JP7540413B2 - Coaxial cable and its manufacturing method - Google Patents

Description

The present invention relates to a coaxial cable and its manufacturing method.

A coaxial cable for transmitting high-frequency signals is known that uses an insulator with a two-layer structure consisting of a porous core layer and a solid skin layer (see, for example, Patent Document 1).

JP 2005-25999 A

In recent years, camera sensors have become widely used in industrial robots and collaborative robots used in manufacturing lines that weld and assemble automotive parts. Coaxial cables are used as wiring materials for transmitting signals from camera sensors in such industrial robots.

Since such coaxial cables are wired to moving parts that are subject to repeated bending, such as the arms of robots, they must be resistant to breakage due to bending or twisting. Furthermore, coaxial cables must have good transmission characteristics that comply with interface standards, for example.

In the coaxial cable described in Patent Document 1, the porous core layer is crushed by repeated bending and twisting, degrading the transmission characteristics, and the durability against bending and twisting cannot be sufficiently obtained. It is also possible to replace the porous core layer in the coaxial cable of Patent Document 1 with a solid core layer, but in this case, a gap is generated between the solid core layer and the skin layer, and this gap changes the characteristic impedance in the longitudinal direction of the cable, which may degrade the transmission characteristics.

Therefore, the present invention aims to provide a coaxial cable that has good transmission characteristics and is less likely to break when bent or twisted, and a method for manufacturing the same.

The present invention aims to solve the above problems by providing a coaxial cable comprising a conductor, an insulating layer arranged to surround the periphery of the conductor, a shielding layer arranged to surround the periphery of the insulating layer, and a sheath arranged to surround the periphery of the shielding layer, the insulating layer having a first insulating layer made of a non-foamed resin composition arranged to surround the periphery of the conductor, and a second insulating layer made of a non-foamed resin composition arranged to surround the periphery of the first insulating layer, the thickness of the second insulating layer being three times or more the thickness of the first insulating layer, the second insulating layer being arranged to surround the periphery of the first insulating layer without being bonded to the first insulating layer, a gap suppressing layer that suppresses gaps between the first insulating layer and the second insulating layer, and an outer layer arranged to surround the periphery of the gap suppressing layer and bonded to the gap suppressing layer.

In addition, the present invention aims to solve the above problems, and provides a method for manufacturing a coaxial cable including a conductor, an insulating layer provided to surround the periphery of the conductor, a shielding layer provided to surround the periphery of the insulating layer, and a sheath provided to surround the periphery of the shielding layer, in which the step of forming the insulating layer includes a step of forming a first insulating layer made of a non-foamed resin composition by tube extrusion molding so as to surround the periphery of the conductor, and a step of forming a second insulating layer made of a non-foamed resin composition so as to surround the periphery of the first insulating layer, and the step of forming the second insulating layer includes a step of providing a void suppressing layer by solid extrusion molding so as to surround the periphery of the first insulating layer without bonding to the first insulating layer, and a step of providing an outer layer by solid extrusion molding so as to surround the periphery of the void suppressing layer and bonded to the void suppressing layer.

The present invention provides a coaxial cable that has good transmission characteristics and is less likely to break when bent or twisted, and a method for manufacturing the same.

1 is a cross-sectional view showing a cross section perpendicular to the longitudinal direction of a coaxial cable according to an embodiment of the present invention. 1 is a cross-sectional view showing a cross section perpendicular to the longitudinal direction of a coaxial cable of a comparative example in which the second insulating layer is made up of a single layer. 1 is a flow diagram showing a method for manufacturing a coaxial cable according to an embodiment of the present invention. FIG. 1 is a diagram illustrating a bending resistance test.

[Embodiment]
Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

Figure 1 is a cross-sectional view showing a cross section perpendicular to the longitudinal direction of a coaxial cable according to this embodiment. As shown in Figure 1, the coaxial cable 1 includes a conductor 2, an insulating layer 3 arranged to surround the periphery of the conductor 2, a shielding layer 4 arranged to surround the periphery of the insulating layer 3, and a sheath 5 arranged to surround the periphery of the shielding layer 4.

