JP4111764B2 - Thin coaxial cable and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a thin coaxial cable having good electrical characteristics and high frequency characteristics and a method for manufacturing the same.
[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.
[0003]
In addition, due to the downsizing and thinning of information terminals and notebook computers, coaxial cables are also required to have a small diameter. In general, in order to obtain a coaxial cable with good high-frequency characteristics (low transmission loss and low delay time), the dielectric constant of the electrically insulating coating layer formed between the center conductor and the outer shield layer should be as small as possible. It is important to.
[0004]
Therefore, a low dielectric constant resin such as a fluorine resin or a polyolefin resin is often used for the insulating coating layer, and the insulating coating layer is often foamed to reduce 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 shield layer 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 fluorine resin or a polyolefin resin is used for the insulating coating layer, there is a problem that it is difficult to form a metal plating layer by electroless plating or the like.
[0007]
In addition, in order to perform the plating process, a support portion for the plating layer is required around the center conductor, and this support portion requires a portion that seamlessly surrounds the periphery of the center conductor in an annular shape or the like.
[0008]
Such a support portion requires a predetermined thickness, and when the support portion is formed, it becomes one of the factors that increase the outer diameter. On the other hand, when the insulating coating layer is foamed to reduce the apparent dielectric constant, the plating treatment liquid enters the voids in the foamed portion 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. As a matter of course, in the case of such a plating process, there are problems associated with the treatment of the surface treatment chemical, the plating chemical, and the waste liquid.
[0009]
In addition, foam extrusion technology is difficult to ensure extrusion stability, especially when extruding small-diameter products, because the outer diameter of the insulating coating layer fluctuates slightly. It was.
[0010]
Furthermore, when the closed cell foam layer is formed, since the bubbles are independent, the bubbles may expand under the influence of heat during soldering. On the other hand, open-cell foaming has a problem that the compressive strength is weak.
[0011]
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 high-frequency characteristics.
[0012]
Another object of the present invention is to provide a coaxial cable that can be sufficiently reduced in diameter even when a shield layer is formed by a metal conductor instead of plating, and a method for manufacturing the same.
[0013]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a small diameter including a center conductor, an electrically insulating coating layer covering the outer periphery of the center conductor, and an outer shield conductor layer provided on the outer periphery of the coating layer. In the coaxial cable, the covering layer has one or more columnar portions extending outward from the center, and the outer shield conductor layer is provided so as to be in contact with the outer periphery of the columnar portion, In addition, one or more voids continuous in the longitudinal direction were provided.
[0014]
According to the thin coaxial cable configured as described above, since one or more gaps continuous in the longitudinal direction are provided inside the outer shield conductor layer, the dielectric constant between the center conductor and the outer shield conductor layer is provided. Can be reduced.
[0015]
The columnar portion is composed of a plurality of portions extending radially at equal angular intervals in a transverse section, and can be extended along the longitudinal axis direction of the small-diameter coaxial cable while maintaining the interval.
[0016]
The columnar portion can be formed in a spiral shape along the longitudinal direction.
The gap may occupy 10% or more of the area of the portion excluding the central conductor and the outer shield conductor layer in the cross section.
[0017]
A plurality of the gaps may be arranged uniformly in the circumferential direction with the center conductor as the center.
[0018]
The outer shield conductor layer can be formed of a hollow compression stranded wire.
[0019]
The outer shield conductor layer is formed by winding a metal tape or metal foil excellent in electrical conductivity, such as copper, or a metal laminate film obtained by laminating these metal tape or metal foil with a plastic film around the outer periphery of the columnar portion. can do.
[0020]
The outer shield conductor layer is composed of a metal pipe having excellent electrical conductivity such as copper, and a semi-finished product in which a covering layer having the columnar portion is formed on the outer periphery of the center conductor is inserted into the metal pipe. However, the metal pipe can be drawn and stretched with a die.
