JPH09204819A - Insulative covering material for high tension cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a material for insulative covering suitable for manufacturing a high tension cable which excels in the voltage withstand characteristic and the flexibleness and will not easily degrade even though the electric wire gets a high temp. through a long time of continued service. SOLUTION: An insulative covering material for a high tension cable consists of a matrix rubber made from 70-95wt.% rubber-nature ethylene-α-olefine-diene copolymer containing 70-85mol% ethylene and 5-30wt.% ethylenepropylene copolymer containing no less than 75mol% ethylene, wherein 5-30 parts by weight filler is contained in 100 parts by weight matrix rubber, followed by a bridging process using a vulcanizing agent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an insulating coating material for a high-voltage cable, and more particularly to an insulating coating material suitable for use in a high-voltage cable as a part of an ignition device of an internal combustion engine.

[0002]

2. Description of the Related Art A high voltage cable for supplying a high voltage from a high voltage pulse generator to an ignition plug is used in an ignition device for an engine of an automobile or the like. Such a high voltage cable has high withstand voltage and low voltage. In addition to capacitance characteristics, good flame resistance and heat resistance are also required. As an insulating coating for such a high-voltage cable, it is known that a polyolefin resin, which is a blend of polyethylene and an ethylene-α-olefin copolymer, is cross-linked by electron irradiation.
No. 6-114224), and an ethylene-propylene copolymer containing 75 mol% or more of ethylene, to which a flame retardant is added and which is cross-linked with peroxide, is also known (JP-A-3-1842).
No. 13).

However, a high-voltage cable having such a polyolefin-based insulating coating generally tends to have insufficient flexibility. Therefore, in order to increase the flexibility of the insulation coating material, we investigated a method of blending polyolefin rubber with a low Mooney viscosity, and found that when the wire heats up when energized and the temperature rises, the wax-like substance becomes a coating material for the wire. It has been found that there is a problem that durability is impaired, such as leakage to the outside from the outside to contaminate the surroundings and at the same time lowering the withstand voltage.

[0004]

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a high voltage cable which is excellent in withstand voltage and flexibility and which is not easily deteriorated even if the electric wire becomes hot due to continuous use for a long time. Therefore, it is an object of the present invention to provide an insulating coating material suitable for manufacturing such a high-voltage cable with high reliability.

[0005]

An insulating coating material for a high voltage cable according to the present invention which can achieve the above object is 7
70-95% by weight of a rubbery ethylene-α-olefin-diene copolymer containing 0-85 mol% of ethylene, and 75 mol%
Ethylene propylene copolymer containing the above ethylene 5
With respect to 100 parts by weight of the base rubber composed of 30% by weight,
It is characterized in that it contains 5 to 30 parts by weight of a filler and is crosslinked with a vulcanizing agent.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The base rubber used in the insulating coating material of the present invention comprises a rubber-like ethylene-α-olefin-diene copolymer and an ethylene-propylene copolymer. As the rubbery ethylene-α-olefin-diene copolymer, for example, an ethylene propylene diene copolymer is preferable, and such a copolymer has an ethylene content within the range of 70 to 85 mol%. When the ethylene content is less than this range, a vulcanizate having sufficient mechanical strength cannot be obtained, the deterioration is not sufficiently improved, and when it is too high, the workability is deteriorated, which is not preferable.

The ethylene-propylene copolymer is 75
Although it is a semi-hard resin that contains more than mol% of ethylene, if the amount of ethylene is less than this range, it will be easier to knead with the rubbery ethylene-α olefin-diene copolymer, but the strength of the vulcanizate Cannot be improved sufficiently,
Further, when the amount of ethylene is too large, there is a problem that the kneading workability deteriorates, so it is desirable that the amount of ethylene does not exceed 85 mol%.

The rubber-like ethylene-α-olefin-diene copolymer and the ethylene-propylene copolymer are blended in such a proportion that the rubber-like ethylene-α-olefin-diene copolymer is 70 to 95% by weight, and the ethylene-propylene copolymer is Is 5
-30% by weight. If the blending ratio of the ethylene-propylene copolymer is less than 5% by weight, the deterioration resistance is not sufficiently improved, and if it exceeds 30% by weight, the kneading operation becomes difficult, which is not desirable.

The filler used in the insulating coating material of the present invention is not particularly limited as long as it has a reinforcing property, and among them, talc or clay is preferably used. The amount of such reinforcing filler compounded is such that the base rubber 1
The amount of the filler is in the range of 5 to 30 parts by weight with respect to 00 parts by weight. If the compounding amount of the filler is less than 5 parts by weight, the kneading workability is poor, and conversely, if it exceeds 30 parts by weight, the dielectric constant increases and the electrostatic capacity of the high voltage cable is increased.

Further, the insulating coating material of the present invention is coated on the core wire and then crosslinked. The vulcanizing agent to be blended here is a peroxide type vulcanizing agent from the viewpoint of electrical characteristics. Is preferred. The amount of such a peroxide-based vulcanizing agent is practically desirable to be 2 parts by weight or more, but if the amount is too large, the electrical characteristics may be impaired, so 10 parts by weight or less is desirable. .

The high-voltage cable manufactured by using the insulating coating material of the present invention is flexible even after being used for a long period of time such that it is used in an ignition device for an automobile engine and has a high temperature due to a load of a high-voltage pulse. In addition to maintaining the properties, the withstand voltage characteristics are not impaired.

[0012]

EXAMPLES As a rubber-like ethylene-α-olefin-diene copolymer A, ethylene-propylene copolymer B, filler C, antioxidant D, activator E, vulcanization accelerator F, and vulcanizing agent G, The following materials were prepared, and the insulating coating compositions were prepared by using these materials and having the formulations shown in Table 1.

