JPH04322B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an insulating tape for forming a fireproof layer in a rubber or plastic insulated fireproof electric wire. Even if the protective sheath of fire-resistant wires with rubber or plastic insulation is made of a flame-retardant rubber or plastic composition, under fire,
Since not only the insulating layer but also the sheath is burned down, the fireproof layer alone can continue to supply the necessary power to fire extinguishing facilities such as sprinklers and evacuation equipment such as elevators for the time necessary for people to evacuate, for example 30 minutes. It is required to maintain insulation performance. Conventionally, as the constituent material for the above-mentioned fireproof layer, a tape made of soft laminated mica laminated with a backing layer has been mainly used because of its excellent insulating properties at high temperatures.On the other hand, unfired or Although laminated mica, which is made of semi-fired hardened mica, is cheaper than calcined hard mica or soft laminated mica, it is only used as an auxiliary because it has problems with electrical properties at high temperatures. The current situation is that there is no such thing. By the way, according to the research conducted by the present inventors, it has been found that the hard laminated material is made mostly of fine unfired or semi-fired hard mica with a grain size of 30 mesh or more and has an airtightness of at least 100 Gurley seconds/100 c.c. Mica has excellent electrical insulation properties and voltage strength at high temperatures. The present invention proposes an insulating tape as set forth in the claims based on such new knowledge. The laminated mica used in the present invention has a structure in which fine hard mica scales are densely accumulated and has excellent filling and softness, so it has good windability around a conductor. The large partial peeling of mica scales seen in composite mica is extremely rare, and it can be applied to conductors with few defects. Furthermore, as is clear from the performance comparison of Examples and Comparative Examples described below, the tape of Examples is used as a fireproof layer wound directly on a conductor and exhibits excellent electrical properties at high temperatures. The reason for this is considered by the present inventors as follows. In other words, it is generally believed that when hard mica is heated to a high temperature of 700°C or higher, it releases bound water and cracks occur in the mica pieces. Cracks create electrical weaknesses in the assembled mica layer, but
Most of the mica scales used in the present invention are fine particles with a particle size of 30 mesh or more, so even if cracks occur in each fine particle, the cracks will be uniformly dispersed.
Moreover, under normal conditions, mica scales are deposited so densely that they have a high airtight density of 100 Gurley seconds/100 c.c. or more as aggregated mica, so even if cracks occur in individual scales, there will be no cracks. The mica scales protect the cracks, and as a composite mica, electrical weak points are unlikely to occur. This is considered to be one of the reasons for the high performance of the tape of the example. Another reason is that, as mentioned above, based on the good windability of the mica assembly used in the present invention, the fireproof layer made of the example tape is not as good as the comparative example tape when it is wound on the conductor. It is also considered that there are fewer electrically defective parts compared to the fireproof layer. The aggregated mica used in the present invention is unfired or semi-fired (in the present invention, semi-fired means 900℃,
It refers to a product whose heating loss after heating for 1 hour is approximately 3% by weight. ) hard mica (muscovite) is pulverized by a normal method such as the water jet method to produce fine particles with an aspect ratio of, for example, 100 or more, and then made into paper using a circular mesh paper machine, a fourdrinier paper machine, etc. I can do it. In this case, most of the mica scales to be made into paper, particularly 70% by weight or more of the total weight, and further 90% by weight or more of the total weight, are 30 meshes or more, preferably 50 meshes or more. For the reasons mentioned above,
The airtightness of the assembled mica is preferably high, particularly preferably at least 200 Gurley seconds/100 c.c. If the airtightness is 500 Gurley seconds/100 c.c. or more, or 1000 Gurley seconds/100 c.c. or more, even better withstand voltage characteristics can be obtained. Here, the airtightness of the laminated mica is the value without varnish or adhesives, so when measuring the airtightness of the laminated mica sample containing such agents, the measurement sample must be heated at 400℃ for 1 hour in advance. It is best to burn out these agents by heating to a certain degree. As long as the mica assembly has the above-mentioned airtightness, its thickness is not particularly limited, but it is preferably selected from the range of 50 μm/200 μm to ensure good windability. As the backing material to be bonded to the laminated mica, materials known as backing materials for insulating tapes for fire-resistant electric wires may be used, such as glass fiber woven fabrics, non-woven fabrics, and plastic films such as Tatesof (trade name) polyethylene, polypropylene, and polyester. . However, unfired or semi-fired hard mica tends to have a slightly lower insulation resistance at high temperatures than fired hard mica or soft mica. In order to improve the low insulation resistance of this laminated mica, as a backing material,
Preference is given to materials containing at least 20% by weight of non-combustible materials such as glass, asbestos, etc. If a combustible material such as plastic film is used as the backing material, the backing material layer will be burned down in the event of a fire, leaving only the laminated mica layer.
If a backing material made of or containing a noncombustible material is used, the noncombustible material will remain together with the aggregated mica even in the event of a fire, and the remaining noncombustible material layer itself or the microscopic particles present in the layer. This is because the air layer acts to increase the insulation resistance of the fireproof layer. For example, when the tape of the present invention having such a non-combustible backing material layer is wrapped in two or more layers on a conductor, depending on the way the tape is used, there may be a The above-mentioned nonflammable material layer can be present between the mica layers. Preferred as backing material are therefore non-combustible materials, especially glass fiber cloth, having a thickness of at least 30 μm, in particular at least 40 μm. Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples. Prepare the wide (130 mm width) insulating tapes of the examples and comparative examples shown in Table 1, and
Insulation resistance and dielectric strength at 840°C were measured for each square sample piece using the following test methods. Test method: Two test sheets were sandwiched between stainless steel flat disk electrodes with a diameter of 50 mm, and the sample was heated to 840°C according to the heating curve specified in JIS A 1304 while applying a voltage of AC600V. The insulation resistance of the piece was measured. After heating for 30 minutes, the voltage was increased at a rate of 100 V/sec while the temperature was maintained at 840° C., and the applied voltage at which dielectric breakdown of the sheet occurred was measured.

[Table] Using the insulating tapes of Comparative Example 1 and Example 3 (however, the tape width was 10 mm), the assembled mica layer was wrapped around a stranded copper conductor with a conductor cross section of 8 mm ² with a 1/2 wrap, facing the conductor side. Two types of fire-resistant electric wires were obtained by winding the wires in layers and applying a 1 mm thick polyethylene insulating layer and a 2 mm thick polyvinyl chloride sheath thereon. Each fire-resistant electric wire is exposed in the exposed wiring condition specified in Fire and Disaster Management Agency Notification No. 7.
When an 840°C fire resistance test was conducted, the electrical wire using the tape of Comparative Example 1 had an insulation resistance of 0.1 MΩ at 840°C, and dielectric breakdown occurred when 1500V was applied after 30 minutes of heating, but the wire using the tape of Example 3 The electric wire is
The insulation resistance at 840℃ is 0.6MΩ, and
No dielectric breakdown occurred even when 1500V was applied for 1 minute.

Claims (1)

[Claims] 1 At least 70 particles with a particle size of 30 mesh or more
% by weight of unfired or semi-fired hard mica and has a tightness of at least 100 Gurley seconds/100 c.c., and is laminated with a backing material layer. insulation tape.