Dual core twisted shielded cable

Abstract

Provided is a two-core twisted shielded cable that has excellent communication characteristics and enables high levels of manufacturing efficiency and wiring to be maintained. A two-core twisted shielded cable (1) includes two insulated electric wires (10) twisted together, each having a conductor (11) and an insulator (12) that covers the conductor; a metal foil shield layer (20) disposed around the two insulated electric wires in a lateral wrap; a metal braid (30) disposed around the outside of the metal foil shield layer; and a sheath (40) disposed around the outside of the metal braid, with a characteristic impedance in the range of 100 ± 5 Ω. The insulator is foamed from a material having a hardness of 60 or greater and 70 or less as measured based on ISO / DIS 868, and the metal foil shield layer includes a resin layer (21) in contact with the insulated electric wires and a metal layer (22) disposed on the surface of the resin layer and in contact with the metal braid, with a ratio of the thickness of the metal layer to the thickness of the resin layer, metal layer thickness / resin layer thickness, of 0.40 or greater and 1.20 or less.

Description

Technical Field

[0001] This invention relates to a two-core stranded shielded cable. Background Technology

[0002] Conventional communication cables typically employ a structure where individual wires are twisted together and then horizontally wound with a metal foil for shielding. The wires are arranged in a circular shape, or twisted together in a roughly circular bundle, with a braid added around the perimeter and a sheath placed around the outer edge (Patent Document 1). However, this structure, which involves twisting the wires together and horizontally winding the metal foil, can potentially damage the wires during manufacturing. This damage can cause resonance at specific frequencies, leading to communication errors or deterioration in reflection loss, thus potentially reducing communication performance. Therefore, structures designed to suppress resonance at specific frequencies are known as follows: First, structures where two wires are parallel are known (Patent Documents 2 and 3). Additionally, structures where two conductors are wrapped together are known (Patent Document 4). Furthermore, structures with longitudinally attached metal foil are known (Patent Document 5).

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2015-153497

[0006] Patent Document 2: Japanese Patent Application Publication No. 2015-185527

[0007] Patent Document 3: Japanese Patent Application Publication No. 2016-201273

[0008] Patent Document 4: Japanese Patent Application Publication No. 2014-38777

[0009] Patent Document 5: Japanese Patent Application Publication No. 2019-61766 Summary of the Invention

[0010] The technical problem that the invention aims to solve

[0011] However, in structures like those in Patent Documents 2 and 3 where the two lines are parallel, the communication cable needs to be manufactured while maintaining the parallelism of the two lines with high precision. This necessitates a reduction in manufacturing speed, leading to increased costs due to decreased manufacturing efficiency. Furthermore, in structures like those in Patent Document 4 where two conductors are wrapped together, and in structures like those in Patent Document 5 where a metal foil is added longitudinally, the cable is difficult to bend, thus limiting the locations where it can be laid and reducing its usability. Similarly, structures like those in Patent Document 1 where individual wires are twisted together and the metal foil is wound laterally may generate resonance, reducing communication characteristics. Structures like those in Patent Documents 2-5, which suppress resonance and improve communication characteristics, suffer from reduced manufacturing efficiency and deteriorated wiring performance.

[0012] This invention was made to solve such problems, and its purpose is to provide a twin-core stranded shielded cable with excellent communication characteristics that can maintain manufacturing efficiency and wiring performance at a high level.

[0013] means for solving problems

[0014] The present invention discloses a twin-core stranded shielded cable comprising: two stranded insulated wires, each insulated wire having a conductor and an insulator covering the conductor; a metal foil shielding layer disposed around the two insulated wires in a transversely wound manner; a metal braid disposed on the outer periphery of the metal foil shielding layer; and a sheath disposed on the outer periphery of the metal braid. The characteristic impedance of the twin-core stranded shielded cable is in the range of 100 ± 5 Ω. The insulator is foamed from a material having a hardness of 60 or more and 70 or less as measured by ISO / DIS 868, which is equivalent to the JIS K 7215 D hardness. The metal foil shielding layer comprises: a resin layer in contact with the two insulated wires; and a metal layer disposed on the surface of the resin layer and in contact with the metal braid. The ratio of the thickness of the metal layer to the thickness of the resin layer, i.e., metal layer thickness / resin layer thickness, is 0.40 or more and 1.20 or less.

