Patent ID: 6962637

Claim:
A method for making a tubular film comprising, in sequence, the steps of: winding a thermoplastic sheet film on a columnar member with at least two turns so that leading and trailing ends of the wound film are positioned approximately on a line normal to an outer surface of the columnar member without overlapping each other; fitting a tubular molding member over the columnar member with the wound film, wherein a difference between an outer diameter of the columnar member and an inner diameter of the tubular molding member results in a gap between the columnar member and the tubular molding member when the tubular molding member is fitted over the columnar member, and wherein a thermal coefficient of expansion of the columnar member is larger than a thermal coefficient of expansion of the tubular molding member; and heating the columnar member with the wound film and the tubular molding member to a temperature at which the wound film is softened and the gap is narrowed to weld the leading and trailing ends of the wound film and to form the at least two turns of the thermoplastic sheet film into the tubular film having a uniform thickness.