved heat resistance, particularly in terms of electrical characteristics. The present invention relates to an electric wire provided with a coating layer made of a composition.

[0002]

2. Description of the Related Art Among fluorine-based polymers, ethylene-tetrafluoroethylene copolymer (ETFE) has extremely excellent mechanical strength, and has heat resistance in terms of mechanical strength by crosslinking. Is known to improve. In addition, various studies have been made to further improve the heat resistance of the crosslinked ETFE.
JP-A-9-100141, JP-A-7-14431, JP-A-7-14667 and the like disclose that ETFE is mixed with a rubber having excellent heat resistance, for example, fluororubber and the like, and is crosslinked to 200 ° C. It is disclosed that superior heat resistance can be obtained.

[0003]

However, in the above-mentioned heat resistance improving technology, when only a small amount is mixed so that the mechanical strength does not decrease, the heat resistance in terms of electric characteristics hardly improves. There was a problem. Also, in order to improve the heat resistance of uncrosslinked ETFE, there is only means to change the structure of the polymer itself, such as changing the copolymerization ratio or adding a third component,
Even if such a means is employed, the effect is small in terms of electrical characteristics as compared with the improvement in heat resistance in terms of mechanical strength, and unbalanced performance tends to be obtained.

[0004] The present invention has been made based on these points, and it is an object of the present invention to have excellent mechanical strength and to use a relatively small amount of a compounding agent in an uncrosslinked state. It is still another object of the present invention to provide a heat-resistant insulating composition in which heat resistance, particularly in terms of electrical characteristics, is significantly improved, and an electric wire provided with a coating layer made of the composition.

[0005]

In order to achieve the above object, a heat-resistant insulating composition according to the present invention comprises tetrafluoroethylene micropowder based on 100 parts by weight of a copolymer mainly composed of ethylene and tetrafluoroethylene. 2
It is characterized by being mixed in an amount of not less than 10 parts by weight and not more than 10 parts by weight. At this time, it is conceivable to use low molecular weight polytetrafluoroethylene fine particles having an average particle diameter of 50 μm or less as the tetrafluoroethylene micropowder. In addition, an electric wire according to another aspect of the present invention includes a coating layer made of the above-described heat-resistant insulating composition.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Known copolymers mainly composed of ethylene and tetrafluoroethylene include binary copolymers having various polymerization ratios and multipolymers copolymerized with other fluorine-containing monomers. And any of them may be used.

[0007] Tetrafluoroethylene micropowder is used mainly for improving the heat resistance of the resulting composition, particularly for improving the heat resistance in terms of electrical characteristics, and for secondary purposes, mechanical strength (particularly abrasion resistance). Is used to improve the content of the copolymer, which is 2 parts by weight or more to 100 parts by weight of the copolymer mainly composed of ethylene and tetrafluoroethylene.
0 parts by weight or less are mixed. If the mixing amount is less than 2 parts by weight,
If the effect of improving heat resistance is not exhibited, and if it exceeds 10 parts by weight, the mechanical strength (in particular, elongation) and extrudability of the obtained composition will be reduced.

[0008] Examples of the tetrafluoroethylene micropowder include fine particles of low molecular weight polytetrafluoroethylene. Although various particle sizes are known,
In the present invention, preferably, the average particle diameter is 50 μm
The average particle diameter is more preferably 0.1 μm or more and 2 or less.
Fine particles of low molecular weight polytetrafluoroethylene having a particle size of 0 μm or less are used. If the average particle diameter exceeds 50 μm, the kneading operation becomes extremely difficult because the particles are not uniformly dispersed in a copolymer mainly composed of ethylene and tetrafluoroethylene. Those having an average particle diameter of 0.1 μm or more and 20 μm or less are easily dispersed and kneaded in a copolymer mainly composed of ethylene and tetrafluoroethylene, and the mechanical strength of the obtained composition is high. It is particularly preferable because it is significantly improved.

In the present invention, in addition to the above components,
Various conventionally known additives such as fillers and pigments can be appropriately compounded as needed. Those which do not cause decomposition or foaming at a processing temperature of 200 ° C. or more and 400 ° C. or less may be appropriately used.

The composition of the present invention is completed by kneading the above constituent materials with a known kneader such as an internal mixer, a single-screw kneader or a twin-screw kneader.

