Threaded plastic bottle cap

Claim 1

An improved bottle cap for use with a bottle having a threaded neck opening into the bottle, said cap being constructed of flexible plastic material and having a top wall, a cylindrical side wall depending from the top wall and a thread on the inner surface of the side wall for cooperating with the thread on the neck of the bottle, the improvement comprising: (a) a primary annular sealing flange extending downwardly from the top wall of the cap in a radial inward direction for engagement with the top wall surface of the bottle neck as aligned directly therebelow when the cap is threaded onto the bottle neck, said primary sealing flange: (1) being biased in an upwardly direction by contact with the top wall surface of the bottle neck when the cap is fully threaded onto the bottle neck, (2) having a radial length sufficient to cover a major portion of the surface area of said top wall surface and span surface irregularities therein, and (3) being sufficiently flexible to accommodate such surface irregularites and maintain sealing contact with the top wall surface in a direction extending completely around said bottle neck; and (b) an annular groove in the inner surface of the top wall of the cap axially aligned directly above the primary sealing flange and extending radially inwardly of the free end of the flange for reception thereof when the cap is fully threaded onto said bottle neck, (1) said groove having a depth sufficient to leave the upper surface of the primary flange free of contact with any other cap structure and to leave a space above said sealing flange which is in communication with the interior of said bottle neck when the cap is fully threaded thereon so as to permit pressurized atmosphere in the bottle to act on the upper surface of said sealing flange to press it against the top wall surface of the bottle neck.