Method of forming side seams for zippered bags or packages

A method for manufacturing plastic bags or packages wherein a longitudinally extending continuous plastic zipper having male and female profiles on interior surfaces of the plastic bag or package provides a resealable closure between two plies of plastic sheet material, said plastic sheet plies being welded together with a transverse seal at preselected intervals separated by a distance corresponding to the width of the bags or packages being produced to thereby provide side seals separating said bags or packages, said method comprising the steps of:

• providing a continuous plastic zipper with male and female profiles between two plies of said plastic sheet material which form the interior surfaces of said bag or packages;
• directing heat from between said two plies to a relatively short length of said continuous plastic zipper profiles whereby to presoften sections of said male and female profiles within said relatively short length of plastic zipper;
• and,
• making a transverse crosswise seam across said two plies of plastic sheet material and through said presoftened male and female profile sections.