Finishing process for non-woven sheets of strand material

Claim 1

A PROCESS FOR PREPARING A BONDED NONWOVEN SHEET OF ORGANIC POLYMER FILM-FIBRILS, SAID SHEETING HAVING UNIFORM OPACITY, HIGH DELAMINATION RESISTANCE, HIGH ABRASION RESISTANCE, AND GOOD FOMATION, WHICH COMPRISES: PROVIDING A LIGHTLY CONSOLIDATED NONWOVEN FILM-FIBRIL SHEET HAVING A BASIS WEIGHT OF 10 TO 200 G./M2, A COEFFICIENT OF VARIATION IN BASIS WEIGHT LESS THAN 0.15, AND A DENSITY OF 0.11 TO 0.26 G./CM3; PASSING SAID LIGHTLY CONSOLIDATED FILMFIBRIL SHEET THROUGH A CONSTANT CLEARANCE BETWEEN A PAIR OF HARD CALENDAR ROLLS AT SUBSTANTIALLY ROOM TEMPERATURE, SAID CLEARANCE BEING ADJUSTED TO PROVIDE A NEW SHEET THICKNESS BETWEEN 0.5 AND 0.85 OF THE THICKNESS OF THE LIGHTLY CONSOLIDATED FILM-FIBRIL SHEET; PASSING SAID SHEET THROUGH A HEATING ZONE, WHILE UNDER RESTRAINT TO PREVENT SHRINKAGE, AND RAISING THE TEMPERATURE OF EITHER FACE OF THE SHEET TO WITHIN 7*C. OF THE UPPER LIMIT OF THE MELTING RANGE OF THE FILM-FIBRILS BUT NOT SUBSTANTIALLY ABOVE SAID UPPER LIMIT; THEN COOLING THE SHEET WHILE UNDER RESTRAINT TO A TEMPERATURE BELOW THAT AT WHICH THE SHEET DISTORTS OR SHRINKS.