JPH0487216A - Heat resistant insulated wire - Google Patents

Abstract

PURPOSE:To obtain excellent adhesion between two layers and improve mechanical characteristics and heat resistance by composing an inner layer and an outer layer which are two insulator layers of a cross linking material of fluorine base rubber composition and specifying the cross linking degree of the composition for the outer layer and the thickness of the outer layer. CONSTITUTION:An inner layer and an outer layer which are two insulator layers are composed of a cross linking material of a composition containing fluorine based rubber. The cross linking degree of the composition forming the outer layer is set so as to be bigger than the cross linking degree of the composition forming the inner layer. Further the thickness of the outer layer is 50% or less of the thickness of the total insulator layer. The fluorine rubber composition forming the inner layer of the insulator layer is composed of cross linked fluorine rubber compounded of various compounding agents. Thereby it is possible to obtain the heat resistant insulated wire being provided with the insulator layer having surpassing mechanical characteristics, heat resistance and the like.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a heat-resistant insulated wire suitable as an insulated wire for use in microwave ovens, heater cords, automobile wiring, and the like.

(Prior art) Fluororubber has excellent heat resistance, electrical insulation, oil resistance, chemical resistance, and flame retardancy, and is used as a wiring material for electronic devices that require heat-resistant parts such as microwave ovens. It is also used as an insulating material for heater cords, sensor cords, and the like. Among fluororubbers, tetrafluoroethylene-propylene copolymers are cheaper than other fluoroelastomers, and are therefore widely used as insulation coating materials for electric wires and cables in addition to the above-mentioned applications.

(Problems to be Solved by the Invention) It is said that crosslinked fluororubbers, such as tetrafluoroethylene-propylene copolymers, have insufficient mechanical properties such as tensile strength, toughness, and abrasion resistance. There's a problem.

In order to solve this problem, a method of mixing ethylene-tetrafluoroethylene copolymer with tetrafluoroethylene-propylene copolymer (Japanese Patent Laid-Open No. 59-13950
4), a method of mixing polyvinylidene fluoride (JP-A-59-230030), and a method of mixing ethylene-vinyl acetate copolymer (JP-A-63-28471).
Publication No. 2), etc. have been proposed.

In the method described in JP-A-59-139504, since the melting point of the ethylene-tetrafluoroethylene copolymer is as high as 260°C, the kneading temperature and the processing and forming temperature are 300°C.
It is necessary to raise the temperature to ℃. This reduces processing workability and causes problems such as burning of the material.

Furthermore, in the method described in JP-A-59-230030, since the melting point of polyvinylidene fluoride is relatively low at 200°C, processing is easier than in the conventional example.

However, polyvinylidene fluoride has poor compatibility with the tetrafluoroethylene-propylene copolymer, making it difficult to uniformly knead both components.

Furthermore, in the method described in JP-A-63-284712, the ethylene-vinyl acetate copolymer can be processed at temperatures below 200°C, and is also compatible with the tetrafluoroethylene-propylene copolymer. good. but,
The aging properties and flame retardance of the mixture deteriorated, and no dramatic improvement was observed in the mechanical properties.

Further, the extrusion grade of tetrafluoroethylene-propylene fluororubber is black because it has been fired, and it is difficult to color it as it is. Therefore, there is usually a problem that either titanium oxide is added to whiten the product and then colored, or that adding titanium oxide lowers the aging properties.

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, an object of the present invention is to provide a heat-resistant insulated wire having an insulating layer having excellent mechanical properties, heat resistance, etc.

(Means and effects for solving the problems) The heat-resistant insulated wire of the present invention, which has been made to achieve the above object, has two insulator layers, an inner layer and an outer layer, formed from different constituent materials around a conductor. In the heat-resistant insulated wire, the inner layer and the outer layer are formed from a crosslinked product of a composition containing fluororubber, and the degree of crosslinking of the composition forming the outer layer is
The inner layer of the insulator layer has a structure in which the degree of crosslinking is set to be greater than the crosslinking degree of the composition forming the inner layer, and the thickness of the outer layer is 50% or less of the thickness of the total insulator layer. The fluororubber composition (hereinafter referred to as "composition for inner layer") that forms the composition is a mixture of crosslinked fluororubber and various compounding agents.

Examples of fluorine rubbers include tetrafluoroethylene-α-olefin copolymers such as tetrafluoroethylene-propylene copolymers, vinylidene fluoride-hexafluoropropylene copolymers, and tetrafluoroethylene-perfluoroethylene copolymers: Examples include fluoride copolymers with vinylidene fluoride, perfluoroalkoxyethylene, and hexafluoropropylene; fluorosilicone elastomers, fluorophosphacene elastomers, and the like.

Among these, tetrafluoroethylene-α-olefin copolymer and vinylidene fluoride-hexafluoropropylene copolymer are preferred because of their heat resistance and low cost.
More preferred is a tetrafluoroethylene-propylene copolymer.

Examples of the crosslinking aid include allyl compounds, sulfur compounds, organic amines, and methacrylates. Among these, allyl compounds such as triallyl anurate and triallylisonoanurate are preferred. The blending amount of this crosslinking aid is preferably 3 to 20 parts by weight per 100 parts by weight of the fluororubber.

Various compounding agents include calcium oxide, magnesium oxide, calcium hydroxide, magnesium hydroxide, aluminum hydroxide, calcium carbonate, aluminum carbonate, zinc oxide, magnesium silicate, aluminum silicate, silicic anhydride, talc, and fired resin. Examples include inorganic fillers such as, pigments, stabilizers, anti-aging agents, etc.

