JP2008226618A - Covered wire by porous ptfe resin insulating layer, and coaxial cable using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a covered wire by a porous polytetrafluoroethylene (hereinafter referred to as "PTFE") insulating layer of which PTFE insulating layer is made porous, which has a pulling force between the center conductor and an insulating layer even if the dielectric loss is reduced, and which has an excellent attenuation even in a high frequency region, and provide a coaxial cable using the covered wire by the porous PTFE insulating layer, and its manufacturing method. <P>SOLUTION: In the paste extrusion molding using a tubing extrusion method in which the PTFE resin-made insulating layer 12 is formed at the outer periphery of the center conductor 11 by covering when the PTFE resin is extruded to cover the center conductor 11, after the PTFE resin is covered, in a state of being not tightly adhered to the insulating layer 12, on the center conductor 11, and stretched and made porous in a continuous furnace such that a gap q exists between the insulating layer 12 and the center conductor 11 in an unbaked state the insulating layer is shrinked in baking, to manufacture a porous fluororesin insulating electric wire 10 which is imparted with the pulling force between the center conductor and the insulating layer. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a porous PTFE resin insulating layer coated electric wire excellent in attenuation characteristics in a high frequency region and a coaxial cable using the same. In the present invention, polytetrafluoroethylene is abbreviated as PTFE.

  Coaxial cables are used for high-frequency signal transmission in base station equipment or broadcasting equipment of communication equipment such as mobile phones and the base station equipment. In high-frequency transmission, the dielectric loss increases as the frequency increases for the same insulating material. Therefore, it is preferable to select and use an insulating material having a small relative dielectric constant and dielectric loss tangent to reduce the dielectric loss. . Therefore, a semi-rigid coaxial cable is conventionally used in which PTFE, which is a fluororesin having a low dielectric loss, is used as an insulating material, and the outer periphery thereof is covered with a copper tube. However, since the insulating layer of the semi-rigid coaxial cable is PTFE-rich, its attenuation characteristic has not been sufficient due to the high frequency up to the gigahertz region in recent signal transmission services.

  In response to market demand for improvement in dielectric properties in the gigahertz range, as a method of realizing a porous insulator, a fully fired PTFE sheet is made porous by punching or pre-porous by stretching. A method of producing a porous PTFE insulated wire in which an insulating layer is formed by horizontally winding and laminating a fired or unfired PTFE sheet on a central conductor has been adopted. However, the process of winding and laminating the PTFE sheet around the outer periphery of the center conductor tends to increase the processing cost because it is complicated and requires a large number of mechanical devices. The work becomes more difficult.

Therefore, as a method of obtaining a porous PTFE insulating layer without winding a sheet, there is a method of extruding PTFE on the outer periphery of the center conductor by a pressure extrusion method, stretching, and heating and firing. There is a problem that does not adhere. As a technique for improving this, in Patent Documents 1 and 2 below, using a two-layered preform having an inner layer of PTFE containing a substance that functions as a pore-forming agent and an outer layer of only normal PTFE, There has been a proposal that a porous structure and adhesion to the central conductor can be obtained at the same time by extrusion molding by pressure extrusion and heating and firing.
Japanese Patent Publication No. 6-18087 JP 2001-67944 A

  However, the inclusion of a substance that functions as a pore-forming agent is a factor that adversely affects the dielectric properties of the insulating layer obtained as a result, and is a result that conflicts with the use of PTFE to improve the dielectric properties. There is a drawback that the goodness of expensive PTFE cannot be exhibited.

  The pressure extrusion method can achieve molding conditions that achieve both the adhesion between the center conductor and the insulating layer and the porous PTFE resin, but the unfired PTFE porous body is like a sponge. Because it is easy to deform, when the PTFE porous body is turned by passing through a pulley or the like before firing, the outer periphery of the insulator cannot be deformed to maintain a perfect circle, and the deformed shape is fired and solidified. There is a problem. In addition, when coated by the pressure extrusion method, the PTFE resin is extruded in a state of being in close contact with the center conductor, so that the PTFE resin is extruded from the tip of the die and simultaneously stretched to become porous. The stretching at room temperature has a problem that it becomes a porous state with non-uniform porosity in the longitudinal direction. Both problems cause unevenness in the relative dielectric constant of the PTFE resin insulating layer, which causes deterioration of attenuation characteristics.