[0021]
The coating layer can be formed by extruding a fluorine-based resin such as FEP or PFA, or a synthetic resin such as amorphous polyolefin resin or PEN (polyethylene naphthalate).
[0022]
The thin coaxial cable of the present invention can have an outermost diameter of 1 mm or less.
[0023]
An electrically insulating protective coating layer can be provided on the outer periphery of the outer shield conductor layer.
[0024]
Further, the present invention provides a method for producing a small-diameter coaxial cable by extruding a covering portion including an annular portion covering the center conductor and a columnar portion protruding outward from the annular portion on the outer periphery of the center conductor. Then, this is continuously supplied, and the outer periphery of the columnar part is wrapped with a hollow compression stranded wire coating, a metal foil, a laminate film, etc. A conductor layer was formed, and then an outer coating layer was formed on the outer periphery of the outer shield conductor layer as needed.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail based on examples.
1 and 2 show a first 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, a covering layer 14, and an outer shield conductor layer 16.
[0026]
The center conductor 12 is made of, for example, a copper wire having a circular cross section. The covering layer 14 is electrically insulating, and in the case of this embodiment, the covering layer 14 has an annular portion 18 that covers the outer periphery of the center conductor 12 and a columnar portion 20 that protrudes from the outer periphery of the annular portion 18. is doing.
[0027]
The covering layer 14 is formed by, for example, extruding a fluorine-based resin such as FEP or PFA, or a synthetic resin such as amorphous polyolefin resin or PEN (polyethylene naphthalate) on the outer periphery of the center conductor 12 to form an annular portion 18 and a columnar portion. 20 can be integrally formed.
[0028]
In the case of the present embodiment, the covering layer 12 has four columnar portions 20 extending outward from the center, and the cross-sectional shape thereof is substantially cross-shaped. Each columnar portion 20 extends radially at equal angular intervals (90 °) in the cross section, and extends linearly along the longitudinal axis direction of the thin coaxial cable 10 while maintaining this interval. ing.
[0029]
The outer shield conductor layer 16 is provided so as to be in contact with the outer periphery of the columnar portion 20 of the covering layer 14. The outer shield conductor layer 16 is partitioned by the columnar portion 20 inside the outer shield conductor layer 16, and Four voids 22 that are continuous in the direction are provided.
[0030]
In this case, four air gaps 22 are equally arranged in the circumferential direction with the center conductor 12 as the center, and in the cross section, the area is larger than the area of the portion excluding the center conductor 12 and the outer shield conductor layer 16. It is desirable that the ratio occupies 10% or more.
[0031]
In the case of the present embodiment, the outer shield conductor layer 16 is formed of a hollow compression stranded wire. Such a compression stranded wire is formed in a hollow shape by arranging a plurality of strands 24 on the same circumference and passing the compression dies while twisting each strand 24 in one direction. The shape is maintained without breaking. The outer diameter of the thin coaxial cable 10 of the present embodiment can be 1 mm or less.
[0032]
According to the small-diameter coaxial cable 10 configured as described above, four gap portions 22 that are continuous in the longitudinal direction are provided inside the outer shield conductor layer 16, so that the center conductor 12 and the outer shield conductor layer 16 are provided. The dielectric constant between can be reduced.
[0033]
FIG. 3 shows a second embodiment of the small-diameter coaxial cable according to the present invention. The same or corresponding parts as those in the above-mentioned embodiment are designated by the same reference numerals and the description thereof is omitted. Only the feature points will be described.
[0034]
The embodiment shown in the figure is a modification of the first embodiment, and an electrically insulating protective coating layer 26 is provided on the outer periphery of the outer shield conductor layer 16 constituted by the hollow stranded wire of the first embodiment. ing.
[0035]
As with the coating layer 14, the protective coating layer 26 is made of, for example, fluorine resin such as FEP or PFA, or synthetic resin such as amorphous polyolefin resin or PEN (polyethylene naphthalate) on the outer periphery of the outer shield conductor layer 16. It can be formed by extrusion.