[0011]

EXAMPLES Examples of the present invention will be described below together with comparative examples. ETFE (trade name: Tefzel 750, manufactured by Mitsui DuPont Fluorochemicals Co., Ltd.) was used as the copolymer mainly composed of ethylene and tetrafluoroethylene, and the average particle diameter of the tetrafluoroethylene micropowder was as follows. 3 μm low molecular weight polytetrafluoroethylene fine particles were used.

[0012] The compounding materials shown in Table 1 are sufficiently kneaded with a twin-screw kneader, and the resulting composition is pelletized.
= 24 and fed to a 30 mmφ extruder,
Under the temperature condition of 0 ° C. and the head of 320 ° C., the wire diameter is 0.18.
19mm tinned annealed copper wire twisted together, outer diameter 0.9
The conductor was extruded and coated with a thickness of 0.25 mm on the circumference of a conductor having a thickness of 0.2 mm to produce an electric wire having a finished outer diameter of 1.4 mm.

Using the thus obtained five types of wires (Examples 1 to 3, Comparative Examples 1 and 2) as samples, mechanical strength (tensile strength and elongation, wear resistance) , Heat resistance (residual breakdown voltage), and extrudability (appearance state) were evaluated. The results are shown in Table 1.

The evaluation method is as follows. Mechanical strength Tensile strength and elongation were measured in accordance with JIS C 3005 (1986). Heat resistant 200 ° C tetrafluoroethylene-hexafluoropropylene copolymer (FEP)
The tensile strength is 20 MPa or more and the elongation is 20
0% or more was regarded as a pass line. Wear resistance is JASO
The minimum abrasion resistance was measured according to the blade reciprocation method (load amount 510 g) of the abrasion resistance test of D608-92. The larger the numerical value (the number of times), the stronger the resistance of edges and the like, which is preferable.

Heat resistance Heat-resistant insulation (coating layer) of about 10 mm was cut off at both ends of the sample, and conductors were twisted with each other. This was left in a thermostat kept at 250 ° C. After that, it was taken out and the dielectric breakdown voltage was measured. Then, the number of days when the dielectric breakdown voltage residual ratio was less than 50% was measured. The dielectric breakdown voltage is obtained by immersing the insulator (coating layer) in water,
An AC voltage having a waveform close to a sine wave of 60 Hz was applied between the conductor and the ground to increase the voltage at a speed of 500 v / sec, and the voltage when the insulator (coating layer) was broken was measured. The longer the numerical value (the number of days), the better the heat resistance in terms of electrical characteristics, and the more preferable.

Extrusion processability The appearance of each sample was visually checked, and a sample with irregularities on the surface was indicated as "poor".

[0017]

[Table 1]

As can be seen from Table 1, Examples 1 to 3 provided with a coating layer composed of a composition obtained by mixing ETFE with a predetermined amount of tetrafluoroethylene micropowder used tetrafluoroethylene micropowder at all. Compared with Comparative Example 1 in which the mixture is not mixed, the heat resistance in terms of electrical characteristics is improved, and the mechanical strength (wear resistance) is also significantly improved. In particular, the effect of improving the abrasion resistance is such a remarkable effect that it cannot be considered at all when an inorganic filler or the like usually used for the purpose of improving the heat resistance is blended. Comparative Example 2 in which tetrafluoroethylene micropowder was mixed, but the weight ratio of which exceeded the upper limit of the preferred range of the present invention, was inferior in mechanical strength (elongation) and extrudability.

[0019]

As described in detail above, the composition of the present invention comprises:
It has excellent mechanical strength and remarkably improved heat resistance, particularly in terms of electrical characteristics, in an uncrosslinked state. Therefore, for example, it is suitable as a coating material for electric wires used in automobiles, aircraft, thermal equipment, and the like.

Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location C08L 23:08)

Claims (3)

[Claims] 1. A heat-resistant insulating material comprising a mixture of 100 parts by weight of a copolymer mainly composed of ethylene and tetrafluoroethylene and 2 to 10 parts by weight of tetrafluoroethylene micropowder. Composition. 2. The heat-resistant insulating composition according to claim 1, wherein low molecular weight polytetrafluoroethylene fine particles having an average particle diameter of 50 μm or less are used as the tetrafluoroethylene micropowder. 3. An electric wire comprising a coating layer comprising the heat-resistant insulating composition according to claim 1.