Description:CROSS-REFERENCE TO RELATED APPLICATION
The present application claims priority from Japanese Patent Application No. 2024-86406 filed on May 28, 2024, the content of which is hereby incorporated by reference into this application.

TECHNICAL FIELD OF THE INVENTION
The present invention relates to a LAN cable.

BACKGROUND OF THE INVENTION
LAN cables are cables each used to build a LAN (Local Area Network). Such a LAN cable has been known to have a structure including a sheath that covers an outer periphery of an insulated electrical wire having an insulated layer formed on an outer periphery of a conductor, in which a non-halogen flame-retardant resin composite is used for the sheath.
Among the LAN cables, a LAN cable for railway vehicles may be required to have extremely high flame retardancy that satisfies fire safety (single-wire flame retardant test) of the EN standard that is the European unified standard, and may be also required to satisfy physical properties such as cable strength, elongation, low-temperature property, or the like.
In satisfying such high flame retardancy, a method of increasing a mixture content of a flame retardant is generally conceivable. However, too many mixture content of the flame retardant decreases the physical properties of the sheath. Therefore, it is difficult to provide a LAN cable in which these properties are satisfied by only the sheath.
Therefore, as the LAN cable that satisfies the properties described above, a LAN cable has been known, the LAN cable as a whole satisfying the properties because of including a flame-retardant tape such as polyimide film provided between the insulated electrical wire and the sheath covering the outer periphery thereof, in which the sheath has a predetermined degree of crosslinking (see, for example, Japanese Patent Application Laid-open Publication No. 2021-64623 (Patent Document 1)).

SUMMARY OF THE INVENTION
Incidentally, in recent years, such a LAN cable has been also required to have a small diameter. However, in the above-described application, it is necessary to ensure the high flame retardancy, and therefore, the flame-retardant tape provided between the sheath and the insulated electrical wire cannot be removed. Consequently, there has been a limit in the reduction in the diameter.
Accordingly, an objective of the present invention is to provide a LAN cable capable of reducing the diameter and ensuring the high flame retardancy.
A LAN cable according to an embodiment is a LAN cable including: an intertwined pair wire formed by intertwining two insulated electrical wires; a bundled intertwined wire formed by intertwining a plurality of the intertwined pair wires; and a sheath covering an outer periphery of the bundled intertwined wire. The LAN cable has an outside diameter of 8.8 mm or less, and the sheath is made of a non-halogen flame-retardant resin composite containing base polymer, metal hydroxide, and carbon black. A content of the metal hydroxide is 180 to 190 parts by mass per 100 parts by mass of the base polymer, and a content of the carbon black is 15 to 20 parts by mass per 100 parts by mass of the base polymer. The insulated electrical wire has an outside diameter of 1.5 mm or less, and the bundled intertwined wire has an outside diameter of 6.5 mm or less.
A LAN cable according to an embodiment is a LAN cable including: a bundled intertwined wire formed by intertwining a plurality of insulated electrical wires; and a sheath covering an outer periphery of the bundled intertwined wire. The LAN cable has an outside diameter of 8.8 mm or less, and the sheath is made of a non-halogen flame-retardant resin composite containing base polymer, metal hydroxide, and carbon black. A content of the metal hydroxide is 180 to 190 parts by mass per 100 parts by mass of the base polymer, and a content of the carbon black is 15 to 20 parts by mass per 100 parts by mass of the base polymer. The insulated electrical wire has an outside diameter of 2.5 mm or less, and the bundled intertwined wire has an outside diameter of 5.5 mm or less.
According to the LAN cable of the embodiment, the LAN cable capable of reducing the diameter and ensuring the high flame retardancy can be provided.

BRIEF DESCRIPTIONS OF THE DRAWINGS
FIG. 1 is a schematic cross-sectional view of a LAN cable according to an embodiment;
FIG. 2 is a schematic cross-sectional view of a test cable according to another embodiment;
FIG. 3 is a schematic cross-sectional view of a LAN cable according to a modification example of FIG. 1;
FIG. 4 is a schematic cross-sectional view of a LAN cable according to another modification example of FIG. 1;
FIG. 5 is a schematic cross-sectional view of a LAN cable according to a modification example of FIG. 2; and
FIG. 6 is a schematic cross-sectional view of a LAN cable according to another modification example of FIG. 2.

