JPH05258615A - Insulated electric cable and its manufacture - Google Patents

Abstract

PURPOSE:To provide a fluororesin-type insulated electric cable with good electric properties and mechanical properties and lightweight and provide its manufacturing method. CONSTITUTION:After the outer circumference of a conductor 2 is coated with a thin film of a thermally fusible fluororesin such as tetrafluoroethylene- perfluoroalkyl vinyl ether copolymer resin as a peeling layer 3, a coating is formed further on the outer circumference by paste-extrusion of a mixture of fine hollow spherical bodies made of glass and unsintered tetrafluororesin fine powder. Then, the coating layer is sintered to give an insulator layer 4 and at the same time to be fused with the peeling layer 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluororesin-based insulated wire which is excellent in electrical characteristics and mechanical characteristics and can be reduced in weight, and a method for manufacturing the same.

[0002]

Fluorine resins such as tetrafluoroethylene resin (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer resin (FEP) and tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin (PFA) have electrical characteristics. Since it is superior to other polymer materials in terms of heat resistance and cold resistance and is chemically stable, it has been widely used as an insulator material for electric wires. Insulated wires using such fluororesin,
Even with a thin insulator, it has the same or better performance as a normal insulated wire, so it is possible to make the wire smaller and thinner without sacrificing reliability, which is extremely useful in reducing the capacity and weight of the equipment. .. For this reason, the fluororesin insulated wire has been prized as internal wiring for aircraft and electronic devices that require high reliability and high density.

By the way, the progress of these devices in recent years has been remarkable, and the conventional fluororesin-insulated electric wire coated with the resin as it is may not be able to deal with it particularly in terms of electrical characteristics, and foaming is an effective solution. Alternatively, the use of a fluororesin insulator which has been made porous by stretching has been investigated (Japanese Patent Laid-Open No. 3-97746).
No. 59-149608).

[0004]

However, any of the fluororesin-insulated electric wires in which the insulator layer is made porous by the above method has the following drawbacks.

That is, the porous tetrafluoroethylene resin sheet obtained by the stretching method described in Japanese Patent Publication No. 42-13560 is formed into a fibrous fine continuous porous structure. , Inherently weak against compressive forces,
The compressed portion has a property that the internal pores are crushed and easily change to a non-porous structure. Therefore, even if a sheet with a high porosity is used, when it is wound around a conductor to form an insulator, some of the pores are crushed due to the tension applied during manufacturing, and the desired characteristics cannot be obtained. It was difficult. The tendency is more remarkable as the sheet having higher porosity is used. Further, such collapse of the pores increases the specific gravity of the insulating layer, which has been an obstacle to reducing the weight of the insulated wire. Further, the porous tetrafluoroethylene resin formed into a tape or sheet by stretching is contracted when heated, and the porosity is likely to decrease, so that heat fusion is difficult. Therefore, when it is used as an insulator for electric wires, it is merely wrapped around the outer circumference of the conductor and is not integrated as an insulator layer. There are some problems to be solved in the insulated wire using the continuous porous tetrafluoroethylene resin sheet, such as instability.

In addition, the foaming of the insulating layer by foaming is
A resin that is melted by blowing a volatile organic liquid such as nitrogen gas or hydrocarbon as a foaming agent in a gaseous or liquid form into a molten fluororesin containing a foam nucleating agent at a high pressure from the middle part of the extruder cylinder. Utilizes that the foaming agent contained in the resin expands on the basis of the foam nucleating agent as it exits the extruder. According to this method, it is possible to obtain a foamed insulator with independent porosity in which the pores are not communicated, but the object is a heat-meltable fluororesin that plasticizes and shows fluidity when heated above the melting point. It is limited and cannot be applied to a tetrafluoroethylene resin having an extremely high melt viscosity that hardly flows even above the melting point. However, even when a heat-meltable fluororesin is used, the viscosity of the resin in the molten state is generally higher than that of other foaming resins, and the processing temperature and processing pressure become high, so it is possible to control the foaming rate. However, since the bubble diameters of the obtained foams are all 100 μm or more and the variation is large, there is a drawback that an insulated wire having uniform and stable electrical characteristics over the entire length in the longitudinal direction cannot be obtained. Further, even with such an independent pore foamed insulator, when it receives a compressive force, it is not as much as an insulator with a continuous pore structure, but since the pores are collapsed and the electrical characteristics are changed, Improvement of mechanical strength against compression has also been desired.