The coaxial cable 1 is used as wiring material for transmitting signals from a camera sensor in industrial robots, collaborative robots, or similar automated devices used in manufacturing lines for welding and assembling automobile parts, for example. In such applications, coaxial cables 1 of various lengths, such as 5 m to 50 m, can be used depending on the structure of the industrial robot or the length of the manufacturing line. For this reason, the coaxial cable 1 is required to have excellent electrical properties so that it can transmit signals reliably and also be capable of transmitting signals over long distances. Specifically, the coaxial cable 1 is required to have low capacitance, high characteristic impedance, and low signal attenuation.

Furthermore, in such applications, the coaxial cable 1 is required to be wired to a moving part that is subject to repeated bending, such as the arm of a robot, and therefore is required to be resistant to breakage due to bending or twisting. In other words, the coaxial cable 1 according to this embodiment is required to have both good transmission characteristics suitable for long-distance transmission and excellent bending resistance and twisting resistance.

(Conductor 2)
The conductor 2 is a stranded conductor formed by twisting together a plurality of metal wires 2a. The conductor 2 is preferably formed by group twisting a plurality of metal wires 2a. This makes it easier for the metal wires 2a to move relative to each other when repeatedly bent or twisted, and makes it less likely for breakage to occur due to bending or twisting, compared to a case in which the conductor 2 is formed by concentrically twisting a plurality of metal wires 2a.

The metal wires 2a used in the conductor 2 should have an outer diameter of 0.05 mm or more and 0.08 mm or less to improve bending resistance and twisting resistance. In addition, to further improve bending resistance and twisting resistance, the metal wires 2a used in the conductor 2 should have an elongation of 5% or more and a tensile strength of 330 MPa or more. In this embodiment, 19 metal wires 2a made of tin-plated copper alloy wires with an outer diameter of 0.08 mm are bundled and twisted to form a conductor 2 equivalent to 28 AWG (American wire gauge). The outer diameter of the conductor 2 is approximately 0.40 mm. The outer diameter of the conductor 2 is, for example, 0.25 mm or more and 0.4 mm or less.

The twist pitch of the conductor 2 is preferably 10 to 14 times the outer diameter of the conductor 2. By making the twist pitch 10 times or more the outer diameter, the twistability can be improved. By making the twist pitch 14 times or less the outer diameter, the bending resistance can be improved. By making the twist pitch 10 to 14 times the outer diameter of the conductor 2, both bending resistance and twistability can be achieved.

(Shield layer 4)
In the coaxial cable 1, an insulating layer 3 is formed so as to surround the periphery of the conductor 2, and a shielding layer 4 is formed so as to surround the periphery of the insulating layer 3. Details of the insulating layer 3 will be described later. The shielding layer 4 is a layer provided as a measure against leakage of a transmission signal and against incoming noise from the outside, and is made of metal wires made of copper or a copper alloy, or a braided shield made of braided copper foil threads.

The shield layer 4 is preferably constructed by laminating multiple braided shield layers. This makes the signal transmitted through the conductor 2 (e.g., the signal transmitted from the camera sensor) less susceptible to the effects of external noise. In this embodiment, a two-layer shield layer 4 is used in which a first braided shield 41 and a second braided shield 42 are laminated.

In addition, it is preferable to use copper alloy wires as the metal wires constituting the first and second braided shields 41, 42. In this embodiment, a braided shield with a braid density of 85% is used as the first and second braided shields 41, 42, which is made by braiding metal wires made of tin-plated copper alloy wires with an outer diameter of 0.08 mm. By using metal wires made of copper alloy wires, the conductor resistance of both braided shields 41, 42 can be reduced, and the shielding effect can be further improved. The outer diameter of the metal wires is, for example, 0.08 mm or more and 0.11 mm or less. In addition, as the copper alloy wire used for the metal wires, for example, one containing at least one of metal elements such as Sn (tin), Ag (silver), In (indium), Mg (magnesium), Ti (titanium), and Mn (manganese) in a predetermined content, with the remainder being copper and unavoidable impurities, can be used.

In this embodiment, the first and second braided shields 41, 42 have the same configuration, but the outer diameter, material, or braid density of the metal wires used may be different between the two braided shields 41, 42. In this embodiment, the first and second braided shields 41, 42 are made only of metal wires made of tin-plated copper alloy wires, but this is not limited thereto, and the first and second braided shields 41, 42 may be made of braided shields in which copper foil threads and metal wires made of copper alloy are braided to cross each other.

