Communication cable and method for manufacturing the same

Abstract

To provide a communication cable conforming to Category 8 standards that exhibits stable electrical characteristics even in a high-frequency band of 2000 MHz.SOLUTION: A communication cable 1 includes a cable core 10 including a plurality of twisted pairs 8, and a shield tape 30 covering the cable core 10. The cable core 10 has a twist pitch of 30 mm or more and less than 40 mm, and the shield tape 30 is an aluminum foil tape.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a communication cable and a method for manufacturing the same.

Background Art

[0002] Communication cables such as LAN (Local Area Network) cables are used for connecting various devices, such as between servers, between a server and a switch, and between a server and a personal computer. Such communication cables are standardized by ANSI / TIA, etc., and are classified into multiple categories according to transmission speed, transmission frequency band, etc.

[0003] Conventionally, in ANSI / TIA standards and the like, many communication cables that meet the standard characteristics of Category 6A with a transmission frequency band of 500 MHz have been developed. The communication cable generally has a cable core including a plurality of twisted pairs, a wrapping covering the cable core, a shielding layer covering the wrapping, and an outer sheath covering the shielding layer (for example, Patent Document 1). In the communication cable, usually, the cable core is twisted at a pitch of about 100 mm. Further, as the shielding layer, a laminated tape in which an aluminum layer is disposed on a polyethylene terephthalate (hereinafter, also referred to as "PET") film is often used from the viewpoint of strength and the like.

[0004] On the other hand, in recent years, in ANSI / TIA standards and the like, a Category 8 standard with a transmission frequency band of 2000 MHz has been established.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Disclosure of the Invention

Problems to be Solved by the Invention

[0006] For communication cables that meet the above Category 8 standard, stable electrical characteristics at frequencies higher than Category 6A etc. are required, and in particular, excellent electrical characteristics are required even in the frequency range of 1000 MHz or higher. However, in conventional communication cables, spike portions were likely to occur in the frequency range exceeding 1000 MHz and up to 2000 MHz for input impedance (Zin) and return loss (RL). The "spike portion" refers to a sudden disturbance in the waveform. Also, in the frequency range exceeding 1000 MHz, it was difficult for the insertion loss (IL) etc. to meet the Category 8 standard.

[0007] The main object of the present invention is to provide a communication cable that can meet the Category 8 standard and has stable electrical characteristics even in a high-frequency band of 2000 MHz.

Means for Solving the Problems

[0008] To solve the above problems, the present invention provides a cable core including a plurality of pairs of twisted wires and a shielding tape covering the cable core, wherein the twist pitch of the cable core is 30 mm or more and less than 40 mm, and the shielding tape is an aluminum foil tape.

Effects of the Invention

[0009] According to the communication cable of the present invention, it is possible to meet the Category 8 standard and stabilize the electrical characteristics even in a high-frequency band of 2000 MHz.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

DETAILED DESCRIPTION OF THE INVENTION

[0011] The communication cable of the present invention is very useful as a so-called LAN twisted pair cable. However, the use of the communication cable of the present invention is not limited to this use. Further, an embodiment of the communication cable of the present invention will be described with reference to the drawings, but the communication cable of the present invention is not limited to this embodiment.

[0012] FIG. 1 shows a cross-sectional view perpendicular to the longitudinal direction of a communication cable 1 according to an embodiment of the present invention. The communication cable 1 of this embodiment has a cable core 10, a spiral winding 20, a shielding tape 30, and an outer sheath 40.

[0013] In a conventionally known communication cable, the twist pitch of the cable core is about 100 mm, and a laminated tape of a PET film and an aluminum layer has been often used as the shielding tape. Note that the "twist pitch" in this specification refers to the distance in the longitudinal direction of the communication cable required for the cable core to rotate 360°, and when the cable core includes a cross intervention described later, it refers to the distance in the longitudinal direction of the communication cable required for the cross intervention to rotate 360°. In the conventional communication cable having the above structure, it has been difficult to stably maintain electrical characteristics in the high-frequency region.

[0014] In contrast, as a result of intensive studies by the present inventors, when the twist pitch of the cable core 10 is 30 mm or more and less than 40 mm, and the shielding tape 30 is an aluminum foil tape, the electrical characteristics become very stable even in the frequency range exceeding 1000 MHz and up to 2000 MHz. For example, it has been clarified that a communication cable capable of meeting the Category 8 standard can be obtained.

