Fire-resistant cable

Abstract

To provide a fire-resistant cable including a flame retardant, the cable ensuring prevention of short circuit caused by conductive carbide even when exposed to fire.SOLUTION: A fire-resistant cable (1) comprises a conductor (10), a fire-resistant layer (11) covering the conductor (10), an insulator layer (12) covering the fire-resistant layer (11), and a sheath (13) covering the insulator layer (12), the sheath (13) comprising aluminum hydroxide, magnesium hydroxide, and red phosphorus.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a fire-resistant cable. [Background technology]

[0002] Fire-resistant cables capable of supplying electricity for a certain period of time even in the event of a fire are known. Fire-resistant cables are used, for example, for electrical wiring in disaster prevention facilities in buildings, underground shopping malls, etc. Patent Document 1 discloses such a fire-resistant cable. This fire-resistant cable has a fire-resistant layer, an insulator layer, and a sheath, in that order, on a conductor. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-177874 Summary of the Invention [Problem to be solved by the invention]

[0004] As mentioned above, fire-resistant cables are required to have the ability to supply electricity for a certain period of time in the event of a fire, i.e., fire resistance. In addition to fire resistance, fire-resistant cables are also required to be flame-retardant. Flame resistance is the ability of a fire-resistant cable to prevent the cable from becoming a source of fire and spreading during a fire. To impart flame resistance to a fire-resistant cable, it is possible to include a flame retardant in the sheath of the fire-resistant cable. However, depending on the type of flame retardant included in the sheath, conductive char may be more likely to be produced when the fire-resistant cable burns. The formation of conductive char may cause a short circuit, which may adversely affect the electrical properties. In other words, it may adversely affect the cable's ability to supply electricity for a certain period of time during a fire.

[0005] An object of the present invention is to provide a fire-resistant cable containing a flame retardant, which is less likely to suffer from short circuits caused by conductive charcoal even in the event of a fire. [Means for solving the problem]

[0006] In order to solve the above problem, according to one aspect of the present invention, A fire-resistant cable having a conductor, a fire-resistant layer covering the conductor, an insulating layer covering the fire-resistant layer, and a sheath covering the insulating layer, The fire-resistant cable is characterized in that the sheath contains aluminum hydroxide, magnesium hydroxide, and red phosphorus. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a fire-resistant cable that contains a flame retardant and is less likely to suffer from short circuits caused by conductive carbides even in the event of a fire. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a cross-sectional view of a fire-resistant cable according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, a fire-resistant cable according to an embodiment of the present invention will be described, but the fire-resistant cable of the present invention is not limited to the following embodiment. In this specification, the symbol "to" indicating a numerical range means that the upper limit and the lower limit are included in the range.

[0010] FIG. 1 shows a cross-sectional view of a fire-resistant cable 1 according to an embodiment of the present invention. As shown in FIG. 1, the fire-resistant cable 1 has a conductor 10, a fire-resistant layer 11 covering the conductor 10, an insulating layer 12 covering the fire-resistant layer 11, and a sheath 13 covering the insulating layer 12. In FIG. 1, three fire-resistant cables 1 are twisted together to form a single cable. The fire-resistant cable 1 may be a combination of multiple cables as shown in FIG. 1, or may be used alone. Alternatively, the fire-resistant cable 1 may be a combination of multiple insulated wires, each having a conductor 10, a fire-resistant layer 11 covering the conductor 10, and an insulating layer 12 covering the fire-resistant layer 11, with the multiple insulated wires being covered by a single common sheath 13.

[0011] As described above, the fire-resistant cable 1 includes the conductor 10, the fire-resistant layer 11 covering the conductor 10, the insulator layer 12 covering the fire-resistant layer 11, and the sheath 13 covering the insulator layer 12. Each of these will be described below.

[0012] There are no particular limitations on the conductor 10 as long as it can conduct electricity. Examples of materials for the conductor 10 include copper. In this embodiment, the conductor 10 is a copper wire.

