Abstract: A silica optical fiber is provided, which contains a pure-silica core and a cladding layer formed on the pure-silica core, wherein the pure-silica core contains a C element and has a content of elements belonging to the third period-the seventh period of the periodic table, except Si element that constitutes the quartz structure, of not more than 100 ppm. The present invention can provide a silica optical fiber superior in the resistance to high energy electromagnetic waves such as UV light and &ggr;-rays.

Abstract: A foamable composition containing a base polymer containing a polyethylene mixture of a low density-polyethylene having a density of 0.91-0.925 g/cm3 and a high density polyethylene having a density of 0.94-0.97 g/cm3, and a fluororesin powder and/or a boron nitride powder as a nucleator, wherein the high density polyethylene has an swelling ratio smaller than that of the low density polyethylene and a melt flow rate greater than that of the low density polyethylene, and is contained in a proportion of not less than 50 percent by weight of the polyethylene mixture, and the base polymer has a shear viscosity (temperature:170° C., shear rate:1216 sec−1) of not more than 3150 poise, and a coaxial insulating cable having an electrically insulating layer formed of a foam having an expansion ratio of not less than 70% and obtained by foaming the above foamable composition are provided.

Abstract: A silica optical fiber is provided, which contains a pure-silica core and a cladding layer formed on the pure-silica core, wherein the pure-silica core contains a C element and has a content of elements belonging to the third period-the seventh period of the periodic table, except Si element that constitutes the quartz structure, of not more than 100 ppm. The present invention can provide a silica optical fiber superior in the resistance to high energy electromagnetic waves such as UV light and &ggr;-rays.

Abstract: An insulating material for coaxial cables, made at least in part with a polyolefin resin capable of heat-melt extrusion and a fluororesin powder as a nucleator, which material being capable of foam extrusion in the presence of a foaming agent; a coaxial cable made at least in part with a foam insulating layer prepared from the insulating material; and a method for producing a coaxial cable, by extruding, on a conductor, the insulating material to form a foam insulating layer. The insulating material for coaxial cables of the present invention containing a fluororesin powder such as PTFE as a nucleator provides a foamed article having fine and uniform cells, and a high expansion ratio. Such foamed article is superior in electric properties, and the coaxial cable having such insulating layer is superior in attenuation property. The material of the invention can obviate drying of the insulating layer, which contributes to an improved production efficiency of the coaxial cable and reduced production cost.

Abstract: A nucleator for foaming comprising a fluororesin powder comprising particles having a particle size of 0.1-0.5 .mu.m in a proportion of at least 50% by number and containing particles having a particle size of not less than 5 .mu.m in a proportion of not more than 40% by number, a foamable composition comprising this nucleator and an organic polymer, a foam made therefrom, and a production method of the foam. The nucleator of the present invention can produce a foam made from an organic polymer improved in expansion ratio, fineness of the cells, uniformity of foaming and the like by the use of an extremely small amount thereof. It is preferably used for forming an insulating foam layer of a high frequency coaxial cable.

Abstract: It is disclosed that a metal cored board which comprises an electrically conductive layer whose one surface at least composed of a hardly oxidizable metal, an insulating organic polymer layer baked on the surface of the hardly oxidizable metal, and a metal core adhered on the insulating organic polymer layer, and a method for manufacturing a metal cored board, which comprises a step to coat the surface of a hardly oxidizable metal layer of an electrically conductive metal foil with an insulating varnish, a step to bake a layer of the varnish, and a step to adhere a metal core on the baked varnish layer.

Abstract: It is disclosed that a metal cored board which comprises a base metal core, an easily solderable metal plating layer formed on one surface of the base metal core, an electrically insulating layer formed on the another surface of the base metal core, and an electrically conductive metal layer formed on the electrically insulating layer, a method for manufacturing a metal cored board, which comprises a step to plate both surface of a base metal core with an easily solderable metal, a step to form an electrically insulating layer on one surface of the easily solderable metal plating layer, and a step to form an electrically conductive metal layer on the electrically insulating layer.