DESCRIPTIONS OF THE PREFERRED EMBODIMENTS
Hereinafter, a LAN cable according to the present invention will be described with reference to embodiments.
Note that the same components are denoted by the same reference symbols throughout all drawings for describing the embodiments in principle, and the repetitive description thereof is omitted. Note that hatching may be omitted even in a cross-sectional view in order to make the drawings easy to see. Similarly, hatching may be put even in a plan view.
The following description uses terms “insulated electrical wire”, “intertwined pair wire”, and “bundled intertwined wire”. The insulated electrical wire is an electrical wire in which a linear conductor is covered with an insulating layer. The intertwined pair wire is an electric wire in which two (in other words, a pair of) insulated electrical wires are intertwined. The bundled intertwined wire is an electrical wire in which two or more intertwined pair wires or three or more insulated electrical wires are intertwined. The conductor is a wire made of a conductive material. As described later, the conductor may be a single wire or may adopt an intertwined wire structure in which a plurality of bare wires are intertwined, or adopt a single wire or a bare wire, a surface of which includes a plated film formed thereon.
[LAN Cable]
A LAN cable according to the present embodiment will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view of the LAN cable according to the embodiment. As illustrated in FIG. 1, the LAN cable according to the present embodiment is a LAN cable 10 including: an intertwined pair wire 8 formed by intertwining a pair of insulated electrical wires 3 of a plurality of the insulated electrical wires 3 each having an insulating layer 2 on an outer periphery of a conductor 1; a braid 4 provided so as to cover an outer periphery of the intertwined pair wire 8; and a sheath 5 further covering the braid 4. This LAN cable 10 is configured as a bundled intertwined wire 7 formed by intertwining a plurality of the intertwined pair wires 8, and a shield 6 is provided on the outer periphery of each of the plurality of intertwined pair wires 8.
In such a LAN cable, the high frame retardancy required under a flame retardant test represented by overseas standards such as EN45545 is generally achieved by a predetermined flame-retardant layer such as a flame-retardant tape formed between the sheath 5 and the insulated electrical wire 3 (directly below the sheath 5). However, a cable diameter becomes thicker by the amount of this flame-retardant tape.
In contrast, the LAN cable 10 according to the present embodiment without such a flame-retardant tape can achieve the flame retardancy that satisfies the above-described standards, and can achieve the reduced-diameter cable, and therefore, is a LAN cable particularly suitable for railway vehicles.
[Insulated Electrical Wire]
The insulated electrical wire 3 includes the insulating layer 2 on the outer periphery of the conductor 1. A material of the conductor 1 is not specifically limited, and any publicly known conductor may be used. For example, copper or a copper alloy can be used. A configuration of the conductor 1 is not particularly limited, either. However, adoption of a single wire or an intertwined wire structure in which a plurality of bare wires are intertwined is preferable in consideration of bendability of the cable. In addition, an appropriately-plated conductor is also applicable, such as tin plating.
A material of the insulating layer 2 is not particularly limited. However, polyethylene is preferable, or polyethylene with a dielectric constant of 2.5 or less is more preferable. Since the dielectric constant of polyethylene is 2.5 or less, an electrostatic capacity of the insulating layer is small. Therefore, transmission property of the LAN cable is further improved. The dielectric constant of the entire insulating layer is preferably 2.5 or less. In this case, the transmission property of the LAN cable is further improved. The dielectric constant of the entire insulating layer is more preferably 1.9 or more and 2.3 or less, and even more preferably 1.9 or more and 2.1 or less.
Examples of the polyethylene are, for example, low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), linear very low-density polyethylene (VLDPE), high-density polyethylene (HDPE), or the like. More preferable polyethylene is low-density polyethylene having a density of 0.930 or less and an MFR (melt flow rate) of 0.30 or less. Single use of any one of the polyethylene described above may be applied, or a two or more types of them may be blended and used.
The insulating layer 2 may further contain an antioxidant, a copper inhibitor, a colorant, or the like. A mixture content of each of the antioxidant, the copper inhibitor, the colorant and the like is not particularly limited. However, a mixture content that brings the dielectric constant of the entire insulating layer 2 into 2.5 or less is preferable. The mixture content of the colorant or the like, is preferably 5 mass% or less, and more preferably 2 mass% or less. In addition, the insulating layer 2 may not contain the flame retardant. By use of a sheath having properties described below, the LAN cable 10 that satisfies the high flame retardancy is achieved even if the insulating layer 2 is a resin composite not containing the flame retardant.
The polyethylene described here may be foamed by using a publicly known method. For example, the polyethylene can be foamed by a method using, for example, inert gas such as nitrogen or using a chemical foaming agent such as ADCA (azodicarbonamide) or the like. An extent of foaming of the polyethylene is preferably 15 mass% or more.
[Intertwined Pair Wire]
The intertwined pair wire 8 is formed by intertwining the two insulated electrical wires 3. As described above, this LAN cable 10 has a feature including the intertwined pair wire 8. As the LAN cable illustrated FIG. 1, an example with four sets of the intertwined pair wires 8 each made of the two insulated electrical wires 3 is illustrated.
In this case, an outside diameter r1 of the insulated electrical wire 3 configuring the intertwined pair wire 8 is configured to be a small diameter of, for example, 1.5 mm or less, and the shield 6 is provided outside a core thereof. The outside diameter r1 of the insulated electrical wire 3 is preferably 1.43 mm or less. In the present embodiment, the sheath 5 is made of a resin composite with sufficiently high flame retardancy. Therefore, it has been found that the flame retardancy of the LAN cable can be ensured even when the outside diameter r1 of the above-described insulated electrical wire 3 is made small as described above in order to achieve the small diameter of the LAN cable 10 as another issue to achieve the small outside diameter of the LAN cable. Therefore, the LAN cable 10 that has the small diameter and the high flame retardant, which has not be achieved so far, can be provided. By the small outside diameter r1 of the insulated electrical wire 3, a content of a flammable insulating layer to be used in the insulated electrical wire 3 can be reduced, and therefore, the small outside diameter also works as an advantage in ensuring the flame retardancy of the LAN cable 10.
The shield 6 is configured to be wrapped around the intertwined pair wire 8, and, for example, a shielding tape including a base material layer formed by molding a resin such as polyethylene terephthalate into a tape shape, and a metal layer formed by adhering an aluminum sheet onto a surface of the base material layer can be used.
The above explanation has described here that the insulating layer 2 may be the foamed layer. However, the insulating layer 2 may be an insulating layer having a multilayer structure including the foamed layer. If the insulating layer 2 of this multilayer structure has, for example, a structure with three layers that are an inner layer, an intermediate layer, and an outer layer in this order from the conductor 1 side, the inner layer and the outer layer are preferably configured as a skin layer while the intermediate layer is preferably configured as the foamed layer. Alternatively, the structure may be a two-layer structure in which the inner layer is the foamed layer while the outer layer is the skin layer. By such combination of the skin layer and the foamed layer, the outside diameter of the insulated electrical wire 3 can be made small to achieve the small diameter of the LAN cable. Furthermore, since the structure of the insulating layer 2 includes such a foamed part (air), the favorable dielectric constant can be achieved.
As described above, this insulating layer 2 is made of, for example, a polyethylene material. For example, all of the inner layer, the intermediate layer, and the outer layer are made of polyethylene such that each of the inner layer and the outer layer may be the skin layer made of polyethylene while the intermediate layer may be the foamed layer made of polyethylene.