Rubber-like ethylene / propylene / diene copolymer A1: EP-21 (manufactured by Nippon Synthetic Rubber, ML _{1 + 4} : 38)
[100 ° C], ethylene content: 74 mol%) Rubber-like ethylene / propylene / diene copolymer A2: E
P-51 (Nippon Synthetic Rubber, ML _{1 + 4} : 38 [100
° C], ethylene content: 81 mol%) Rubbery ethylene-α olefin-diene copolymer A3:
Mitsui Elastomer K9720 (Mitsui Petrochemical, M
L _{1 + 4} : 40 [100 ° C.], ethylene content: 89 mol%) Rubbery ethylene-α olefin-diene copolymer A4:
EPT3045 (Mitsui Petrochemical, ML _{1 + 4} : 40 [10
0 ° C.], ethylene content: 66 mol%) Ethylene propylene copolymer B1: EP-02P (manufactured by Nippon Synthetic Rubber, ML _{1 + 4} : 24 [100 ° C.], ethylene content: 81 mol%) Ethylene propylene copolymer B2: EPT0045 (Mitsui Petrochemical, ML _{1 + 4} : 24 [100 ° C.], ethylene content: 58 mol%) Filler C1: Burgess KE (manufactured by Burgess Pigment,
Silane-treated clay) Filler C2: Whiten SSB (Shiraishi calcium, heavy calcium carbonate) Filler C3: Hytron (Takehara Chemical, talc) Anti-aging agent D: Antage MB (Kawaguchi Chemical) Activator E: Active Zinc flower AZO (manufactured by Shodo Chemical Co., Ltd.) Vulcanization accelerator F: NK ester TMPT (manufactured by Shin-Nakamura Chemical) Vulcanizing agent G: DCP (manufactured by Mitsui Petrochemical, dicumyl peroxide)

[0014]

[Table 1]

These compositions were extrusion-coated on a core wire for a high-voltage cable having a diameter of 1.2 mm to a thickness of 1.8 mm, steam-vulcanized at 205 ° C. for 2 minutes, and then braided and sheathed. Was applied to prepare high-voltage cables having a diameter of 7 mm and having the structure shown in FIG. In the figure, 1 is a core wire, 2 is an insulating coating, 3 is a braid, and 4 is a protective sheath.

An insulating coating was cut out from each of the high-voltage cables thus obtained and heat-treated at 200 ° C. for 24 hours to determine the heating loss (%). Also, examine the change in the number average molecular weight and the weight average molecular weight before and after the heat treatment,
These are summarized in Table 2. Here, ex2 or ex3 in the value of the average molecular weight is × 10 ² or × 10, respectively.
It is a symbol that means ³ .

Also, these high-voltage cables C are cut out to a length of 1 m, connection terminals 5 are attached to the ends, and they are connected to a high-voltage power supply device E capable of outputting a 20 kV DC peak voltage pulse 6000 times per minute as shown in FIG. And the capacitance to ground is 25
A spark discharge was generated in the three-needle gap G by adjusting to 0 pF, and a durability test was performed at room temperature for 100 hours, and the presence or absence of a leak W from the insulating coating was evaluated by ◯ and ×. Also,
A cable from which the sheath 4 and the braid 3 are removed is cut into a length of 30 cm, and one end 10 cm is fixed horizontally and the other is hung freely, and the difference in the hung height of the free end is measured and an endurance test is performed. The change in flexibility before and after the examination was examined, and the degree of change was evaluated in three grades, in order of decreasing magnitude.

On the other hand, a high-voltage cable was cut out to a length of 104 cm, and both ends were peeled by 2 cm, then tied in a loop and immersed in a 5% salt water bath, and a high voltage was applied between the bath and the cable conductor. Then, the voltage that causes dielectric breakdown was measured within 5 seconds after the application. Then, the change in withstand voltage before and after the durability test was examined, and the change in capacitance (pF / m) between the core wire and the surface of the electric wire sheath was also examined. and again,
The breaking strength of the high-voltage cable C was measured at a pulling speed of 500 mm / min, and the results are also shown in Table 2.

[0019]

[Table 2]

[0020]

INDUSTRIAL APPLICABILITY The insulating coating material for a high-voltage cable of the present invention is less deteriorated even when a high-voltage pulse is continuously loaded for a long time under harsh conditions, and there is no leakage or the like to maintain flexibility. Since excellent withstand voltage characteristics are maintained, there is an effect that a high-voltage cable with high reliability and long life can be obtained.

[Brief description of drawings]

FIG. 1 is a perspective view showing a structure of a high voltage cable.

FIG. 2 is a conceptual diagram illustrating a method of a spark discharge durability test of a high voltage cable.

[Explanation of symbols]

 1 core wire 2 insulation coating 3 braid 4 sheath 5 connection terminal C high-voltage cable E high-voltage power supply device G 3 needle gap W leaked material

Claims (3)

[Claims] 1. From 70 to 95% by weight of a rubbery ethylene-α-olefin-diene copolymer containing 70 to 85 mol% of ethylene and 5 to 30% by weight of an ethylene-propylene copolymer containing 75 mol% or more of ethylene. Base rubber 100
An insulating coating material for a high-voltage cable, which comprises 5 to 30 parts by weight of a filler with respect to parts by weight and is crosslinked with a vulcanizing agent. 2. The insulating coating material for a high voltage cable according to claim 1, wherein the filler is talc or clay. 3. The insulating coating material for a high voltage cable according to claim 1, wherein the vulcanizing agent is a peroxide type vulcanizing agent.