Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Noninterengaged fiber-containing paper-free web or sheet...
Patent
1981-11-30
1985-03-26
Ives, Patricia C.
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Noninterengaged fiber-containing paper-free web or sheet...
428303, 428402, 428326, 428338, 428513, 4285375, 1621681, 1621641, B32B 2732, D21H 512
Patent
active
045073589
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to an insulating paper sheet and more particularly to an insulating paper sheet for a power cable.
BACKGROUND ART
Recently, synthetic fiber, synthetic resin film or such film laminated with insulating paper, like kraft paper, is applied as insulation material of low power loss or low dielectric loss for use with an ultrahigh voltage, oil filled cable intended for large capacity transmission line.
However, synthetic resin film, for example, has the drawbacks that it has low chemical resistance to insulation oil conducted through the above-mentioned cable. The film, when impregnated with oil, swells and tends to increase oil flow resistance, and readily gives rise to buckling and creases when the cable is bent. Where the synthetic resin film is applied in combination with insulating paper, then the combined mass does indeed produce a smaller increase in physical resistance to oil flow resulting from swelling, but is still accompanied with the drawbacks that when swelling, the combined mass obstructs radial oil flow within the cable insulation and shows a noticeable polar effect on an impulse breakdown voltage.
It is accordingly an object of this invention to provide an insulating paper sheet having excellent electric and mechanical properties and great ease of handling.
Another object of the invention is to provide insulating paper for a power cable which is free of the above-mentioned drawbacks accompanying the conventional art insulating paper.
DISCLOSURE OF THE INVENTION
According to an aspect of the invention, there is provided an insulating paper sheet prepared from a mixture of natural fibers and synthetic resin flakes.
According to another aspect of the invention, there is provided an insulating paper sheet which is formed by laminating with heat and pressure first and second insulating paper sheet components each prepared from a mixture of natural fibers and synthetic resin flakes, and in which the mutually facing portions of the laminated mass contains a larger amount of synthetic resin flakes than the other portions of said mass.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an oblique view of an insulating paper sheet embodying this invention;
FIG. 2 graphically indicates the relationship between the thickness of a polypropylene flakes applied in the production of a power cable from an insulating paper sheet embodying this invention and impulse breakdown stress;
FIG. 3 is an enlarged view of the interior of the insulating paper sheet embodying the invention; and
FIG. 4 graphically shows changes with temperatures in the oil flow resistance of various types of insulating paper sheets used in the manufacture of a power cable.
BEST MODE OF CARRYING OUT THE INVENTION
An insulating paper sheet embodying this invention is manufactured in the following manner. First, there are provided natural fibers like those of kraft pulp. The insulating paper sheet is prepared by adding synthetic resin flakes to beaten kraft pulp. The ordinary paper-making machine is applicable in the production of said insulating paper sheet. Synthetic resin flakes are produced by crushing a synthetic resin film. The synthetic resin is preferrably to be polypropylene. In addition, ethylene tetrafluoride, polyethylene, polycarbonate, etc. may be used as synthetic resin material.
The insulating paper sheet thus prepared is calendered to have an increase in density or impermeability, a decrease in thickness and an increase in surface smoothness, and is further treated by heated press rolls to provide greater mechanical strength. The upper portion of a slurry consisting of a mixture of beaten pulp and synthetic resin flakes contains a larger amount of synthetic resin flakes lighter than said beaten pulp. Therefore, the upper portion 11 of an insulating paper sheet produced from the above-mentioned slurry by a Fourdrinier machine contains, as shown in FIG. 1, a larger amount of synthetic resin flakes than the other portion 12.
For the object of this invention, the insulating paper sheet 10
REFERENCES:
patent: 2765247 (1956-10-01), Graham
patent: 3271231 (1966-09-01), Moggio et al.
patent: 3745060 (1973-07-01), Jumentier et al.
patent: 3855056 (1974-12-01), Maeda et al.
patent: 3904804 (1975-09-01), Tabara et al.
patent: 3953282 (1976-04-01), Tabara et al.
patent: 4092457 (1978-05-01), Fujita et al.
patent: 4273825 (1981-06-01), Nishiyama et al.
Miura Isao
Moutai Tsuneaki
Takaoka Michio
Ives Patricia C.
The Fujikura Cable Works Limited
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