JPS631734B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to insulation of oil-filled electrical equipment. Recently, in oil-filled electrical equipment, such as oil-filled capacitors and oil-filled cables, instead of using conventional insulating paper such as kraft paper, the insulator is made of plastic film, a combination of tape and insulating paper, or a combination of plastic and paper. Laminate is used. Furthermore, recently, capacitors and cables in which the entire dielectric layer is made of roughened plastic film or tape have been developed for the purpose of downsizing equipment, and some of these have been put into practical use. For example, polypropylene film or tape dissolves and swells when exposed to aromatic oils. Particularly in the case of capacitors and cables that use a roughened film for all of the dielectric layers, the oil passages are caused by dissolution and swelling. This makes it difficult to downsize and extend the lifespan of equipment. The present invention relates to oil-filled electrical equipment that uses a roughened polypropylene film or tape that solves the above-mentioned problems as part or all of the insulator, thereby achieving miniaturization and longer life of the equipment. Many methods have been proposed for roughening the surface of polypropylene film or tape. Mechanical methods include sandblasting and embossing the surface of polypropylene film, but it is difficult to obtain sufficient surface roughness to improve insulating oil impregnation, so roughening treatment is not recommended. If applied too strongly, insulation defects will occur, making it unsuitable for use as an electrical insulating material. Another method is to create a surface layer containing a mixture of α crystals and β crystals by changing the crystallization conditions during the cooling process of a melt-extruded unstretched sheet, and then obtain a network-like unevenness by stretching.
Since commonly used polypropylene has very little β-crystal formation, the resulting surface roughness is insufficient to improve the impregnability of insulating oil and the long-term stability of oil-filled electrical equipment. For this reason, methods such as contacting the melt-extruded unstretched sheet with a cooling drum for a long time and annealing the unstretched sheet at high temperatures have been proposed, but these methods create fine cavities inside the stretched film, reducing its performance as an insulating material. Problems such as deterioration of stretching film formability occur, making this method impractical. As a result of various studies on polypropylene suitable for surface roughening, the present invention has found that the polypropylene specified in the present invention has the characteristics that β-crystal formation is easy and a roughened film with good insulating oil impregnation property can be easily obtained. This heading led to the present invention. The present invention provides isotactic treatment of the boiling heptane insoluble portion of polypropylene. Pentad fraction is 0.955,
The polypropylene is preferably 0.96 or more, and the content of the boiling heptane soluble portion of the polypropylene is 9.0% by weight, preferably 8.0% by weight or less.The polypropylene is formed into a sheet having a surface layer containing a mixture of α crystals and β crystals, and is biaxially stretched. An oil-filled electrical device characterized in that a roughened film is used to form an insulating layer of a capacitor element or a cable. First, the isotactic treatment of the boiling heptane insoluble portion of the polypropylene described above. The pentad fraction and the content of boiling heptane soluble parts are determined as follows. Boil 5g of polypropylene with 500ml of xylene
After completely dissolving the mixture, lower the temperature to 20°C and leave it for 4 hours. Thereafter, it is filtered and separated into a xylene soluble part and an insoluble part at 20°C. Next, the xylene-insoluble portion at 20° C. is further extracted with boiling heptane for 8 hours using a Soxhlet extractor to separate it into an extraction residue and an extract. This extraction residue is used as the boiling heptane insoluble part. The value obtained by subtracting this dry weight from the total polypropylene weight subjected to measurement and dividing by the total polypropylene weight, expressed as a weight percentage, is the content of the boiling heptane soluble portion. Isotactic. What is the petutad fraction?A.
Macromolecules 6 , 925 by Zambelli et al.
(1973), i.e. ¹³ C
- Isotactic chain in pentad units of a polypropylene molecular chain measured using NMR, in other words, the fraction of propylene monomer units at the center of a chain in which five consecutive propylene monomer units are meso-bonded. If the isotactic pentad fraction is less than 0.955, the amount of β crystals produced will be small. Furthermore, if the boiling heptane soluble portion exceeds 9.0% by weight, it is difficult to form β crystals, and the performance when used as a capacitor is significantly inferior. Further, the polypropylene used in the present invention can contain a heat stabilizer, an antioxidant, a β-crystal nucleating agent, and other additives as necessary. In the present invention, the sheet having a surface layer containing α and β crystals from the polypropylene can be prepared by a known method, for example, a method of slowly cooling at least one side of a melt-extruded sheet, a method of rapidly cooling one side and slowly cooling the other side, It can be obtained by a method using polypropylene containing a known β-crystal nucleating agent in at least one outer layer of a composite sheet, a method using polypropylene having a lower intrinsic viscosity than the polypropylene used in other layers, etc. in at least one outer layer. In the present invention, the β-crystal content of the surface layer of the unstretched sheet needs to be 0.15 or more in terms of K value. When the K value is 0.15 or less, the surface roughness of the film obtained by stretching is insufficient to improve the insulating oil impregnation properties. The roughened biaxially stretched film used in the present invention is obtained by stretching a sheet having a surface layer in which α crystals and β crystals are mixed, obtained by the above method, at a stretching temperature that is higher than the melting point of the β crystals and lower than the melting point of the α crystals. It is obtained by Furthermore, the stretching method in the present invention can be a method normally used in industry, such as a stretching machine such as a tender type or a tubular type. Examples of the use of the roughened polypropylene film used in the oil-filled electrical equipment of the present invention will be described below, but the present invention is not limited thereto. Usage example 1 Melt flow rate is 2.0, isotactic of boiling heptane insoluble area. Pentad fraction is 0.965,
Using a T-die extruder, polypropylene with a boiling heptane soluble content of 6.8% by weight was heated to 290% by weight.
Melt extrusion was carried out at °C, and then slowly cooled using heating rolls to obtain a sheet with a thickness of 0.8 mm. This sheet was stretched 5 times in one direction with a roll having a surface temperature of 150°C, and then a tenter type stretching machine (165
℃) in the direction perpendicular to the direction of the first stage.
The film was stretched twice and heat treated at 135°C to obtain a roughened biaxially stretched polypropylene film with a thickness of 18 μm. Usage example 2 Melt flow as polypropylene. Late is
2.1. The surface was roughened biaxially in the same manner as in Example 1, except that the isotactic pentad fraction of the boiling heptane insoluble part was 0.963 and the content of the boiling heptane soluble part was 7.5% by weight. A stretched film was produced. Comparative example 1 Melt flow. Rate 2.0, isotactic of boiling heptane insoluble part. Pentad fraction 0.950,
A roughened biaxially stretched film was obtained in the same manner as in Use Example 1, except that polypropylene having a boiling heptane soluble content of 11.2% by weight was used. Comparative Example 2 Melt flow as polypropylene. Late
2.2. Isotactics of the insoluble part of boiling heptane.
A roughened biaxially stretched film was produced in the same manner as in Use Example 1, except that polypropylene having a pentad fraction of 0.946 and a boiling heptane soluble content of 7.0 weight percent was used. A roughened biaxially stretched film was formed using Usage Examples 1 and 2 and Comparative Examples 1 and 2 produced as described above, and an all-film capacitor was manufactured.
Tested. Test capacitor A capacitor element consisting of a dielectric layer formed from three 18 μm thick biaxially stretched films (polypropylene) between electrodes made of aluminum foil was fabricated, heated, dried under reduced pressure, and then impregnated with the insulating oil shown in Table 1. It was made into a capacitor. Capacity of capacitor is 50KVA.