[0015] First, as a result of the studies by the present inventors, it was demonstrated that there is a close relationship between the frequency of the spike portion generated in the input impedance (Zin) and the return loss (RL), and the twist pitch of the cable core. For example, in a communication cable with a twist pitch of 90 mm, a spike portion occurred around a frequency of 1109 MHz in the input impedance (Zin) and the return loss (RL). When the twist pitch of the communication cable was set to 110 mm, the frequency of the spike portion became around 911 MHz. When the twist pitch of the communication cable was set to 130 mm, the frequency of the spike portion became around 777 MHz. Furthermore, when the twist pitch of the communication cable was set to 50 mm, the spike portion was around a frequency of 2050 MHz. That is, the smaller the twist pitch, the higher the frequency of the spike portion. And when the twist pitch is 50 mm or less, it becomes difficult for a spike portion to occur below a frequency of 2000 MHz.

[0016] The reason is considered as follows. Generally, wavelength = wave speed / frequency, and this relationship also holds between the frequency and wavelength of the signal transmitted in the cable. Here, the speed of the signal transmitted in the cable is expressed as the speed of light × NVP, and NVP (Nominal Velocity of Propagation) is about 0.7. Therefore, when this is applied to the above formula (wavelength = wave speed / frequency), the wavelength of the electrical signal with a frequency of 2000 MHz is 300,000,000 [m / s] × 0.7 / 2 [GHz] = 105 mm. Here, when the wavelength of the signal transmitted in the cable corresponds to an integer multiple (here, 2 times) of the twist pitch, it is considered that they resonate and spike portions are likely to occur. Therefore, if the twist pitch is set to 50 mm or less, which is less than 1 / 2 (= 52.5 mm) of the wavelength of the signal at a frequency of 2000 MHz, it is considered that the above resonance is less likely to occur in the frequency range of 2000 MHz or less, and spike portions are less likely to occur.

[0017] On the other hand, when the twist pitch of the cable core is set to 50 mm or less, as described above, although the maximum spike portion shifts to the frequency range above 2000 MHz and can be generally suppressed, as shown in the graph of the input impedance (Zin) in Fig. 2A and the graph of the reflection loss (RL) in Fig. 2B, it was also confirmed that spike portions remain near a frequency of 1200 MHz. Also, simply setting the twist pitch of the cable core to 50 mm or less made it difficult to improve the insertion loss amount (IL) and the like. In contrast, when the shielding tape 30 was made of an aluminum foil tape, the spike portions near a frequency of 1200 MHz disappeared, and the insertion loss amount (IL) and the like improved. The reason is considered as follows.

[0018] Fig. 3A shows a schematic diagram of the shielding tape 310 in a cross-section parallel to the length direction of a conventional communication cable. Fig. 3B shows a side view of the communication cable (in a state where the shielding tape 310 is wound). In the communication cable, the shielding tape 310 is composed of a PET film 310a and an aluminum layer 310b, and these are wound in a helical shape and overlap with a certain width at a time. In this case, as shown in Fig. 3A, at the overlapping part of the shielding tapes 310, the PET film 310a is disposed between the two aluminum layers 310b. That is, electricity does not conduct between the two aluminum layers 310b. Therefore, as shown in Fig. 3B, the current (the dotted line represented by C in Fig. 3B) propagating through the shielding tape 310 flows in a helical shape along the winding direction of the shielding tape 310. As a result, it is considered that the current flowing through the shielding tape 310 and the signal flowing inside the communication cable interact with each other, resulting in the generation of spike parts or the failure to improve electrical characteristics.

[0019] Fig. 4A shows a schematic diagram of the shielding tape 30 in a cross-section parallel to the length direction of the communication cable of this embodiment, and Fig. 4B shows a side view of the communication cable (in a state where the shielding tape 30 is wound). In the communication cable of this embodiment, the shielding tape 30 is composed of an aluminum foil tape. Therefore, even if the shielding tape 30 is wound in a helical shape and overlaps with a certain width at a time, electricity can conduct at the overlapping part of the shielding tapes 30. Therefore, the current (the dotted line represented by C in Fig. 4B) propagating through the shielding tape 30 travels linearly in the length direction of the communication cable. Thus, it is difficult for the current flowing through the shielding tape 30 and the signal flowing inside the communication cable to interact with each other. As a result, for example, as shown in the graph of the input impedance (Zin) in Fig. 5A and the graph of the reflection attenuation amount (RL) in Fig. 5B, the spike part near the frequency of 1200 MHz disappears, and it is considered that other electrical characteristics also become stable.