  The present invention can easily obtain a uniform high porosity and a high adhesion force with the central conductor at the same time without including a pore-forming agent that causes adverse effects on dielectric properties, and has excellent attenuation characteristics. Another object of the present invention is to provide a porous PTFE resin insulating layer-coated electric wire and a coaxial cable using the same.

  The porous PTFE resin insulation layer-covered electric wire of the present invention is a paste extrusion molding using a tubing extrusion method in which a PTFE resin insulation layer is formed on the outer periphery of a central conductor. After forming the gap so as to leave a gap between the conductor and drying and removing the extrusion aid contained in the PTFE resin for paste extrusion molding, the insulating layer is made porous by stretching, and this porous insulation is formed. The layer is fired into a semi-fired state or a completely fired state, and the insulating layer is contracted in the radial direction so that the insulating layer is brought into close contact with the central conductor, and a central conductor pulling force is applied to the insulating layer. It is. That is, the porous PTFE resin insulation layer-coated electric wire of the present invention is coated with PTFE resin in a state in which the PTFE resin is not adhered to the center conductor when the PTFE resin is extrusion coated on the center conductor, and the PTFE resin is stretched in a continuous furnace to be porous. Since the PTFE resin is shrunk in the radial direction during firing and the PTFE resin and the center conductor are brought into close contact with each other to provide a pulling force between the center conductor and the insulating layer. A coaxial cable using the same can be obtained.

  In the present invention, when the PTFE resin is extrusion-coated, the PTFE resin is extruded not by the pressure extrusion method but by the tube extrusion method in order to cover the PTFE resin without being in close contact with the center conductor.

  In order to achieve close contact during firing, the gap between the outer diameter of the central conductor and the inner diameter of the PTFE resin layer is preferably as narrow as possible within a range in which non-uniformity is not caused in the porous formation by contact with the central conductor. The extruded PTFE resin is regulated by a mandrel whose inner diameter is a mold. On the other hand, the outer diameter side is regulated by a die which is a mold. The inner peripheral surface of the die is tapered toward the tip for gradually narrowing the outer diameter of the PTFE resin molding, and the same shape to stabilize the flow state of the PTFE resin, continuing to the taper. And a land portion having a straight cylindrical section. Further, the mandrel has a central conductor passing through the central hole, and the outer peripheral surface has a tapered portion tapered toward the tip, and a tip portion having a straight cylindrical shape that is continuous with the tapered portion. Yes. Since the PTFE resin extrusion molding method of the present invention is a tubing extrusion method in which the mandrel tip is located at the land portion of the die, the PTFE resin is extruded into a tube shape, and only the thickness of the mandrel tip is inserted into the tube. The center conductor is inherent with a gap of. The gap between the center conductor and the PTFE resin layer is determined by the thickness of the mandrel because the center conductor is supplied through the center hole of the mandrel. Therefore, it is desirable that the thickness of the mandrel is 0.18 mm or less considering that the PTFE resin layer is brought into close contact with the central conductor.

