Reduced curl battery separator and method

摘要

A curl resistant battery separator of a noncellulosic nonwoven substrate extrusion coated on at least one surface with a cellulose film and process for making such separator by contacting a nonwoven noncellulosic textile substrate with a cellulose or cellulose derivative solution on at least one side of said substrate; converting the solution to a solid cellulose or cellulose derivative, preferably having a degree of polymerization of at least 350, more preferably at least 600, to form a coated substrate; washing said substrate in an aqueous solution; drying the coated substrate under biaxial tension to provide a battery separator having a moisture content of from about 4 to 25 wt. % based on the bone dry gauge of the separator(BDG); and then holding the separator for at least 8 hours at elevated temperatures of at least 40 DEG C. in the presence of a controlled amount of moisture to produce a separator which is stabilized against curling and has a moisture content between about 4 to 25 wt. % BDG and, preferably having a absorption rate of at least 6 mm/5 min. and a 30% KOH absorption of at least 200 g/m2.