[0036]
Even with the thin coaxial cable 10a configured as described above, the same effects as the first embodiment can be obtained.
[0037]
FIG. 4 shows a third embodiment of the small-diameter coaxial cable according to the present invention. The same or corresponding parts as those in the above-mentioned embodiment are designated by the same reference numerals and the description thereof is omitted. Only the feature points will be described.
[0038]
The embodiment shown in the figure includes the central conductor 12 and the covering layer 14 having the same configuration as the first embodiment, but is characterized by the outer shield conductor layer 16b.
[0039]
That is, in the case of the present embodiment, the outer shield conductor layer 16b is made of a metal tape or metal foil excellent in electrical conductivity such as copper, or a metal laminate film obtained by laminating these metal tape or metal foil with a plastic film. It is comprised, and the member selected from these is wound around the outer periphery of the columnar part 14b and formed.
[0040]
In this case, the tape or the like is wound so that there is no gap in the longitudinal axis direction of the cable 10b. The thin coaxial cable 10b configured as described above can obtain the same effects as those of the first embodiment.
[0041]
FIG. 5 shows a fourth embodiment of the small-diameter coaxial cable according to the present invention. The same or corresponding parts as those in the above embodiment are designated by the same reference numerals and the description thereof is omitted. Only the feature points will be described.
[0042]
The embodiment shown in the figure includes the central conductor 12 and the covering layer 14 having the same configuration as the first embodiment, but is characterized by the outer shield conductor layer 16c.
[0043]
That is, in the case of the present embodiment, the outer shield conductor layer 16c is made of a metal pipe having excellent electrical conductivity such as copper, and the covering layer 14 having the columnar portion 14b is formed on the outer periphery of the center conductor 12. The semi-finished product is formed by drawing and stretching the metal pipe with a die while being inserted into the metal pipe. Even with the thin coaxial cable 10c configured as described above, the same effects as those of the first embodiment can be obtained.
[0044]
In the case of the third and fourth embodiments shown in FIGS. 4 and 5, the protective coating layer 26 shown in the second embodiment can be formed on the outer periphery of each shield conductor layer 16b, 16c.
[0045]
FIG. 6 shows a fifth embodiment of a small-diameter coaxial cable according to the present invention. The same or corresponding parts as those in the above embodiment are designated by the same reference numerals and the description thereof is omitted. Only the feature points will be described.
[0046]
The embodiment shown in the figure is an external view of a semi-finished product in which a coating layer 14d is formed on the outer periphery of the central conductor 12, and the coating layer 14d has an annular portion 18d and a columnar portion 20d.
[0047]
The annular portion 18d covers the outer periphery of the center conductor 12 in a ring shape as in the first embodiment, but the columnar portion 20d is a substantially single structure extending outward from the center. Thus, the columnar portion 20d is formed so as to circulate spirally at a predetermined pitch on the outer periphery of the annular portion 18d. Such a columnar portion 20d can be formed by rotating a die in one direction while extruding a synthetic resin.
[0048]
In the case of this embodiment, when any one of the outer shield conductor layers 16, 16b, 16c shown in the above embodiment is formed on the outer periphery of the columnar portion 20d, a spiral gap portion 22d is formed therein. Since it is formed, the same effect as the above embodiment can be obtained.
[0049]
Next, the manufacturing method of the thin coaxial cable which concerns on this invention is demonstrated. The manufacturing method described below is a specific example of manufacturing the thin coaxial cable 10a having the cross-sectional shape shown in FIG. 3, and in this manufacturing method, a semi-finished product having the cross-sectional shape shown in FIG. 7 is first manufactured. The
[0050]
In this semi-finished product, a 0.1 mm center conductor 12 is led to a crosshead die, passed through a nozzle having the shape shown in FIG. NP-100: A product name, manufactured by Daikin Industries, Ltd., having a dielectric constant of 2.1) was coated to obtain a semi-finished product.