[0013] The fire-resistant layer 11 is a layer for imparting fire resistance to the fire-resistant cable 1. There are no particular limitations on the fire-resistant layer 11 as long as it can impart fire resistance to the fire-resistant cable 1. The fire-resistant layer 11 is, for example, a layer containing mica. The fire-resistant layer 11 may further contain silica. For example, the fire-resistant layer 11 is a layer formed by wrapping fire-resistant tape. The wrapping method may be vertical or horizontal wrapping. Examples of fire-resistant tape include mica tape. Examples of mica tape include glass mica tape in which mica is bonded to glass cloth, and film mica tape in which mica is bonded to a plastic film made of polyethylene or the like. Fire-resistant tape such as mica tape may be wrapped around the conductor 10, and then glass yarn may be further wrapped on top of it. The fire-resistant layer 11 may be composed of a single layer or multiple layers.

[0014] The insulator layer 12 is a layer having insulating properties. The insulator layer 12 is formed by extrusion molding of a thermoplastic resin such as polyvinyl chloride or polyolefin. Examples of polyolefins include low-density polyethylene (LDPE), medium-density polyethylene (MDPE), high-density polyethylene (HDPE), very-low-density polyethylene (VLDPE), linear low-density polyethylene (LLDPE), polypropylene, polyisobutylene, ethylene-vinyl acetate copolymer (EVA), ethylene-ethyl acrylate copolymer (EEA), ethylene-methyl acrylate copolymer (EMA), ethylene-propylene copolymer, ethylene-propylene-diene terpolymer, and ethylene-butene copolymer. Furthermore, copolymers of ethylene with α-olefins such as propylene, butene, pentene, hexene, and octene or cyclic olefins using a metallocene catalyst can also be used. These may be used alone or in combination.

[0015] Additives such as antioxidants and ultraviolet stabilizers may be added to the insulating material forming the insulator layer 12 as needed.

[0016] The sheath 13 is a layer that covers the insulator layer 12. The sheath 13 contains aluminum hydroxide, magnesium hydroxide, and red phosphorus. In this embodiment, aluminum hydroxide, magnesium hydroxide, and red phosphorus function as flame retardants. The inclusion of these three flame retardants in the sheath reduces the occurrence of short circuits caused by conductive charcoal when the fire-resistant cable 1 burns, and can suppress adverse effects on the electrical characteristics. The reason for this is presumed to be as follows.

[0017] Red phosphorus generally functions as a flame retardant by forming a film called char when the sheath 13 burns during a fire, blocking oxygen. On the other hand, aluminum hydroxide and magnesium hydroxide generally undergo dehydration decomposition as the temperature rises, and this process is accompanied by a large heat absorption, thereby functioning as a flame retardant. When comparing aluminum hydroxide and magnesium hydroxide, aluminum hydroxide has a lower dehydration decomposition temperature, while magnesium hydroxide has a higher dehydration decomposition temperature. Specifically, aluminum hydroxide begins dehydration decomposition at approximately 200°C, while magnesium hydroxide begins dehydration decomposition at approximately 300-350°C.

[0018] If the sheath 13 contains magnesium hydroxide, which has a high dehydration decomposition temperature, it is likely to generate conductive carbides that have adverse effects on electrical properties, such as short circuits, when the fire-resistant cable 1 burns in a fire.However, if the sheath 13 contains aluminum hydroxide, which has a low dehydration decomposition temperature, with less magnesium hydroxide, the sheath 13 will be more likely to incinerate when burned, suppressing the generation of conductive carbides and preventing adverse effects on electrical properties.

[0019] The mass ratio of aluminum hydroxide, magnesium hydroxide, and red phosphorus in the sheath 13 is preferably 1-8:1-8:0.45, more preferably 2-7:1-6:0.45, and particularly preferably 3-6:2-5:0.45. The ratio of the total mass of aluminum hydroxide, magnesium hydroxide, and red phosphorus to the mass of the sheath 13 is preferably 30 to 60 mass %.

[0020] The sheath 13 contains a resin as a base material in addition to the aluminum hydroxide, magnesium hydroxide, and red phosphorus. Examples of the resin include polyolefin. Specifically, the sheath 13 is formed by extrusion molding a resin containing aluminum hydroxide, magnesium hydroxide, and red phosphorus.

