JPH0241129B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a mica tape assembly for forming a fireproof layer in rubber or plastic insulated fireproof wires. Fireproof electric wire is 840 specified in the Fire and Disaster Management Agency notification.
In the °C combustion test, it is required to have an insulation resistance of 0.4 MΩ or more during 30 minutes of combustion, and a withstand voltage strength of 1500 VAC or more at a high temperature of 840 °C immediately after 30 minutes of combustion. In the case of rubber or plastic insulated fire-resistant wires, even if flame-retardant measures are taken in the protective sheath composition, they will actually be destroyed in a fire, so it is not possible to pass the Fire and Disaster Management Agency regulations based solely on the insulation of the fire-resistant layer. Necessary for wire design. On the other hand, for rubber- and plastic-insulated fire-resistant wires that use laminated mica tape as a fireproof layer, since the cost of laminated mica tape accounts for an extremely large proportion of the total cost of all coating layers, laminated mica tape is It is becoming necessary to take measures such as simplifying the structure of the laminated mica tape as much as possible or reducing the number of layers of laminated mica tape, but all of these measures reduce the insulation performance of the laminated mica refractory layer at high temperatures. It is fraught with danger. There are two types of mica: hard mica and soft mica. Recognizing that hard mica has poor heat resistance, whereas soft mica has superior heat resistance, we use laminated mica for fire-resistant electric wires. Soft mica products have been in practical use up until now, but although soft mica laminated mica has excellent insulation properties, it does not necessarily have sufficient voltage strength at high temperatures of 800°C or higher. For this reason, there is a problem in that it is difficult to make the above-mentioned improvements such as making the fireproof layer thinner. By the way, according to research conducted by the present inventors, mixing hard mica into soft mica unexpectedly increases the withstand voltage at high temperatures without significantly affecting the insulation and flexibility of the composite mica. Characteristics are significantly improved. The present invention was completed based on the above-mentioned new findings, and consists of a paper assembly made by mixing soft mica with 20 to 400 parts of hard mica per 100 parts (by weight, the same shall apply hereinafter) of the soft mica. It consists of a mica layer and a backing layer, and is characterized in that the heat loss of the assembled mica layer at 400°C is 10% by weight or less. The reason why the heat loss of the assembled mica layer is limited as described above will be explained below. A part of the adhesive used to bond the laminated mica layer and the backing layer may penetrate into the laminated mica layer, or the laminated mica layer itself may be pre-impregnated with an organic varnish to increase its mechanical strength. For these reasons, the assembled mica layer often contains flammable substances such as adhesives and organic varnishes. If a large amount of such flammable substances are contained, no improvement in voltage resistance characteristics due to the presence of hard mica will be observed.
The reason for the above-mentioned negative effects of combustible materials is not clear at present, but the burning of combustible materials creates a large number of through holes in the assembled mica layer, and in the state where such a large number of through paths are created, hard It is thought that the effect of mica addition becomes poor. Therefore, in the present invention, the loss on heating of the assembled mica layer is preferably as small as possible, particularly preferably 10% by weight or less. Incidentally, combustible substances that adversely affect the high-temperature withstand voltage characteristics of the tape exist inside the composite mica layer, and are present on or near the outer surface of the composite mica layer, or on or near the inner surface in contact with the backing layer. Those that exist in the left do not have as much of a negative impact. Therefore, in the present invention, the heat loss of the assembled mica layer is determined by peeling off and collecting 95% of the entire assembled mica layer, leaving a very small amount on the inside that cannot be separated from the backing layer. The sample was heated for ~2 hours to remove organic components, the weight difference between the sample before and after the heating was determined, and the loss on heating was calculated as follows. If the value is 20% by weight or less, it can be used in the present invention. Heating loss = sample weight before heating - sample weight after heating / sample weight before heating x 100 The soft mica used in the present invention is obtained by beating raw mica ore into scales using a water jet or the like. Mica ore is also called phlogopite. The particle size of this soft mica is 8 to 400.
Metsuyu's one is good. Hard mica is also obtained by crushing raw ore into scales, similar to the above-mentioned soft mica. This raw ore is also called muscovite. There are two types of hard mica: calcined and uncalcined, but the former is made by calcining raw ore at a temperature of 700 to 1000°C and then beating it into flakes. Although one or both of the two may be used here, it is preferable to use a fired one. The particle size of hard mica is also 8.