[0051]
In this case, cooling after coating was not particularly performed. The cross-sectional shape after coating is a cross shape shown in FIG. 7 in which an annular portion 18 and a rib (corresponding to the columnar portion 20) are provided on the outer periphery of the center conductor 12, the rib thickness is 0.06 mm, and the rib tip is The maximum width as the apex was 0.28 mm, and the ratio of the hollow portion in the virtual circle connecting the rib apexes was 50%.
[0052]
Next, 37 pieces of 0.03 mm silver-plated copper wire are placed on the virtual circumference connecting the vertices of the ribs to the obtained semi-finished product, and then taken up into a 0.34 mm diameter die at a take-up speed of 20 m / min. However, the compression molding of the copper wire used as the external shield conductor layer 16 (molding method for obtaining a compression stranded wire) was performed.
[0053]
As a result, a coaxial cable having a three-layer structure of the center conductor 12, the covering layer 14, and the outer shield conductor layer 16 having a diameter of the outer shield conductor layer 16 as shown in FIG.
[0054]
Next, the obtained cable is led to a crosshead die, and FEP resin (NP-100: trade name, manufactured by Daikin Industries) is used with a round die having a diameter of 3φ while taking it at a take-up speed of 11 m / min. The protective coating 26 was formed at 04 mm to obtain a thin coaxial cable 10a having a final outer diameter of 0.42 mm shown in FIG.
[0055]
As a result of measuring the characteristic impedance of the obtained thin coaxial cable 10a, it was found to be 50Ω, and the equivalent dielectric constant of the coating layer 14 was 1.55. The unit weight was 0.468 g / m.
In order to confirm the effect of the manufacturing method of the present embodiment, a coaxial cable was manufactured by the following procedure (comparative example).
[0056]
Comparative Example When a 0.1 mm silver-plated copper wire is used as the central conductor as in the above manufacturing method, the diameter after forming the coating layer is FEP resin (relative dielectric constant 2. In 1), it must be 0.33 mm.
[0057]
Therefore, in order to satisfy such specifications, a 0.1 mm center conductor is guided to the crosshead base, passed through a round die with a diameter of 3φ at a take-off speed of 11 m / min, and FEP at an extrusion temperature of 350 ° C. The extrusion insulating layer coating of resin (NP-100: trade name, manufactured by Daikin Industries, relative dielectric constant 2.1) was adjusted to 0.33 mm.
[0058]
Next, the obtained insulation coated conductor having an outer diameter of 0.33 mm was guided to a shield horizontal winding machine, and the outer conductor was coated with 38 0.03 mm silver-plated copper wires at a take-off speed of 20 m / min. A cable having a three-layer structure of a central conductor of 39 mm, a covering layer, and an outer shield conductor layer was obtained.
[0059]
Next, the cable obtained was guided to a crosshead die and pulled at a take-up speed of 11 m / min, and the FEP resin (NP-100: trade name, manufactured by Daikin Industries, relative dielectric constant 2) was used with a round die with a diameter of 3φ. .1) formed a protective coating with a resin thickness of 0.04 mm, resulting in a coaxial cable with a final outer diameter of 0.47 mm. The characteristic impedance of this coaxial cable was measured and found to be 50Ω. The equivalent dielectric constant of the insulating layer was 2.1.
[0060]
Further, the unit weight is 0.586 g / m, which is higher than that of the example.
As can be seen from this comparative example, when the coating layer does not have a hollow structure, in order to achieve the same characteristic impedance of 50Ω, the outer diameter of the coaxial cable is inevitably even when the same resin is used as the coating layer. Was confirmed to be large and heavy.
[0061]
【The invention's effect】
As described above in detail, according to the thin coaxial cable and the manufacturing method thereof according to the present invention, the shield layer is formed by a metal conductor instead of plating, while having good and stable high frequency characteristics. Even in this case, the diameter can be sufficiently reduced.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a first embodiment of a thin coaxial cable according to the present invention.