At this time, a thickness of the intermediate layer is preferably 0.25 mm to 0.4 mm, and more preferably 0.25 mm to 0.37 mm. Furthermore, a total thickness of the two-layer structure is preferably 0.35 mm to 0.45 mm, or a total thickness of the three-layer structure is preferably 0.35 mm to 0.45 mm.
[Braid]
The braid 4 is made by braiding a combination of a plurality of metal wires, and is provided to reduce noise in the LAN cable 10 or improve strength of the LAN cable 10 itself. The braid 4 is, for example, a cross braid. The metal wires of copper, a copper alloy, or the like can be used as the metal wires that configure the braid 4.
[Sheath]
The sheath 5 is made of the non-halogen resin composite having the base polymer, the metal hydroxide, and the carbon black. In the present embodiment, these components are mixed at a specific ratio, and each of the components will be described in detail below.
(Base Polymer)
The base polymer contains polyolefin, maleic anhydride modified polyolefin, and ethylene-vinyl acetate copolymer.
(1) Polyolefin
The polyolefin used here is polyolefin having a melting point of 110°C or higher. The melting point can be determined by differential scanning calorimetry (DSC). By use of this polyolefin having the melting point of 110°C or higher, oil resistance of the sheath 5 can be improved.
As an oil-resistant test, there is a method of immersing a test piece into IRM 902 test oil heated to 100°C for 72 hours, and then, evaluating a change rate from the tensile property before the immersion to the tensile property after the immersion. If the melting point is, for example, lower than 110°C, the crystals are melted during the oil-resistant test, and therefore, it is difficult to prevent the oil from diffusing, and the change rate of the tensile property is made high.
Examples of the polyolefin having the melting point of 110°C or higher are low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, polypropylene, or the like. However, the high-density polyethylene has low elongation at break because of having too high crystallinity, and therefore, the polypropylene is easy to collapse in crosslinking based on electron-beam irradiation. In order to balance the properties, it is preferable to use the low-density polyethylene, and it is more preferable to use the linear low-density polyethylene.
(2) Maleic Anhydride Modified Polyolefin
The maleic anhydride modified polyolefin is polyolefin modified with maleic anhydride.
Examples of polyolefin that can be used as a modified material are ethylene-α-olefin such as low-density polyethylene, linear low-density polyethylene, very low-density polyethylene, ethylene-methyl acrylate copolymer, ethylene-ethyl acrylate copolymer, ethylene-butene-1 copolymer, ethylene-hexene-1 copolymer, and ethylene-octene-1 copolymer.
A method of modifying the polyolefin with maleic anhydride is not limited, and the polyolefin can be obtained by a reaction using only heat. In addition, maleic anhydride in the maleic anhydride modified polyolefin may be graft-copolymerized or block-copolymerized.
A mixture content of the maleic anhydride modified polyolefin is set to 10 to 35 parts by mass per 100 parts by mass of the base polymer. When the mixture content is less than 10 parts by mass, the required low-temperature property cannot be satisfied. When it is more than 35 parts by mass, initial elongation at break is insufficient.
In order to obtain a higher low-temperature property, the mixture content of the maleic anhydride modified polyolefin is preferably set to 25 to 35 parts by mass per 100 parts by mass of the base polymer.
(3) Ethylene-Vinyl Acetate Copolymer
When the ethylene-vinyl acetate copolymer is used as the base polymer, an endothermic reaction caused by removal of acetic acid during combustion is caused, and thus, the flame retardancy can be improved. The high flame retardancy is provided when an acetic acid content (CH3COO- content) in 100 mass% of the base polymer is set to 2.3 mass% or higher.
(Metal Hydroxide)
The metal hydroxide used here is a flame retardant. As the metal hydroxide, for example, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or the like can be used. Among these materials, aluminum hydroxide or magnesium hydroxide is preferably used. An amount of heat absorbed during decomposition of calcium hydroxide is about 1000J/g, while an amount of heat adsorbed by aluminum hydroxide or magnesium hydroxide is 1500 to 1600J/g, which is higher. Therefore, the flame retardancy is improved by mixture of aluminum hydroxide or magnesium hydroxide.
The magnesium hydroxide is more preferably used. The magnesium hydroxide has a higher decomposition temperature than that of the aluminum hydroxide, and therefore, moldability is improved.
In order to improve dispersibility or the like, a surface of the metal hydroxide is treated with a silane coupling agent, a titanate-based coupling agent, fatty acid such as stearic acid.
A mixture content of the metal hydroxide is 180 to 190 parts by mass per 100 parts by mass of the base polymer. If the mixture content is less than 180 parts by mass, the sufficient flame retardancy cannot be obtained. If it is more than 190 parts by mass, the elongation at break decreases.
(Carbon Black)
The carbon black used here is a flame-retardant auxiliary agent. Although a type of the carbon black to be mixed is not particularly limited. However, FT or MT-class carbon is preferably used in terms of the elongation at break or the like.
In order to ensure a predetermined flame retardancy, it is necessary to mix a large amount of the metal hydroxide as the flame retardant. However, the mixture of the large amount of the flame retardant has a risk of reduction in mechanical properties of the resin composite. Thus, the carbon black is mixed as the flame-retardant auxiliary agent. A mixture content of the carbon black is 15 to 20 parts by mass per 100 parts by mass of the base polymer. The more the mixture content of the carbon black is, the better the flame retardancy is. However, if the content is more than 20 parts by mass, coarse particles are generated due to aggregation of the carbon black, and thus, the initial elongation at break and low-temperature properties are reduced.
(Other Additives)
In addition to the above-described materials, it is possible to mix a crosslinking agent, a crosslinking auxiliary agent, an ultraviolet absorber, a light stabilizer, a softener, a lubricant, a colorant, a reinforcing agent, a surfactant, an inorganic filler, an antioxidant, a plasticizer, a metal chelator, a foaming agent, a compatibilizer, a process aid, a stabilizer, or the like.
Note that a flame-retardant auxiliary agent other than the above-described carbon black may be mixed as the flame-retardant auxiliary agent. Examples of the flame-retardant auxiliary agent are a phosphorus-based flame-retardant auxiliary agent such as red phosphorus or a triazine-based flame-retardant auxiliary agent such as melamine cyanurate, but they may generate phosphine gas or cyan gas, and thus, must be carefully handled. Any other flame-retardant auxiliary agent can be applied. For example, clay, silica, zinc stannate, zinc borate, calcium borate, hydroxylated dolomite, silicone, or the like, can be used.
(Gel Fraction)
A gel fraction is a method to check a degree of crosslinking of a polymer. A method of measuring the gel fraction will be described below. First, a test specimen (W1) is weighted, and is immersed into xylene heated to 110°C for 24 hours. After the immersion, the test specimen is left to stand under an atmospheric pressure at 20°C for 3 hours, and is vacuum-dried at 80°C for 4 hours. A weight ratio ((W2/W1)×100, unit [%]) between a weight (W2) of the test specimen after this and a weight (W1) of the same before the immersion in xylene is defined as the gel fraction. If the gel fraction is less than 85%, it cannot be said that the oil resistance is sufficient.
Types of the crosslinking are chemical crosslinking using an organic peroxide, a sulfur compound, silane or the like, electron-beam or radiation irradiation crosslinking or the like, chemical crosslinking using other chemical reactions, and the like, and any of these crosslinking methods can be applied. Among them, the electron-beam irradiation crosslinking is more generally used than other irradiation crosslinking, and has no risk of scorch during injection molding, and therefore, is preferably used as the crosslinking process of the present embodiment.
[Outside Diameter of Cable]
In addition, in the present embodiment, a feature point of the LAN cable 10 is that its outside diameter is 8.8 mm or less. As a result of enthusiastic examination on this configuration of the highly flame-retardant cable, it has been found that the smaller the outside diameter of the cable is, the easier the occurrence of the combustion in the flame retardant test based on EN 45545 or the like is.
The inventors have newly found that, even in a case without the flame-retardant tape and with the small cable diameter under such conditions, a highly flame-retardant LAN cable that satisfies the flame retardant requirements in the flame retardant test described above can be provided.
At this time, a thickness of the sheath 5 is preferably 0.68 mm to 0.92 mm, and more preferably 0.72 mm to 0.88 mm. If the thickness exceeds 0.92 mm, it is easier to ensure the flame retardancy, but it is more difficult to satisfy the small diameter required in the present embodiment. In addition, if the thickness is less than 0.68 mm, the sufficient flame retardancy may not be ensured.
[Method of Manufacturing LAN Cable]
The LAN cable 10 of the present embodiment is manufactured as, for example, follows. First, the resin composite to be the insulating layer 2 of the insulated electrical wire 3 is prepared, and then, the conductor 1 is prepared. Then, the resin composite for the insulating layer is extruded by an extruder to cover a periphery of the conductor 1, thereby forming the insulating layer 2 having a predetermined thickness. In this manner, the insulated electrical wire 3 can be manufactured.
The insulating layer 2 can be made of a general-purpose material, but a non-halogen polymer is preferably used. Examples of this polymer are polyolefin such as high-density polyethylene, middle-density polyethylene, low-density polyethylene, linear low-density polyethylene, linear very low-density polyethylene, and ethylene-acrylic acid ester copolymer.
In the present embodiment, after the insulated electrical wire 3 is manufactured, the resin composite configuring the insulating layer 2 can be crosslinked by, for example, the electron-beam crosslinking method.
If the electron-beam crosslinking method is used, the resin composite is molded as the insulating layer 2 of the insulated electrical wire 3, and then, is irradiated with, for example, electron beam of 1 to 30 MRad to be crosslinked.
The resultant two insulated electrical wires 3 are intertwined to be the intertwined pair wire 8. Four sets of the intertwined pair wire 8 having the shield 6 obtained by wrapping a shielding tape around the intertwined pair wire 8 are intertwined. Then, the braid 4 is formed so as to cover the intertwined pair wires by the publicly known method. Furthermore, the resin composite of the present embodiment is extruded around the outer periphery of the resultant braid 4 to form the sheath (covering layer) 5 having a predetermined thickness. In this manner, the LAN cable 10 of the present embodiment can be manufactured.
Next, a structure of the LAN cable according to the embodiment will be described below. FIG. 1 is a schematic cross-sectional view of the LAN cable according to an embodiment. As illustrated in FIG. 1, the LAN cable 10 includes the bundled intertwined wire 7, the braid 4 covering the outer periphery of the bundled intertwined wire 7, and the sheath 5 covering the outer periphery of the braid 4. The outer periphery of the braid 4 is in contact with the sheath 5. The bundled intertwined wire 7 has four intertwined pair wires 8. The four intertwined pair wires 8 are intertwined. The intertwined pair wire 8 includes two insulated electrical wires 3. The two insulated electrical wires 3 are intertwined. The two insulated electrical wires 3 are in contact with each other. The insulated electrical wire 3 includes the conductor 1 and the insulating layer 2 covering the outer periphery of the conductor 1. The LAN cable 10 illustrated in FIG. 1 does not include the flame-retardant tape between the intertwined pair wires 8 and the sheath 5.
In the example illustrated in FIG. 1, the bundled intertwined wire 7 further includes four shields 6. One of the shields 6 covers the outer periphery of one of the intertwined pair wires 8. That is, the bundled intertwined wire 7 includes four sets of the shields 6 and the intertwined pair wires 8 each covered with the shield 6. The four sets of intertwined pair wires 8, each of which is covered with the shield 6, are intertwined. The shield 6 is in contact with the braid 4. The shield 6 is in contact with the intertwined pair wire 8.
An outer shape of a cross section of the LAN cable 10, that is, an outer shape of a cross section of the sheath 5, is circular. An outer shape of a cross section of the shield 6 is circular. In the example illustrated in FIG. 1, the outer shape of the sheath 5 and the outer shape of each of the four shields 6 are true circles. However, the outer shape of the sheath 5 and the outer shape of the shield 6 include not only the true circle case but also a substantially apparently circle case (in which a difference between lengths of two diameters that are perpendicular to each other is small enough to be negligible). The four shields 6 have rotational symmetry around a center Q1 of the circle of the outer shape of the cross section of the LAN cable 10 as an axis of rotation. For example, in the example illustrated in FIG. 1, the figure formed by the four shields 6 overlaps with itself when rotating by 90 degrees around the center Q1 as the axis of rotation, and therefore, this figure is four-fold symmetric. Two shields 6 are point-symmetric to each other around the circle center Q1. As illustrated in FIG. 1, the bundled intertwined wire 7 includes two sets of two shields 6 that are point-symmetric. In the present embodiment, the LAN cable 10 includes two or more intertwined pair wires 8. In the LAN cable 10, the four shields 6 are intertwined to have a helical form in a longitudinal direction. That is, when the cross section perpendicular to the longitudinal direction of the LAN cable 10 continuously changes in the longitudinal direction of the LAN cable 10, positions of the shields 6 rotate so as to draw a circle around the center Q1 of the circle. In addition, the two insulated electrical wires 3 included in the intertwined pair wires 8 have a double helical structure. In the present embodiment, the outside diameter r1 of the insulated electrical wire 3 is 1.5 mm or less, and the outside diameter r2 of the bundled intertwined wire 7 is 6.5 mm or less. The outside diameter r2 of the bundled intertwined wire 7 is a diameter of a circle formed by rotation of the shields 6 around the center Q1 of the circle. In the example illustrated in FIG. 1, the outside diameter r2 of the bundled intertwined wire 7 is a diameter of an inscribed circle inside each of the plurality of shields 6. The outside diameter r2 of the bundled intertwined wire 7 can be measured by, for example, measuring and averaging the outside diameters r2 of the bundled intertwined wires 7 at three different cross sections of the LAN cable 10.
A LAN cable according to another embodiment will be described. Note that the same components are denoted by the same reference symbols in principle throughout all the drawings for describing the embodiments, and the repetitive description thereof may be omitted.
FIG. 2 is a schematic cross-sectional view of a test cable according to another embodiment. A test cable 50 illustrated in FIG. 2 differs from the LAN cable 10 illustrated in FIG. 1 in that the test cable 50 has no intertwined pair wire. The test cable 50 illustrated in FIG. 2 includes four insulated electrical wires 3. The four insulated electrical wires 3 are intertwined. The number of the insulated electrical wires 3 of the test cable 50 needs to be two or more. The number of the insulated electrical wires 3 of the test cable 50 is preferably three or more. The insulated electrical wires 3 are in contact with the braid 4. The four insulated electrical wires 3 have the rotational symmetry around the center Q1 of the circle formed by the outer shape of the cross section of the test cable 50 as the axis of rotation. For example, in the example illustrated in FIG. 2, the figure formed by the four insulated electrical wires 3 overlaps with itself when rotating by 90 degrees around the center Q1 as the axis of rotation, and therefore, this figure is four-fold symmetric. Two insulated electrical wires 3 on the opposite side to each other across the center Q1 among the four insulated electrical wires 3 are point-symmetric to each other around the circle center Q1. As illustrated in FIG. 2, the bundled intertwined wire 7 includes two sets of two insulated electrical wires 3 that are point-symmetric. The four insulated electrical wires 3 are intertwined to have a helical form in a longitudinal direction. When the cross section perpendicular to the longitudinal direction of the test cable 50 continuously changes in the longitudinal direction of the test cable 50, positions of the insulated electrical wires 3 rotate so as to draw a circle around the center Q1 of the circle. In the present embodiment, the outside diameter r1 of the insulated electrical wire 3 is 2.5 mm or less, and the outside diameter r2 of the bundled intertwined wire 7 is 5.5 mm or less. The outside diameter r2 of the bundled intertwined wire 7 is a diameter of a circle formed by rotation of the insulated electrical wires 3 around the center Q1 of the circle. In the example illustrated in FIG. 2, the outside diameter r2 of the bundled intertwined wire 7 is a diameter of an inscribed circle inside each of the four insulated electrical wires 3. The outside diameter r2 of the bundled intertwined wire 7 can be measured by, for example, measuring and averaging the outside diameters r2 of the bundled intertwined wires 7 at three different cross sections of the test cable 50.
