JPH0644411B2 - Press board for low dielectric constant oil immersion insulation - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a press board for oil immersion insulation (hereinafter, simply referred to as a press board). More specifically, it relates to a press board having a low dielectric constant obtained by mixing poly-4-methylpentene-1 fiber and kraft pal.

(Prior Art) A conventional oil-immersed insulation pressboard is kraft pulp 100.
It is a press board composed of weight% and has a high dielectric constant of 4.7. As a press board having a reduced dielectric constant, some of the inventors of the present invention firstly used a low dielectric constant oil-immersed insulation made by stacking 100% by weight kraft pulp paper and a mixed paper of kraft pulp and polymer fibers. A press board is proposed (Japanese Patent Application No. 60-298118).

As insulating papers other than pressboards, low dielectric constant insulating papers made by mixing polymer fibers and pulp-like objects (synthetic fibres), melting under heating and pressing (Japanese Patent Publication No. 38-139).
Japanese Unexamined Patent Publication (Kokai) No. 57-124811 discloses a composite semi-insulating insulating paper obtained by fusing two or more mixed papers of polymer fibers and kraft pulp and fusing and integrating the polymer fibers. .

(Problems to be Solved by the Invention) The insulating paper described in Japanese Patent Publication No. 38-13921 uses a synthetic fibrid as the pulp, and the whole sheet is heated and pressurized to be melted to produce the sheet. A press board having a good oil impregnation property cannot be obtained. Further, the synthetic insulating paper described in JP-A-57-124811 is a thin insulating paper having a thickness of 0.15 mm or less, and it is premised that it is wound around a conductor, so that the winding is supported as an oil-immersed insulating material. There is a problem that it has not enough compressive strength and poor oil impregnation property.

The present inventors have earnestly studied to obtain a press board having a good oil impregnation property, a compressive strength enough to support a winding wire, and a low dielectric constant. As a result, a press that solves the above-mentioned problems by stacking a plurality of wet papers made of a specific amount of kraft pulp having a specific degree of water and a specific amount of poly-4-methylpentene-1 fibers, pressurizing and heating to integrate them. It was found that a board was obtained, and the present invention was completed based on this finding.

As is clear from the above description, the purpose of the present invention is a press board with high compressive strength, excellent oil impregnation property, low dielectric constant, and no surface fluff, and an electric field that tends to concentrate in the oil gap between insulators. It is an object of the present invention to provide a press board for low-dielectric-constant oil-immersed insulation having a thickness of 0.5 mm or more, which has a large effect of relaxing.

(Means for Solving Problems) The present invention has the following configurations.

Wet from an aqueous slurry obtained by mixing more than 70% by weight of kraft pulp having a water content of 200 to 400 ml (CSF) and less than 90% by weight with poly 4-methylpentene-1 fiber 10% by weight or more and less than 30% by weight. A press board for low dielectric constant oil-immersed insulation, in which a wet paper web is formed by papermaking, and a plurality of wet paper webs are stacked, heated and dried under pressure, and only the surface of the press board is further heat-treated at a temperature of 220 ° C. or higher.

In general, an oil-immersed insulation type press board is characterized in that, when the dielectric constant of the press board is reduced, the stress of the electric field applied to the oil gap between the press board insulators is relaxed.
As the amount of mixed poly-4-methylpentene-1 fibers in the pressboard increases, the dielectric constant decreases and the electric field relaxation effect increases, but the compressive strength decreases. Since the compressive strength of the pressboard is required to be 7.3 kg / mm ² (80 ° C) or more, poly 4
-Methylpentene-1 fiber mixed paper amount is described in JP-A-57-1
As described in Japanese Patent No. 24811, it is not practical for a pressboard to set the content to 30% by weight or more from the viewpoint of compression strength, and it is important to set the content to less than 30% by weight based on the total weight of the pressboard. .

The dielectric constant of the pressboard is preferably 3.8 or less, more preferably 3.5 or less (4.7 for the conventional pressboard) from the viewpoint of the electric field relaxation effect of the oil gap. The mixed amount of one fiber is 10% by weight or more, preferably 15% by weight or more, based on the total weight of the pressboard. Therefore, in JP-A-57-124811, 30
In the present invention, poly-4-
Methylpentene-1 fiber mixed amount is less than 30% by weight 10
It is necessary to set the content to be at least wt%, which is particularly different.