The crosslinked fluororubber composition (hereinafter referred to as "outer layer composition") forming the outer layer of the insulating layer can be the same as the above-mentioned inner layer composition, but the degree of crosslinking of the outer layer composition may be , it is necessary that the degree of crosslinking be greater than that of the composition for the inner layer. The degree of crosslinking of these compositions is indicated by the gel fraction of the fluororubber contained in the composition in a tetrahydrofuran (THF) solution.

By adjusting the degree of crosslinking of the inner layer and outer layer compositions in this manner, the mechanical strength of the outer layer can be increased. Further, regarding the degree of crosslinking of these compositions, it is preferable that the gel fraction of both the inner layer composition and the outer layer composition is 80% or more. If the gel fraction is less than 80%, the mechanical strength and the strength of the electric wire itself are unfavorably reduced.

In addition to the above components, the outer layer composition also contains polyvinyl acetate, ethylene-vinyl acetate copolymer, low-density polyethylene, high-density polyethylene, ultra-low-density polyethylene, polyvinylidene fluoride, and ethylene-tetrafluoroethylene copolymer. It is possible to mix resins such as a combination of resins and fluororubbers other than the fluororubbers exemplified above. By blending these resins, etc., it is possible to prevent the insulator layer before crosslinking from deforming due to external physical stimulation.

The blending amount of these resins, etc. is preferably 50 parts by weight or less per 100 parts by weight of fluororubber. If the blending amount exceeds 50 parts by weight, it is undesirable because processability and aging properties are also reduced.Furthermore, the composition for the outer layer is not suitable for cold flow during uncrosslinking, which causes poor appearance and sparks. In order to reduce the adhesion (stickiness) between members and wires, silicone resin, a graft copolymer of silicone resin and polyolefin, etc. can also be blended. The blending amount of these resins is 20 parts by weight per 100 parts by weight of fluororubber.
Parts by weight or less are preferred. If the blending amount exceeds 20 parts by weight, the mechanical strength of the electric wire will decrease and the aging characteristics will also decrease, which is not preferable.

In the heat-resistant insulated wire of the present invention, it is necessary that the thickness of the outer layer is 50% or less of the thickness of the entire insulator layer. If this ratio exceeds 50%, the elongation and aging characteristics of the wire will decrease, and the manufacturing cost will also increase. The thickness of this outer layer is preferably 10-40% of the total insulator layer thickness.

(Example) Examples 1 to 10 and Comparative Examples 1 to 9 The inner layer composition and the outer layer composition shown in Table 1 were simultaneously coated by double extrusion around the conductor (extruder head temperature -1
60-220°C). Next, an electron beam of 10 Mrad was irradiated to cause electron beam crosslinking, thereby obtaining electric wires of each example and comparative example. Note that Comparative Examples 6 to 9 are examples of electric wires having only a negative insulator layer.

Regarding these electric wires, elongation, tensile strength, residual elongation rate and residual tensile strength after aging treatment at 250°C for 4 days, 15
Relative comparisons of cut-through properties (cutting resistance test), abrasion resistance, and manufacturing costs at 0°C were evaluated. The wear resistance was expressed as the number of times until the insulator became conductive when the head with a head angle of 90° was repeatedly slid under a load of 150 g. In addition, the manufacturing cost is indicated by △ for the standard, and hereinafter indicated by low price (◯) and high price (×). Furthermore, using each composition shown in Table 1, a thickness of 2
A sheet of 1.0 mm in diameter was prepared, irradiated with an electron beam of 10 Mrad, and then the gel fraction in the THF solution was measured. The above results are shown in Tables 2 and 3.

(Effects of the Invention) The heat-resistant insulated wire of the present invention has two insulating layers, an inner layer and an outer layer, formed from a crosslinked product of a fluororubber composition,
and the degree of crosslinking of the composition for the outer layer is set to be greater than the degree of crosslinking of the composition for the inner layer, and further, the thickness of the outer layer is 50% or less of the thickness of the total insulating layer. .

Since both the inner layer and the outer layer constituting the insulating layer are formed from fluororubber in this manner, the adhesion between the two layers is good, and peeling between the inner layer and the outer layer does not occur.

In addition, both the inner layer and the outer layer are formed from a crosslinked material, and in particular, the outer layer is formed from a crosslinked material with a higher degree of crosslinking than the inner layer, and the inner layer contributes to increased elongation and improved aging characteristics, and the outer layer contributes to an increase in mechanical properties, and the insulator layer as a whole has excellent mechanical properties. Furthermore, the mechanical properties do not deteriorate much even after aging under predetermined conditions.

Furthermore, colorants and additive resins for preventing deformation when uncrosslinked need only be added to the outer layer, and as a result, the amount of colorants and the like used can be reduced, and the aging properties can be improved. Furthermore, in place of the colorant, a cheaper filler or the like can be added in an amount greater than the amount of the colorant, thereby reducing the overall manufacturing cost.

The heat-resistant insulated wire of the present invention can be used not only as an electric wire, but also as a wire.
It is suitable for various fields such as heater cords, sensor cords, electronic devices such as microwave ovens, and automobiles.

Claims (1)

[Claims] A heat-resistant insulated wire having two insulator layers, an inner layer and an outer layer, formed from different constituent materials around a conductor, wherein the inner layer and the outer layer are formed from a crosslinked body of a fluororubber composition, and the outer layer is The degree of crosslinking of the composition forming the inner layer is set to be greater than the degree of crosslinking of the composition forming the inner layer, and the thickness of the outer layer is set to be 5 times the thickness of the total insulator layer.
A heat-resistant insulated wire characterized by having a heat resistance of 0% or less.