JPS6140189B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a polypropylene laminate paper that has excellent impulse withstand voltage and is used when wound around a conductor of an electrical device, and an insulated conductor using the same. In recent years, with the increase in the voltage of electrical equipment, attempts have been made to improve insulating paper tapes that are suitable for this.One example of this is an insulating paper made by laminating conventional electrical insulating paper and plastic tape made of polyolefin or fluororesin. Among polyolefins, polypropylene is particularly important because of its excellent properties and relatively low cost. By the way, in transformer windings and power cables, temporary overload currents on power transmission lines can cause the conductor temperature to rise above 140°C, albeit for a short time, and some of the plastic material may become immersed in oil. It melts and precipitates in the form of wax when the temperature drops, impeding the cooling of the equipment and causing adverse effects such as swelling of the plastic tape and preventing the transmission of hydraulic pressure to the insulating layer. Further, there are further requirements such that the laminated insulating paper must have excellent tan δ and ε, and must have excellent impulse strength. This invention was made in view of the above situation, and the first invention is a polypropylene (PP) tape whose extraction amount by normal heptane at 70°C is 3% by weight or less, and a fiber paper tape is thermally bonded to one or both sides of the tape. It is a laminated tape in which polypropylene is crystallized at a temperature below the heat distortion temperature,
It is a polypropylene laminated paper characterized by being further embossed as necessary,
The second invention resides in an insulated conductor, ie, an oil-immersed insulated power cable or an insulated conductor for electrical equipment, in which the polypropylene laminate paper is longitudinally attached or wrapped around the conductor as an insulating layer. Therefore, when the polypropylene laminated paper according to the present invention is used to construct an insulating layer of an electrical device, the polypropylene constituting the insulating layer will not be exposed to oil even in the temporarily high temperature state of the electrical device as described above. There is no risk of dissolution, and it has a high degree of crystallinity.
Moreover, due to the effect of the embossing process, the thickness swelling becomes negligible, and does not pose any problem to the cooling of the equipment or the transmission of hydraulic pressure through the insulating layer. The amount of polypropylene extracted by normal heptane in the polypropylene laminated paper of the present invention is 3%.
The following means that it has high isotacticity, and the fiber paper tape is thermally bonded to both sides, and the polypropylene is crystallized below the heat distortion temperature, so it has excellent oil resistance, and it is also embossed. Table 1 shows that the characteristics are further improved when

[Table] An increase in the isotacticity of polypropylene and a decrease in oil-soluble components is synonymous with a decrease in the amorphous region, as seen in the decrease in the amount of normal heptane dissolved. In polypropylene obtained by the conventional polymerization method, the amount dissolved in normal heptane is 4 to 10% by weight, but the present invention is characterized in that the amount dissolved in normal heptane is 3% by weight or less. This has, of course, been made possible by a new polymerization process, and the values shown in Table 1 are actually measured values for 2.6% by weight of normal heptane, which has excellent oil resistance that could not be obtained with conventional polypropylene. It shows. Furthermore, in the present invention, the polypropylene used in the polypropylene laminated paper is subjected to crystallization treatment. This shows that even if the amount of normal heptane dissolved is 2.6% by weight, the amount dissolved in the final laminate tape varies considerably depending on the degree of crystallization treatment. In other words, depending on the processing conditions, the crystallinity of the polypropylene constituting the laminated paper may not reach the maximum crystallization limit of the polypropylene itself, so the selection of processing conditions is an extremely important factor. That will be understood. The present invention requires processing below the heat distortion temperature (115°C) in order to achieve the maximum crystallinity most economically and without deteriorating the fiber paper. This shows that a stable crystallization process can be performed and that it is possible to economically manufacture a laminate tape. Further, although the embossing treatment does not affect the progress of crystallization, it has the effect of mitigating the apparent thickness swelling, which is explained as follows. That is, the polypropylene polymer film is locally strongly pressed by embossing and penetrates deeply into the fiber paper space, so that the apparent surface area of the polypropylene polymer film increases. Even if the pressure value is the same during embossing, if the pressure is applied using a flat roll, the polypropylene film will only come into contact with the fiber paper evenly, and the surface of the film will only be slightly uneven. When it is impregnated with insulating oil, it swells almost uniformly in the thickness direction. On the other hand, in the case of an embossed polypropylene laminated paper tape, the surface area is increased by the embossing process, and the swelling is dispersed in response to this increase in area, resulting in an apparent decrease in the swollen thickness. For example, if the apparent area of a polypropylene polymer film increases approximately twice, the swollen thickness will be reduced to 1/2.
decreases to Table 1 above shows such a relationship. Next, considering the influence of the crystallinity of polypropylene film on cable characteristics, for example, Table 2
As shown. That is, Table 2 is 275KV, 2000mm ²
This is shown for OF cables, as the degree of crystallinity increases, swelling decreases, so oil flow resistance decreases, and the bendable radius of the cable also decreases. In addition, when the degree of crystallinity is the same, the embossed one has lower oil flow resistance, and the bendable radius of the cable can be made almost as small as that of kraft insulating paper. An insulator can be formed.

【table】

[Table] In implementing the present invention, tan δ is lowered,
Of course, it is preferable to use low-density thin paper as the fiber paper tape in order to improve the impulse breakdown voltage. As described above, the laminated paper and insulated conductor of the present invention have extremely superior oil flow resistance and bendable radius when made into a cable than conventional polypropylene laminated paper, and also have excellent electrical properties such as impulse breakdown. It is something that exists.

Claims (1)

[Claims] 1. A fiber paper tape is adhered to one or both sides of a polypropylene tape whose extraction amount by normal heptane at 70°C is 3% by weight or less, and is crystallized at a temperature below the heat distortion temperature of the polypropylene. Polypropylene laminated paper characterized by: 2. The polypropylene laminated paper according to claim 1, wherein the tape is embossed. 3 Polypropylene laminate paper with a fiber paper tape adhered to one or both sides of a polypropylene tape with an extraction amount of 3% by weight or less by normal heptane at 70°C, and crystallized at a temperature below the heat distortion temperature of the polypropylene. An insulated conductor characterized by being vertically attached or wound around a conductor.