[0015] Invention Effects

[0016] According to the present invention, a twin-core stranded shielded cable with excellent communication characteristics and the ability to maintain manufacturing efficiency and wiring performance at a high level can be provided. Attached Figure Description

[0017] Figure 1 This is a perspective view showing a wire harness of a twin-core stranded shielded cable having an embodiment of the present invention.

[0018] Figure 2 It is shown Figure 1 An enlarged view of a double-core twisted shielded cable.

[0019] Figure 3 Is with Figure 2 A cross-sectional view of a double-core twisted shielded cable perpendicular to the axial direction.

[0020] Figure 4 This is a graph showing the relationship between frequency and RL (Return Loss) in each sample of the embodiment.

[0021] Figure 5 This is a graph showing the relationship between the frequency of each sample in the embodiment and LCTL (Longitudinal Conversion Transfer Loss, ground balance).

[0022] Explanation of reference numerals in the attached figures

[0023] 1: Twin-core twisted shielded cable

[0024] 10: Insulated wires

[0025] 11: Conductor

[0026] 12: Insulator

[0027] 20: Metal foil shielding layer

[0028] 21: Resin layer

[0029] 22: Metal layer

[0030] 30: Metal woven fabric

[0031] 40: Sheath

[0032] c: speed of light

[0033] D: Distance

[0034] f1, f2: Extraction frequency

[0035] mpitch: winding spacing

[0036] wpitch: twist pitch

[0037] εr: Dielectric constant

[0038] μr: Permeability of vacuum Detailed Implementation

[0039] Hereinafter, the present invention will be described according to preferred embodiments. Furthermore, the present invention is not limited to the embodiments shown below, and appropriate modifications can be made without departing from the spirit of the invention. In addition, in the embodiments shown below, some parts of the structure are omitted from the illustrations and descriptions; however, regarding the details of the omitted technology, well-known or publicly known techniques will be appropriately applied within the scope that does not contradict the content of the following description.

[0040] First, refer to Figures 1 to 3 The structure of the twin-core twisted shielded cable of this embodiment will be described. Figure 1 This is a perspective view showing a wire harness of a twin-core stranded shielded cable equipped with this embodiment of the present invention. Figure 2 It is shown Figure 1 An enlarged view of a double-core twisted shielded cable. Figure 3 Is with Figure 2 A cross-sectional view of a double-core twisted shielded cable perpendicular to the axial direction.

[0041] like Figure 1 As shown, the double-core twisted shielded cable 1 of this embodiment is, for example, one of the cables constituting a wiring harness in a vehicle. Figure 1 As shown, the wire harness WH includes a double-core twisted shielded cable 1 and other components such as cables O.

[0042] Other cables O, such as thick wires like power lines and thin wires like other signal lines, have a conductor portion O1 and an insulating portion O2 that covers the conductor portion O1. Additionally, the twin-core twisted shielded cable 1 and other cables O are wrapped with resin tape RT, or fitted with corrugated tubes, terminals, connectors, etc. (not shown).

[0043] like Figure 2 As shown, the double-core twisted shielded cable 1 includes two insulated wires 10, a metal foil shielding layer 20, a metal braid 30, and a sheath 40.

[0044] The two insulated wires 10 are the portion of the double-core twisted shielded cable 1 that contains the transmission path for transmitting signals. They are constructed by twisting (stretching) conductors 11 and insulators 12 covering the conductors 11 together in a helical manner. The conductors 11 are the signal transmission path, and may be, for example, a stranded wire composed of two or more wires twisted together, but may also be a single wire. Furthermore, the cross-sectional area of ​​the conductors 11 is assumed to be 0.22 sq or less, but is not particularly limited to this.