(Sheath 5)
The sheath 5 is a layer that forms the outermost layer of the coaxial cable 1 and serves to protect the coaxial cable 1 from external forces. In this embodiment, the sheath 5 is made of a resin composition mainly composed of polyvinyl chloride (PVC). The sheath 5 may be made of a resin mainly composed of polyurethane (PU), for example. In this embodiment, the thickness of the sheath 5 is about 0.45 mm, and the outer diameter of the sheath 5 (outer diameter of the coaxial cable 1) is about 4.1 mm (4.6 mm or less). The thickness of the sheath 5 is, for example, 0.4 mm or more and 1.0 mm or less.

(Insulating layer 3)
The insulating layer 3 is a layer formed of an insulating resin composition so as to surround the periphery of the conductor 2. In the present embodiment, the insulating layer 3 has a first insulating layer 31 made of a non-foamed resin composition provided so as to surround the periphery of the conductor 2, and a second insulating layer 32 made of a non-foamed resin composition provided so as to surround the periphery of the first insulating layer 31.

In addition, if a foamed resin is used for the first insulating layer 31 or the second insulating layer 32, there is a risk that the insulating layer 3 will be crushed when bent or twisted, resulting in deterioration of the transmission characteristics. In order to suppress deterioration of the transmission characteristics due to such crushing of the insulating layer 3, in this embodiment, a non-foamed resin composition is used for both the first insulating layer 31 and the second insulating layer 32 (i.e., the entire insulating layer 3).

The first insulating layer 31 is formed by tube extrusion using a non-foamed resin composition with a low dielectric constant around the conductor 2. That is, the first insulating layer 31 is a non-solid extrusion layer. By forming the first insulating layer 31 by tube extrusion (that is, making the first insulating layer 31 a non-solid extrusion layer), the resin material constituting the first insulating layer 31 does not flow into the gaps between the metal wires 2a constituting the conductor 2 (is formed non-solid), so that partial gaps are generated between the conductor 2 and the first insulating layer 31. As a result, when the coaxial cable 1 is bent, the conductor 2 and the first insulating layer 31 can move independently, and the conductor 2 is less likely to receive tensile force from the first insulating layer 31, improving bending resistance and twisting resistance.

The first insulating layer 31 is in contact with the conductor 2 and has a large effect on the transmission characteristics, so it is desirable that the dielectric constant of the first insulating layer 31 is as low as possible, and it is desirable that the first insulating layer 31 is composed of a resin composition with a dielectric constant ε of 2.3 or less. In this embodiment, a resin composition containing a fluororesin as a main component, which has a low dielectric constant and a high surface slipperiness, is used as the first insulating layer 31. As the fluororesin used for the first insulating layer 31, for example, tetrafluoroethylene-hexafluoropropylene copolymer (FEP) (ε=2.1), tetrafluoroethylene-perfluoroalkylvinylether copolymer (PFA) (ε=2.1), etc. can be used. In this embodiment, the less expensive FEP is used for the first insulating layer 31 to reduce costs.

The thickness of the first insulating layer 31 is preferably 0.2 to 0.4 times the outer diameter of the conductor 2. By making the thickness of the first insulating layer 31 0.2 times or more the outer diameter of the conductor 2, it is possible to suppress a decrease in strength due to the first insulating layer 31 becoming too thin, and to ensure sufficient strength that is unlikely to crack even when repeatedly bent and twisted. In addition, by making the thickness of the first insulating layer 31 0.4 times or less the outer diameter of the conductor 2, it is possible to suppress a decrease in the flexibility (flexibility) of the coaxial cable 1 due to the first insulating layer 31 becoming too thick. More specifically, it is preferable that the thickness of the first insulating layer 31 is 0.20 mm or less. Here, the first insulating layer 31 made of FEP and having a thickness of about 0.12 mm is formed. The outer diameter of the first insulating layer 31 is about 0.64 mm. It is preferable that the thickness of the first insulating layer 31 is 0.10 mm or more.

