JP4544815B2 - Small coaxial cable - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a small-diameter coaxial cable having good electrical characteristics.
[0002]
[Background Art and Problems to be Solved by the Invention]
Recently, coaxial cables are being used for antenna wiring of personal digital assistants, wiring for connecting an LCD and a CPU, etc. in response to an increase in information amount and high-speed transmission. In addition, with the miniaturization and thinning of information terminals and notebook computers, coaxial cables are also required to have a small diameter.
[0003]
In general, in order to obtain a coaxial cable having good electrical characteristics, it is important to make the dielectric constant of the insulating coating layer formed on the outer periphery of the center conductor as small as possible.
[0004]
Therefore, a low dielectric constant resin such as a fluororesin or a polyolefin resin is often used for the insulating coating layer, and it is often foamed to lower the apparent dielectric constant.
[0005]
On the other hand, in order to reduce the diameter of the coaxial cable, it is effective to change the outer conductor formed on the outer periphery of the insulating coating layer from a braided metal wire to a metal plating layer.
[0006]
However, when a low dielectric constant resin such as a fluororesin or a polyolefin resin is used for the insulating coating layer, there is a problem that electroless plating becomes difficult.
[0007]
In addition, when the insulating coating layer is foamed in order to lower the apparent dielectric constant, the plating treatment liquid enters the voids in the foamed part to increase the apparent dielectric constant, or the plating treatment liquid that has entered the voids. However, there has been a problem that the outer conductor is corroded to hinder the electrical characteristics of the coaxial cable.
[0008]
Furthermore, foam extrusion technology is difficult to ensure extrusion stability, especially when extruding small-diameter products, the outer diameter of the insulating coating layer slightly changes, which is also one of the factors hindering electrical characteristics. It was. The present invention has been made in view of such conventional problems, and an object of the present invention is to obtain a thin coaxial cable having good and stable electrical characteristics .
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a central conductor, an insulating coating layer provided on the outer periphery of the central conductor, having a continuous void in the longitudinal direction, and provided on the outer periphery of the insulating coating layer. An outer conductor layer formed by plating, and the insulating coating layer includes an inner annular portion that covers an outer periphery of the central conductor, and a plurality of connecting portions that extend outward from the inner annular portion, An outer annular portion that joins the outer periphery of the connecting portion, and a thin coaxial cable that defines a circumferential direction of the gap portion at the connecting portion, wherein the insulating coating layer is The gap portion occupies 10% or more in area ratio, the insulating coating layer has different types of resin forming the inner annular portion and the connecting portion and the outer annular portion, and the inner annular portion and the connecting portion have a relative dielectric constant. The outer ring part is formed of a resin having a rate of 2.5 or less. It is formed of a synthetic resin having an electric power of 3 or less, and the resin forming the inner ring part and the connecting part is PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), FEP (tetrafluoroethylene-hexafluoropropylene copolymer). The outer annular portion forming resin is made of a syndiotc polystyrene resin. The resin is made of a fluororesin selected from coalescence) and PTFE (polytetrafluoroethylene).
[0010]
The insulating coating portion can be formed of a synthetic resin having a maximum continuous use temperature of 200 ° C. or higher.
[0012]
The thin coaxial cable of the present invention can have an outermost diameter of 1 mm or less.
In the thin coaxial cable of the present invention, a protective coating layer can be formed on the outer periphery of the outer conductor layer.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 shows an embodiment of a thin coaxial cable according to the present invention. The small-diameter coaxial cable 10 shown in the figure includes a center conductor 12, an insulating coating layer 14, an outer conductor layer 16, and a protective coating layer 18.
[0014]
For the central conductor 12, a thin wire of copper or copper alloy having excellent strength and conductivity, or a single wire or a stranded wire plated with a highly conductive metal is used. In order to obtain a coaxial cable having a smaller diameter. It is desirable to use a single wire.
[0015]
The insulating coating layer 14 is formed of a thermoplastic resin, and an inner annular portion 14a that covers the outer periphery of the center conductor 12, and four couplings that extend radially outward from the outer periphery of the inner annular portion 14a. The part 14b and the outer annular part 14c which connects between the outer ends of each connection part 14b are provided.
[0016]
In the case of the present embodiment, the four connecting portions 14b are arranged at equal angular intervals along the circumferential direction, so that the four gap portions 20 continuous in the longitudinal direction are centered on the central conductor 12. These are equally arranged in the circumferential direction, and the gap portion 20 is partitioned into small spaces by the connecting portion 14b.
[0017]
Note that the number of the gap portions 20 is not limited to four, and may be two or more, and the outer end portion thereof does not reach the outer peripheral edge of the insulating coating layer 14, that is, the outer edge of the outer annular portion 14c. To form.
[0018]
Further, the area ratio of the gap 20 to the insulating coating layer 14 is 10% or more in the cross section of the insulating coating layer 14 .
[0019]
In order to form the plurality of gaps 20 in the insulating coating layer 14, a die having a center hole for insertion of the center conductor 12 and a plurality of divided holes installed adjacent to the outer periphery of the center hole is used. The resin can be formed by extruding the molten resin from the center hole and the divided hole while the center conductor 12 is inserted therethrough.
[0020]
As a similar technique in the case of obtaining an extruded product having the void portion 20 as in the present embodiment, for example, there is a deformed hollow fiber, and a similar technique can be obtained by processing a die (nozzle) for such a hollow fiber. If a die having a structure is manufactured, it can be used for manufacturing the thin coaxial cable of this embodiment.
[0021]
In addition, as a method for forming the gap portion 20, a die having a center hole for insertion of the center conductor 12 and a plurality of radially divided holes extending radially outward from the outer periphery of the center hole is used. An inner annular portion 14a that covers the outer periphery of the central conductor 12 by extruding a molten thermoplastic resin from the central hole and the divided holes while the central conductor 12 is inserted therein, and a plurality of outwardly extending from the inner annular portion 14a. After obtaining an intermediate molded body having a connecting portion 14b and similar to a die, the intermediate molded body is guided to the head portion of the melt extruder, and is connected to the outer peripheral edge of the connecting portion 14b by an annular covering die. It is also possible to form the void 20 in the insulating coating layer 14 by extrusion coating the annular portion 14c.
[0022]
The outer conductor layer 16 is formed on the outer periphery of the insulating coating layer 14. When the outer conductor layer 16 is formed by metal plating, plasma treatment, flame treatment, After chromic acid or sulfuric acid strong acid treatment or etching treatment with sulfuric acid, phosphoric acid, chromic acid (bichromic acid) aqueous solution, etc., sensitizing with acidic solution of stannous chloride and further using palladium chloride After activation with hydrochloric acid acidic solution, electroless plating is performed.
[0023]
In this case, the metal plating layer may have a two-layer structure of an electroless plating anchor metal layer and an electrically conductive metal layer (Japanese Patent Laid-Open No. 6-187847) provided on the outer periphery of the metal layer.
[0024]
The insulating protective coating layer 18 provided on the outermost periphery is not necessarily required, but in the case of the present embodiment, it is formed so as to cover the outer conductor layer 16, for example, extrusion coating of polyvinyl chloride resin (PVC) Alternatively, it is formed by a film formed by application of acrylic resin, polyimide resin or the like.
[0025]
Moreover, in this invention, the insulation coating layer 14 differs in the kind of resin which forms the inner annular part 14a and the connection part 14b, and the outer annular part 14c . Further, the inner annular portion 14a and the connecting portion 14b are formed of a resin having a relative dielectric constant of 2.5 or less, and the outer annular portion 14c is formed of a synthetic resin having a relative dielectric constant of 3 or less.
[0026]
Moreover, the insulation coating part 14 can be formed with the synthetic resin whose continuous use maximum temperature is 200 degreeC or more.
[0027]
The resin forming the inner ring portion 14a and the connecting portion 14b is made of PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), FEP (tetrafluoroethylene-hexafluoropropylene copolymer), PTFE (polytetrafluoroethylene). It can be composed of a selected fluororesin.
[0028]
In addition, the thin coaxial cable 10 shown in FIG. 1 can be sufficiently thinned if the outermost diameter is 1 mm or less.
[0029]
Hereinafter, more specific examples of the present invention will be described, but the present invention is not limited to the following examples.
Example 1
The center conductor (silver-plated copper wire with an outer diameter of 0.1 mm) 12 is heated by a heating device using an electric burner so that the surface temperature becomes 100 ° C., and then led to a crosshead die, as shown in FIG. The die (nozzle) 50 was inserted.
[0030]
The die 50 shown in the figure has a center hole 50a for insertion of the center conductor 12, and four radial holes 50b extending radially outward from the outer periphery of the center hole 50a.
[0031]
The inner diameter of the center hole 50 a is larger than the outer diameter of the center conductor 12. Further, the four radial holes 50b have substantially the same shape, and are arranged at equal intervals in the circumferential direction around the center hole 50a.
[0032]
FEP (Daikin Industries) with a relative dielectric constant of 2.1 at an extrusion temperature of 350 ° C. using a die 50 having such a shape, with the center conductor 12 being inserted into the center hole 50a and being taken at a speed of 30 m / min. Co., Ltd .: trade name NP-100) is extrusion coated from the center hole 50a and the radial hole 50b, and as shown in FIG. 3, an inner annular portion 14a covering the outer periphery of the center conductor 12, and the inner ring An intermediate molded body 36 a having four connecting portions 14 b extending outward from the portion 14 a and having a substantially cross shape similar to the die 50 was obtained.