  The production of the porous PTFE resin insulation layer-coated electric wire of the present invention can be carried out by an apparatus used when extrusion coating a normal solid PTFE resin. What is important is that the tip portion of the mandrel is designed to enter the land portion which is a cavity extending from the minimum position of the taper portion of the die as described above. A PTFE resin powder containing an extrusion aid is preformed, the preform is inserted into an extrusion cylinder, and extruded between the tube-shaped insulating layer made of PTFE resin and the central conductor by a method of extruding in a heart-thick manner by an extrusion piston. Can be manufactured so that there is a gap. The porosification is performed by the take-up speed of the manufactured electric wire, that is, the take-up speed of the central conductor, and the porosity is controlled by the take-up speed. PTFE resin coated with a moderate gap on the central conductor cannot be stretched in the non-molten state and can be stretched in the molten state. Therefore, when the temperature reaches around the melting temperature, the PTFE resin The film is drawn while following the drawing speed of the central conductor while drawing, and is made porous by this drawing. After being stretched, the PTFE resin is heated and fired from a half-fired state to a fully-fired state, thereby shrinking in the radial direction and closely contacting the central conductor. If the wire take-up speed is increased, the draw ratio is increased, so that the porosity is increased. However, the adhesion strength decreases as the porosity increases. The pulling force of the central conductor from the porous PTFE insulating layer was used as an index of adhesion. In order to use it as an electric wire, it is desirable that the pulling force is 10 N / 100 mm or more, preferably 20 N / 100 mm or more. In the present invention, since the object is to provide a porous PTFE resin insulation layer-coated electric wire having excellent attenuation characteristics that can handle high frequencies up to the gigahertz range, the porosity is 30% or more, that is, the effective relative dielectric constant is A porous PTFE insulating layer having a porosity of 1.75 or less, preferably 45 to 75%, that is, an effective relative dielectric constant of 1.24 to 1.55 is desirable. Therefore, as conditions for achieving the object of the present invention, the effective relative dielectric constant of the porous PTFE insulating layer is 1.75 or less, and the pulling force is 10 N / 100 mm or more. More preferably, the effective relative dielectric constant is in the range of 1.24 to 1.55.

  According to the present invention, normally, a high-porosity is obtained without using a paste extruder for producing a solid PTFE insulated wire, mixing a foaming agent, a pore-forming agent, etc. with PTFE resin powder or forming a two-layer structure of an insulating layer. Provided are a porous PTFE resin insulating layer-coated electric wire and a coaxial cable using the same, which can simultaneously and easily obtain a high adhesive force with a central conductor.

  As shown in FIG. 1 (a), the porous PTFE resin insulation layer-covered electric wire 10 of the present invention is composed of a central conductor 11 and a porous PTFE insulation layer 12 coated on the outer periphery thereof. The center conductor 11 may be a conductor made of a highly conductive wire that is not corroded by fluorine gas, such as a silver-plated copper-clad steel wire or a silver-plated annealed copper wire, or a conductor made of a stranded wire using these highly conductive wires. It is not limited. The outer diameter and the insulating outer diameter of the center conductor 11 of the porous PTFE resin insulating layer-covered electric wire 10 are not particularly limited.

  The manufacturing method of the porous PTFE resin insulation layer-coated electric wire 10 can be carried out by an apparatus used when extrusion coating a normal solid PTFE resin. As the PTFE powder, PTFE fine powder obtained by an emulsion polymerization method is used. The PTFE fine powder is not particularly limited in terms of the degree of modification by copolymerization and the average particle size. 15 to 25 parts by weight of an extrusion aid is added to 100 parts by weight of PTFE fine powder, and the extrusion aid is sufficiently adsorbed on the PTFE fine powder, and then compressed to form a preform 12 '.

  The prepared preform 12 'is inserted into an extrusion cylinder and subjected to extrusion processing. In the case of the tubing extrusion method, the tip portion A of the paste extruder is opened as shown in FIG. 2, and the preform 12 'is gradually formed by a taper portion a' of the die a and a taper portion b 'of the mandrel b. The tube-like insulating layer 12 is extruded from the gap p between the die a and the mandrel b while undergoing compression deformation. In the drawing, a ″ of the die a indicates a land portion, and b ″ indicates a tip portion of the mandrel b. The extruded insulating layer 12 is indirectly covered with the central conductor 11 with a gap q corresponding to the thickness of the tip end b ″ of the mandrel b. At this time, although the center conductor 11 is taken up at the take-up speed of the manufactured electric wire, the extruded insulating layer 12 is dried in the drying furnace, and the insulating layer 12 is heated and stretched to near the melting temperature. Until it passes through the drying furnace at a speed slower than that of the central conductor 11. After the melted insulating layer 12 is stretched, it is heated and fired and cooled from a semi-fired state to a fully fired state, thereby shrinking in the radial direction and closely contacting the central conductor 11.