FIG. 2 is an external explanatory view of the thin coaxial cable shown in FIG.
FIG. 3 is a cross-sectional view showing a second embodiment of the thin coaxial cable according to the present invention.
FIG. 4 is a cross-sectional view showing a third embodiment of the thin coaxial cable according to the present invention.
FIG. 5 is a cross-sectional view showing a fourth embodiment of the thin coaxial cable according to the present invention.
FIG. 6 is an external explanatory view showing a fifth embodiment of the thin coaxial cable according to the present invention.
FIG. 7 is a cross-sectional view of a semi-finished product obtained intermediately by the method for producing a thin coaxial cable according to the present invention.
FIG. 8 is an explanatory diagram of a die used in the method for manufacturing a thin coaxial cable according to the present invention.
[Explanation of symbols]
10, 10a, 10b, 10c Thin coaxial cable 12 Central conductor 14 Cover layer 16 Outer shield conductor layer 18 Annular portion 20 Columnar portion 22 Gaps 26 Protective cover layer

Claims (12)

In a thin coaxial cable comprising a center conductor, an electrically insulating coating layer covering the outer periphery of the center conductor, and an outer shield conductor layer provided on the outer periphery of the coating layer,
The coating layer has one or more columnar portions extending outward from the center,
A thin coaxial cable characterized in that the outer shield conductor layer is provided so as to be in contact with the outer periphery of the columnar portion, and one or more void portions continuous in the longitudinal direction are provided inside the outer shield conductor layer. . The columnar portion is composed of a plurality of portions extending radially at equal angular intervals in a transverse section, and extends along the longitudinal axis direction of the small-diameter coaxial cable while maintaining the intervals. Item 2. The thin coaxial cable according to Item 1. The small-diameter coaxial cable according to claim 1, wherein the columnar portion is formed in a spiral shape along a longitudinal direction. 4. The method according to claim 1, wherein the gap portion occupies an area ratio of 10% or more with respect to the area of the portion excluding the central conductor and the outer shield conductor layer in the cross section thereof. Small-diameter coaxial cable as described. 5. The small-diameter coaxial cable according to claim 1, wherein a plurality of the gaps are evenly arranged in the circumferential direction with the center conductor as a center. 6. The small-diameter coaxial cable according to claim 1, wherein the outer shield conductor layer is formed of a hollow compression stranded wire. The outer shield conductor layer is formed by winding a metal tape or metal foil excellent in electrical conductivity, such as copper, or a metal laminate film obtained by laminating these metal tape or metal foil with a plastic film around the outer periphery of the columnar portion. 6. The small-diameter coaxial cable according to claim 1, wherein the coaxial cable is a small-diameter coaxial cable. The outer shield conductor layer is composed of a metal pipe having excellent electrical conductivity such as copper, and a semi-finished product in which a covering layer having the columnar portion is formed on the outer periphery of the center conductor is inserted into the metal pipe. 6. The small-diameter coaxial cable according to claim 1, wherein the metal pipe is formed by drawing and stretching with a die. 9. The small diameter according to claim 1, wherein the coating layer is formed by extruding a fluorine-based resin such as FEP or PFA, or a synthetic resin such as amorphous polyolefin resin or PEN (polyethylene naphthalate). coaxial cable. The thin coaxial cable according to any one of claims 1 to 9, wherein an outermost diameter is 1 mm or less. 11. A small-diameter coaxial cable according to claim 1, wherein an electrically insulating protective coating layer is provided on an outer periphery of the outer shield conductor layer. On the outer periphery of the central conductor, a covering portion having an annular portion covering the central conductor and a columnar portion protruding outward from the annular portion is extruded and continuously supplied. An outer shield conductor layer is formed by any method of winding a hollow compression stranded wire coating, a metal foil, a laminate film, or the like on the outer periphery, or extending a copper pipe, and then the outer shield conductor layer A method for producing a thin coaxial cable, wherein an outer covering layer is formed on the outer periphery as needed.

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