The second insulating layer 32 is a non-foamed layer for maintaining the thickness of the insulating layer 3 to maintain the desired characteristic impedance (75Ω in this case) and suppressing return loss. The thickness of the second insulating layer 32 is at least three times the thickness of the first insulating layer 31, and more preferably at least six times. The second insulating layer 32 is formed of a resin composition having a lower melting point than the resin composition (resin composition mainly composed of fluororesin) used for the first insulating layer 31, and is formed in a non-adhesive manner with respect to the first insulating layer 31. By making the first insulating layer 31 and the second insulating layer 32 non-adhesive, the first insulating layer 31 can move independently of the second insulating layer 32, and the first insulating layer 31 is less likely to receive a tensile force from the second insulating layer 32, thereby improving the bending resistance and twisting resistance of the coaxial cable 1. Thus, in this embodiment, the first insulating layer 31 is configured to be non-adhesive with respect to both the conductor 2 and the second insulating layer 32, and the bending resistance and twisting resistance of the coaxial cable 1 are further improved.

In this embodiment, the second insulating layer 32 is made of a resin composition mainly composed of polypropylene. The second insulating layer 32 may be made of a resin composition mainly composed of polyethylene. The polypropylene used for the second insulating layer 32 in this embodiment is relatively hard and has a lower melting point than the fluororesin used for the first insulating layer 31, so the first insulating layer 31 and the second insulating layer 32 are not melted and integrated and bonded by the heat during extrusion of the second insulating layer 32. Therefore, if the non-foamed second insulating layer 32 having a thickness three times or more the thickness of the first insulating layer 31 is formed thick in one go, as in the comparative coaxial cable 10 shown in FIG. 2, a large gap 6 (for example, a gap 6 in which the linear distance between the outer surface of the first insulating layer 31 and the inner surface of the second insulating layer 32 is larger than the outer diameter of the metal wire constituting the conductor 2) may be generated between the first insulating layer 31 and the second insulating layer 32. When such a large gap 6 occurs, the gap 6 can affect the dielectric constant and distance between the conductor 2 and the shield layer 4, causing a change in the characteristic impedance in the longitudinal direction of the cable, which can degrade the transmission characteristics.

Therefore, in this embodiment, when the thickness of the second insulating layer 32 is three times or more the thickness of the first insulating layer 31, the second insulating layer 32 is formed in at least two layers, and the occurrence of a large gap 6 between the first insulating layer 31 and the second insulating layer 32 is suppressed. That is, the second insulating layer 32 has a void suppression layer 32a as an innermost layer that is not bonded to the first insulating layer 31 so as to surround the side periphery of the first insulating layer 31, and an outer layer 32b that is bonded to the void suppression layer 32a so as to surround the side periphery of the void suppression layer 32a.

At this time, the thickness of the void suppression layer 32a should be set to a thickness that reduces the difference in cooling time between the inner surface of the void suppression layer 32a (the surface facing the outer surface of the first insulating layer 31) and the outer surface of the void suppression layer 32a (the surface in contact with the outer layer 32b) when cooling the void suppression layer 32a after it is formed. As a result, in the cable 1, the void suppression layer 32a is provided on the side circumference of the first insulating layer 31 in a state in which the inner surface of the void suppression layer 32a is suppressed from shrinking toward the outer surface side of the void suppression layer 32a. Therefore, in the cable 1, it is possible to suppress the occurrence of a large void 6 between the second insulating layer 32 and the first insulating layer 31.

As shown in FIG. 1, a small gap 6 remains between the first insulating layer 31 and the second insulating layer 32 (void suppression layer 32a). For example, the gap 6 is configured so that the linear distance between the outer surface of the first insulating layer 31 and the inner surface of the second insulating layer 32 (the inner surface of the void suppression layer 32a) is smaller than the outer diameter of the metal wire constituting the conductor 2, and more specifically, the linear distance is configured so that it is smaller than 1/4 times the outer diameter of the metal wire. However, since this gap 6 is very small, the effect on the transmission characteristics is minimized. In addition, by leaving a small gap 6, the first insulating layer 31 and the second insulating layer 32 can easily move independently when the coaxial cable 1 is bent, and the bending resistance and twisting resistance of the coaxial cable 1 can be further improved.

The void suppression layer 32a and the outer layer 32b are each formed by solid extrusion. That is, after the first insulating layer 31 is formed by tube extrusion, the void suppression layer 32a is formed by solid extrusion so as to surround the periphery of the first insulating layer 31, and then the outer layer 32b is formed by solid extrusion so as to surround the periphery of the void suppression layer 32a, thereby forming the second insulating layer 32. By forming the void suppression layer 32a and the outer layer 32b by solid extrusion, the concentricity of the insulating layer 3 in the cable longitudinal direction can be made 85% or more. This makes it difficult for the characteristic impedance of the coaxial cable 1 to change in the cable longitudinal direction, thereby improving the transmission characteristics.

