JPS6247327B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to insulating paper, particularly insulating paper for power cables.

Super-voltage OF for large-capacity power transmission
(OiFilled) Synthetic resin films or laminates of this film and insulating paper such as kraft paper have recently been used as insulating materials with low loss, ie, low dielectric loss, used in cables.

However, the synthetic resin film has a drawback that it has low oil resistance against the insulating oil flowing inside the cable, increases oil flow resistance due to swelling, and is prone to buckling and wrinkles when the cable is bent.
On the other hand, when a synthetic resin film and insulating paper are used in combination, the increase in oil flow resistance due to swelling is alleviated to some extent, but problems remain with oil flow in the radial direction and the polarity effect on impulse voltage is large. There are drawbacks.

One object of the present invention is to provide an insulating paper with excellent electrical and mechanical properties and good workability.

Another object of the present invention is to provide an insulating paper for power cables which overcomes the above-mentioned disadvantages of the prior art.

According to a first aspect of the present invention, as shown in FIG. 1, a fiber paper 2 is formed by forming natural fibers on both upper and lower surfaces of a mixed paper 1 formed by forming a paper from a mixture of natural fibers and synthetic resin flakes, 2 is provided, and this three-layer structure is heated and pressed, for example, by passing it through a pair of heated rolls, and is fused together to provide an insulating paper.

According to a second aspect of the present invention, as shown in FIG. 2, a fiber paper 4 made of natural fibers is heated on one side of a mixed paper 3 made of a mixture of natural fibers and synthetic resin flakes. The mixed paper 3 includes a portion with a high content of synthetic resin flakes and a portion with a low content of synthetic resin flakes, and the portion with a high content of synthetic resin flakes is fused together with the fiber paper 4. Provided is an insulating paper which is directly bonded to the insulating paper and has a portion having a low content of synthetic resin flakes exposed to the outside air. Note that in the mixed papers shown in FIGS. 1 and 2, the dots indicate the amount of synthetic resin flakes. In the present invention, the mixed papers 1 and 3 are formed by, for example, beating kraft pulp, adding synthetic resin flakes thereto, and then paper-making it with a normal paper machine. Synthetic resin flakes are prepared by grinding synthetic resin films. The preferred synthetic resin is polypropylene, but other materials such as tetrafluoroethylene, polyethylene, and polycarbonate may also be used. The fiber layers 2 and 4 are preferably made of kraft paper with a thickness of several μm to 15 μm.

Furthermore, in a mixed solution of beaten pulp and synthetic resin flakes, the synthetic resin flakes tend to exist above the natural fibers of the pulp due to the influence of density and hydrophobicity. In a mixed paper layer obtained by papermaking using a Fourdrinier paper machine, the amount of synthetic resin flakes is greater in the portion near the top surface than in the other portions.
Therefore, this mixed paper layer is preferably used for producing the insulating paper of the second embodiment.

When paper is made using a cylinder paper machine instead of a fourdrinier paper machine, a mixed paper layer in which synthetic resin flakes are uniformly distributed in natural fibers is obtained. Therefore, this mixed paper layer is preferably used for producing the insulating paper of the first embodiment.

A polypropylene film is crushed using a crusher to preferably have a thickness of 5 to 9 μm, a length and a width of 2
~5 mm randomly shaped polypropylene flakes are molded.

Industrially, the thickness of polypropylene flakes is 5
It is difficult to make the thickness thinner than ~9 μm.

Flake size (i.e. length and width)
If is too large, the distribution of flakes in the natural fibers will be uneven, and the influence of oil swelling will be large, and the entanglement of natural fibers will be interrupted by the flakes, reducing the mechanical strength of the insulating paper.

When the mixing ratio of synthetic resin flakes to natural fibers is constant, as the size of the flakes increases, the number of flakes decreases and the impulse characteristics deteriorate. On the other hand, if the size of the flakes is made extremely small, the barrier effect disappears and the impulse withstand voltage deteriorates. The preferred length and width of the synthetic resin flakes are 2 to 5 mm.

The insulating paper of the present invention produced as described above may be further subjected to pressure and heat treatment in a subsequent step.

The insulating paper of the present invention has the following advantages.

Since it is mixed with synthetic resin, it has low loss.

Since the synthetic resin flakes form a thin multilayer structure in the insulating paper, the impulse characteristics are improved and polarity effects are eliminated.

Because synthetic resin flakes are mixed with natural fibers, the oil flow resistance in the radial direction in power cables is smaller than insulating paper made by laminating synthetic resin film onto paper.

Swelling of synthetic resins by oil is reduced by the presence of natural fibers.

By overlapping and heating and pressurizing, the non-uniformity of the dispersion of the synthetic resin flakes is compensated for and the uniformity of the distribution is improved.

Since both sides of the insulating paper are essentially made of natural fibers, there is no problem of synthetic resin flakes adhering to the hot roll during subsequent secondary processing, and the winding process on conductors is as good as with kraft paper. .

As described above, the insulating paper of the present invention is preferably used as an insulator for power cables, but is not limited thereto, and can also be used as other electrical insulating materials.

[Brief explanation of the drawing]

FIGS. 1 and 2 are cross-sectional views showing the structure of the insulating paper of the present invention. 1, 3...Mixed paper, 2, 4...Fiber paper.

Claims (1)

[Claims] 1. An insulating paper made by fusing fiber paper made by making natural fibers on both upper and lower surfaces of a mixed paper made by making a paper from a mixture of natural fibers and synthetic resin flakes by pressurizing and heating. . 2. The insulating paper according to claim 1, wherein the synthetic resin is polypropylene. 3. The insulating paper according to claim 1, wherein the fiber paper is kraft paper. 4. The insulating paper according to claim 1, wherein the synthetic resin flakes have a thickness of 5 to 9 μm, and a length and width of 2 to 5 mm. 5. Fiber paper made by making natural fibers on one side of mixed paper made from a mixture of natural fibers and synthetic resin flakes is fused together by pressure heating,
The papermaking includes a part with a high content of synthetic resin flakes and a part with a low content of synthetic resin flakes, and the part with a high content of synthetic resin flakes is bonded to the fiber paper, and the part with a low content of synthetic resin flakes is bonded to the fiber paper. An insulating paper characterized by having parts exposed to the outside air. 6. The insulating paper according to claim 5, wherein the synthetic resin is polypropylene. 7. The insulating paper according to claim 5, wherein the fiber paper is kraft paper. 8. The insulating paper according to claim 5, wherein the synthetic resin flakes have a thickness of 5 to 9 μm, and a length and width of 2 to 5 mm.