Patent ID: 7347908

Claim:
A method of forming a zipper joint joining first and second zipper strips made of thermoplastic material, wherein said first zipper strip comprises a first base and a first longitudinal closure element projecting from said first base, and said second zipper strip comprises a second base and second and third longitudinal closure elements projecting from said second base, said first longitudinal closure element being profiled to project between and interlock with the profiles of said second and third longitudinal closure elements, said method comprising the following steps: (a) arranging said first and second zipper strips so that said first longitudinal closure element projects between and is interlocked with said second and third longitudinal closure elements; (b) supplying sufficient ultrasonic wave energy into a first volume having a first width to cause the material of said interlocked first and second zipper strips in said volume of first width to fuse together to form a leakproof zipper joint, including at least said first longitudinal closure element being fused to said second and third longitudinal closure elements in said first volume; and (c) applying an amount of pressure in said first volume during step (b), the amount of pressure applied causing relatively little deformation of said first through third longitudinal closure elements.