Method of producing an easily openable container closure having a shell and a sealing member

A method for producing a shell of a unitary structure comprising a top and a cylindrical skirt, said top having an annular top surface portion leading to the upper end of said skirt and a linking piece leading to a part of the inner peripheral edge of the annular top surface portion, a pull ring connected to said linking piece, said annular top surface portion and skirt having a pair of weakening lines extending from both side edges of said linking piece, which method comprises:

• (a) forming at least one set of lance slits in a flat metal blank, said lance slits having at least two discontinuous portions spaced a predetermined distance from each other in the circumferential direction,
• (b) forming a pair of weakening lines spaced from each other at a predetermined distance in the circumferential direction, said weakening lines extending over a predetermined distance from near the lance slits toward the center of a circular portion of the blank located inwardly of the lance slits,
• (c) punching out an opening of a predetermined dimension in the circular portion at a position located inwardly of the lance slits,
• (d) at least after the lance slit-forming step (a) and the weakening line-forming step (b), drawing the circular portion located inwardly of the lance slits to form a shell having a circular top with said opening therein and a substantially cylindrical skirt continuous therewith,
• (e) at least after the drawing step (d), forming a slit in said circular top extending around said opening from near the inside end of one of said weakening lines to the vicinity of the inside end of the other weakening line, said slit being spaced a predetermined distance outwardly from said opening in the radial direction,
• (f) after the punching step (c) and the slit-forming step (e), bending the portion between said opening of the circular top and the slit to form a pull ring, and
• (g) after the bending step (f), separating the thus formed shell from the metal blank.