Patent ID: 7871481

Claim:
A manufacturing method of a hermetic plastic zipper wherein the plastic zipper comprises a pair of engaging portions formed on the surfaces of plastic films and has a readily peelable plastic layer prolonging in a lengthwise direction of the plastic zipper at the engaging portions or in the neighborhood thereof, the method is characterized in that while the engaging portions are brought into a engaged state, the portion of the plastic zipper where the readily peelable plastic layer exists is inserted between an ultrasonic horn and an anvil, and the readily peelable layer is welded by using ultrasonic wave under a condition wherein the distance L between the ultrasonic horn and the anvil is uniformly held at a distance of H≧L≧0.85H wherein H stands for a maximum thickness of the plastic zipper under the engaged state, and the plastic zipper sandwiched between the ultrasonic horn and the anvil is moved in a lengthwise direction thereof, whereby the readily peelable plastic layer is welded continuously in a lengthwise direction of the zipper.