JP7139975B2 - communication cable - Google Patents

Description

The present invention relates to communication cables.

As a conventional technique, four insulated wire cores with the same outer diameter are twisted into a star-shaped quad, covered with a pressing insulation layer on the outside, an electromagnetic shield layer is formed on the outside, and a thermoplastic material is formed on the outside. A telecommunication cable having a resin sheath layer is known (see, for example, Patent Document 1).

JP-A-11-144532

In order to save space and reduce the weight of conventional electronic communication cables, if the conductor size is reduced by reducing the diameter of the insulated core, the conductor resistance increases and the transmission characteristics deteriorate. Therefore, it has been difficult for conventional electronic communication cables to reduce the conductor size while satisfying the required standard values.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a communication cable having a reduced diameter without impairing transmission characteristics.

In order to solve the above problems, the present invention has at least four electric wires in which conductors are covered with an insulator, a film-like substrate, and a metal layer provided on the substrate, and at least four electric wires. and a shield tape spirally wound so that a part overlaps with the outer diameter of the twisted strand of at least four electric wires is 4 mm or less, and the thickness of the metal layer is 30 μm or more. Provide communication cables.

ADVANTAGE OF THE INVENTION According to this invention, the communication cable which diameter was reduced can be provided, without impairing a transmission characteristic.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the communication cable which concerns on one embodiment of this invention, (a) is a figure which shows an external appearance, (b) is sectional drawing which shows a cross section perpendicular|vertical to a longitudinal direction. (a) is a cross-sectional view schematically showing a cross section of a portion where shield tapes overlap, and (b) is a cross-sectional view showing a cross section perpendicular to the longitudinal direction of an insulator. (a) is a graph relating to characteristic impedance when an insulator with an increased degree of foaming is used, and (b) is a graph of attenuation of a comparative example having a thin metal layer. (a) is a graph showing the relationship between the depth of the current region and the frequency, and (b) is a graph showing the amount of attenuation in one embodiment with a thick metal layer. It is a figure which shows the communication cable which concerns on other embodiment of this invention, (a) is a figure which shows an external appearance, (b) is sectional drawing which shows a cross section perpendicular|vertical to a longitudinal direction.

[Embodiment]
BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1(a) is a diagram showing a communication cable according to this embodiment, and FIG. 1(b) is a sectional view showing a section perpendicular to the longitudinal direction. FIG. 2(a) is a cross-sectional view schematically showing the cross section of the portion where the shield tape overlaps, and FIG. 2(b) is a cross-sectional view showing a cross section perpendicular to the longitudinal direction of the insulator. FIG. 3(a) is a graph of characteristic impedance when using an insulator with an increased degree of foaming, and FIG. 3(b) is a graph of attenuation of a comparative example with a thin metal layer. FIG. 4A is a graph showing the relationship between the depth of the current region and the frequency, and FIG. 4B is a graph showing attenuation in this embodiment having a thick metal layer. In FIG. 3A, the horizontal axis is frequency (MHz) and the vertical axis is characteristic impedance (Ω). In FIGS. 3(b) and 4(b), the horizontal axis represents frequency (MHz) and the vertical axis represents attenuation (dB/100 m). In FIG. 4A, the horizontal axis is the frequency (MHz) and the vertical axis is the depth of the current region (μm).

Note that in each drawing according to the embodiments described below, the ratio between figures may differ from the actual ratio. Also, "A to B" indicating a numerical range is used in the sense of A or more and B or less.

As shown in FIGS. 1(a) to 2(a), a communication cable 1 includes four electric wires 2 each having a conductor 20 covered with an insulator 21, a film-like substrate 50, and one surface of the substrate 50. and a shield tape 5 spirally wound so as to partially overlap the four electric wires 2, and the twisted outer in which the four electric wires 2 are twisted The diameter D2 is ₄ mm or less, and the thickness L of the metal layer 51 is 30 μm or more. The twisted outer diameter D2 of the four electric wires ₂ in this embodiment is 3 mm or less.

This communication cable 1 is provided between four electric wires 2 and a shield tape 5 and has a flame-retardant tape 4 made of a flame-retardant material. Further, the communication cable 1 includes a braided shield 6 covering the circumference of the shield tape 5 and a sheath 7 covering the braided shield 6. - 特許庁

The communication cable 1 is, for example, a LAN (Local Area Network) cable used for inter-vehicle communication MVB (Multifunction Vehicle Bus) of railway vehicles and inter-train communication WTB (Wire Train Bus) of a railway network. This communication cable 1 connects, for example, surveillance cameras and computers mounted on railroad vehicles to each other. The communication cable 1 of the present embodiment is, for example, a cable conforming to the Category 5e standard. The communication cable 1 of this embodiment transmits signals of 1 MHz to 100 MHz, for example. 2. Description of the Related Art In recent years, the number of cables used has increased along with the increase in the amount of information transmission between and in-vehicle electronic devices due to the sophistication of railway vehicles. Therefore, cables are required to have a smaller diameter for space saving and weight reduction. The communication cable 1 of this embodiment has a configuration that allows the diameter to be reduced without impairing transmission characteristics.