~400 mesh is good. The amount of hard mica used is as described above,
The amount of hard mica used is 25 per 100 parts of soft mica.
If it is less than
When the amount is more than 400 parts per 100 parts, the low insulation properties and rigidity of the hard mica itself become obvious, and the high temperature insulation properties and flexibility of the tape deteriorate. Therefore, the preferred amount of hard mica used is 50 to 200 parts per 100 parts of soft mica. In the present invention, it is essential that soft mica and hard mica be mixed in the above ratio.
By doing so, it is possible to obtain a composite mica which has excellent flexibility under normal conditions, exhibits excellent tape winding properties, and has excellent both insulating properties and withstand voltage properties at high temperatures. Incidentally, in composite mica tapes made by laminating hard laminated mica and soft laminated mica, or in combination with hard laminated mica tapes and soft laminated mica tapes, the tape winding properties are poor due to the presence of the hard laminated mica layer, so it is difficult to Since the high-temperature withstand voltage improving effect of hard mica is not exhibited, the object of the present invention cannot be achieved. In the present invention, the above-mentioned soft mica and hard mica are made into a laminated mica using an ordinary paper machine or the like. At this time, as other components, inorganic powders such as aluminum hydroxide, magnesium hydroxide, and silica powder may be coated on the above-mentioned aggregated mica to form a composite, or may be mixed with the above-mentioned mica and made into paper. good. As the backing layer material, materials commonly used in laminated mica tapes for fire-resistant electric wires are used, such as glass cloth, plastic film, nonwoven fabric, glass yarn (trade name: Tatesof, yarn glued vertically and horizontally), and the like. The backing layer material and the laminated mica may be bonded together using silicone resin, epoxy resin, or the like. At this time, these resins may be impregnated into the aggregated mica as long as the amount is less than the above-mentioned amount. The present invention will be explained in more detail below with reference to Examples and Comparative Examples. Examples 1 to 15, Comparative Examples 1 to 12 Various slurries with different mixing ratios (parts by weight) of hard mica and soft mica were mixed and paper-milled, and the thickness
Various laminated mica sheets of 120 μm were obtained. The calcined hard mica used here is made from roughly crushed raw ore.
It is baked at 1000℃ for 30 minutes and then beaten into scales. Next, a glass cloth having a thickness of 30 μm was bonded to each sheet using silicone resin to obtain tapes with backing layers of Examples and Comparative Examples shown in Table 1. 1/4 of each tape of the example and comparative example (both tape width 6 mm) was placed on a copper conductor with an outer diameter of 1.2 mm.
The tape winding property was examined by wrapping two layers in a lap. As a result, in the case of each tape of Example and Comparative Examples 1 to 10, good tape winding was performed, but in the case of Comparative Example
When the tape of Comparative Example 11 and Comparative Example 12 was used, the mica laminated layer and the backing layer were partially peeled off, and the mica laminated layer fell off. After wrapping with tape, the thickness is 0.8
mm polyethylene insulating layer with a further thickness of 1.5 mm
A fire-resistant electric wire was obtained by applying a polyvinyl chloride sheath of mm. Each fire-resistant wire was subjected to an 840°C fire resistance test as notified by the Fire and Disaster Management Agency, and the minimum insulation resistance during 30 minutes of heating and the dielectric breakdown voltage after 30 minutes of heating were measured. These test results are shown in Table 1 along with the tape structure. As is clear from Table 1, when the tapes of the examples of the present invention were used, satisfactory results were obtained in both tape winding and wire insulation properties.
On the other hand, Comparative Examples 1 to 8 where the heating loss is excessive
In the case of , the insulation properties are poor, while in the case of Comparative Examples 11 and 12, in which the content of hard mica is excessive, there are problems in tape windability and insulation resistance. Comparative example 9,
In the case of 10, the characteristics are better than other comparative examples, but
The dielectric breakdown voltage is low because the amount of hard mica is too small or it is not included.

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Claims (1)

[Claims] 1 Consists of a backing layer and a laminated mica layer made by mixing soft mica and 25 to 400 parts by weight of hard mica per 100 parts by weight of the soft mica, and the loss on heating at 400°C of the laminated mica layer is 10% by weight. A laminated mica tape for fire-resistant electric wires, characterized by the following: