PURPOSE: To reduce the pore opening as well as increase the porosity and improve the permeability of a molded object obtained from the paste extrusion of an ethylene tetrafluoride resin fine powder having a specific number-average molecular weight, by heat-treating to improve the crystallinity of this object after sintering and then orienting it at least monoaxially.
CONSTITUTION: 100wt. parts of a tetrafluoroethylene resin fine powder having a number-average molecular weight of at most one million, and 15W40pts.wt. of a liquid lubricant are mixed together and extruded to be molded. The molded object from the paste extrusion is then sintered. The sintering is performed at a temperature of 327°C or higher, which is the transition point of tetrafluoroethylene resin. After sintered, a heat treatment is carried out to improve the crystallinity of the molded object. After that, the heat treatment allows the temperature of the sintered object to rise to its melting point or higher, preferably the order of 350°CW380°C, and then cools it gradually. The crystallinity is preferably higher than 90%. Then, the molded object of high crystallinity obtained from the heat treatment is oriented at least monoaxially. It is prefered that the orientation is made in the ratio of at least five times (areal ratio) in order to obtain a porous film having high porosity and excellent permeability.
YAMANOUCHI SHOSUKE
JPS5342794A | 1978-04-18 |