Easily openable container lid

An easily openable container lid for a container that has a cylindrical mouth-neck section having an annular locking ridge formed at an upper end part of an outer peripheral surface, the cylindrical mouth-neck section is to be sealed to have a positive internal pressure after a gas-containing liquid is accommodated within the container,

• the container lid comprising a shell and a liner, wherein
• the shell comprises a flat circular top panel wall, a skirt wall having an arcuate part extending arcuately radially outward and downward from a peripheral edge of the flat circular top panel wall in a longitudinal cross sectional view and a linear part extending vertically downward to follow the arcuate part, and a grip piece extending from a lower end of the skirt wall,
• the flat circular top panel wall, the skirt wall and at least a base part of the grip piece are integrally formed of a metal sheet, and a pair of scores each including a first portion and a second portion are formed, where the first portions extend upward on the skirt wall from both sides of the grip piece, and the second portions extend arcuately between an upper end part of the skirt wall and a peripheral edge part of the flat circular top panel wall,
• the liner, which is disc-shaped and made of a synthetic resin, is disposed on an inner surface of the flat circular top panel wall of the shell,
• the container lid is attached to the cylindrical mouth-neck section by swaging a lower part of the linear part of the skirt wall radially inward below the annular locking ridge of the cylindrical mouth-neck section,
• the respective first portions of the pair of scores extend straight and vertically from the lower end of the skirt wall to a site above an upper end of the lower part of the linear part, and
• t1>t2>t3, wherein t1 denotes a material residual thickness of the pair of scores at a site of the first portions, ranging from the lower end of the skirt wall of the first portions, above the upper end of the lower part of the linear part of the skirt wall and to an intermediate part of the linear part other than the lower part, t2 denotes a material residual thickness of the pair of scores at a remainder of the first portions, and t3 denotes a material residual thickness of the pair of scores at the second portions and at third portions.