(Electric wire 2)
As shown in FIGS. 1(a) and 1(b), the electric wire 2 of this embodiment is helically twisted around the linear body 3. As shown in FIGS. The linear body 3 is made of polyethylene (PE) or the like and has a circular cross section. The cross-sectional shape of linear body 3 is not limited to a circular shape. All the electric wires 2 are in direct contact with the outer peripheral surface of the linear body 3 .

The electric wire 2 has a conductor 20 formed by twisting a plurality of strands and an insulator 21 covering the conductor 20 . As the wire, for example, a copper wire, a copper alloy wire, or the like can be used, and a wire whose outer periphery is plated with a metal such as tin or nickel may be used. In this embodiment, a tin-plated annealed copper wire is used as the wire used for the conductor 20 . As shown in FIGS. 1(a) and 1(b), the conductor 20 is constructed by twisting seven strands. The outer diameter d of this conductor 20 is 0.615 mm. Also, the cross-sectional area of the conductor 20 is 0.25 mm ² . Furthermore, the outer diameter D2 of the four electric wires ₂ is 2.97 mm. The outer diameter D2 of the four electric wires ₂ is the twisted outer diameter of the four electric wires 2 spirally twisted around the linear body 3, that is, the outer diameter of the assembly (cable core). means.

The insulator 21 includes a sealing layer 210 provided around the conductor 20, a reinforcing layer 212 provided radially away from the sealing layer 210, and a foamed resin between the sealing layer 210 and the reinforcing layer 212. and a foam layer 211 provided therebetween, and the foam layer 211 is configured to have a degree of foaming that provides a dielectric constant εr corresponding to the required characteristic impedance Z0.

The sealing layer 210 and reinforcing layer 212 are formed using polyethylene. The foam layer 211 is formed using foamed polypropylene or irradiation-crosslinked foamed polyethylene. The foam layer 211 of the present embodiment is irradiation crosslinked foamed polyethylene. The irradiation-crosslinked foamed polyethylene is formed into a sponge-like shape containing a large number of cells 211a using a foaming agent, and is further irradiated with an electron beam to improve heat resistance and mechanical properties.

The sealing layer 210 and the reinforcing layer 212 are provided to reinforce the pressure and gas from escaping along the conductor 20 when the degree of foaming is increased.

(Flame-retardant tape 4)
The flame-retardant tape 4 is formed in a tape shape using flame-retardant resin such as polyimide. The flame-retardant tape 4 is spirally wound so as to partially overlap at least four electric wires 2 . This flame-retardant tape 4 is provided because fire safety (flame retardancy and low smoke emission) is required because the communication cable 1 is wired in railway vehicles at high density.

(Shield tape 5)
As shown in FIG. 2A, the shield tape 5 is spirally wound so that the substrate 50 is on the flame-retardant tape 4 side and the metal layer 51 is on the braided shield 6 side. The shield tape 5 is spirally wound in the opposite direction to the flame-retardant tape 4 .

The substrate 50 of this embodiment is formed using polyethylene terephthalate (PET). Moreover, the metal layer 51 is formed using copper, aluminum, or the like. Metal layer 51 of the present embodiment is formed using aluminum.

(Braided shield 6)
The braided shield 6 is formed by weaving a tin-plated annealed copper wire into a mesh. This braided shield 6 suppresses noise from the outside and is connected to the ground.

(Sheath 7)
The sheath 7 is made of polyvinyl chloride (PVC), polyethylene (PE), irradiation-crosslinked flame-retardant polyolefin, or the like. The sheath 7 of the present embodiment is formed using irradiation-crosslinked flame-retardant polyolefin having high flame retardancy. The sheath 7 using this radiation-crosslinked flame-retardant polyolefin is halogen-free and has high durability against external factors such as chemicals and oil. If the sheath 7 is made of a halogen-free material, the communication cable 1 according to this embodiment will be a non-halogen communication cable.

(Evaluation of transmission characteristics)
In the following, the characteristic impedance _Z0 and the amount of attenuation will be described as evaluation of transmission characteristics. This characteristic impedance _Z0 is the ratio of voltage to current. Attenuation is the energy ratio between the input signal and the output signal.