  The present invention also provides a coaxial cable by applying an outer conductor to the outer periphery of the porous fluororesin insulated electric wire 10 obtained by the above manufacturing method. A method for producing a coaxial cable includes a method of coating a copper pipe on the outer periphery of the porous fluororesin insulated wire 10, a method of coating a copper corrugated tube, a method of braiding silver-plated annealed copper wire, and a method of coating tin on the braided wire For example, a known coaxial cable manufacturing method can be employed.

  “Polyfluorocarbon PTFE fine powder F104” manufactured by Daikin Industries, Ltd. was used. To this, 20 parts by weight of “Isopar E” manufactured by Exxon Chemical Co., Ltd., which is a synthetic isoparaffinic hydrocarbon solvent, is added as an extrusion aid to 100 parts by weight of PTFE powder and left at 35 ° C. for 12 hours or more. Was sufficiently adsorbed. This PTFE powder mixture was compression molded in a preforming machine to produce a cylindrical preform having an outer diameter of 37.4 mm, an inner diameter of 16.2 mm, and a height of 600 mm. Using a paste extruder with a cylinder outer diameter of 38.1 mm, the preform was inserted into a mandrel with a wall thickness of 0.18 mm using a silver-plated soft single wire with a diameter of 1 mm as the central conductor, a ram speed of 10 mm / min, and a take-off speed of 3 Adjust between 6 to 4.6 m / min, and pass through a heating furnace with a drying section of about 4 m length and a baking section of about 2 m, thereby drying the extrusion aid and stretching around the PTFE resin melting temperature. Then, after the process of firing from half firing to complete firing by subsequent firing, four types of insulating outer diameters of 2.29 mm (Example 1), 2.35 mm (Example 2) having different porosities are obtained. Porous fluororesin insulated wires of 45 mm (Example 3) and 2.50 mm (Example 4) were produced.

  As comparative examples, three types of insulation outer diameters of 2.64 mm (Comparative Example 1), 2.77 mm (Comparative Example 2), and 2 types with different porosities are obtained by a pressure extrusion method, which is a conventional method for producing a solid PTFE insulator. A porous fluororesin insulated wire of .76 mm (Comparative Example 3) was produced.

  The porosity was measured for these porous fluororesin insulated wires. The specific gravity before the porous body was made porous was A, and the specific gravity after the porous body was made B was calculated by the following formula (A). Specific gravity was measured by an underwater substitution method (A method) defined in JIS-K-7112.

Formula (A): Porosity (%) = (A−B) / A × 100
The effective relative dielectric constant was measured by connecting a cavity resonator manufactured by Kanto Electronics Application Development Co., Ltd. to a network analyzer manufactured by Agilent Technology Co., Ltd. at a measurement temperature of 23 ° C. and a measurement frequency of 5.8 GHz.

  The center conductor pull-out force is obtained by attaching a test body having a PTFE resin insulation layer length of 100 mm to a test body attachment part of a tensile tester, a center conductor on one side, and a PTFE resin insulation layer on the other, and a tensile speed of 10 mm / min. The maximum load when the central conductor was removed from the PTFE resin insulation layer was measured, and the value was defined as the central conductor pulling force.