FIG. 3 is a schematic cross-sectional view of a LAN cable according to another embodiment. A LAN cable 10A illustrated in FIG. 3 differs from the LAN cable 10 illustrated in FIG. 1 in that the LAN cable 10A further includes an intertwined upper tape 11, a separator 12, a shielding tape 13, and an inclusion 14. In addition, the LAN cable 10A illustrated in FIG. 3 differs from the LAN cable 10 illustrated in FIG. 1 in that the bundled intertwined wires 7 of the LAN cable 10A has no shield 6. The insulated electrical wire 3 of each of the plurality of (in FIG. 3, four) intertwined pair wires 8 has a double helical structure in the LAN cable 10A. Each of the plurality of (in FIG. 3, four) intertwined pair wires 8 has a helical form in the longitudinal direction. When a cross section perpendicular to the longitudinal direction of the LAN cable 10A continuously changes in the longitudinal direction of the LAN cable 10A, the positions of the insulated electrical wires 3 rotate so as to draw a circle. A region through which the insulated electrical wires 3 pass when rotating to draw the circle is a region P1 surrounded by a dotted line in FIG. 3. In addition, the insulated electrical wires 3 of the intertwined pair wires 8 are all arranged alongside in the same direction. In the example illustrated in FIG. 3, the insulated electrical wires 3 of the two intertwined pair wires 8 that face each other across the center Q1 of the circle formed by the outer shape of a cross section of the LAN cable 10A are arranged alongside in a direction extending from the center Q1 of the circle toward the outside. In contrast, the insulated electrical wires 3 of the other two intertwined pair wires 8 that face each other across the center of the LAN cable 10A are arranged alongside in a direction perpendicular to the direction extending from the center Q1 of the circle toward the outside. The outside diameter r2 of the bundled intertwined pair wires 7 is a diameter of a circle formed by rotation of the intertwined pair wires 8 around the center Q1 of the circle.
The inclusion 14 that is an insulating filler has a center inclusion 14a and outer inclusions 14b. As illustrated in FIG. 3, the center inclusion 14a is surrounded by the four intertwined pair wires 8. The outer inclusions 14b are located between the bundled intertwined wire 7 and the intertwined upper tape 11.
The intertwined upper tape 11 circumferentially surrounds the bundled intertwined wires 7 and the inclusion 14. The intertwined upper tape 11 is in contact with the bundled intertwined wires 7 and the outer inclusions 14b. The separator 12 that is a sheath inside the braid 4 covers the intertwined upper tape 11. The separator 12 is in contact with an outer circumstance of the intertwined upper tape 11. The shielding tape 13 covers the separator 12. The shielding tape 13 is in contact with an outer periphery of the separator 12. The braid 4 covers the shielding tape 13. The braid 4 is in contact with an outer periphery of the shielding tape 13.
In the example illustrated in FIG. 3, the center inclusion 14a is made of Kevlar (insulating fiber material), and the outer inclusion 14b is made of PP yarn (insulating fiber material). The intertwined upper tape 11 is made of, for example, a PET tape. The separator 12 is made of, for example, polyolefin. The shielding tape 13 is made of, for example, a two-layer structure. For example, a layer in contact with the braid 4 among two layers of the shielding tape 13 is made of an aluminum sheet, and a layer not in contact with the braid 4 among the two layers of the shielding tape 13 is made of the PET tape. The braid 4 is made of, for example, a plurality of Sn-plated soft copper wires. The Sn-plated soft copper wire has a thickness of, for example, 0.1 mm.
Since the LAN cable 10A illustrated in FIG. 3 includes the separator 12, a shield lower diameter r4 can be ensured. This can improve an impedance property of the LAN cable 10A. The shield lower diameter r4 described here is a lower distance of a shielding layer for shielding. The shielding layer is made of the braid 4 and the shielding tape 13. That is, the shield lower diameter r4 is an inside diameter of the shielding tape 13.
FIG. 4 is a schematic cross-sectional view of a LAN cable according to another embodiment. A LAN cable 10B illustrated in FIG. 4 differs from the LAN cable 10A illustrated in FIG. 3 in that the LAN cable 10B has no inclusion and has no intertwined upper tape. In addition, the LAN cable 10B differs from the LAN cable 10A illustrated in FIG. 3 in that the insulated electrical wires 3 of each of the four intertwined pair wires 8 are all arranged alongside in a direction extending from the center Q1 of a circle formed by an outer shape of a cross section of the LAN cable 10B toward the outside. In the example illustrated in FIG. 4, the plurality of insulated electrical wires 3 are radially arranged alongside from the center Q1 of the circle. The outside diameter r2 of the bundled intertwined wire 7 is a diameter of a circle formed by rotation of the intertwined pair wires 8 around the center Q1 of the circle. In the example illustrated in FIG. 4, the outside diameter r2 of the bundled intertwined wire 7 is a diameter of an inscribed circle inside each of the plurality of the intertwined pair wires 8.
FIG. 5 is a schematic cross-sectional view of a LAN cable according to another embodiment. A LAN cable 50A illustrated in FIG. 5 differs from the test cable 50 illustrated in FIG. 2 in that the LAN cable 50A further includes an intertwined upper tape 51 and a shielding tape 53. The intertwined upper tape 51 circumferentially surrounds the bundled intertwined wire 7. The intertwined upper tape 51 is in contact with the bundled intertwined wire 7. The intertwined upper tape 51 includes an intertwined upper tape 51a and an intertwined upper tape 51b. The intertwined upper tape 51a circumferentially surrounds the bundled intertwined wire 7. The intertwined upper tape 51a is in contact with the bundled intertwined wire 7. The intertwined upper tape 51b circumferentially surrounds the intertwined upper tape 51a. The intertwined upper tape 51b is in contact with the intertwined upper tape 51a. The shielding tape 53 circumferentially surrounds the intertwined upper tape 51. The shielding tape 53 is in contact with the intertwined upper tape 51. The shielding tape 53 circumferentially surrounds the intertwined upper tape 51b. The shielding tape 53 is in contact with the intertwined upper tape 51b. The braid 4 circumferentially surrounds the shielding tape 53. The braid 4 is in contact with the shielding tape 53. The outside diameter r2 of the bundled intertwined wire 7 is a diameter of a circle formed by rotation of the insulated electrical wires 3 around the center Q1 of the circle. In the example illustrated in FIG. 5, the outside diameter r2 of the bundled intertwined wire 7 is a diameter of an inscribed circle inside each of the four insulated electrical wires 3.
In the example illustrated in FIG. 5, the intertwined upper tape 51a is made of the PET tape, and the intertwined upper tape 51b is made of LDPE. The shielding tape 53 is made of, for example, a two-layer structure. For example, a layer in contact with the braid 4 among two layers of the shielding tape 53 is made of an aluminum sheet, and a layer not in contact with the braid 4 among the two layers of the shielding tape 53 is made of the PET tape.
The intertwined upper tape 51a is wound by, for example, gap winding (with gap). A clearance of this gap winding (with gap) is, for example, 1 mm or less. The intertwined upper tape 51b is wound by, for example, gap winding (with gap). A clearance of this gap winding (with gap) is, for example, 1 mm or less.
FIG. 6 is a schematic cross-sectional view of a LAN cable according to another embodiment. A LAN cable 50B illustrated in FIG. 6 differs from the test cable 50 illustrated in FIG. 2 in that the LAN cable 50B further includes a separator 52 and a shielding tape 53. The separator 52 circumferentially surrounds the bundled intertwined wire 7. The separator 52 is in contact with the bundled intertwined wire 7. The shielding tape 53 circumferentially surrounds the separator 52. The shielding tape 53 is in contact with the separator 52. The braid 4 circumferentially surrounds the shielding tape 53. The braid 4 is in contact with the shielding tape 53.
[Working Examples]
Next, the present invention will be further described in more detail, based on working examples. However, the present invention is not limited to these working examples.
[Preparation Examples 1 to 3 of Sheath Material]
Sheath materials were prepared in accordance with the mixture ratios in Table 1 and Table 2. In the mixture ratios, a pellet formed by subjecting to kneading using a pressure kneader to reach 220°C was prepared as the sheath material.
[Table 1]

