| 摘要 |
PROBLEM TO BE SOLVED: To obtain a porous polytetrafluoroethylene film with a low pressure loss, high strengths, and a high PF value (filtration efficiency) by mixing a fine polytetrafluoroethylene(PTFE) powder with a liq. lubricant, sheeting the mixture in the uncured state, monoaxially stretching the sheet, and thermally treating the resultant porous PTFE film under specified conditions. SOLUTION: A fine PTFE powder is suitably used. A liq. lubricant (e.g. liq. paraffin) is used in an amt. of 5-50 wt.% of the powder. The sheet usually has a thickness of 0.05-0.5 mm and is stretched at 325 deg.C or lower. The thermal treating is conducted at 350-450 deg.C for 0.01-1.00 sec. The resultant porous film has an endothermic peak at 330±8 deg.C on the crystal melting curve, a crystal conversion rate of 0.35-0.80, a pressure loss lower than 20 mmH2 O, and a PF value of 24 or higher. |