Further, with such an amount of mixed paper, the compressive strength of the pressboard is increased, the dielectric constant is decreased, and the electric field relaxation effect of the oil gap can be increased. Further, in the above-mentioned JP-A-57-124811, the entire semi-synthetic insulation is melted by heating. However, the mixed press board of the present invention is hot pressed at a temperature of 110 ° C to 190 ° C and a pressure of 10 to 50 kgf / cm ^2. It is characterized by being heated and dried for integration, and further characterized in that only the surface of the pressboard is heated to a high temperature in order to reduce fuzz on the surface.

The poly-4-methylpentene-1 fiber used in the present invention is preferably a fiber having a thickness of 6 denier or less and a length of 2 to 10 mm obtained by melt-spinning poly-4-methylpentene-1 having good heat resistance and oil resistance. JIS231 as kraft pulp
The grade used for the second type of pressboard (hereinafter referred to as PB-) specified in 1 is preferable. or,
The water content of the kraft pulp used is 200 to 400 ml (C
SF) is good, and when it exceeds 400 ml (CSF), beating is insufficient and pulp entanglement is poor, and when the pressboard is used, the tensile strength required for the pressboard does not appear,
The compressive strength also decreases. On the other hand, if it is less than 200 ml (CSF), beating will proceed too much, and the strength of the pulp itself will drop, and the strength of the press board will be insufficient and the oil impregnation property will deteriorate.

The pressboard of the present invention has a thickness of 6 denier or less and a length of 2 to
Wet paper is formed by wet papermaking from an aqueous slurry obtained by mixing 10 mm of poly-4-methylpentene-1 fiber and kraft pulp, and an arbitrary number of wet paper sheets are stacked at a temperature of 110 ° C.
At 190 ° C., a pressure of 10 to 50 kgf / cm ² is applied by hot pressing with a hot press to dry and integrate. At this time, for the purpose of eliminating the fluff on the surface, preventing the drop of the lightning impulse breakdown voltage due to the fluff, and preventing the fluff coming off,
The surface is heat-treated for a short time at a temperature of ℃ or more. A preferable heating temperature is 230 ° C to 280 ° C. The heat treatment may be surface treatment with one or more hot rolls, or a special high temperature iron, iron, hair dryer or hot air bath may be used. The heat treatment time varies depending on the treatment method,
For example, in the case of using the above-mentioned hot roll, it ends instantly, but in the case of a hot air tank, a holding time is required for 1 minute or more, and for example, when the treatment temperature is 250 ° C., 5 minutes are required.

(Examples) Hereinafter, the present invention will be described with reference to Examples, but the present invention is not limited thereto. The characteristics of the oil-immersed pressboards in Examples and Comparative Examples were measured as follows. The dielectric constant uses an electrode made by Nissin Electric Co.,
A test piece (90 mm in diameter) that had been vacuum-dried in vacuum and impregnated with insulating oil was sandwiched between the electrodes at a pressure of 0.25 kgf / cm ² and impregnated with insulating oil for measurement. The compressive strength is 13 mm square, and the test piece (oil immersion) is piled on the height of about 16 to 18 mm, and the breaking load is measured using an autograph at a compression speed of 0.5 mm / min and a measurement temperature of 80 ° C. And calculated from the cross-sectional area.
Oil impregnability is obtained by stacking 8 pressboards of 50mm x 200mm x 1.6mmt, leaving 5 one side and applying epoxy adhesive on 5 sides to cure, 110 ° C, 24 hours, 0.3To
It was vacuum dried at rr, then soaked in oil, and after standing for 48 hours at 25 ° C. under atmospheric pressure, the oil impregnation distance in the layer direction was measured.

