Plastic container closure

A plastic container closure which is applied to a container having an annular top surface extending substantially horizontally, a cylindrical outer peripheral surface extending substantially vertically, and an annular boundary surface extending from the top surface to the outer peripheral surface substantially arcuately in a sectional view, the top surface, the outer peripheral surface, and the boundary surface being formed in an upper end part of a mouth-and-neck portion of the container, the container closure comprising:

• a circular top panel wall;
• and
• a cylindrical skirt wall extending downwardly from a peripheral edge of the top panel wall, and wherein
• an annular seal piece and an annular contact piece are integrally formed in an outer peripheral edge portion of an inner surface of the top panel wall, the annular seal piece extending downwardly obliquely in a radially inward direction, and being brought into intimate contact with the outer peripheral surface in the mouth-and-neck portion, whereby the annular seal piece is deflected radially outwardly, and the annular contact piece being brought into contact with the boundary surface in the mouth-and-neck portion.