[0045] The conductor 11 is not particularly limited as long as it meets the physical properties such as conductivity required for signal transmission. For example, it can be made of soft copper wire, aluminum wire, copper alloy wire, aluminum alloy wire, silver-plated soft copper wire, tin-plated soft copper wire, and tin-plated copper alloy wire. In particular, the conductor 11 is preferably composed of a single layer structure without plating, such as soft copper wire, aluminum wire, copper alloy wire, or aluminum alloy wire. By constructing the conductor 11 with a single layer structure without plating, it is possible to prevent the deterioration of the conductivity of the conductor 11 caused by the diffusion of plating elements toward the inside of the conductor 11 or alloying with elements on the inside of the plating. Therefore, compared with a plated conductor 11, communication performance can be maintained for a longer period of time.

[0046] Insulator 12 is a component that covers conductor 11 to insulate conductor 11. Insulator 12 can be made of materials such as PE (polyethylene), PP (polypropylene), or PTFE (polytetrafluoroethylene), but PP is preferred from the viewpoint of heat resistance and manufacturing versatility. Insulator 12 is foamed from a material with a hardness (equivalent to JIS K 7215 D hardness) of 60 or higher and 70 or lower, as measured by ISO / DIS 868. In the following description, unless otherwise specified, the hardness is explained using JIS K 7215 D hardness as an example. If the D hardness of insulator 12 is less than 60, insulator 12 is prone to deformation when stress is applied to insulated wire 10. Due to the deformation of insulator 12, conductor 11 is flattened and damaged, which easily leads to resonance and thus deteriorates communication characteristics. If the D hardness exceeds 70, insulator 12 becomes too hard, making the stranding of the two insulated wires 10 difficult and degrading manufacturing efficiency. Furthermore, if the D hardness is 62 or higher, the insulator 12 is less prone to deformation, which is therefore preferred. Additionally, if the D hardness is 67 or lower, the stranding of the two insulated wires 10 becomes easier, which is also preferred.

[0047] The insulator 12 is manufactured, for example, by foam extrusion molding. This is because, when the insulator 12 is not a foaming material, it is difficult to control the relative permittivity and to control the characteristic impedance of the twin-core stranded shielded cable 1 within the desired range. Two methods for foaming the insulator 12 can be listed: chemical foaming and physical foaming. Chemical foaming is a process that uses a thermally decomposable chemical foaming agent to foam the base resin. For example, a thermally decomposable chemical foaming agent is used by extruding a mixture of the base resin and a masterbatch containing the thermally decomposable chemical foaming agent, thereby decomposing and foaming due to the heat during extrusion. On the other hand, physical foaming is a process that foams the base resin by injecting inert gases such as nitrogen, carbon dioxide, or argon into an extrusion cylinder. The inactive gas mixes into the base resin, forming bubbles.

[0048] The insulator 12 is preferably foamed using a physical foaming process. This is because, unlike chemical foaming, it avoids using azodicarbonamide (ADCA) and bis(oxo)benzenesulfonylhydrazine (OBSH), substances of very high concern under REACH regulations, as these have high dielectric constants and can contribute to deterioration of insertion loss in the GHz band. Furthermore, unlike chemical foaming, it eliminates the need for uniform dispersion of the foaming agent, resulting in faster production speeds. Additionally, when the insulator 12 is foamed using a physical foaming process, the internal bubbles created by foaming are inert gas bubbles. That is, the insulator 12 has internal bubbles (pores) created by foaming, but these pores are filled with inert gas.

[0049] The average foam diameter of the insulator 12 is preferably 30 μm or less in the cross-sectional direction of the insulated wire 10, and preferably 60 μm or less in the length direction of the insulated wire 10. More preferably, the average foam diameter of the insulator 12 is 20 μm or less in the cross-sectional direction of the insulated wire 10, and 55 μm or less in the length direction of the insulated wire 10. By making the average foam diameter of the insulator 12 30 μm or less in the cross-sectional direction and 60 μm or less in the length direction, it is easy to form bubbles that are nearly spherical and have a small and uniform foam diameter, ensuring communication stability when used as a communication cable. It should be noted that the average foam diameter can be confirmed by observing the cross-section obtained by cutting the insulated wire 10 along the cross-sectional or length direction using an electron microscope, measuring the bubble diameter, and calculating its average value. Alternatively, it can be confirmed by observing the cross-section of the insulated wire 10 in the cross-sectional or length direction non-destructively using X-ray microscopy (CT), measuring the bubble diameter, and calculating its average value.