[0020] Furthermore, the inventors of the present invention examined the margin of the reflection attenuation amount (RL). The "margin" is the difference between the standard value of each frequency and the measured total frequency, and the "worst margin" is the smallest value among the above differences. The larger the numerical value, the larger the margin, indicating that the reflection attenuation amount (RL) characteristic is good. According to the examination by the inventors of the present invention, it was revealed that when the twist pitch of the cable core 10 is 30 mm or more and less than 40 mm, the worst margin is large and the reflection attenuation amount (RL) characteristic is dramatically improved.

[0021] The reason is considered as follows. When the twist pitch of the cable core 10 (the collective twist pitch of the counter-twisted wires 8 described later) is long, the twisting is likely to be disturbed, and when the twist pitch is short, the twisting is less likely to be disturbed and is easy to stabilize. When the twist pitch is disturbed, an inconsistency in characteristic impedance occurs, and the reflection attenuation amount (RL) characteristic is disturbed. Therefore, a shorter twist pitch is effective for improving the reflection attenuation amount (RL) characteristic.

[0022] Hereinafter, a more specific configuration of the communication cable of the present embodiment will be described. In the communication cable 1 of the present embodiment, the cable core 10 has a plurality of pairs (here, 4 pairs) of counter-twisted wires 8 and a cross interposition 9 for separating the plurality of counter-twisted wires 8 from each other. Each counter-twisted wire 8 has a configuration in which two insulated electric wires 6 in which a conductor 2 is covered with an insulator 4 are twisted together. Usually, the conductor 2 is composed of a soft copper wire, and the insulator 4 is composed of a polyethylene resin.

[0023] Here, the diameter of the cross section perpendicular to the length direction of the conductor 2 is not particularly limited, but is preferably 0.405 mm or more and 0.510 mm or less, and a diameter corresponding to 26 to 24 AWG (American Wire Gauge) is preferable. As described above, in the present embodiment, the twist pitch of the cable core 10 is 50 mm or less. Therefore, when the diameter of the conductor 2 is within the above range, the cable core 10 can be twisted without difficulty.

[0024] Further, the cross member 9 extends in the longitudinal direction of the communication cable 1 and is a member for isolating the twisted pairs 8 from each other and separating them so that they do not come into contact. The shape of the cross member 9 is not particularly limited as long as it can isolate a plurality of twisted pairs 8. Also, the cross member 9 is made of a polyethylene resin.

[0025] As described above, the cross member 9 is twisted along the longitudinal direction of the communication cable 1, and accordingly, the twisted pairs 8 are also twisted while being separated by the cross member 9. The twist pitch at this time may be 50 mm or less, but it is preferably 30 mm or more and 50 mm or less so that it can be twisted without difficulty or from a manufacturing perspective, and more preferably 30 mm or more and less than 40 mm in consideration of the worst margin of the return loss (RL).

[0026] Around the cable core 10, a wrapping 20 is installed. The wrapping 20 is a member for keeping the distance between the conductor 2 and the shielding tape 30 in the cable core 10 constant. The type of the wrapping 20 is not particularly limited, but in this embodiment, the wrapping 20 can be, for example, a high-density polyethylene tape. Also, the winding method of the wrapping 20 is not particularly limited, and in this embodiment, it is wound horizontally along the longitudinal direction of the cable core 10. In this specification, "wound horizontally" means winding a long tape in a spiral shape along the longitudinal direction of the cable core 10, and winding while overlapping the side edge portion of the tape on the tape that has been wound first. The thickness and number of layers of the wrapping 20 are not particularly limited as long as they do not impair the object and effect of this embodiment.

[0027] Around the wrapping 20, a shielding tape 30 is installed. The shielding tape 30 is composed of an aluminum foil tape as described above. In this specification, "aluminum foil tape" refers to a tape composed only of aluminum.

[0028] In the above-mentioned shielding tape 30 (aluminum foil tape), the thickness is not particularly limited, but is preferably 30 mm or more and 50 mm or less, and more preferably 35 mm or more and 45 mm or less. If the thickness of the shielding tape 30 is too thin, the strength may be insufficient. On the other hand, if it is too thick, it may be difficult to wind.

[0029] Also, the width of the above-mentioned shielding tape 30 (aluminum foil tape) is not particularly limited, but is preferably 10 mm or more and 20 mm or less, and more preferably 12 mm or more and 15 mm or less. If the width of the shielding tape 30 is too narrow, it will take time to wind. On the other hand, if the width of the shielding tape 30 is too wide, the handleability will be low.

[0030] Here, the winding method of the shielding tape 30 is not particularly limited, but in this embodiment, it is preferable that the shielding tape 30 is wound horizontally along the length direction of the cable core 10. In this embodiment, the shielding tape 30 is wound so as to overlap with a certain width.

