Patent ID: 7025841

Claim:
A method comprising the following steps: (a) continuously moving first and second strips of thermoplastic material at the same linear speed along a path that passes between an ultrasonic horn and a rotary anvil, the movement of said first and second strips being such that respective successive sections of said first and second strips pass between said horn and said anvil, wherein said first and second strips comprise respective interlockable profiles that are interlocked with each other; (b) continuously rotating said anvil at a rate of angular rotation such that a contact portion of said anvil has a tangential velocity component equal to or approximately equal to said linear speed of said first strip and second strips during contact therewith; and (c) activating said ultrasonic horn to transmit ultrasonic wave energy at least during a period when said contact portion of said rotating anvil is generally opposite to said horn, the total amount of ultrasonic wave energy transmitted into adjacent portions of said first and second strips being sufficient to meld said adjacent portions together in regions that are spaced at regular intervals longitudinally along said first and second strips, wherein said horn does not rotate about a pivot point during activation, and said horn and anvil do not form any melded regions that are laterally displaced relative to said melded regions along said first and second strips.