[Table 2]

[Sheath Materials]
Note that the used materials in Table 1 are as follows:
(Polymer)
PE: “SP1510 (Tm117°C)” produced by Prime Polymer Co., Ltd.
EVA: “EvaFlex EV45X” produced by Dow-Mitsui Polychemicals Co., Ltd.
Modified polyolefin: “TAFMER MH5040” produced by Mitsui Chemicals, Inc.
(Flame retardant)
Magnesium hydroxide: “Magseeds S4” produced by Konoshima Chemical Co., Ltd.
Carbon black: “ASAHI THERMAL” produced by Asahi Carbon Co., Ltd.
[Evaluation on Sheath Materials]
The following properties of the resultant resin composites were evaluated.
(1-1) Flame Retardancy (VFT) of Sheath Materials
A test cable for the flame retardancy evaluation was prepared using the resultant resin composites. This test cable was prepared as the test cable 50 with the configuration illustrated in FIG. 2, the cable being covered with the sheath material of a thickness of 0.8 mm, and being crosslinked by irradiation at an irradiation dose of 5 MRad to prepare a cable with an outside diameter of 5.8 mm.
The flame retardancy of the resultant test cable was evaluated based on a vertical combustion test in conformity with the standards EN60332-1-2. A test cable that passed the test was evaluated to be " ", and a test cable that failed the test was evaluated to be " ".
(1-2) Initial Tensile Test of Sheath Materials
A dumbbell specimen was prepared by peeling off the sheath from the resultant test cable with the configuration illustrated in FIG. 2 as similar to the above description. Then, a tensile test using the test specimen was performed under a condition of a tensile speed of 250 mm/min in conformity with EN60811-501. Regarding the elongation, a test specimen with elongation that is less than 125% was evaluated to be " " (fail), and a test specimen with elongation that is 125% or more was evaluated to be " " (pass).
In addition, regarding the tensile strength, a test specimen with tensile strength that is less than 10 MPa was evaluated to be " " (fail), and a test specimen with tensile strength that is 10 MPa or more was evaluated to be " " (pass with margin).
(1-3) Oil-Resistant Test of Sheath Materials
A dumbbell specimen was prepared by peeling off the sheath from the resultant test cable with the configuration illustrated in FIG. 2 as similar to the above description. In conformity with EN60811-404, the test specimen was immersed in oil IRM902 heated at 100°C for 72 hours, and was stretched at a displacement speed of 250 mm/min to measure a load and an elongation applied until it is broken. A tensile-strength change rate ((A2/A1) × 100[%]) and an elongation-at-break change rate ((B2/B1) × 100[%]) were calculated from the tensile strength (A1) and the elongation at break (B1) of the test specimen not immersed yet in the test oil and from the tensile strength (A2) and the elongation at break (B2) of the test specimen immersed in the test oil. A test specimen with the tensile-strength change rate in a range of 75 to 125% and the elongation-at-break change rate in a range of 65 to 135% was evaluated to be “Good” ( ), and a test specimen with the tensile-strength change rate in a range of 70 to 75% or 125 to 130% and the elongation-at-break change rate in a range of 60 to 65% or 135 to 140% was evaluated to be “Fair” (△).
(1-4) Fuel-Resistant Test of Sheath Materials
A dumbbell specimen was prepared by peeling off the sheath from the resultant test cable with the configuration illustrated in FIG. 2 as similar to the above description. In conformity with EN60811-404, the test specimen was immersed in oil IRM903 heated at 70°C for 168 hours, and was stretched at a displacement speed of 250 mm/min to measure a load and an elongation applied until it is broken. A tensile-strength change rate ((A2/A1) × 100[%]) and an elongation-at-break change rate ((B2/B1) × 100[%]) were calculated from the tensile strength (A1) and the elongation at break (B1) of the test specimen not immersed yet in the test oil and from the tensile strength (A2) and the elongation at break (B2) of the test specimen immersed in the test oil. A test specimen with the tensile-strength change rate in a range of 70 to 130% and the elongation-at-break change rate in a range of 60 to 140% was evaluated to be “Pass” ( ).
(1-5) Low-Temperature Property Test of Sheath Materials
In conformity with EN60811-504, a low-temperature bending test using the test cable was performed. The test was performed with “N = 2” under conditions of -40°C and -50°C. A case in which both two test species have passed the test (no cracks or breaks) was evaluated to be " ", and a case in which only one test specimen has passed the test was evaluated to be "△".
[Working Example 1]
Then, the LAN cable with the configuration illustrated in FIG. 1 was prepared as follows. A conductor with a diameter of 0.565 mm was covered with a polyethylene layer of 0.01 mm that serves as an inner layer, with a foamed polyethylene layer of 0.36 mm as an intermediate layer that has an extent of foaming of 30%, and with a polyethylene layer of 0.05 mm as an outer layer.
The above-described conductor specimen was crosslinked by irradiation at an irradiation dose of 22 Mrad to prepare an insulated electrical wire with an outside diameter of 1.40 mm including an insulating layer with a thickness of 0.42 mm.
Then, four sets of two (paired) intertwined insulated electrical wires, on which an aluminum laminated PET tape was longitudinally wrapped, were prepared. Then, the four sets were intertwined and covered with a copper braid, and besides, were covered with the sheath material with the thickness of 0.78 mm prepared in the preparation example 1 as shown in Table 1, and were crosslinked by irradiation at the irradiation dose of 5 Mrad to prepare the LAN cable with the configuration illustrated in FIG. 1 as the working example 1.
[Working Example 2]
Then, a conductor with a diameter of 0.565 mm was covered with a polyethylene layer of 0.01 mm that serves as an inner layer, with a foamed polyethylene layer of 0.30 mm as an intermediate layer that has an extent of foaming of 50%, and with a polyethylene layer of 0.05 mm as an outer layer.
The above-described conductor specimen was crosslinked by irradiation at an irradiation dose of 22 Mrad to prepare an insulated electrical wire with an outside diameter of 1.30 mm including an insulating layer with a thickness of 0.36 mm.
Then, four sets of two (paired) intertwined insulated electrical wires, on which an aluminum laminated PET tape was longitudinally wrapped, were prepared. Then, the four sets were intertwined and covered with a copper braid, and besides, were covered with the sheath material with the thickness of 0.78 mm prepared in the preparation example 1 as shown in Table 1, and were crosslinked by irradiation at the irradiation dose of 5 Mrad to prepare the LAN cable with the configuration illustrated in FIG. 1 as the working example 2.
Table 3 shows the properties of configurations of the resultant LAN cables, including comparative examples to be described below.
[Comparative Example 1]
As a related-art example, a LAN cable with the configuration illustrated in FIG. 1 was prepared as a comparative example 1 so as to include the sheath materials of the working example 1 prepared in the preparation example 3.
[Comparative Examples A to C]
In each of the working examples 1 and 2 and the comparative example 1, note that a LAN cable including a polyimide flame-retardant tape horizontally wound between the copper braid and the sheath at a 1/4 wrap was prepared, and these LAN cables were designated as the comparative examples A to C, respectively.
(Table 3)

