Threaded plastic bottle cap

#The invention relates to a plastic threaded cap for bottles containing liquid under vacuum or pressure.

#Bottle caps for carbonated beverages have for many years been constructed of metal. These caps are either crimped to the neck of the bottle or threaded onto the bottle. More recently the industry has turned to the use of plastic caps constructed either for a snap fit onto the bottle or threaded engagement with cooperating threads on the neck of the bottle. Plastic caps of the threaded construction are either designed for use with glass bottles or plastic bottles. The former use requires internal sealing configurations which can accommodate imperfections usually found in the top of the neck of glass bottles as resulting during their manufacturing or caused by rough handling. A typical plastic cap design for glass bottles is disclosed in U.S. Pat. No. 4,090,631. Although specifically constructed for glass bottles, these caps can also be used for plastic bottles. However, their construction is of such intricate design that the molding dies have to be correspondingly intricate. This in turn makes the molds subject to damage of the delicate parts during handling.

#In constructing plastic caps as opposed to metal caps, more attention has to be given to the internal sealing flanges found on these caps so as to provide a suitable sealing of the contents in the bottle. This is more difficult with plastic caps because of their inherent physical characteristics which tend to permit the sealing effect to be lost during handling and storage of the bottles. In the use of plastic caps, there has also been encountered what is called the projectile effect which is caused by the cap providing too good a seal with the bottle neck. Where this occurs, the pressure within the bottle is not released until the cap is almost completely unthreaded. At this time, the internal pressure, instead of being released gradually, is released just at the time the cap is completely unthreaded and this causes the cap to be blown off the bottle with some force. This is particularly a problem where plastic caps are used with plastic bottles because plastic bottles do not have the usual inperfections that glass bottles have.

#FIG. 1 is an enlarged cross-sectional view of the cap of the present invention;

#FIG. 2 is an enlarged cross-sectional view of the cap shown in FIG. 1 in fully threaded position on the neck of a bottle;

#FIG. 3 is a greatly enlarged cross-sectional view of the outer annular seal of the cap in undistorted position; and

#The bottle cap as shown in FIGS. 1 and 2 includes a top wall 1, a cylindrical side wall 2 depending from the top wall and having an outer knurled surface 2' and a thread 3 on its internal surface. The thread is adapted to cooperate with an external thread 4 on the neck 5 of a bottle 6. For effecting sealing of the cap to the bottle, first and second flanges 7 and 8 are provided. Both of these flanges are annular in shape and extend downwardly from the top wall of the cap. The bottle cap shown in the drawings is a 28 mm cap and is constructed of suitable plastic such as polyethylene.

#The first flange has an outer surface 9 which is convex in shape. The maximum diameter of this surface is greater than the inner diameter of the neck of the bottle so that, as the cap is threaded onto the bottle with this flange moving into the neck, it will flex radially inwardly to effect sealing against the inner surface 10 of the bottle neck.

#The second sealing flange 8 is spaced radially outwardly of the first flange 7 and is oriented for engagement with the top surface 11 of the bottle neck at the outer periphery 12 thereof. This outer periphery is shown as being beveled. The second flange has a normal, generally triangular cross-sectional shape with inner and outer side walls extending downwardly from the top wall of the cap in a direction tapering toward each other. The inner wall includes an uppermost wall portion 13 extending toward the side wall 2 of the cap and a lowermost wall portion 14 extending axially of the side wall of the cap. The tip of the lowermost wall portion 14 intersects with the outer wall 15 of the flange to define a lower flange tip 16.