[0031] When winding the shielding tape 30, the overlapping width of the shielding tape 30 is preferably about 1 / 4 or more and 1 / 2 of the width of the shielding tape 30. Also, the winding pitch at this time is preferably 10.0 mm or more and 13.5 mm or less. When the overlapping width and the winding pitch are within the above ranges, the performance of the communication cable 1 is more likely to be stable. The winding pitch refers to the length of the shielding tape 30 required to make one turn (360°) of the push winding 20 when the shielding tape 30 is wound spirally around the push winding 20.

[0032] Also, an outer sheath 40 is formed on the outer periphery of the shielding tape 30. The outer sheath 40 is made of polyvinyl chloride resin. The outer sheath 40 is a so-called sheath, which covers the outer periphery of the shielding tape 30 and forms the outermost layer of the communication cable 1.

[0033] Next, the manufacturing method of the above-mentioned communication cable 1 will be described. First, as the conductor 2, a single wire of soft copper wire is prepared. Then, while transporting the conductor 2 in the length direction, polyethylene resin is extruded from the die of an extruder to coat the conductor 2 with the insulator 4, thereby forming an insulated wire 6. Subsequently, two insulated wires 6 are twisted together to form a pair-twisted wire 8, and four pairs of pair-twisted wires 8 are arranged along the cross-interposition 9 to form a cable core 10.

[0034] Thereafter, the cable core 10 is twisted at a predetermined pitch (in this embodiment, a pitch of 30 mm or more and less than 40 mm), and the extrusion wrap 20 (high-density polyethylene tape) is wound around the cable core 10 horizontally.

[0035] Around the extrusion wrap 20, a shielding tape 30 (aluminum foil tape) is wound horizontally at the above-mentioned winding pitch and overlapping width. Thereafter, while transporting the cable core 10 around which the extrusion wrap 20 and the shielding tape 30 are wound in the length direction, polyvinyl chloride resin is extruded from the die of an extruder to coat the shielding tape 30 with the outer sheath 40. Thereby, the communication cable 1 is manufactured.

[0036] According to the above-described embodiment, a communication cable having stable electrical characteristics even at a high frequency and capable of satisfying, for example, the Category 8 standard can be obtained.

Example

[0037] (1) Experimental Example 1 (1.1) Sample 1 As the conductor, a soft copper wire (single wire) with an outer diameter of 0.585 mm (AWG23) was prepared. And as the resin of the insulator, high-density polyethylene was prepared and extruded from the die of an extruder to coat the conductor with the insulator. Thereafter, two insulated wires with an outer diameter of 1 mm were twisted together to form a pair-twisted wire with an outer diameter of about 2 mm. Subsequently, a cross-interposition was prepared, and four pairs of pair-twisted wires were arranged along the cross-interposition to form a cable core, and the cable core was twisted at a pitch of 90 mm.

[0038] After that, three press rolls (high-density polyethylene tapes) were prepared and wound around the cable core horizontally. Further, an Al / PET tape (Al thickness: 30 μm, PET thickness: 12 μm, width: 20 mm) was prepared as a shielding tape and wound around the periphery of the press roll horizontally. At this time, the winding pitch was set to 18.9 mm, and it was wound with an overlap of 5 mm (1 / 4 lap) each time. After that, polyvinyl chloride was prepared as the resin for the outer sheath, and this was extruded from the die of an extruder to coat the shielding tape with the outer sheath, and a communication cable with an outer diameter of about 8.8 mm was manufactured.

[0039] (1.2) Samples 2 to 6 In Sample 1, the twist pitch of the cable core was changed as shown in Table 1 below. Other than that, a communication cable was manufactured in the same manner as Sample 1.

[0040] (1.3) Evaluation Each sample was cut out to 30 m, and for each cut-out piece, the input impedance (Zin), return loss (RL), and insertion loss (IL) were measured using a LAN cable automatic measuring device (ES-2G manufactured by BETA LASER MIKE) and evaluated according to the following criteria.

[0041] · Zin high-frequency spike 〇: No spike part is confirmed in the frequency band above 1000 MHz ×: A spike part is confirmed in the frequency band above 1000 MHz

[0042] · RL 〇: Meets the Category 8 standard of ANSI / TIA standard ×: Does not meet the Category 8 standard of ANSI / TIA standard

[0043] · RL worst margin The margin is the difference between the standard value of each frequency and the measured all frequencies. The worst margin is the smallest value among the above differences. The larger this numerical value is, the larger the margin is, indicating better characteristics. The numerical values are shown in Table 2 below.

