PREFORM FOR FORMING CAN BODY OF SYNTHETIC RESIN AND MANUFACTURE OF CAN BODY OF SYNTHETIC RESIN USING THE SAME

摘要

PURPOSE:To form a flange for encircling a cover of can only by injection molding without the need for a cutting step by providing a flange expanding outwardly from the side wall at the edge of the opening of a cylindrical preform with a bottom, wherein the thickness of the flange is smaller than the maximum thickness of the side wall at a predetermined ratio or less. CONSTITUTION:A preform 10 consists of a bottom wall 12, side wall 14, flange 20 expanding radially outwardly from the wall 14 at the edge of an opening and shoulder 18 connecting the flange with the wall 14. The flange 20 has a thickness T3 that is equal to one-third or smaller than the maximum thickness T2 of the wall 14, preferably in the range 0.3-0.7mm in the region where a cover of can is encircled by the flange. The transition in thickness from the wall 14 to the flange 20 occurs at the shoulder 18. A mold for injection molding includes a neck mold for defining at least the outer wall surface of the flange 20 and the shoulder 18, a cavity mold for defining the remaining outside wall and a core mold for defining the internal wall. After the molding, the core and cavity molds rate removed and the preform is held and transferred by the neck mold to be subjected to a biaxial drawing blow molding to be formed into a can body.