[Evaluation on LAN Cables]
The resultant LAN cables in the working examples 1 and 2, the comparative example 1, and the comparative examples A to C were evaluated regarding the flame retardancy (VFT), the initial tensile test, the oil-resistant test, the fuel-resistant test, and the low-temperature property test, based on the operation and the evaluation criteria similar to those for the above-described evaluation on the sheath materials. In addition, a tensile test after aging was also performed to the resultant LAN cables. Table 3 also shows the result thereof.
(2-1) Tensile Test After Aging of Cables
A dumbbell specimen was prepared by peeling off the sheath from the resultant cable. Then, the test specimen was processed at “120°C × 240 h”, and then, was stretched at a displacement speed of 250 mm/min to measure the load and the elongation applied until it is broken. A tensile-strength change rate ((A2/A1) × 100[%]) and an elongation-at-break change rate ((B2/B1) × 100[%]) were calculated from the tensile strength (A1) and the elongation at break (B1) of the test specimen not heated yet and from the tensile strength (A2) and the elongation at break (B2) of the test specimen heated. In the evaluation, a test specimen with the tensile-strength change rate of 70 to 130% and the elongation-at-break change rate of 70 to 130% was evaluated to be “Pass” ( ).
From the above results, in the working examples 1 and 2, it has been found that a sheath with a predetermined resin composition can ensure the high frame retardancy even without the frame-retardant tape between the sheath and the insulated electrical wire, which results in a LAN cable that also satisfies the physical properties such as the sheath strength, elongation, low-temperature property. It was also confirmed that the working example 2 provides a cable that can be made smaller in the diameter.
In contrast, in the comparative example 1, it has been found that it is necessary to use the frame-retardant tape to provide the sufficient flame retardancy for railway vehicles.
In the foregoing, the invention made by the inventors of the present application has been concretely described based on the embodiments. However, it is needless to say that the present invention is not limited to the foregoing embodiments, and various modifications can be made within the scope of the present invention.
, C , Claims:1. A LAN cable comprising:
an intertwined pair wire formed by intertwining two insulated electrical wires;
a bundled intertwined wire formed by intertwining a plurality of the intertwined pair wires; and
a sheath covering an outer periphery of the bundled intertwined wire,
wherein the LAN cable has an outside diameter of 8.8 mm or less,
the sheath is made of a non-halogen flame-retardant resin composite containing base polymer, metal hydroxide, and carbon black,
a content of the metal hydroxide is 180 to 190 parts by mass per 100 parts by mass of the base polymer,
a content of the carbon black is 15 to 20 parts by mass per 100 parts by mass of the base polymer,
the insulated electrical wire has an outside diameter of 1.5 mm or less, and
the bundled intertwined wire has an outside diameter of 6.5 mm or less.

