JPS6351323B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention significantly improves the properties of composite electrical insulating paper in which kraft fiber paper is pressure-adhered to at least one side of a polypropylene film, particularly the adhesion and swelling properties of the polypropylene film and kraft fiber paper in insulating oil. It is about the method. Composite electrical insulating paper, which is made by laminating kraft fiber paper on at least one side of a polypropylene film, has features such as low dielectric loss and high withstand voltage, so it is attracting worldwide attention as an insulator for ultra-high voltage OF cables. has been done. Insulators for ultra-high voltage OF cables are required to have dielectric properties such as a dielectric constant ε of about 2.5 and a dielectric loss tangent tan δ of about 0.05 (%). It is necessary to increase the ratio occupied by film to, for example, 60% or more. However, for composite electrical insulating paper in which polypropylene film accounts for 60% or more, the rate of increase in thickness in insulating oil,
That is, the swelling ratio becomes large, and when the cable is bent, for example, the insulating paper becomes "wrinkled" and "cut", which causes a problem of lowering the withstand voltage value of the cable. Conventionally, composite electrical insulating paper has been manufactured by applying kraft fiber paper along at least one side of a polypropylene film extruded from an extruder having a T-die, and then bonding and integrating the film with a pressurized water-cooled roll. In this case, the polypropylene film extruded from the T-die is subjected to its own weight in a molten state before reaching the pressurized water-cooled roll, so that the formed film is oriented in the extrusion direction, and the resulting composite film is It has been found that when electrically insulating paper is immersed in insulating oil, the polypropylene film layer exhibits swelling anisotropy, making it easy for the kraft fiber paper layer and the polypropylene film layer to separate. The present invention has been made to overcome these problems, and provides a method for improving the properties of composite electrical insulating paper, particularly the adhesion and swelling properties between polypropylene film and kraft fiber paper during insulation. This is what we provide. The present invention is a composite electrically insulating paper obtained by bonding kraft fiber paper under pressure to one or both sides of a polypropylene film extruded using an extruder.
After applying the polypropylene film layer used in the composite electrically insulating paper to a heating roll so that the temperature is higher than the crystal melting point of the polypropylene film and the surface pressure applied to the composite electrically insulating paper is 10 g/cm ² or more, It is characterized in that it is allowed to cool in air until the temperature of the polypropylene film layer becomes 30° C. or more lower than the crystalline melting point of the polypropylene film. In the present invention, polypropylene film is
This film is obtained by melt-extruding polypropylene pellets with excellent dielectric properties using an extruder using a T-die or the like. In the present invention, first, a composite electrically insulating paper is obtained by superimposing and pressurizing kraft fiber paper on one or both sides of a polypropylene film extruded using an extruder using a conventional method. Next, the temperature of the polypropylene film layer used in the composite electrically insulating paper was set to be higher than the crystalline melting point of the polypropylene by placing the composite electrically insulating paper obtained in this way on a heating roll, and at this time, the composite electrically insulating paper was The applied surface pressure is maintained at 10 g/cm ² or more, preferably about 50 to 100 g/cm ² .
The reason why the temperature of the polypropylene film layer is limited to a temperature higher than the crystal melting point of the polypropylene is that the orientation imparted to the polypropylene film can be relaxed. At temperatures lower than the crystalline melting point of polypropylene, heating rolls have no effect on the adhesion between polypropylene film and kraft fiber paper in insulating oil. Also, the reason why the surface pressure applied to the composite electrical insulating paper is limited to 10 g/cm2 ^{or more} is that by applying such surface pressure, the molten polypropylene sufficiently sinks into the fiber gaps of the kraft fiber paper, and the adhesion between the polypropylene film and the kraft fiber paper is achieved. This is because the quality is greatly improved. When the obtained composite electrically insulating paper is placed on a heating roll, the composite electrically insulating paper is pressed against the heating roll, so that the heat transfer from the heating roll to the composite electrically insulating paper is good, and therefore the surface of the heating roll is It is sufficient that the temperature is 10 to 20°C higher than the crystalline melting point of the polypropylene film. It is preferable to use two or more metal rolls as the heating rolls and to pass the composite electrically insulating paper through each roll while being in sufficient contact with the rolls, since a constant surface pressure can be applied. In the present invention, the composite electrically insulating paper is placed on a heated roll and then cooled. In this cooling step, it is necessary to allow the polypropylene film layer to cool in air until the temperature of the polypropylene film layer becomes 30° C. or more lower than the crystalline melting point of the polypropylene film. The reason for this is that the crystallization temperature range of polypropylene film is below the crystal melting point of polypropylene film and up to a temperature 30°C lower than the crystal melting point, so it is important to perform sufficient slow cooling within this temperature range at least. This is because it is effective in increasing the degree of crystallinity, and therefore in reducing the rate of increase in thickness of the obtained composite electrically insulating paper in insulating oil, that is, the rate of swelling. When cooling in air, cooling is performed only by heat dissipation, resulting in poor heat transfer, and sufficient slow cooling is performed, resulting in a large effect of increasing the degree of crystallinity. Generally, from the viewpoint of productivity, it is preferable to let the material cool in the air for about 2 to 3 m after passing through the heating roll, and then cool it with a water-cooled roll or the like. It is particularly preferable to carry out the method of the present invention immediately after the step of pressurizing and adhering kraft fiber paper to at least one side of a polypropylene film extruded using an extruder, since this can improve productivity and properties. . Next, the present invention will be explained with reference to Examples and Comparative Examples. Comparative Example 1 Polypropylene (crystal melting point 170℃) was extruded into a 90μ thick film using an extruder, and 30μ thick kraft fiber paper was layered on both sides of the film and bonded together using a pressure roll (surface temperature 15℃). to become
A composite electrical insulation paper was obtained. Example 1 The composite electric insulating paper obtained in Comparative Example 1 was
The sample was passed between heating rolls at 185°C at a surface pressure of 50 to 70 g/cm ² and left to cool in the air up to a point 2 m away from the heating roll. Note that the temperature of the composite electrically insulating paper at this time reached 130°C. Then, it was introduced into a cooling roll (surface temperature: 15°C) and further cooled. Example 2 The composite electrical insulating paper obtained in Comparative Example 1 was
The sample was passed between heating rolls at 175°C at a surface pressure of 50 to 70 g/cm ² and left to cool in the air up to a point 2 m away from the heating roll. The temperature of the composite electrical insulation paper reached 120℃. Then, it was introduced into a water-cooled roll (surface temperature: 15°C) and further cooled. Example 3 The composite electrical insulating paper obtained in Comparative Example 1 was
The sample was passed between heated rolls at 185°C at a surface pressure of 100 to 150 g/cm ² and left to cool in the air up to a point 2 m away from the heated roll. Note that the temperature of the composite electrically insulating paper at this time reached 130°C. Then, it was introduced into a water-cooled roll (surface temperature: 15°C) and further cooled. Example 4 The composite electrically insulating paper obtained in Comparative Example 1 was
The sample was passed between heating rolls at 185°C at a surface pressure of 10 to 30 g/cm ² and left to cool in the air up to a point 2 m away from the heating roll. The temperature of the composite electrical insulation paper reached 130℃. Then, it was introduced into a water-cooled roll (surface temperature: 15°C) and further cooled. Comparative Example 2 The composite electrical insulating paper obtained in Comparative Example 1 was
The sample was passed between heating rolls at 160°C at a surface pressure of 50 to 70 g/cm ² and left to cool in the air up to a point 2 m away from the heating roll. At this time, the temperature of the composite electrically insulating paper reached 110°C. Then, it was introduced into a water-cooled roll (surface temperature: 15°C) and further cooled. Comparative Example 3 The composite electrical insulating paper obtained in Comparative Example 1 was
The material was passed through a heating roll at 185° C. to the extent that it lightly touched the material, and was allowed to cool in the air up to a point 2 m away from the heating roll. The temperature of the composite electrical insulation paper reached 130℃. Then, it was introduced into a water-cooled roll (surface temperature: 15°C) and further cooled. Comparative Example 4 The composite electrical insulating paper obtained in Comparative Example 1 was
The sample was passed between heated rolls at 185°C at a surface pressure of 50 to 70 g/cm ² and allowed to cool in the air up to a point 10 cm away from the heated roll. Note that the temperature of the composite electrically insulating paper at this time reached 180°C. Then, it was introduced into a water-cooled roll (surface temperature: 15°C) and further cooled. The composite electrically insulating papers obtained in Examples 1 to 4 and Comparative Examples 1 to 4 described above were each dried at 100°C and 0.1 mmHg for 24 hours, and an oil obtained by impregnating them with dodecylbenzene (DDB). The dielectric properties of the soaked paper were measured. As a result, the dielectric constant is 2.44~
2.50, and the dielectric loss tangent tanδ at 80℃ is 0.045
It was 0.054 (%), which was good. Further, the obtained composite electrically insulating paper was vacuum-dried in the same manner, then immersed in DDB at 100°C, and the rate of increase in thickness after being left for 240 hours was measured. The results are shown in Table 1. Furthermore, the resulting composite electrically insulating paper was similarly vacuum dried, then immersed in DDB at 100°C, and after being left for 24 hours, the adhesive strength between the kraft fiber paper and the polypropylene film layer was measured. The results are shown in Table 1.