[0033]
The intermediate molded body 36a had a maximum cross section height and maximum width of 0.24 mm, respectively. Next, the obtained intermediate molded body 36a was introduced into a round pipe-covering die, and a syndiotactic polystyrene having a relative dielectric constant of 2.9 at an extrusion temperature of 300 ° C. (made by Idemitsu Petrochemical Co., Ltd .: trade name Zarek) SP130) was formed in an annular shape to form an outer annular portion 14c that connects between the outer ends of the coupling portion 14b, thereby obtaining a coated conductor 54 having a cross-sectional shape shown in FIG.
[0034]
The coated conductor 54 had an outer diameter of φ0.34 mm. Next, the resulting coated conductor 54 is etched with a mixed aqueous solution of sulfuric acid, phosphoric acid, and chromic acid, sensitized with an acidic solution of stannous chloride, and activated with an acidic solution of palladium chloride. After electroless copper plating and electrolytic copper plating are performed to form an outer conductor layer 16 having a thickness of 0.01 mm, an FEP coating having a thickness of 0.1 mm is applied as a protective coating layer 18, and a thin coaxial with an outer diameter of 0.55 mm is provided. A cable 10 was obtained.
[0035]
At this time, the outer conductor layer 16 formed by plating was sufficiently adhered to the insulating coating layer 14 and was not peeled off even when passing through the guides in the process of applying the protective coating layer 18. .
[0036]
The obtained small-diameter coaxial cable 10 has a cross-sectional shape as shown in FIG. 4, the ratio of the gap 20 in the insulating coating layer 14 is 20%, and the apparent relative dielectric constant is 2.27. The characteristic impedance was 50Ω. Further, as in Example 1, moisture and the like did not enter the gap 20 during the plating process, and the relative dielectric constant did not increase.
[0037]
When the obtained thin coaxial cable 10 is connected to a connector using solder, the insulation coating portion 14 is not melted and the connector can be connected while maintaining good characteristics. .
[0038]
【The invention's effect】
As described above in detail in the embodiments, according to the present invention, since a plurality of independent voids are continuously formed in the longitudinal direction in the insulating coating layer on the outer periphery of the central conductor, the outer conductor is plated. The liquid does not enter the voids by the pretreatment for forming the layer, and the dielectric performance is not deteriorated.
[0039]
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an embodiment of a thin coaxial cable according to the present invention.
FIG. 2 is an explanatory view of a die used in the method for producing a thin coaxial cable according to the present invention.
FIG. 3 is a cross-sectional view of an intermediate molded body manufactured by the die shown in FIG.
4 is a cross-sectional view of a coated conductor in which an outer annular portion is formed on the intermediate molded body shown in FIG.
5 is a cross-sectional view of a coaxial cable in which an outer conductor layer and a protective coating layer are provided on the coated conductor of FIG.
[Brief description of symbols]
DESCRIPTION OF SYMBOLS 10 Small diameter coaxial cable 12 Center conductor 14 Insulation coating layer 16 Outer conductor layer 18 Protective coating layer 20 Cavity 22, 32, 50 Dies

Claims (2)

A central conductor; an insulating coating layer provided on an outer periphery of the central conductor and having a continuous gap in a longitudinal direction; and an outer conductor layer provided on an outer periphery of the insulating coating layer and formed by metal plating. ,
The insulating coating layer includes an inner annular portion that covers the outer periphery of the center conductor, a plurality of connecting portions that extend outward from the inner annular portion, and an outer annular portion that joins the outer peripheral edges of the connecting portions; A small-diameter coaxial cable that defines a circumferential direction of the gap portion at the connecting portion,
The insulating coating layer, in its transverse cross section, the voids occupy 10% or more by area ratio,
The insulating coating layer is different in the type of resin forming the inner annular portion and the connecting portion and the outer annular portion,
The inner annular portion and the connecting portion are formed of a resin having a relative dielectric constant of 2.5 or less, and the outer annular portion is formed of a synthetic resin having a relative dielectric constant of 3 or less .
The resin forming the inner ring portion and the connecting portion is selected from PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), FEP (tetrafluoroethylene-hexafluoropropylene copolymer), and PTFE (polytetrafluoroethylene). Made of fluororesin
The thin coaxial cable is characterized in that the forming resin of the outer annular portion is made of syndiot polystyrene resin . The small-diameter coaxial cable according to claim 1, wherein the insulating coating layer is formed of a synthetic resin having a maximum continuous use temperature of 200 ° C or higher.

Images