Method and apparatus for continuously stretching polymer films

An apparatus for continuously stretching polymer films in a film width direction comprising:

• a pair of welding heads for holding, welding, and splicing an overlapped portion of said polymer films in an overlapping direction, each said welding head having a film contact surface to contact with said overlapped portion and a film heating surface to heat said overlapped portion, a length Lp of said film contact surface in a conveying direction of said polymer films and a length Lh of said film heating surface in said conveying direction satisfying Lh<Lp, said film heating surface being approximately flush with said film contact surface and extending from a center portion toward ends of said film contact surface in said conveying direction at approximately equal lengths, center portions of said film contact surface and said film heating surface being approximately aligned to each other in said conveying direction;
• a film conveying device for overlapping a rear end of a preceding polymer film and a front end of a trailing polymer film as said overlapped portion in such a manner that center portions of said overlapped portion and said film heating surface are approximately aligned with each other in said conveying direction and a length Lo of said overlapped portion in said conveying direction satisfies Lh<Lo<Lp;
• a heating control device for controlling a temperature of said film heating surface such that ends of said overlapped portion in said conveying direction are heated during said welding to a temperature at which said polymer films are welded to each other.