Patent ID: 8663530
Filing Date: 2014-03-04
Classification: B29C,B29K,B29L,B32B,C08J

Abstract:
1. A method for producing a water-proof sound-transmitting membrane, comprising the steps of: extrusion-molding a paste containing a polytetrafluoroethylene fine powder and a processing aid forming a molded sheet; stretching the sheet as a molded product of the paste or a sheet obtained by roll-pressing the molded product of the paste, in a first direction at a lower temperature than a melting point of polytetrafluoroethylene; stacking a plurality of the stretched sheets; stretching the stacked sheets in a second direction intersecting with the first direction at a lower temperature than the melting point of polytetrafluoroethylene; and firing the stacked sheets at a temperature equal to or higher than the melting point of polytetrafluoroethylene so that the stacked sheets are integrated with each other by a binding force acting between polytetrafluoroethylene matrices, the steps being performed in this order; wherein stretching ratios at which the sheets are stretched in the first direction and the second direction, before firing are adjusted so that the water-proof sound-transmitting membrane has a surface density of 1 to 20 g/m