[0021] Examples of polyolefins include low-density polyethylene (LDPE), medium-density polyethylene (MDPE), high-density polyethylene (HDPE), very-low-density polyethylene (VLDPE), linear low-density polyethylene (LLDPE), polypropylene, polyisobutylene, ethylene-vinyl acetate copolymer (EVA), ethylene-ethyl acrylate copolymer (EEA), ethylene-methyl acrylate copolymer (EMA), ethylene-propylene copolymer, ethylene-propylene-diene terpolymer, and ethylene-butene copolymer. Metallocene-catalyzed copolymers of ethylene with α-olefins such as propylene, butene, pentene, hexene, and octene, as well as cyclic olefins, can also be used. These may be used alone or in combination. The sheath 13 (resin) may also contain flame retardants other than aluminum hydroxide, magnesium hydroxide, and red phosphorus. Examples of flame retardants other than aluminum hydroxide, magnesium hydroxide, and red phosphorus include metal oxides such as antimony oxide and molybdenum oxide, metal hydrates, halogen-based flame retardants, and phosphorus-based flame retardants.

[0022] (effect) The sheath 13 of the fire-resistant cable 1 according to the embodiment of the present invention contains aluminum hydroxide, magnesium hydroxide, and red phosphorus, which can suppress the occurrence of short circuits caused by conductive carbides during combustion. [Example]

[0023] The present invention will be described in more detail below by showing examples, but the present invention is not limited to the following examples.

[0024] (Fire-resistant cable manufacturing) The fire-resistant cables of Examples 1 and 2 and Comparative Examples 1 to 3 were produced as follows. First, a copper wire was prepared, and mica tape was wrapped around the prepared copper wire to form a fire-resistant layer. An insulator layer was formed by extruding low-density polyethylene around the fire-resistant layer. A flame-retardant polyethylene containing aluminum hydroxide, magnesium hydroxide, and red phosphorus in a mass ratio of 3:5:0.45 was extruded around the insulator layer to form a sheath, thereby producing the fire-resistant cable of Example 1.

[0025] Fire-resistant cables of Example 2 and Comparative Examples 1 to 3 were produced in the same manner as Example 1, except that the mass ratios of aluminum hydroxide, magnesium hydroxide, and red phosphorus were set to 6:2:0.45, 0:8:0.45, 8:0:0.45, and 0:10:0, respectively. The mass ratios of aluminum hydroxide, magnesium hydroxide, and red phosphorus in Examples 1 and 2 and Comparative Examples 1 to 3 are shown in Table 1. In Examples 1 and 2 and Comparative Examples 1 to 3, the total mass ratio of aluminum hydroxide, magnesium hydroxide, and red phosphorus to the sheath was set to a range of 30 to 60 mass%.

[0026] (Fire Resistant Cable Evaluation) The performance of the fire-resistant cables manufactured as described above in Examples 1 and 2 and Comparative Examples 1 to 3 was evaluated in accordance with JCS 7509:2020 "1-hour fire-resistant cable test method (small heating furnace)." Specifically, an exposure test and a conduit test were conducted as shown in Table 1. The exposure test examines the fire resistance of a 1.3m fire-resistant cable when a load twice its own weight is applied to the cable, while the conduit test examines the fire resistance of a 1.3m fire-resistant cable when inserted into a 400mm metal conduit with both ends filled with rock wool.

[0027] In the exposure test and the conduit test, the dielectric strength was checked before, during, and after heating. The dielectric strength was evaluated by whether or not dielectric breakdown occurred when the voltage shown in Table 1 was applied for the time shown in Table 1. Tests that did not experience dielectric breakdown were rated "good," and those that did experience dielectric breakdown were rated "poor." The evaluation results are shown in Table 1.

[0028] In addition, in the exposure test and the conduit test, the insulation resistance was measured at 0 and 60 minutes of heating time. The insulation resistance was required to be 50 MΩ or more at 0 minutes of heating time, and 0.4 MΩ or more at 60 minutes of heating time. Test pieces that met the required insulation resistance were rated "good," and those that did not were rated "poor." The evaluation results and measured insulation resistance values ​​are shown in Table 1.

[0029] In addition, the breakdown voltage was measured in both the exposure test and the conduit test. The breakdown voltage is the voltage value at which dielectric breakdown occurs when a voltage is applied to a fire-resistant cable. The measurement results are shown in Table 1. Flame retardancy was also measured in the exposure test. Flame retardancy was measured by measuring the charred length (burning distance) of the cable after the test with a metal ruler, with a result of 150 mm or less being rated "good" and one exceeding 150 mm being rated "poor." The evaluation and measurement results are shown in Table 1. After 60 minutes of heating, electrical continuity was checked using a tester. Those that were conductive were rated "good," and those that were not conductive were rated "bad." The evaluation results are shown in Table 1.