[0050] When the foaming rate of the insulator 12 is above 25% and below 55%, it is easy to control the characteristic impedance of the twin-core stranded shielded cable 1 within the desired range, and therefore it is preferred. Similar to the average foaming diameter, the foaming rate can be confirmed by observing the cross-section of the twin-core stranded shielded cable 1, taking the proportion of the area occupied by the foam in the cross-sectional area of ​​the insulator 12 as the foaming rate, and calculating the average value of the foaming rate in both the cross-sectional and length directions.

[0051] When the relative permittivity of the insulator 12 is 1.55 or higher and 2.07 or lower, it is easier to control the shape and characteristic impedance of the two insulated wires 10 within the desired range, and therefore this is preferred. Examples of methods for adjusting the relative permittivity include adjusting foaming conditions such as the foaming rate during foam extrusion molding, but this method is not limited to these.

[0052] The metal foil shielding layer 20 is a shielding component that protects the two insulated wires 10 from external electromagnetic noise, such as... Figure 2 As shown, it is arranged in a horizontally wound manner around the insulated wire 10. The reason for the horizontal winding is that if it were added vertically, the metal foil shielding layer 20 would become too rigid, making it difficult to bend the twisted shielded cable 1, thus limiting the places where it can be wired and worsening the wiring performance.

[0053] like Figure 3 As shown, the metal foil shielding layer 20 includes a resin layer 21 and a metal layer 22. The resin layer 21 supports the metal layer 22 and is also in contact with the insulated wire 10. The resin layer 21 is made of a flexible, insulating resin, such as PET (polyethylene terephthalate) film. The metal layer 22 is a layer that absorbs electromagnetic noise. It is disposed on the outer surface of the resin layer 21 via an adhesive layer (not shown) and is in contact with the metal braid 30. The metal layer 22 is made of a metal that absorbs electromagnetic noise, such as aluminum (Al) or copper (Cu), but aluminum is preferred in terms of cost.

[0054] The ratio of the thickness of the metal layer 22 to the thickness of the resin layer 21 in the metal foil shielding layer 20 (metal layer thickness / resin layer thickness) is between 0.40 and 1.20. If the ratio is less than 0.40, the thickness of the metal layer 22 becomes too thin relative to the resin layer 21, the metal foil shielding layer 20 becomes stiff, and it is not easy to wind it onto the insulated wire 10, thus deteriorating the manufacturing efficiency of the twin-core stranded shielded cable 1. If the ratio exceeds 1.20, the thickness of the metal layer 22 becomes too thick relative to the resin layer 21, the resin layer 21 cannot support the metal layer 22, and the metal layer 22 is prone to deformation and wrinkling. If wrinkles occur in the metal layer 22, the distance between the insulated wire 10 and the metal layer 22 changes in the wrinkled and non-wrinkled areas, the characteristic impedance becomes unstable, RL and LCTL deteriorate, and the communication characteristics worsen. In addition, if the ratio of metal layer thickness to resin layer thickness exceeds 1.20, the resin layer 21 becomes too thin, and the metal foil shielding layer 20 is prone to breakage during the manufacturing of the twin-core twisted shielded cable 1, resulting in deteriorated manufacturing efficiency.

[0055] The total thickness of the metal foil shielding layer 20 is preferably 15 μm or more and 50 μm or less. If the total foil thickness is 15 μm or more, the metal foil shielding layer 20 is less likely to break during the manufacture of the twisted-core shielded cable 1, thus improving manufacturing efficiency. Furthermore, if the total foil thickness is 50 μm or less, the metal foil shielding layer 20 is easier to wind around the insulated wire 10 during the manufacture of the twisted-core shielded cable 1, further improving manufacturing efficiency.