The characteristic impedance _Z0 required by Category 5e is 100Ω. Therefore, the relative dielectric constant ε _r targeted by the diameter reduction is 1.38 when the required characteristic impedance Z ₀ is rearranged. As a result of this calculation, in order for the communication cable 1 to satisfy the characteristic impedance Z ₀ (100±15Ω) required by Category 5e, it is necessary to lower the dielectric constant ε _r of the insulator 21 from 2.26 to 1.38. There is

The dielectric constant _εr of the foamed insulator can be calculated by the following equation (1).
ε _r =ε _A ^(1−V) (1)
ε _A : dielectric constant of polyethylene: 2.26
V: degree of foaming The target dielectric constant ε _r of the insulator 21 is 1.38, so substituting this value yields a degree of foaming V of 60%. Therefore, the degree of foaming is preferably 60% or more.

As shown in FIG. 3(a), the communication cable produced with the degree of foaming of 60% had the characteristic impedance _Z0 within the standard lower limit and standard upper limit of category 5e. In addition, the lower limit of the shaded area in FIG. 3A is the standard lower limit (85Ω), and the upper limit is the standard upper limit (115Ω). The solid line in FIG. 3(a) is the measured characteristic impedance _Z0 .

As shown in FIGS. 3(a) and 3(b), the communication cable with the degree of foaming of 60% satisfies the standard value of category 5e, while the attenuation amount exceeds the standard value.

The increase in attenuation is due to (1) resistance loss (inner conductor loss) due to current flowing in the inner conductor (conductor 20), (2) loss due to heat generation of the insulator (insulator 21) (dielectric loss), and (3) external The main causes are thought to be resistance loss (outer conductor loss) due to current flowing through the conductor (shielding tape 5) and (4) loss due to leakage of electrical energy (radiation loss).

(1) Since the cross-sectional area of the conductor 20 is set to 0.25 mm ² in order to reduce the diameter of the communication cable 1, the internal conductor loss is lower than that of a conductor with a standard cross-sectional area (0.5 mm ² ). is an unavoidable loss. (2) The contribution of dielectric loss to the increase in attenuation is minimal in the signal frequency range of 1 MHz to 100 MHz.

(3) Outer conductor loss and (4) radiation loss can be suppressed by suppressing the current flowing through the braided shield 6, as shown in FIG. 4(a). Therefore, the attenuation amounts when the metal layer 51 is thin and when the metal layer 51 is thick will be described below.

FIG. 4(a) is a graph of the frequency of the signal and the depth of the current region. The dotted line in FIG. 4A indicates the thickness of the metal layer of the comparative example, the lower side of the dotted line corresponds to the shield tape side, and the upper side corresponds to the braided shield side. 4A indicates the thickness (2L) of the metal layer 51 of this embodiment, the lower side of the solid line corresponds to the shield tape 5 side, and the upper side corresponds to the braided shield 6 side.

The current region shown in FIG. 4A indicates the depth through which the current flows. For example, when the thickness of the metal layer of the shielding tape of the comparative example is 7.5 μm, the thickness of the metal layer of the portion where the metal layer is spirally wound and overlapped is 15 μm (2×7.5 μm). ), a current flows through the shield tape in the vicinity of 100 MHz. At other frequencies, on the other hand, the current flows not only through the shielding tape, but also into deeper regions, and thus through the braided shield. Therefore, if the metal layer is thin, radiation losses increase.

However, in the communication cable 1 of the embodiment, the thickness of the metal layer 51 is 30 μm, and the thickness of the overlapping portion is 60 μm (2×30 μm). Although current flows to the braided shield 6 side in a narrow range, current flows only to the shield tape 5 at most frequencies. Therefore, when the metal layer is thick, it is expected to suppress the increase in radiation loss.

FIG. 4B shows the result of measuring the attenuation amount when the thickness of the metal layer 51 is 30 μm (the overlapping portion is 60 μm) with a solid line. When the thickness of the overlapped portion of the metal layer 51 was set to a thickness sufficient for the skin depth through which current flows, the attenuation satisfied the standard value.

As described above, the communication cable 1 according to the embodiment has a small diameter as a whole by thinning the wire 2 and increasing the thickness of the metal layer 51 of the shield tape 5. ₀ and attenuation can be satisfied. In other words, the communication cable 1 can prevent degradation of attenuation by preventing signal loss, and can be made thinner. The communication cable 1 of the present embodiment has an outer diameter D3 of 4.63 mm _, which can be made thinner than a cable with a standard outer diameter (eg, 8.1 mm).

(Actions and effects of the embodiment)
As described above, the communication cable 1 according to the present embodiment includes four electric wires 2 in which the conductors 20 are covered with the insulator 21, the film-like substrate 50, and the metal layer 51 provided on the substrate 50. and a shield tape 5 spirally wound so as to partially overlap the four electric wires 2, and the twisted outer diameter D2 of the twisted four electric wires ₂ is 4 mm or less. The thickness L of the metal layer 51 is set to 30 μm or more.