【table】

[Table] As shown in Table 1, the composite electrical insulating paper produced by the method of the present invention has a small thickness increase rate after immersion in insulating oil, that is, a small swelling rate, and a high adhesive strength.
It had excellent physical properties. Next, a semiconducting layer was provided on the 2000 mm ² copper conductor, and the composite electrically insulating paper obtained in Example 1 and Comparative Example 1 was wrapped around this to a thickness of 15 mm, and the same external semiconducting layer and aluminum covering were applied. These cables were vacuum dried at 100°C and 0.1mmHg for 120 hours. After this, the conductor was impregnated with DDB, heated for 6 hours so that the conductor temperature reached 85℃ by energizing the conductor, cooled to room temperature, and after bending 20 times, the impact breakdown voltage was measured and shown in Table 2. Got the results.

[Table] Also, as a result of disassembling this cable, Example 1
In the cable using composite insulating paper, no paper wrinkles or cut parts were observed in the insulating paper layer, and the cable was in good condition. On the other hand, in the cable using the composite insulating paper of Comparative Example 1, the occurrence of paper wrinkles and the presence of cut portions in the insulating paper layer were observed, and dielectric breakdown occurred at the cut portions.

Claims (1)

[Claims] 1 Composite electrical insulating paper obtained by bonding kraft fiber paper under pressure to at least one side of a polypropylene film extruded using an extruder, the polypropylene film layer used for the composite electrical insulating paper having a temperature higher than the crystalline melting point of the polypropylene. and the surface pressure applied to the composite electric insulating paper is 10 g/cm ² or more, and then the temperature of the polypropylene film layer is lowered by 30 ° C or more than the crystalline melting point of the polypropylene film. A method for improving the properties of composite electrically insulating paper, characterized by cooling it in air until it becomes dry.