In this embodiment, the void suppression layer 32a and the outer layer 32b are made of the same resin composition (a resin composition whose main component is polypropylene). The void suppression layer 32a and the outer layer 32b are melted together and bonded together by the heat generated when the outer layer 32b is extruded. However, a line (a circular line in a cross section perpendicular to the longitudinal direction) 32c appears at the boundary between the void suppression layer 32a and the outer layer 32b. Depending on the presence or absence of this line, it can be determined whether the second insulating layer 32 has a two-layer structure as in this embodiment.

In this embodiment, the void suppression layer 32a and the outer layer 32b are made of the same resin composition, but the void suppression layer 32a and the outer layer 32b may be made of different resin compositions. However, in order to prevent the void suppression layer 32a and the outer layer 32b from being formed into a gap, it is preferable to use a combination of resin compositions in which the void suppression layer 32a and the outer layer 32b are melted and integrated and bonded by the heat during extrusion of the outer layer 32b. For example, a resin composition mainly composed of polypropylene can be used for the void suppression layer 32a, and a resin composition mainly composed of polyethylene can be used for the outer layer 32b. The resin composition constituting the outer layer 32b has a lower melting point than the resin composition constituting the void suppression layer 32a, so that the void suppression layer 32a and the outer layer 32b are easily melted and integrated and bonded. In addition, it is preferable that the resin composition constituting the void suppression layer 32a is harder than the resin composition constituting the outer layer 32b.

In addition, if the void suppression layer 32a is made too thick, there is a risk of a large void 6 occurring between the void suppression layer 32a and the first insulating layer 31, so the void suppression layer 32a needs to be formed relatively thin. Specifically, it is desirable for the thickness of the void suppression layer 32a to be between two and four times the thickness of the first insulating layer 31.

In addition, it is desirable that the thickness of the void suppression layer 32a is equal to or smaller (thinner) than the thickness of the outer layer 32b. In other words, it is desirable that the thickness of the outer layer 32b is equal to or larger than the thickness of the void suppression layer 32a. In other words, it is desirable that the thickness of the void suppression layer 32a is equal to or smaller than the thickness of the entire second insulating layer 32. In this embodiment, the entire thickness of the second insulating layer 32 is about 0.88 mm, and in this case, it is desirable that the thickness of the void suppression layer 32a is equal to or smaller than 0.44 mm. By setting the thickness of the void suppression layer 32a to the above-mentioned thickness, it is possible to suppress the occurrence of a large void 6 between the first insulating layer 31 and the second insulating layer 32.

(Method of Manufacturing Coaxial Cable 1)
3, when manufacturing the coaxial cable 1, first, in step S1, a conductor forming process is performed in which a plurality of metal wires 2a are bundle-twisted to form the conductor 2. Then, in step S2, an insulator forming process is performed in which the insulating layer 3 is formed.

In the insulating layer forming process of step S2, first, in step S21, a first insulating layer forming process is performed in which a first insulating layer 31 made of a non-foaming resin composition (here, a resin composition mainly composed of fluororesin) is formed by tube extrusion molding so as to surround the side circumference of the conductor 2. Then, in step S22, a second insulating layer forming process is performed in which a second insulating layer 32 made of a non-foaming resin composition is formed so as to surround the side circumference of the first insulating layer 31.

