Patent ID: 6946047

Claim:
A method for manufacturing a zipper without shift in injection molding comprising the steps of: forming a bank of continuous zipper teeth on an inner side of each of two parallel zipper strips by injection molding; wherein an inner side of each zipper strip has a respective connecting strip; scraping a part of zipper teeth on each zipper strip; melting two layers of film so that each film encloses two sides of each zipper strip at the part without zipper teeth by thermal pressing technology; punching an opening at an inner lateral side of each film and the opening passing through each zipper strip, but the connecting strip at an inner side of the zipper strip is remained and one side of the opening is adjacent to the connecting strip; guiding the two zipper strips into upper and lower engaging piece molds; and tensioning the zipper strips within the mold so as to place the zipper strips on the molds flatly; injection-molding upper engaging pieces at inner sides of the zipper strips and injection-molding lower engaging pieces at inner sides of the films, wherein the lower engaging pieces are protruding into the openings; removing the molds from the zipper strips and removing other undesired objects; and cutting the zipper strips through the openings, thus forming the engaging pieces of a zipper; wherein in the step of forming the opening, the connecting strip at an edge having the films must be retained for fixing the zipper teeth; when the zipper strips are tensioned within the molds, the zipper strips will resist against a pulling force applied thereon; thereby, the zipper strips are precisely positioned in the upper engaging piece mold and the lower engaging piece mold.