By configuring in this way, it is possible to achieve both the reduction in diameter and the transmission characteristics, which are originally in a trade-off relationship, and to realize the communication cable 1 with a reduced diameter without impairing the transmission characteristics. As a result, the manufacturing cost of the communication cable 1 can be reduced by reducing the diameter, and the cost of the product can be reduced.

In addition, the communication cable 1 can achieve the transmission characteristics, physical properties, and fire safety (flame retardancy of the material, low smoke generation), which are the required characteristics of category 5e for vehicles, while being made thinner.

(Other embodiments)
FIG. 5(a) is a diagram showing a communication cable according to another embodiment, and FIG. 5(b) is a sectional view showing a section perpendicular to the longitudinal direction. In this embodiment, portions having the same functions and configurations as those of the above-described embodiment are denoted by the same reference numerals as those of the above-described embodiment, and description thereof will be omitted.

As shown in FIGS. 5(a) and 5(b), the communication cable 1 of this embodiment includes four electric wires 2, a linear body 3, a shield tape 5, a braided shield 6, and a sheath 7. , is configured with In other words, the communication cable 1 of this embodiment does not have the flame-retardant tape 4 .

Since the communication cable 1 of the present embodiment is configured without the flame-retardant tape 4, the diameter can be further reduced.

(Summary of embodiment)
Next, technical ideas understood from the embodiments described above will be described with reference to the reference numerals and the like in the embodiments. However, each reference numeral and the like in the following description do not limit the constituent elements in the claims to the members and the like specifically shown in the embodiment.

[1] At least four electric wires (2) in which conductors (20) are covered with insulators (21), a film-like substrate (50), and a metal layer (51) provided on the substrate (50) and a shield tape (5) spirally wound so as to partially overlap the at least four electric wires (2), wherein the at least four electric wires (2) are twisted together. A communication cable (1) having a combined outer diameter (D ₂ ) of 4 mm or less and a thickness (L) of the metal layer (51) of 30 μm or more.

[2] The communication cable (1) according to [1], wherein the twisted outer diameter (D ₂ ) of the at least four electric wires (2) is 3 mm or less.

[3] The insulator (21) includes a sealing layer (210) provided around the conductor (20) and a reinforcing layer (212) provided radially apart from the sealing layer (210). and a foam layer (211) made of foamed resin and provided between the sealing layer (210) and the reinforcing layer (212), wherein the foam layer (211) has a required characteristic impedance. The communication cable (1) according to [1] or [2], having a degree of foaming that provides a non-dielectric constant according to

[4] The communication cable (1) according to [3], wherein the required characteristic impedance is 100Ω±15 and the degree of foaming is 60% or more.

[5] [1] to [ 4], the communication cable (1) according to any one of the above items.

Although the embodiments of the present invention have been described above, the embodiments described above do not limit the invention according to the scope of claims. Also, it should be noted that not all combinations of features described in the embodiments are essential to the means for solving the problems of the invention.

The present invention can be appropriately modified and implemented without departing from the gist thereof. For example, in the above-described embodiment, the case where four electric wires 2 are used has been described, but six, eight, or ten or more electric wires 2 may be used.

DESCRIPTION OF SYMBOLS 1... Communication cable 2... Electric wire 3... Linear body 4... Flame-retardant tape 5... Shield tape 6... Braided shield 7... Sheath 20... Conductor 21... Insulator 50... Substrate 51... Metal layer 210... Seal layer 211... Foam layer 211a... bubble 212... reinforcement layer

Claims (4)

at least four wires with conductors covered with insulation;
a shielding tape having a film-like substrate and a metal layer provided on the substrate, the shielding tape being spirally wound so as to partially overlap the at least four electric wires;
A flame-retardant tape provided between the at least four electric wires and the shield tape and spirally wound in a direction opposite to the shield tape, and formed using a flame-retardant resin made of polyimide;
with
The twisted outer diameter of the at least four electric wires is 4 mm or less,
The thickness of the metal layer is 30 μm or more,
communication cable. The twisted outer diameter of the at least four electric wires is 3 mm or less,
A communication cable according to claim 1. The insulator is
a sealing layer provided around the conductor;
a reinforcing layer radially spaced apart from the sealing layer;
a foamed layer of foamed resin provided between the sealing layer and the reinforcing layer;
with
The foam layer has a degree of foaming that provides a dielectric constant corresponding to the required characteristic impedance,
A communication cable according to claim 1 or 2. The required characteristic impedance is 100Ω±15,
The degree of foaming is 60% or more,
A communication cable according to claim 3.

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