[0030] In addition, for the fire-resistant cable of Comparative Example 3, items for which no measurement results or evaluations are shown indicate that a short circuit occurred before 60 minutes and therefore no test was performed. In addition, a product that received only a "good" rating in both the exposure test and the conduit test was deemed to have passed. In addition, a product that passed both the exposure test and the conduit test was deemed to have passed the overall assessment.

[0031] [Table 1]

[0032] As can be seen from Table 1, the fire-resistant cables of Examples 1 and 2, which contained all of aluminum hydroxide, magnesium hydroxide, and red phosphorus in the sheath, were judged to pass the overall evaluation. On the other hand, the fire-resistant cables of Comparative Examples 1 to 3, which did not contain any one of aluminum hydroxide, magnesium hydroxide, and red phosphorus in the sheath, were judged to fail the overall evaluation.

[0033] Comparing Example 1, which contains all of aluminum hydroxide, magnesium hydroxide, and red phosphorus, with Comparative Example 1, which contains only magnesium hydroxide and red phosphorus as flame retardants, Example 1 exhibited good insulation resistance, while Comparative Example 1 exhibited poor insulation resistance. This is presumably because Example 1 contained less magnesium hydroxide, which has a high dehydration decomposition starting temperature, and instead contained aluminum hydroxide, which has a low dehydration decomposition starting temperature, thereby suppressing the generation of conductive char when the fire-resistant cable was burned.

[0034] On the other hand, in Comparative Example 2, which contained only aluminum hydroxide and red phosphorus as flame retardants but did not contain magnesium hydroxide, the flame retardancy was poor, and it was found that the flame retardancy was poor when magnesium hydroxide was not contained. Furthermore, in Comparative Example 3, which did not contain red phosphorus, the flame retardancy was significantly poor; for example, when heated for 60 minutes in an exposure test, the fire-resistant cable burned so much that the insulation resistance could not be measured.

[0035] Furthermore, comparing Example 1 and Example 2, Example 2, in which the mass of aluminum hydroxide was greater than the mass of magnesium hydroxide, had higher insulation resistance at 60 minutes in the exposure test and conduit test. From this, it is considered desirable from the viewpoint of insulation resistance that the mass of aluminum hydroxide contained in the sheath be greater than the mass of magnesium hydroxide. On the other hand, between Example 1 and Example 2, Example 1 had better flame retardancy. From this, it is considered that from the viewpoint of flame retardancy, it is desirable that the mass of magnesium hydroxide contained in the sheath be greater than the mass of aluminum hydroxide.

[0036] Furthermore, when performance evaluation was conducted in accordance with JCS 7502:2021 "Cable fire resistance test method (small heating furnace)", the fire-resistant cables of Examples 1 and 2, which contained aluminum hydroxide, magnesium hydroxide, and red phosphorus in the sheath, showed superior insulation resistance and flame retardancy to those of Comparative Examples 1 to 3, as described above. [Industrial Applicability]

[0037] The fire-resistant cable of the present invention is useful for wiring in environments where high fire resistance and flame retardancy are required. [Explanation of symbols]

[0038] 1. Fire-resistant cable 10 Conductors 11 Fireproof layer 12 Insulator layer 13 Sheath

Claims

1. A fire-resistant cable having a conductor, a fire-resistant layer covering the conductor, an insulating layer covering the fire-resistant layer, and a sheath covering the insulating layer, 1. A fire-resistant cable, wherein the sheath contains aluminum hydroxide, magnesium hydroxide, and red phosphorus.

2. 2. The fire-resistant cable according to claim 1, wherein the mass ratio of the aluminum hydroxide to the magnesium hydroxide to the red phosphorus in the sheath is 1-8:1-8:0.

45.

3. 3. The fire-resistant cable according to claim 1, wherein a ratio of a total mass of the aluminum hydroxide, the magnesium hydroxide, and the red phosphorus to a mass of the sheath is 30 to 60 mass%.

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