Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-03-16
2002-11-12
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S217000, C525S232000, C525S238000, C525S240000, C525S241000, C174S256000, C174S11900R, C174S1210AR, C174S1210SR
Reexamination Certificate
active
06479590
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a resin material for an electrical insulating material characterized in comprising an ethylene &agr;-olefin copolymer possessing a superior processability and thermal resistance, in addition to an excellent mechanical strength and electrical insulating properties; an electrical insulating material and electric wire and cable using the same. Specifically, the present invention relates to a resin material for an electrical insulating material possessing superior electrical insulating properties, such as volume resistivity, space charge characteristics, dielectric breakdown strength, and the like; a resin material for an electrical insulating material in which even after cross-linking, degradation of electrical insulating properties, e.g., volume resistivity, space charge characteristics, dielectric breakdown strength, and the like does not occur; and an electrical insulating material formed from the aforementioned resin material and cross-linked product, and electric wire and cable possessing an insulating layer using the same. This application is based on a patent application filed in Japan (Japanese Patent Application No. Hei 10-262105), the contents of which are incorporated herein by reference.
BACKGROUND ART
Conventionally, electrical insulating materials for electric wire and cables fundamentally require a high volume resistivity, and a high dielectric breakdown voltage, in addition to a low dielectric constant and dielectric dissipation factor, for which a polyethylene or the like is generally used. In addition, as an electric power cable for use in mass transmission, such as a high-tension power cable and the like, a cable which uses an insulating material to which oil has been filled (hereinafter referred to as “OF cable”) is routinely employed. However, this OF cable, despite possessing excellent electrical insulating properties, is disadvantageous in that oil often leaks out, which in turn necessitates a means for continuously supplying oil. In recent years, a cross-linked polyethylene has been used which possesses an increased thermal resistance and mechanical strength, and is obtained by means of cross-linking the polyolefin of a polyethylene or the like.
One of the problems associated with this high-tension power cable, which uses a cross-linked polyethylene in its electrical insulating material, relates to the power loss that occurs during high-tension transmission. Hence, the reduction of this aforementioned power loss is highly desirable. It is possible to reduce this power loss by means of increasing the electrical insulating performance of the electrical insulating material, in particular by increasing the volume resistivity.
However, even by simply increasing the volume resistivity at either room temperature or constant temperature, this leads to other problems as described below. For example, in a power cable, the electrical insulating material around the inner conductor will reach 90° C. from the Joule heat of the electric current, however the electrical insulating material around the outer conductor remains at atmospheric temperature. In the case of an electrical insulating material employing a conventional polyethylene in which extreme reductions in the volume resistivity accompany temperature increase, an electrical field is concentrated around the interface of the outer conductor and insulating member, which reduces the dielectric breakdown strength. This phenomenon, in particular, creates large problems with regard to dc electric power cables. Accordingly, it is highly desirable to decrease the temperature dependence of the volume resistivity of the electrical insulating material.
With regard to a method for improving the temperature dependence of the volume resistivity of the electrical insulating material, a method is proposed in which maleic anhydride is grafted to a low pressure process polyethylene (e.g., Japanese Patent Application, First Publication No. Hei 2-10610 and the like). However, as an electrical insulating material, the electric power cables using this low pressure process polyethylene shows an inferior flexibility when compared with convention electric power cables.
In this manner, as an electrical insulating material, electric power cables using a low density polyethylene to which maleic anhydride has been grafted are proposed in Japanese Patent Application, First Publication No. Sho 63-150810, Japanese Patent Application, First Publication No. Sho 63-150811 and Japanese Patent Application, First Publication No. Hei 2-119012. However, the electrical insulating materials used in these electric power cables are disadvantageous in that the volume resistivity is reduced at high temperature.
In addition, in Japanese Patent Application, First Publication No. Hei 5-266723, an electrical insulating material is obtained by means of blending 100 parts by weight of a low density polyethylene, possessing a density of 0.92 g/cm
3
, and 0.5 to 20 parts by weight of a linear low density polyethylene, possessing a density of 0.91 to 0.94 g/cm
3
. However, the improvement of the temperature dependence of the volume resistivity provided by means of this electrical insulating material is inadequate, since this electrical insulating material does not sufficiently improve the volume resistivity around the inner conductor.
In addition, a polyolefin such as polyethylene or the like, which is used as an electrical insulating material for electric wires and cables, may be employed after undergoing cross-linking in order to increase properties such as the thermal resistance and mechanical strength.
As methods for cross-linking a polyolefin such as polyethylene, an electron beam cross-linking method and a chemical cross-linking method, which uses peroxides, are known. However, the electron beam cross-linking method requires large scale equipment, and possesses the disadvantage of high cost. In addition, the chemical cross-linking method, although economical, results in problems due to the existence of an unreacted cross-linking agent, as this residue causes reduction of the volume resistivity, degradation of the space-charge characteristics, and generation of water-treeing.
As a method for improving the electrical insulating properties, e.g., volume resistivity, space charge characteristics, water-treeing resistance, etc., a method in which a maleic anhydride-modified polyolefin is added to polyethylene in order to introduce hydrophilic group is proposed in Japanese Patent Application, Second Publication No. Hei 5-15007. Furthermore, a trial is being conducted in an attempt to improve the electrical insulating properties by means of introducing a double bond into the polyolefin prior to cross-linking, and reducing the addition amount of the cross-linking agent (Japanese Patent Application, First Publication No. Hei 4-11646). However, all of the aforementioned fail to produce both adequate electrical insulating properties, e.g., volume resistivity and the like, and thermal resistance.
On the other hand, technology for improving the electrical insulating properties of electrical insulating material such as the volume resistivity, dielectric breakdown strength and the like is being proposed in which a carbonic acid compound and/or aromatic compound is mixed into a polyolefin. For example, various technologies are being proposed for improving the impulse breakdown strength by means of grafting a styrene to a polyolefin (Japanese Patent Application, First Publication No. Hei. 2-165506); improving the impulse breakdown strength by means of blending a polystyrene into polyethylene (Japanese Patent Application, First Publication No. Sho. 63-301427); improving the electrical insulating properties such as volume resistivity and the like means of blending a maleic acid-modified polyolefin into a polyethylene (Japanese Patent Application, First Publication No. Sho. 62-1000909); improving the dielectric breakdown characteristics by means of blending an aromatic carboxylic acid into a polyolefin (Japanese Patent Application,
Ikeda Masaaki
Shimizu Yoshimi
Japan Polyolefins Co., Ltd.
Nutter Nathan M.
Sughrue & Mion, PLLC
LandOfFree
Electrical insulating resin material, electrical insulating... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electrical insulating resin material, electrical insulating..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electrical insulating resin material, electrical insulating... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2943821