[0056] The metal braid 30 is a component that improves the tensile strength of the twin-core stranded shielded cable 1 and ensures close contact between the metal foil shielding layer 20 and the insulated wire 10. The metal braid 30 functions to absorb low-frequency electromagnetic noise and also serves as a grounding wire for the electromagnetic noise absorbed by the metal foil shielding layer 20. The metal braid 30 is disposed on the outer periphery of the metal foil shielding layer 20 and is a tubular braid made of metal that contacts the metal layer 22. The material and structure of the metal braid 30 can be appropriately selected according to the required strength and noise immunity of the twin-core stranded shielded cable 1. For example, a structure can be formed by braiding multiple bundles of metal wires such as soft copper wire, silver-plated soft copper wire, tin-plated soft copper wire, and tin-plated copper alloy wire. Furthermore, coated fibers with metal plating can be used as an example. Additionally, the metal braid 30 can also be a braid in which multiple metal wires are plated together to form a flat bundle.

[0057] The sheath 40 is a component that protects the insulated wire 10, the metal foil shielding layer 20, and the metal braid 30. It is an insulating component disposed on the outer periphery of the metal foil shielding layer 20 and the metal braid 30. Figure 3 In this example, the sheath 40 is configured as a tube and has a partial gap between it and the inner metal braid 30. However, the structure of the sheath 40 is not limited to... Figure 3 The structure shown can also have additional inclusions in the gaps, or it can be a solid state with the outer periphery of the metal foil shielding layer 20 and the metal braid 30 filled. When the sheath 40 is solid, it is formed by solid extrusion of the components consisting of the insulated wire 10, the metal foil shielding layer 20, and the metal braid 30. The sheath 40 is made of, for example, PE, PP, and PVC (polyvinyl chloride).

[0058] The characteristic impedance of this type of twin-core twisted shielded cable 1 is within the range of 100±5Ω. This is because if the characteristic impedance deviates from the range of 100±5Ω, it will sometimes deviate from the standard characteristic impedance for communication cables.

[0059] In addition, the extraction frequency f1 of the twin-core twisted shielded cable 1 is preferably 6 GHz or higher, as determined by the following formula (1).

[0060] [Formula 1]

[0061]

[0062] In equation (1), D is the distance between the centers of the two insulated wires 10, wpitch is the twisting pitch of the two insulated wires 10, εr is the dielectric constant of the insulator 12, and μr is the permeability of vacuum.

[0063] Here, the inventors of this application, through various experiments and simulations, discovered that the extraction frequency f1 can be determined according to equation (1). It is known that a bandwidth gap (a significant increase in attenuation at a specific frequency) is generally generated in a twisted shielded cable. However, the mechanism of the bandwidth gap is only generally known, and there are actual situations that have not yet been clarified regarding the details. Therefore, the inventors of this application collected multiple data through various experiments and simulations, and based on these multiple data, they discovered equation (1). As a result of verifying the multiple data, the inventors of this application found that the extraction frequency f1 varies with the distance D between the centers of the two insulated wires 10, the twisting pitch wpitch of the two insulated wires 10, and the dielectric constant εr of the insulator 12. In addition, when the twisted shielded cable 1 is used as a communication line, if the extraction frequency f1 is set to 6 GHz or higher, communication up to 12 Gbps can be achieved in the NRZ (Non-Return-to-Zero) communication mode. That is, the extreme deterioration of transmission characteristics caused by the bandwidth gap can be suppressed. Therefore, the dual-core twisted shielded cable 1 of this embodiment is configured such that the extraction frequency f1 obtained by formula (1) is 6 GHz or higher, thereby easily suppressing the deterioration of transmission characteristics.

[0064] Furthermore, the extraction frequency f2 of the twin-core twisted shielded cable 1 is preferably 6 GHz or higher, as determined by the following formula (2).

[0065] [Equation 2]

[0066]

[0067] In equation (2), c is the speed of light, and pitch is the winding spacing of the metal foil shielding layer 20. The inventors of this application conducted various experiments and simulations and found that a further frequency band gap was generated due to factors different from those in equation (1) (the dielectric constant εr of the insulator 12 and the winding spacing pitch of the metal foil shielding layer 20). Moreover, the inventors of this application found that the extraction frequency f2 is determined by equation (2). Therefore, by configuring the system so that the extraction frequency obtained by equation (2) is also 6 GHz or higher, the inventors of this application can easily suppress the deterioration of transmission characteristics.