Therefore, in view of these problems of the prior art, the present invention provides an insulated wire which is light in weight, has excellent electric characteristics, and hardly changes in electric characteristics due to an external force such as compression or bending, and a manufacturing method. To that end.

[0008]

In order to achieve the above object, in an insulated wire according to the present invention, a conductor, a thin film-like release layer made of a heat-meltable fluororesin coated on the outer periphery of the conductor, and the release The insulator layer is thicker than the layer and is made of a fired mixture of an inorganic micro hollow sphere and a tetrafluoroethylene resin, which is fused to the outer periphery of the layer.

Further, in such an insulated wire, a thin-film release layer made of a heat-meltable fluororesin is coated on the outer periphery of the conductor, and then the outer periphery of the release layer is covered with an inorganic micro hollow sphere and an unsintered tetrafluoroethylene resin. It is obtained by coating a mixture of powders by paste extrusion, and then calcining the coating layer to form an insulating layer and at the same time fusion-bonding it to the release layer.

In the present invention, the thin-film heat-meltable fluororesin layer provided as a peeling layer between the conductor and the insulator layer prevents excessive adhesion between the insulator layer and the conductor, so that a wiring or the like can be prevented. It is intended to surely and easily cut off the insulating layer at the end of the insulated wire (hereinafter referred to as a strip) at the time of work, and realizes it by fusion-bonding to the outer insulating layer. ing. Although the peeling layer also acts as an insulator of the insulated wire due to its material, since the dielectric constant is considerably higher than that of the insulator layer laminated on the outer side, in the present invention, the electrical characteristics of the insulated wire are It is desirable that the coating thickness be as thin as possible from the viewpoint of. Therefore, in forming a thin film-like release layer, dispersion or solution state coating is preferable to extrusion coating. The coating thickness varies depending on the size of the insulated wire, but is generally selected within the range of about 5 to 20 μm. From the viewpoint of adhesive strength to the tetrafluoroethylene resin that is the base material of the insulating layer, it is desirable that the heat-fusible fluororesin used for such a purpose be close to the melting point of the tetrafluoroethylene resin. For example, F
There are EP, PFA, tetrafluoroethylene-hexafluoropropylene-perfluoroalkyl vinyl ether terpolymer resin (EPE) and the like. Since these heat-meltable fluororesins are not dissolved in a solvent, methods other than extrusion coating are limited to dispersion coating, for example, tetrafluoroethylene and perfluoro-2,2-dimethyl-1,3. A fluororesin containing a ring structure in the main chain, which is represented by a dioxole copolymer, has good electric properties and has a property of being dissolved in a fluorine-based solvent, so that coating with a solution is possible, and a release layer It is a convenient material when the coating thickness is reduced.

In addition, the tetrafluoroethylene resin and the inorganic micro hollow spheres forming the insulating layer have a particle diameter of 0.1 with a shell wall made of an inorganic material having good heat resistance such as glass or ceramics.
It is a hollow sphere of about 30 μm and has a low dielectric constant, a low dielectric loss tangent, and a low specific gravity by holding air, nitrogen, argon or the like inside the thin shell wall. In the present invention, in order to ensure the smoothness of the surface of the insulating layer and prevent damage to the micro hollow spheres during paste extrusion, the smaller the size of the micro hollow spheres used, the better. Things are used. Specific examples of the inorganic micro hollow spheres include alumina, silica, zirconia,
Some are made of glass, shirasu, etc., but hollow spheres made of silica are preferable from the viewpoint of electrical characteristics and the like. The micro hollow sphere does not necessarily have to be a completely closed sphere, and a foamed sphere having a large number of fine pores can be used, and this sphere is also included in the micro hollow sphere in the present invention. Be done. The mixing ratio of these micro hollow spheres and the tetrafluoroethylene resin is not particularly limited, but if a large amount is added, the number of micro hollow spheres destroyed during paste extrusion will be large, so the amount of electricity will be relative to the blending amount. It is not economical because the characteristics are not improved. Also, if the amount is too small, the compounding effect is small.
It is desirable to mix in the range of ˜50 wt%, preferably 5 to 20 wt%. The surface of the hollow microspheres may be surface-treated with a treating agent such as a silane coupling agent for the purpose of enhancing the affinity for the tetrafluoroethylene resin and improving the mechanical strength of the insulating layer.