【table】

[Table] According to Examples 1 to 8 and Comparative Examples 3 to 6
50KVA oil-filled capacitor in 100℃ atmosphere
Continuously apply an AC voltage of 1.75E (E is the rated voltage),
The residual rate was determined. The results are shown in FIG. As is clear from the figure, the example according to the present invention does not break even after 150 days. The above description has been about capacitors, but the present invention can also be applied to oil-filled power cables using examples 1 and 2.
If a tape is made from a roughened film according to the present invention and the insulating layer is made from a roughened biaxially oriented polypropylene film of the present invention and wound around a conductor, an oil-permeable gap is created between the conductor and the outer surface of the insulating layer. Therefore, an oil-filled power cable with excellent long-term stability can be obtained. Table 2 shows the characteristic values of the biaxially stretched films produced in Use Examples 1 and 2 of the present invention and Comparative Examples 1 and 2.

[Table] Item (a) in Table 2 is melt flow. rate (g/10 min), (b) isotactic boiling heptane insoluble part. Pentad fraction, (c) shows boiling heptane soluble content (weight percent), and flame retardant oil A is TCP/AN=50/50 (weight percent), B is TCP/DTE=50/50 (weight percent). weight percent)
It is. Further, the degree of swelling (weight percent) of the biaxially stretched film in Table 2 indicates the change in weight after 40 hours of immersion at 100°C. Γ The K value of the unstretched sheet is β of the surface layer of the unstretched sheet.
Indicates crystal content. Measuring the K value
Macromolecular Chemie 75 135−137 (1964)
According to the method described. Γ Surface roughness Rz was measured using a reference length of 2.5 mm in accordance with JIS B-0601. Γ Insulating oil impregnation (1) was determined by winding the test film around a core, standing it vertically in a container containing insulating oil (alkylnaphthalene), and measuring the impregnation height (h) after 10 hours. Γ Impregnating property of insulating oil (2) is as follows: 0.02ml of insulating oil (alkyldiphenylethane) is dropped onto the center of a PP film set horizontally (rough side up), and the same polypropylene film is placed on top of it. Gently place the oil on it and measure the spread area of the oil after 10 minutes. Γ Amount of PP dissolved in alkylnaphthalene PP film in 200ml of alkylnaphthalene
Add 100 g of oil and heat at 100°C for 40 hours. After cooling to room temperature, take 100 c.c. of sample oil, mix it with furfural, and measure the amount of PP extracted by furfural. From Table 2, it can be seen that the roughened biaxially stretched film according to the usage example of the present invention has a larger haze value and surface roughness and better impregnability with insulating oil than the comparative example. Further, from Table 2, it is understood that the swelling of the samples according to Comparative Examples 1 and 2 is greater than that of the samples according to the usage examples of the present invention. As can be understood from the above explanation, this phenomenon is caused by the isotactic nature of the insoluble portion of boiling heptane. This is caused by the difference in pentad fraction and boiling heptane soluble content; for example, even if the boiling heptane soluble content is less than 9.0% by weight, large swelling occurs; As mentioned above, especially for boiling heptane insoluble isotactics. The pentad fraction and boiling heptane soluble content (weight percent) define the properties of the polypropylene used in the present invention.

[Brief explanation of the drawing]

FIG. 1 shows the withstand voltage characteristics of an example of the present invention and a comparative example using oil-filled capacitors.

Claims (1)

[Claims] 1. Isotactic insoluble portion of boiling heptane in at least a portion of the insulating layer. The pentad fraction is
0.955 or higher, the boiling heptane soluble content is 9.0
1. An oil-filled electrical device characterized by using a roughened biaxially stretched film obtained by forming and stretching polypropylene having a surface layer containing a mixture of α crystals and β crystals.