METHOD OF FORMING CONTAINER LID HAVING TAMPER-EVIDENT PROPERTY

摘要

PROBLEM TO BE SOLVED: To provide a container lid which is not influenced by a structure of a mouth of a container and does not make an abnormal impulsive sound even if the inside of the container is pressurized. SOLUTION: The tamper-evident container lid 10 comprises a peripheral breakable line formed on a circular top wall and an approximately tubular skirt wall 12 hanging from a periphery of the top wall wherein the skirt wall is sectioned into a main part above the breakable line and a tamper-evident foot below the line, and a plurality of protruding lines extending downward from an annular shoulder surface facing downward formed in a circumferential direction on a lower part of an inner peripheral thread of the skirt wall wherein the breakable line is formed by cutting the skirt wall with a part of the protruding line left. The breakable line is formed by causing two cutting edges to work to an outer peripheral surface of the skirt wall of the container lid which revolves and rotates together with a spindle which is revolved and rotated through a circular revolving orbit, and breaking strength of the plurality of protruding lines has at least two or more kinds of different values.