[0068] Furthermore, the twist pitch wpitch of the two insulated wires 10 is preferably 15 mm or more. This makes it difficult for localized reflection losses to occur, and it is easier to suppress the deterioration of transmission characteristics. The above is a description of the structure of the twin-core twisted shielded cable 1 according to this embodiment.

[0069] Next, the invention will be specifically described based on embodiments, but the invention is not limited to these embodiments. Twelve types of twin-core stranded shielded cables (sample numbers 1-12) with various D-hardness and metal / resin layer thicknesses were manufactured, and their manufacturing efficiency and communication characteristics were evaluated. The specific steps are as follows:

[0070] First, it was tested whether two insulated wires 10, each covered with a conductor 11 (copper single wire) of the same size (0.22 sq), could be twisted together to form a twisted pair (stretched wire) using insulators 12 of the same size, material (PP), manufacturing method (physical foaming), and different D hardness. The twist pitch wpitch during the twisting process was 15 mm or more. Furthermore, the D hardness was measured using a hardness tester (product name: Ascar Rubber Hardness Tester Model D) manufactured by Polymer Instruments Co., Ltd., based on JIS K 7215, on the sheet-shaped insulator 12. Additionally, three test sheets of 2 mm thick insulator 12 in the insulated wire 10 were overlapped to a thickness of 6 mm.

[0071] Next, it was confirmed whether metal foil shielding layers 20 of different thicknesses were wound laterally around the two insulated wires 10 that could be processed into twisted pairs. The metal foil shielding layer 20 was prepared by attaching aluminum (Al) foil or copper (Cu) foil as the metal layer 22 to a PET film as the resin layer 21 via a 3μm thick adhesive layer. Furthermore, for cables that could be wound with the metal foil shielding layer 20, the outer periphery was covered with a PE tube as the sheath 40 to form a two-core twisted shielded cable. The results are shown in Table 1.

[0072] [Table 1]

[0073]

[0074] As shown in Table 1, the D-hardness of the insulator 12 in sample 10 exceeds 70, which is too high. Therefore, even if the insulated wire 10 is twisted, the twisted state cannot be maintained, and the twisted pair opens, making it impossible to maintain the twisted pair configuration. Furthermore, the metal layer thickness / resin layer thickness ratios in samples 1 and 11 exceed 1.20, making the metal layer 22 too thick relative to the resin layer 21 (i.e., the resin layer 21 is too thin). This makes the metal foil shielding layer 20 prone to breakage, sometimes preventing the manufacture of twisted shielded cables. Moreover, in sample 5, the metal layer thickness / resin layer thickness ratio is less than 0.40, making the resin layer 21 too thick relative to the metal layer 22. This causes the metal foil shielding layer 20 to harden, making it impossible to wind the metal foil shielding layer 20 onto the insulated wire 10. Additionally, in sample 6, the metal layer 22 is too thick relative to the resin layer 21, preventing the resin layer 21 from adequately supporting the metal layer 22 and causing wrinkles in the metal layer 22. On the other hand, the D-hardness of samples 3-4, 7-9, and 12 is 60 or higher and 70 or lower, and the metal layer thickness / resin layer thickness is 0.40 or higher and 1.20 or lower. This allows for the stranding of the insulated wire 10, and the metal foil shielding layer 20 can be wound and fixed to the insulated wire 10 without breakage. Therefore, a two-core stranded shielded cable can be manufactured. It should be noted that sample 2 has a D-hardness less than 60, which differs from this embodiment and does not meet the requirement of a D-hardness of 60 or higher. However, its D-hardness is 70 or lower, and the metal layer thickness / resin layer thickness is 0.40 or higher and 1.20 or lower, thus making the manufacture of a two-core stranded shielded cable possible.