Examples 1 to 5 and Comparative Examples 1 to 3 As Examples 1 to 5, the composition shown in Table 1 below gives a thickness of 3
Denier, 5 mm long poly-4-methylpentene-1 fiber and kraft pulp with a water content of 365 ml (CSF) were mixed to form an aqueous slurry, and then wet paper was formed by wet papermaking. Overlap temperature 140 ℃, 40
A press board having a thickness of 1.6 to 1.7 mm was formed by heating, pressurizing and drying by hot pressing at a pressure of kgf / cm ² for 45 minutes. The dielectric constant, compressive strength and oil impregnation distance of the press board were measured and shown in Table 1. In addition, as Comparative Examples 1 to 3, pressboards were prepared in accordance with Examples 1 to 5 at the compounding ratios shown in Table 1 below, and the dielectric constant, compressive strength, and oil impregnation distance of the pressboards were measured. The measured values are shown in Table 1. As is clear from Table 1, poly-4-methylpentene-1
When the mixed amount of fibers is less than 30% by weight from the viewpoint of compressive strength and 15% by weight or more from the viewpoint of dielectric constant, the press having a dielectric constant of 3.5 or less and a compressive strength of 7.3 kg / mm ² or more You can see that you get a board. Also, the temperature 110 to 190
Since it is heat-pressurized and dried at 0 ° C., there is no heat fusion of the poly-4-methylpentene-1 fiber, and the impregnating property of the insulating oil is Comparative Press 3 or Conventional Pressboard (PB-2). A good product was obtained as compared with Comparative Example 1 in which the amount of poly-4-methypentene-1 fiber mixed exceeded the range of the present invention.

Examples 6 to 11 and Comparative Examples 4 to 7 As Examples 6 to 11, poly 4-methylpentene-1 fiber having a composition of 3 denier and a length of 5 mm and having a composition shown in Table 2 described later and a water content of 365 ml (CSF). ) Is mixed to form an aqueous slurry, and wet paper is formed by wet papermaking. 19 wet papers are superposed on each other to have a thickness of 1.6 to 1. I made a 7mm press board. The surface of the pressboard obtained in each example was passed through a hot roll having a roll temperature shown in Table 2 below.
In addition, as Comparative Examples 4 to 7, pressboards were prepared according to Examples 1 to 5 with the formulations shown in Table 2 described later. The pressboards obtained in each of the comparative examples were surface-treated through a hot roll having a roll temperature shown in Table 2 below. The dielectric constant, surface fuzziness and oil impregnation distance were measured using the surface-treated pressboards obtained in each Example and Comparative Example. The results are shown in Table 2. As is clear from Table 2, the surface fluffing of the pressboard could be eliminated by treating with a hot roll at 250 ° C. and 280 ° C. Moreover, the surface impregnation hardly changes the impregnation distance of the insulating oil. Rather, it can be seen that impregnation is easier than in Comparative Example 7 which is a conventional press board (PB-2).

(Effects of the Invention) The press board of the present invention is a press board having a smaller dielectric constant than the conventional press board, good oil impregnation property required for the press board, and no fluffing on the surface, and Since the electric field applied to the oil gap is also relaxed, the oil-immersed insulator can be downsized, which is suitable as a press board for low-dielectric-constant oil-immersed insulation.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Fumihiko Ishizuka, Furushima Prefecture, Saigo Village, Saigo Village, Odakura, Maeyama No. 1 Mitsubishi Paper Mills, Shirakawa Mill (72) Inventor, Etsuo Oe 4026, Kuji Town, Hitachi City, Ibaraki Stock Company Hitachi Research Laboratory, Hitachi, Ltd. (72) Yoshiro Tsukioka, 4026 Kuji Town, Hitachi City, Hitachi, Ibaraki Prefecture Stock Company, Hitachi Research Institute, Hitachi Research Institute, Hitachi, Ltd. (72) 4026, Kuji Town, Hitachi City, Hitachi, Ibaraki Hitachi Co., Ltd. In the laboratory (72) Inventor, Yuzuru Kamata 4026, Kuji-cho, Hitachi City, Ibaraki Prefecture Hitachi Institute, Ltd. (56) References JP-A-57-168418 (JP, A)

Claims (1)

[Claims] 1. A kraft pulp having a water content of 200 to 400 ml (CSF) of more than 70% by weight and less than 90% by weight and poly-4-methylpentene-1 fiber 10% by weight or more, 3
Wet paper is formed by wet papermaking from an aqueous slurry mixed with less than 0% by weight, and a plurality of wet papers are superposed and dried under pressure, and only the surface of the integrated press board is further added.
A press board for low dielectric constant oil-immersed insulation that has been heat-treated at a temperature of ℃ or above.