| 摘要 |
PROBLEM TO BE SOLVED: To enhance the water-holding property of an open-cell sheet formed of a polyolefin polymer by treating it with a fluorine-containing gas to enhance the hydrophilic property of its surface. SOLUTION: Although it is recommended that the expansion rate of an open-cell sheet used for a separator should be set to 1.5 times or more, its strength is degraded and the hole diameters of the foam tend to increase when the expansion rate is set too high, so that 10 times should be used as its upper limit. The sheet can be manufactured by melting polyolefin, spraying it along with a gas and thereby depositing it in a sheet-like form, and its thickness is preferably 50-250μm. A mixture gas containing fluorine and oxygen is preferably used for the gas used during the hydrophilic treatment of the surface of the sheet. In this case, it is recommended that the partial pressure of the fluorine gas, that of the oxygen gas and that of an inert gas are set to 1-20 mmHg, 30-710 mmHg and 45-450 mmHg, respectively. The solution-holding factor of the obtained foam sheet is preferably 100% or more.
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