[0075] Next, for samples 1, 3, 6, 7, and 8 of the fabricated twin-core twisted shielded cables, the relationship between frequency and RL was determined. The results are shown below. Figure 4 . Figure 4 This is a graph showing the relationship between frequency and RL in each sample of the embodiment. Furthermore, a larger RL (the higher up the graph) indicates greater reflection loss and worse communication characteristics. Figure 4 As shown, samples 3, 7, and 8, with a D hardness of 60 or higher and a metal layer thickness / resin layer thickness of 0.40 or higher but less than 1.20, have smaller RL values ​​compared to sample 1, with a D hardness less than 60, and sample 6, with a metal layer thickness / resin layer thickness exceeding 1.20. Therefore, it can be concluded that resonance can be suppressed, resulting in good communication characteristics.

[0076] Next, for samples 3, 6, 7, and 12 of the fabricated twin-core twisted shielded cables, the relationship between frequency and LCTL was determined. The results are shown below. Figure 5 . Figure 5 This is a graph showing the relationship between frequency and LCTL in each sample of the embodiment. Furthermore, a higher LCTL (towards the top of the graph) indicates lower noise immunity and worse communication characteristics. Figure 5As shown, compared with samples 3, 7, and 12 whose metal layer thickness / resin layer thickness is 0.4 or more and 1.20 or less, sample 6, whose metal layer thickness / resin layer thickness exceeds 1.2, has a lower LCTL at low frequencies.

[0077] Furthermore, for samples 3-4, 7-9, and 12 of the fabricated twin-core twisted shielded cables, the extraction frequencies f1 and f2 were calculated based on equations (1) and (2). The result was that the extraction frequencies f1 and f2 of all samples were above 6 GHz. Additionally, as... Figure 4 As shown, no degradation in communication characteristics was observed in samples 3, 7, and 8 at frequencies below 6 GHz, and experiments confirmed that the extraction frequency was above 6 GHz. Based on these results, it can be concluded that the dual-core twisted shielded cable 1 of this embodiment can suppress extreme degradation of transmission characteristics caused by bandwidth gaps.

[0078] Based on the above results, it can be seen that the twin-core twisted shielded cable 1 that meets the requirements of this embodiment has excellent communication characteristics and manufacturing efficiency.

[0079] Thus, the double-core stranded shielded cable 1 of this embodiment includes: two insulated wires 10 having conductors 11 and insulators 12, a metal foil shielding layer 20, a metal braid 30, and a sheath 40, and its characteristic impedance is 100±5Ω. Furthermore, in the double-core stranded shielded cable 1 of this embodiment, the insulator 12 is a foamed material with a D hardness of 60 or higher and 70 or lower, and the metal layer thickness / resin layer thickness is 0.40 or higher and 1.20 or lower. In this structure, by making the D hardness of the insulator 12 60 or higher, the insulator 12 is less prone to deformation under stress, preventing resonance caused by damage to the conductor 11 due to flattening. By making the D hardness 70 or lower, the insulated wires 10 can be stranded, improving manufacturing efficiency. Additionally, by making the metal layer thickness / resin layer thickness 0.40 or higher, the metal foil shielding layer 20 can be wound around the insulated wires 10 during manufacturing, improving manufacturing efficiency. Furthermore, by making the metal layer thickness / resin layer thickness less than 1.20, the metal foil shielding layer 20 is less prone to breakage, improving manufacturing efficiency. Additionally, wrinkles are less likely to form in the metal layer 22, preventing deterioration of RL and LCTL at low frequencies, thus improving communication characteristics. Moreover, by laterally winding the metal foil shielding layer 20, the twisted-core shielded cable 1 is easier to bend compared to the longitudinally attached case, improving wiring performance. Therefore, the twisted-core shielded cable 1 of this embodiment exhibits excellent communication characteristics and maintains high levels of manufacturing efficiency and wiring performance. Specifically, the twisted-core shielded cable 1 does not require special processing such as making the two insulated wires 10 parallel or wrapping the two insulated wires 10 together, enabling the maintenance of communication characteristics up to the high-frequency range while ensuring wiring performance and manufacturing efficiency.