In the second insulating layer forming process of step S22, in step S221, a resin composition (here, a resin composition mainly composed of polypropylene) having a lower melting point than the first insulating layer 31 is formed by solid extrusion molding so as to surround the side periphery of the first insulating layer 31, thereby forming a void suppression layer 32a in a non-adhesive manner relative to the first insulating layer 31. In step S221, the resin composition is solidly extruded around the side periphery of the first insulating layer 31, and then the extruded resin composition is cooled by water cooling or the like to form the void suppression layer 32a. When forming the void suppression layer 32a, the thickness of the resin composition solidly extruded around the side periphery of the first insulating layer 31 is set to a thickness that reduces the difference in cooling time between the surface facing the outer surface of the first insulating layer 31 and the surface on the outer side of the cable in the cable radial direction, so that the void suppression layer 32a can be formed in a state in which the inner surface of the void suppression layer 32a is suppressed from shrinking toward the outer surface side of the void suppression layer 32a. This can prevent large voids 6 from being formed between the first insulating layer 31 and the void suppression layer 32a. Then, in step S222, an outer layer forming process is performed in which the outer layer 32b is bonded to the void suppression layer 32a by solid extrusion molding so as to surround the periphery of the void suppression layer 32a. By performing the outer layer forming process, the void suppression layer 32a and the outer layer 32b are melted and integrated by the heat during the solid extrusion molding, and the second insulating layer 32 is formed. In step S222, the resin composition is solidly extruded around the periphery of the void suppression layer 32a, and then the extruded resin composition is cooled by water cooling or the like to form the outer layer 32b.

Then, in step S3, a shield layer forming process is performed in which a shield layer 4 is formed so as to surround the side periphery of the insulating layer 3. In this embodiment, the first braided shield 41 and the second braided shield 42 are sequentially laminated so as to surround the side periphery of the insulating layer 3, forming a two-layered shield layer 4. Then, in step S4, a sheath forming process is performed in which a sheath 5 is formed so as to surround the side periphery of the shield layer 4. In the sheath forming process, the sheath 5 is preferably formed by tube extrusion molding. This prevents the resin material constituting the sheath 5 from flowing into the shield layer 4, and when the coaxial cable 1 is bent, the sheath 5 and the shield layer 4 can move independently, improving bending resistance and twisting resistance. As a result, the coaxial cable 1 of FIG. 1 is obtained.

(Transmission characteristic test and bending test)
The coaxial cable 1 shown in Fig. 1 was fabricated, and a transmission characteristic test and a bending test were performed on the fabricated coaxial cable 1 of the example. In the transmission characteristic test, the characteristic impedance was tested using a TDR method. Furthermore, the attenuation and return loss were tested using a network analyzer.

As shown in Figure 4, the bending test was performed by hanging a weight with a load W = 2N (0.2 kgf) from the lower end of the sample coaxial cable 1, attaching a bending jig 100 with a curved shape to the left and right of the coaxial cable 1, and bending the coaxial cable 1 along the bending jig 100 to apply a bending angle of ±90° to the left and right directions. The bending R (bending radius) was 20 mm, which is about 5 times the outer diameter of the coaxial cable 1. The bending speed was 30 times/min, and the number of bendings was counted as one round trip in the left and right directions. The coaxial cable 1 was then repeatedly bent, and the conduction of the conductor 2 and the shield layer 4 was checked between both ends of the coaxial cable 1 at each appropriate bending. When the resistance value increased by 20% compared to the resistance value before the test (initial resistance value), it was considered that breakage had occurred, and the number of bendings at that time was determined as the bending life.

In the same manner, a comparative coaxial cable was produced with the same configuration as the example except that the second insulating layer was a single-layer configuration (a configuration without a void suppression layer as shown in Figure 2), and a transmission characteristic test and a bending test were performed in the same manner as the example. The results of the transmission characteristic test are summarized in Table 1. Table 1 also shows the threshold value (pass value) for determining pass for each test item.

As shown in Table 1, it was confirmed that the transmission characteristics of the coaxial cable 1 of the embodiment met the threshold value (passing value) for determining pass. In contrast, the transmission characteristics (characteristic impedance and attenuation) of the coaxial cable of the comparative example did not meet the passing value. This is thought to be due to the occurrence of a large gap 6 between the first insulating layer 31 and the second insulating layer 32 (see Figure 2).

In addition, in the bending test, both the coaxial cable 1 of the embodiment and the coaxial cable of the comparative example had a resistance value that was almost the same as the initial resistance value when the number of bending times reached 1 million, and did not reach the end of its bending life. In particular, the coaxial cable 1 of the embodiment had a resistance value that was almost the same as the initial resistance value even when the number of bending times reached 1.5 million, and did not reach the end of its bending life.