2. The LAN cable according to claim 1,
wherein a braid is provided between the intertwined pair wire and the sheath.

3. The LAN cable according to claim 1,
wherein the content of the metal hydroxide is 180 to 185 parts by mass per 100 parts by mass of the base polymer, and
the content of the carbon black is 15 to 20 parts by mass per 100 parts by mass of the base polymer.

4. The LAN cable according to claim 1,
wherein the insulated electrical wire has a structure in which an insulating layer includes a foamed layer.

5. The LAN cable according to claim 4,
wherein the insulating layer has a three-layer structure, and a total thickness of the three-layer structure is 0.35 to 0.45 mm, or
the insulating layer has a two-layer structure, and a total thickness of the two-layer structure is 0.35 to 0.45 mm.

6. The LAN cable according to claim 1,
wherein a flame-retardant tape is not provided between the intertwined pair wire and the sheath.

7. A LAN cable comprising:
a bundled intertwined wire formed by intertwining a plurality of insulated electrical wires; and
a sheath covering an outer periphery of the bundled intertwined wire,
wherein the LAN cable has an outside diameter of 8.8 mm or less,
the sheath is made of a non-halogen flame-retardant resin composite containing base polymer, metal hydroxide, and carbon black,
a content of the metal hydroxide is 180 to 190 parts by mass per 100 parts by mass of the base polymer,
a content of the carbon black is 15 to 20 parts by mass per 100 parts by mass of the base polymer,
the insulated electrical wire has an outside diameter of 2.5 mm or less, and
the bundled intertwined wire has an outside diameter of 5.5 mm or less.

8. The LAN cable according to claim 7,
wherein a braid is provided between the insulated electrical wire and the sheath.

9. The LAN cable according to claim 7,
wherein the content of the metal hydroxide is 180 to 185 parts by mass per 100 parts by mass of the base polymer, and
the content of the carbon black is 15 to 20 parts by mass per 100 parts by mass of the base polymer.

10. The LAN cable according to claim 7,
wherein the insulated electrical wire has a structure in which an insulating layer includes a foamed layer.

11. The LAN cable according to claim 10,
wherein the insulating layer has a three-layer structure, and a total thickness of the three-layer structure is 0.35 to 0.45 mm, or
the insulating layer has a two-layer structure, and a total thickness of the two-layer structure is 0.35 to 0.45 mm.

12. The LAN cable according to claim 7,
wherein a flame-retardant tape is not provided between the insulated electrical wire and the sheath.