[0080] Furthermore, the extraction frequency f1 of the twin-core twisted shielded cable 1 in this embodiment, calculated by equation (1), is 6 GHz or higher. Therefore, it is possible to perform communication up to 12 Gbps via the NRZ communication mode, and the extreme deterioration of transmission characteristics caused by bandwidth gaps can be suppressed.

[0081] Furthermore, the extraction frequency f2 of the twin-core twisted shielded cable 1 in this embodiment, calculated by equation (2), is 6 GHz or higher. Therefore, it is easy to suppress the deterioration of transmission characteristics.

[0082] On the other hand, in the twin-core twisted shielded cable 1 of this embodiment, the twist pitch wpitch of the two insulated wires 10 is 15mm or more. Therefore, local reflection loss is less likely to occur, and the deterioration of transmission characteristics can be more easily suppressed.

[0083] Furthermore, in the twin-core stranded shielded cable 1 of this embodiment, the insulator 12 is foamed using a physical foaming method that injects inert gas during extrusion molding. The internal bubbles generated by foaming are inert gas bubbles. In this structure, the gas inside the bubbles generated by foaming is an inactive gas. Therefore, compared with the case of foaming by chemical foaming, the dielectric constant εr of the insulator 12 can be reduced, the amount of foaming agent added is also small, the communication performance is excellent, and the environmental impact can also be reduced.

[0084] Furthermore, in the twin-core stranded shielded cable 1 of this embodiment, the conductor 11 of the insulated wire 10 is composed of a single layer structure without plating. In this structure, the surface of the conductor 11 is not plated. Therefore, unlike the case where plating is performed, there is no deterioration in the conductivity of the conductor 11 caused by the diffusion of elements in the plating layer toward the inside of the conductor 11 or alloying with elements on the inside of the plating layer, and the insertion loss does not deteriorate.

[0085] The present invention has been described above based on the embodiments, but the present invention is not limited to the above embodiments. Modifications can be made without departing from the spirit of the present invention, and other technologies can be appropriately combined within the possible scope. Furthermore, known or widely known technologies can also be combined within the possible scope.

[0086] For example, in the above-described embodiment, extrusion molding is used as a method for manufacturing the insulator 12, but the method for manufacturing the insulator 12 may also be die molding or the like.

Claims

1. A double-core stranded shielded cable, characterized in that, The cable comprises: two stranded insulated wires, each insulated wire having a conductor and an insulator covering the conductor; a metal foil shielding layer, the metal foil shielding layer being arranged in a transversely wound manner around the two insulated wires; a metal braid, the metal braiding layer being disposed on the outer periphery of the metal foil shielding layer; and a sheath, the sheath being disposed on the outer periphery of the metal braiding layer, wherein the characteristic impedance of the two-core stranded shielded cable is in the range of 100±5Ω. The insulator is made by foaming a material with a hardness of 60 or higher and 70 or lower as measured by ISO / DIS 868, which is equivalent to the JIS K 7215 D hardness. The metal foil shielding layer comprises: a resin layer in contact with the two insulated wires; and a metal layer disposed on the surface of the resin layer and in contact with the metal braid, wherein the ratio of the thickness of the metal layer to the thickness of the resin layer, i.e., metal layer thickness / resin layer thickness, is 0.40 or more and 1.20 or less.

2. The dual-core stranded shielded cable according to claim 1, characterized in that, With the distance between the centers of the two insulated wires set as D, the twisting pitch of the two insulated wires set as wpitch, the dielectric constant of the insulator set as εr, and the permeability of vacuum set as μr, the extraction frequency f1 calculated by the following equation (1) is above 6 GHz. [Formula 1] 。 3. The dual-core stranded shielded cable according to claim 1, characterized in that, With the speed of light set as c, the winding spacing of the metal foil shielding layer set as mpitch, and the dielectric constant of the insulator set as εr, the extraction frequency f2 calculated by the following equation (2) is above 6 GHz. [Equation 2] 。 4. The dual-core stranded shielded cable according to claim 2, characterized in that, The twist pitch (wpitch) between the two insulated wires is 15 mm or more.

5. The twin-core stranded shielded cable according to any one of claims 1 to 4, characterized in that, The conductors of the two insulated wires are composed of a single layer without plating.

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