(Functions and Effects of the Embodiments)
As described above, in the coaxial cable 1 of this embodiment, the insulating layer 3 has a first insulating layer 31 made of a non-foamed resin composition arranged to surround the side periphery of the conductor 2, and a second insulating layer 32 made of a non-foamed resin composition arranged to surround the side periphery of the first insulating layer 31, and the second insulating layer 32 has a void suppression layer 32a arranged non-adhered to the first insulating layer 31 so as to surround the side periphery of the first insulating layer 31, and an outer layer 32b arranged adhered to the void suppression layer 32a so as to surround the side periphery of the void suppression layer 32a.

By making the first insulating layer 31 and the second insulating layer 32 (void suppression layer 32a) non-adhesive, when the coaxial cable 1 is bent, the first insulating layer 31 and the second insulating layer 32 (void suppression layer 32a) can move independently, and the first insulating layer 31 is less likely to receive tensile force from the second insulating layer 32, improving bending resistance and twisting resistance. In addition, by making the second insulating layer 32 a two-layer structure of the void suppression layer 32a and the outer layer 32b, it is possible to suppress the occurrence of a large void 6 between the first insulating layer 31 and the second insulating layer 32, suppressing the deterioration of the transmission characteristics due to the influence of the void 6, and realizing good transmission characteristics. In addition, by making the first insulating layer 31 and the second insulating layer 32 out of a non-foaming resin composition, the insulating layer 3 is less likely to be crushed when the coaxial cable 1 is bent and twisted, and the deterioration of the transmission characteristics due to bending and twisting can be suppressed. In other words, this embodiment makes it possible to realize a coaxial cable 1 that has good transmission characteristics and is less likely to break when bent or twisted.

(Summary of the embodiment)
Next, the technical ideas grasped from the above-described embodiment will be described by using the reference numerals and the like in the embodiment. However, the reference numerals and the like in the following description do not limit the components in the claims to the members and the like specifically shown in the embodiment.

[1] A conductor (2), an insulating layer (3) arranged to surround the periphery of the conductor (2), a shielding layer (4) arranged to surround the periphery of the insulating layer (3), and a sheath (5) arranged to surround the periphery of the shielding layer (4), wherein the insulating layer (3) has a first insulating layer (31) made of a non-foamed resin composition arranged to surround the periphery of the conductor (2), and a second insulating layer (32) made of a non-foamed resin composition arranged to surround the periphery of the first insulating layer (31). The thickness of the second insulating layer (32) is three times or more the thickness of the first insulating layer (31), the second insulating layer (32) is provided without being adhered to the first insulating layer (31) so as to surround the side circumference of the first insulating layer (31), a gap suppression layer (32a) that suppresses the gap between the first insulating layer (31) and the second insulating layer (32), and an outer layer (32b) that is adhered to the gap suppression layer (32a) so as to surround the side circumference of the gap suppression layer (32a), a coaxial cable (1).

[2] The coaxial cable (1) described in [1], in which the first insulating layer (31) is a non-solid extrusion layer.

[3] A coaxial cable (1) described in [1] or [2], in which the thickness of the outer layer (32b) is greater than the thickness of the void suppression layer (32a).

[4] A coaxial cable (1) described in any one of [1] to [3], in which the void suppression layer (32a) and the outer layer (32b) are composed of the same resin composition.

[5] A coaxial cable (1) described in any one of [1] to [4], in which the first insulating layer (31) is made of a resin composition mainly composed of fluororesin, and the void suppression layer (32a) and the outer layer (32b) constituting the second insulating layer (32) are made of a resin composition mainly composed of polypropylene.

[6] A coaxial cable (1) described in any one of [1] to [5], in which the shield layer (4) is composed of multiple layers of braided shields.

[7] A coaxial cable (1) according to any one of [1] to [6], wherein the insulating layer (3) has a gap (6) between the first insulating layer (31) and the second insulating layer (32), and the linear distance between the outer surface of the first insulating layer (31) and the inner surface of the second insulating layer (32) of the gap (6) is smaller than the outer diameter of the metal wire constituting the conductor (2).

