| 摘要 |
A thermoplastic fluororesin foam having an expansion ratio of 4 to 30 and a closed cell content of 40 % or above and containing no cross-linked structure, wherein at least one interface is present between two layers having different cell densities and which satisfies the relationships 0<Sc</=6 and 0<Cv</=1, wherein Sc and Cv represent, respectively, the dispersion index and coefficient of variation of the maximum diameters of the open cells present in an arbitrary cross section of each layer, and are defined by the following equations: Sc = (LMax.-LMin.)/Lav. (1) Cv = (SD/Lav. (2) wherein LMax., LMin. and Lav. indicate, respectively, the maximum, minimum and average values of the maximum diameters of the open cells, and SD indicates standard deviation. This foam does not cause edge sagging, is stable even when polished for long, is excellent in mechanical strengths such as tear strength and compression strength, has a stable permittivity both before and after being compressed, and is excellent in withstand voltage. Hence it is effectively applicable to various uses including single-crystal silicon wafer, compound semiconductor wafer, glass substrate for liquid crystal, polishing cloth for electronics material such as a color filter for liquid crystal, soft gasket, electrical insulation tape and wire coating material. Further it is applicable to tent cloth, roofing material for membrane structure and insulating tube by virtue of the heat insulating performance thereof.
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