[0012]

In the insulated wire according to the present invention, the peeling layer also acts as an insulator, but since the coating thickness is extremely thin as compared with the insulator layer, the outer insulator layer is substantially the electrical characteristics of the insulated wire. Dominates. This insulator layer has a porous structure with independent porosity as an internal structure, in which tetrafluoroethylene resin particles melted by firing bind and integrate a myriad of minute hollow spheres. The tetrafluoroethylene resin, which serves as a binder for the micro hollow spheres, has the lowest dielectric constant among the insulating materials, and since it is made porous by the presence of the micro hollow spheres, The permittivity drops significantly.

Further, the fine hollow spheres dispersed in the insulating layer are made of an inorganic material having a high hardness such as glass and ceramics, and have a great resistance to a compressive force. When an external force such as compression is applied, the porous structure of the insulator layer does not change significantly. Therefore, the stability of the electric characteristics of the insulated wire is significantly improved, and the weight of the insulated wire is also reduced. Moreover, by using fine hollow spheres having a uniform particle size, it is possible to obtain an insulated wire having no variation in electrical characteristics in the longitudinal direction.

Further, the tetrafluoroethylene resin is excellent in non-adhesiveness and does not adhere to the conductor so strongly as long as it is used as the insulating layer without being made porous, but the inorganic micro hollow sphere is used. In the admixed mixture, the non-adhesive action of the tetrafluoroethylene resin is greatly reduced, and when the conductor is directly coated, the adhesion is too strong and the strip property is extremely poor. When a stranded wire is used as a conductor, this is remarkable because the insulating layer cuts between the wires. Therefore, in the present invention, in order to improve the stripping property without deteriorating the electrical characteristics of the insulating layer, a heat-meltable fluororesin which can be fused to the tetrafluoroethylene resin and which is appropriately adhered to the conductor is used. It is used as a release layer. In this case, the peeling layer made of the heat-meltable fluororesin is fused to the insulator layer by the heat when firing the insulator layer, but the adhesion between the peeling layer and the insulator layer is different from that of the conductor of the peeling layer. Since the peel strength is larger than the adhesive strength, the peeling layer and the insulator layer are not separated when the end portion of the insulated wire is stripped, and the peeling layer is broken and removed together with the insulator layer. Therefore, the peeling layer and the insulating layer can be simultaneously removed by a single operation.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view showing an embodiment of an insulated wire according to the present invention. In the illustrated insulated wire 1, an outer periphery of a conductor 2 is covered with a peeling layer 3 made of a thin film heat-meltable fluororesin, The outer periphery thereof is covered with an insulator layer 4 made of a fired mixture of inorganic micro hollow spheres such as glass microballoons and a tetrafluoroethylene resin in a thickness thicker than that of the peeling layer 3. The insulating layer 4 and the insulating layer 4 are fused together.

Next, a method of manufacturing the insulated wire will be described with reference to FIG. Conductor 2 sent from conductor supply device 20
The die 21 is coated with a dispersion of a heat-meltable fluororesin thinly on the outer periphery thereof, and the dispersion layer is melted in a heating furnace 22 to form a thin-film release layer 3. The conductor 2 coated with the release layer 3 is paste-extruded in the paste extruding device 23 with a mixture of inorganic micro hollow spheres and unsintered tetrafluoroethylene resin powder on the outer periphery thereof under the addition of a liquid lubricant. After removing the liquid lubricant, it is fired in the heating furnace 24 heated to about 400 ° C. By this firing, the inorganic micro hollow spheres and the tetrafluoroethylene resin are bound and integrated to form a porous insulator layer 4 having independent porosity. At that time, the inner release layer 3 is formed.
Melts and fuses with the insulator layer 4. The insulated electric wire 1 in which the peeling layer 3 and the insulating layer 4 are thus integrally covered is sent to the winding device 25.

