Foamed-polyolefin-insulated wire

Details Foamed-polyolefin-insulated wire Foamed-polyolefin-insulated wire

1998-11-20

2001-05-29

Reichard, Dean A. (Department: 2831)

Electricity: conductors and insulators

Conduits, cables or conductors

Insulated

C174S1100PM, C174S1100FC

Reexamination Certificate

active

06239377

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a highly-foamed-polyolefin-insulated wire having a thin insulation thickness used for data transmission in electronic devices and communication cables.
2. Description of the Background
High-speed data transmission requires electric wires used in electronic devices and communication cables to have an insulation layer with a low equivalent dielectric constant, namely, lower than 1.45. To fulfill the requirement of a low equivalent dielectric constant, an insulation layer is usually foamed by using a composite of a chemical foaming agent and polyolefin or using an inert gas. In an insulation layer made of the same material there is a correlation between its foaming degree and equivalent dielectric constant, such that the latter can be reduced by increasing the former. However, if the insulation layer of a wire is merely increased in its foaming degree, it becomes soft and susceptible to dimensional change when it undergoes a sidewall pressure at the time of or after laying of the wire. This will cause a change in electrical characteristics, reducing reliability. In particular, the recent strong demand for miniaturization of devices has compelled dense wiring, causing it to become a critical focus. The stable production of a highly foamed insulation layer with a thinner thickness is also required.
SUMMARY OF THE INVENTION
Through intensive experiments and studies the inventor has found that a highly-foamed polyolefin insulated wire having superior sidewall-pressure deformation resistance expressed by specific parameters, and having excellent electric characteristics including insulation performances is suitable for communication cables. The inventor has further found that a very thin highly foamed polyolefin insulation layer of such wire can be produced by using a mixture of ionomer and polypropylene with a specific ratio between the two components.
The invention discloses the following:
(1) A foamed-polyolefin-insulated wire, 1 mm or less in conductor diameter and 2 mm or less in insulation thickness, having an equivalent dielectric constant of less than 1.45 and a sidewall-pressure deformation not exceeding 20%.
(2) Polyolefin made of a mixture consisting, at a weight ratio in the range from 20:80 to 80:20, of polypropylene and a partial metallic salt of a copolymer including a comonomer containing carboxylic acid or a carboxylic anhydride group.
(3) The foamed-polyolefin-insulated wire of (1) above, wherein a solid (unfoamed) insulation layer of a plastic composite mainly consisting of other polyolefin than that used as the foamed insulation layer is applied over the foamed insulation layer.
(4) The foamed-polyolefin-insulated wire of (3) above, wherein another solid (unfoamed) insulation layer comprising polyethylene or acid-denaturated polyethylene is applied between the foamed insulation layer and the conductor.


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