[8] A method for manufacturing a coaxial cable (1) comprising a conductor (2), an insulating layer (3) arranged to surround the lateral circumference of the conductor (2), a shielding layer (4) arranged to surround the lateral circumference of the insulating layer (3), and a sheath (5) arranged to surround the lateral circumference of the shielding layer (4), wherein the step of forming the insulating layer (3) includes a step of forming a first insulating layer (31) made of a non-foamed resin composition by tube extrusion molding so as to surround the lateral circumference of the conductor (2), and a step of forming a sheath of the first insulating layer (31). A method for manufacturing a coaxial cable, comprising: forming a second insulating layer (32) made of a non-foamed resin composition so as to surround the periphery of the first insulating layer (31); the step of forming the second insulating layer (32) comprises: providing a void suppression layer (32a) by solid extrusion molding so as to surround the periphery of the first insulating layer (31) without bonding to the first insulating layer (31); and providing an outer layer (32b) by solid extrusion molding so as to surround the periphery of the void suppression layer (32a) and bond it to the void suppression layer (32a).

Although the embodiments of the present invention have been described above, the invention according to the claims is not limited to the embodiments described above. It should be noted that not all of the combinations of features described in the embodiments are necessarily essential to the means for solving the problems of the invention.

The present invention can be modified as appropriate without departing from the spirit of the invention. For example, in the above embodiment, the coaxial cable 1 is described as being used for transmitting signals from a camera sensor of an industrial robot or the like, but the use of the coaxial cable 1 is not limited to this. The present invention is extremely effective when applied to a coaxial cable that is wired in a small space and used under conditions where it is repeatedly bent and twisted at a high operating rate, and can be applied to uses other than signal transmission from a camera sensor.

Although not mentioned in the above embodiment, the insulating layer 3 may have one or more insulating layers outside the outer layer 32b. In other words, the outer layer 32b does not have to be the outermost layer of the insulating layer 3.

Reference Signs List 1...coaxial cable 2...conductor 2a...metal wire 3...insulating layer 31...first insulating layer 32...second insulating layer 32a...void suppressing layer 32b...outer layer 4...shield layer 5...sheath

Claims (8)

A conductor;
an insulating layer provided so as to surround a side periphery of the conductor;
a shield layer provided so as to surround a side periphery of the insulating layer;
a sheath provided to surround a side periphery of the shield layer,
the insulating layer includes a first insulating layer made of a non-foamed resin composition provided so as to surround a side periphery of the conductor, and a second insulating layer made of a non-foamed resin composition provided so as to surround a side periphery of the first insulating layer,
The thickness of the second insulating layer is at least three times the thickness of the first insulating layer,
The second insulating layer has a gap suppressing layer that is not bonded to the first insulating layer and that surrounds a side periphery of the first insulating layer and suppresses a gap between the first insulating layer and the second insulating layer, and an outer layer that is bonded to the gap suppressing layer and that surrounds a side periphery of the gap suppressing layer.
Coaxial cable. the first insulating layer is a non-solid extruded layer;
2. The coaxial cable according to claim 1. The thickness of the outer layer is greater than the thickness of the void suppression layer.
3. The coaxial cable according to claim 1 or 2. The void suppression layer and the outer layer are composed of the same resin composition.
A coaxial cable according to any one of claims 1 to 3. The first insulating layer is made of a resin composition containing a fluororesin as a main component,
The void suppression layer and the outer layer constituting the second insulating layer are made of a resin composition mainly composed of polypropylene.
A coaxial cable according to any one of claims 1 to 4. The shield layer is formed by laminating a plurality of braided shield layers.
A coaxial cable according to any one of claims 1 to 5. The insulating layer has a gap between the first insulating layer and the second insulating layer, and the linear distance between the outer surface of the first insulating layer and the inner surface of the second insulating layer is smaller than the outer diameter of the metal wire constituting the conductor.
7. A coaxial cable according to claim 1. A conductor;
an insulating layer provided so as to surround a side periphery of the conductor;
a shield layer provided so as to surround a side periphery of the insulating layer;
a sheath provided to surround a side periphery of the shield layer,
The step of forming the insulating layer includes:
forming a first insulating layer made of a non-foamable resin composition by tube extrusion molding so as to surround a side periphery of the conductor;
forming a second insulating layer made of a non-foamable resin composition so as to surround a side periphery of the first insulating layer;
The step of forming the second insulating layer includes:
providing a void suppression layer by solid extrusion molding so as to surround a side periphery of the first insulating layer without being adhered to the first insulating layer;
and providing an outer layer by solid extrusion molding so as to be adhered to the void-suppressing layer and surround the periphery of the void-suppressing layer.
How coaxial cables are manufactured.

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