A specific example of the insulated wire manufactured by the above method is as follows. A conductor 2 having a diameter of 0.950 mm was obtained by twisting 19 silver-plated annealed copper wires having a diameter of 0.203 mm, and the outer periphery of the conductor 2 was coated with PFA dispersion to form a release layer 3 having a thickness of 0.006 mm. Next, a silane coupling agent (L manufactured by Shin-Etsu Chemical Co., Ltd.
SX-6815) surface-treated glass micro hollow spheres (Asahi Glass Co. Cellstar Z-45 average particle size 52μ
m) To a mixture of 16 parts by weight and 84 parts by weight of unburned tetrafluoroethylene resin fine powder (F-201 manufactured by Daikin Industries, Ltd.) was added solvent naphtha as a liquid lubricant and allowed to stand for a predetermined time. Was extruded and coated on the outer periphery of the release layer 3 using a paste extrusion device. Then, the liquid lubricant contained in the unsintered coating layer is dried and removed in a heating furnace, and further sintered to form an insulator layer 4 having a thickness of 0.4 mm, and an outer diameter of 1.76 mm according to the present invention. Insulated wire 1
Got

As electric characteristics of the insulated wire, a copper pipe was attached to the outside of the insulator layer 4 and a propagation delay time was measured in the state of a semi-rigid coaxial cable.
Since this is s / m, the effective relative permittivity of the insulating layer including the peeling layer can be estimated to be 1.69, and the insulating layer had practically sufficient characteristics. Also, this insulated wire may be bent at a diameter twice the outer diameter, or the insulated layer may be
Even when a load of 0 kg / square meter was applied for 10 minutes, almost no change was observed in the electrical characteristics, and the stability was extremely high.

In the strip property evaluation, a commercially available stripper can be used without any problem, and the weight of the insulated wire according to the present invention is 7.6 per 1 m.
In contrast to the gram, it is confirmed that the insulated wire using the conventional continuous-pore porous tetrafluoroethylene resin tape having the same electrical characteristics has 10 grams per 1 m, which is considerably lightweight. It was

FIG. 3 shows another embodiment of the insulated wire according to the present invention, which is applied to a twisted pair cable. In this case, the insulated electric wire 10 is obtained by further coating the outer periphery of the insulated electric wire 1 of the above-mentioned embodiment with a dispersion of FEP and baking it to coat the outer cover 11 with a thickness of 0.02 mm.
2 are twisted together, and the outer cover 11 is fused. As the electrical characteristics of this twisted pair cable, the propagation delay time was 3.97 ns / m 2, which was practically useful. Furthermore, the insulating layer 4 when the two insulated electric wires 10 are twisted and fused
The crushing or deformation of the wire is, when the cross sections are observed and compared, an insulated wire using a porous tetrafluoroethylene resin tape of the conventional porosity, which is a conventional example, or an insulation layer in which the insulation layer is made porous by foaming. The shape stability of the insulator layer was significantly improved, compared with the number of wires. Even when the outer cover 11 is coated in this manner, there is no problem in stripping property.

In the above embodiment, an example in which a stranded wire is used as a conductor has been described. However, within the technical concept of the present invention, such as changing to a single wire or changing the material and coating thickness of the release layer. Of course, it is possible to make changes.

[0022]

As described above, according to the present invention, it is possible to easily obtain an insulated electric wire which is excellent in electrical and mechanical characteristics, has a good strip property, and can be reduced in weight, and is industrially used. The value is extremely high.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of an insulated wire according to the present invention.

FIG. 2 is a schematic explanatory view showing an example of a method of manufacturing an insulated wire according to the present invention.

FIG. 3 is a sectional view showing another embodiment of the insulated wire according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulated electric wire 2 Conductor 3 Release layer 4 Insulator layer 10 Insulated electric wire 11 Outer coating 23 Paste extruding device 24 Heating furnace

Claims (2)

[Claims] 1. A conductor, a thin-film release layer made of a heat-meltable fluororesin covering the outer periphery of the conductor, and an inorganic micro hollow sphere having a thickness larger than that of the release layer and fused to the outer periphery thereof. And an insulated wire comprising an insulator layer made of a fired mixture of tetrafluoroethylene resin. 2. A conductor is coated with a thin-film release layer made of a heat-meltable fluororesin, and then the release layer is provided with a mixture of inorganic hollow microspheres and unfired tetrafluoroethylene resin powder. A method for producing an insulated wire, which comprises coating by paste extrusion, and then calcining the coating layer to form an insulating layer and at the same time fusion-bonding to a peeling layer.