Comparative Examples 1 to 3 cannot maintain the pulling force of the central conductor when the porosity is 65% or more, and Comparative Examples 2 and 3 are fired while the insulating outer periphery is deformed into an elliptical shape by the turn of the pulley in the drying section. On the other hand, in Examples 1 to 4, the pulling force 13 N / 100 mmL was maintained even at a porosity of 70%, and the insulating outer periphery also maintained a perfect circle. The porous fluororesin insulated electric wire produced by the tubing extrusion method of the present invention can maintain the center conductor pulling force even when made porous at a high rate compared to the electric wire produced by the conventional pressure extrusion method, In addition, since it is stretched immediately before firing, the outer periphery of the insulation can be kept in a perfect circle, and therefore, the effective relative dielectric constant is low due to the high porosity, and the attenuation can be reduced.

A coaxial cable was obtained by covering the outer periphery of the porous fluororesin insulated electric wire of Example 3 with a 0.25 mm thick copper corrugated tube and then a 0.5 mm thick sheath layer made of FEP. The attenuation characteristic was measured using a network analyzer manufactured by Agilent Technologies, Inc. at a measurement temperature of 20 ° C. and a measurement frequency of 1 to 10 GHz. As shown in Table 2, very good attenuation characteristics were shown.

  The cross section of the porous PTFE resin insulating layer shown in Examples 1 to 4 is a state in which the entire insulating layer is clogged with porous PTFE resin as shown in FIG. As long as it has, the shape is not limited. For example, the porous PTFE resin insulation layer-covered electric wire 20 shown in FIG. 1B has a cross-sectional shape in which a tubular porous PTFE insulation layer 22 has three rib portions 22a. Thus, by having a continuous void in the longitudinal direction, the effective relative dielectric constant as the insulating layer 22 can be further improved.

It is sectional drawing of the porous fluororesin insulated wire of this invention, Comprising: (a) shows the case where a tubular part is circular in cross section, (b) shows the case where the tubular part is a cross-sectional variant which has three ribs. Schematic of the positional relationship between the die and mandrel during the tubing extrusion system of the present invention Schematic of the positional relationship between a die and a mandrel in a pressure extrusion method for extruding conventional PTFE resin with a wire.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Porous PTFE resin insulation layer covering electric wire 11 ... Center conductor 12 ... Porous PTFE insulation layer 12 '... Preliminary body A ... Tip part of paste extruder a ... Dies a '... Tapered part of the die a "· · Land part of the die b · · · Mandrel b' ... Tapered part of the mandrel b" · · Tip part of the mandrel p · ... With the die Mandrel gap q ··· Mandrel thickness gap 20 · · · Porous PTFE resin insulation layer coated wire 22 · · · porous PTFE insulation layer 22a · · rib

Claims (6)

  In paste extrusion molding using a tube extrusion method in which an insulating layer made of PTFE resin is formed on the outer periphery of the center conductor, in a non-fired state of PTFE resin, the gap is formed between the insulating layer and the center conductor. After drying and removing the extrusion aid contained in the PTFE resin for paste extrusion, the insulating layer is made porous by stretching, and the porous insulating layer is fired into a semi-fired state or a completely fired state. A porous PTFE resin insulating layer-coated electric wire characterized in that the insulating layer is contracted in a radial direction so that the insulating layer is brought into close contact with the central conductor and a central conductor pulling force is applied to the insulating layer.   2. The porous PTFE resin insulation layer-coated electric wire according to claim 1, wherein the thickness of a mandrel used for paste extrusion molding in a tubing extrusion method is 0.18 mm or less.   3. The porous PTFE according to claim 1, wherein an effective relative dielectric constant of the insulating layer is 1.75 or less, and a central conductor pulling force per 100 mm of the insulator length with respect to the insulating layer is at least 10 N or more. Resin insulation layer covered wire.   4. The porous PTFE resin insulating layer-coated electric wire according to claim 1, wherein the effective relative dielectric constant of the insulating layer is 1.24 to 1.55.   The porous PTFE resin insulation layer-coated electric wire according to any one of claims 1 to 4, wherein a continuous recess extending in the longitudinal direction is formed in the insulation layer.   A coaxial cable obtained by applying an outer conductor to the porous PTFE resin insulating layer-coated electric wire according to claim 1.

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