STRUCTURE OF MICROPOROUS POLYPROPYLENE SHEET

Microporous polypropylene sheet is prepared by biaxially stretching polypropylene sheet containing CaCO3 filler. This sheet is porous. Accordingly, the structure of the sheet was studied in terms of the stretching ratio with the aid of scanning electron microscopy. Reasonably, the larger the stretching ratio, the more porous the resultant sheet. Typically, in stretching ratio of 2.0 x 5.0, porosity becomes 80%. Stretching ratio dependence is studied for the apparent density, pore size, permeability, and water resist pressure. The resultant microporous polypropylene sheet has some characteristic properties of gas permeability for air and water vapor but not for liquid water.