[0044] ·RL High - frequency Spike 〇: No spike part is confirmed in the frequency band above 1000 MHz ×: A spike part is confirmed in the frequency band above 1000 MHz

[0045] ·IL 〇: Meets the Category 8 standard of ANSI / TIA standard ×: Does not meet the Category 8 standard of ANSI / TIA standard ·IL High - frequency Spike 〇: No spike part is confirmed in the frequency band above 1000 MHz ×: A spike part is confirmed in the frequency band above 1000 MHz

[0046]

Table 1

[0047] From the comparison between Samples 1 - 3 and Samples 4 - 6, it was confirmed that by shortening the twist pitch of the cable core, the high - frequency spike parts (the largest spike parts) of the input impedance (Zin) and the return loss (RL) move to the high - frequency side. However, as shown in Table 1 above, in any of Samples 1 - 6, none of the input impedance (Zin), return loss (RL), and insertion loss (IL) met the desired standards.

[0048] (2) Experimental Example 2 (2.1) Sample 7 In Sample 1, a soft copper wire (single wire) with an outer diameter of 0.510 mm (24 AWG) was used as the conductor, the twist pitch of the cable core was set to 40 m, and two sheets of high - density polyethylene tape were used as the overwrap. Otherwise, a communication cable was manufactured in the same manner as Sample 1.

[0049] (2.2) Sample 8 In Sample 7, one sheet of high-density polyethylene tape was used as a roll-up tape, and the winding pitch of the masking tape was changed as shown in Table 2. Other than that, a communication cable was produced in the same manner as Sample 7.

[0050] (2.3) Samples 9 and 10 In Sample 8, the twisting pitch of the cable core was changed as shown in Table 2. Other than that, a communication cable was produced in the same manner as Sample 8.

[0051] (2.4) Sample 11 In Sample 8, the width and winding pitch of the masking tape were changed as shown in Table 2. Other than that, a communication cable was produced in the same manner as Sample 8.

[0052] (2.5) Sample 12 In Sample 11, the masking tape was changed to an aluminum foil tape (thickness 40 μm). Other than that, a communication cable was produced in the same manner as Sample 11.

[0053] (2.6) Samples 13 and 14 In Sample 12, the width and winding pitch of the masking tape were changed as shown in Table 2. Other than that, a communication cable was produced in the same manner as Sample 12.

[0054] (2.7) Samples 15 - 17 In Sample 13, the twisting pitch of the cable core was changed as shown in Table 2. Other than that, a communication cable was produced in the same manner as Sample 13.

[0055] (2.8) Evaluation Each sample was cut out to 30 m, and for each cut-out piece, the input impedance (Zin), return loss (RL), and insertion loss (IL) were measured and evaluated in the same manner as above.

[0056]

Table 2

[0057] As shown in Table 2 above, by not only setting the twist pitch of the cable core to 50 mm or less but also changing the shielding tape to aluminum foil, each spike portion disappeared, and good results were obtained for all of the input impedance (Zin), return loss (RL), and insertion loss (IL). Furthermore, by setting the twist pitch of the cable core to 30 mm or more and less than 40 mm, the worst margin of the return loss (RL) also improved.

Explanation of Signs

[0058] 1 Communication cable 2 Conductor 4 Insulator 6 Insulated wire 8 Twisted pair 9 Cross intervention 10 Cable core 20 Spiral wrapping 30 Shielding tape 40 Outer sheath 310 Shielding tape 310a PET film 310b Aluminum layer

Claims

1. A cable core including a plurality of pairs of twisted wires, and a shielding tape covering the cable core, wherein a twist pitch of the cable core is 30 mm or more and less than 40 mm, and the shielding tape is an aluminum foil tape, a communication cable.

2. In the communication cable according to Claim 1, the shielding tape is wound in a spiral shape, and a winding pitch of the shielding tape is 10 mm or more and 13.5 mm or less, a communication cable.

3. A method for manufacturing a communication cable including a cable core including a plurality of pairs of twisted wires, and a shielding tape covering the cable core, the method including a step of twisting the cable core at a pitch of 30 mm or more and less than 40 mm, and a step of preparing an aluminum foil tape as the shielding tape and winding the shielding tape around the cable core horizontally, a method for manufacturing a communication cable.

4. In the method for manufacturing a communication cable according to Claim 3, in the step of winding the shielding tape horizontally, the shielding tape is wound around the cable core in a spiral shape at a winding pitch of 10 mm or more and 13.5 mm or less, a method for manufacturing a communication cable.

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