Plastic closure with enhanced performance

1. A plastic closure, comprising:

a closure cap having a top wall portion, and an annular skirt portion depending from said top wall portion and extending around an axis,

said skirt portion of said closure cap having an internal thread formation for threaded engagement with an external thread formation of an associated container,

wherein said internal thread formation is configured to exhibit a variation in retention force which decreases in a direction away from said top wall portion of said closure cap when engaged with an external thread formation of an associated container, said internal thread formation being configured to define a plurality of thread profiles, including a thread profile having a relatively large cross-sectional area viewed in a plane containing the axis positioned closer to said top wall portion than another one of said thread profiles having a relatively small cross-sectional area,

wherein at least a portion of said thread formation has a continuously varying thread profile cross section, including a continuously varying depth in said thread profile extending at least 180° about a circumference of said closure cap over which the depth in said thread profile decreases in a direction away from said top wall portion.

2. The plastic closure of claim 1 , wherein said internal thread formation is continuous and wherein said continuously varying thread profile cross section varies continuously throughout the length of the thread.

3. The plastic closure of claim 1 further including a tamper-evident pilfer band at least partially detachably connected to said skirt portion.

4. The plastic closure of claim 1 , wherein said internal thread formation includes one or more discontinuities therein to facilitate gas venting.

5. The plastic closure of claim 1 , wherein said internal thread formation includes a helical engagement surface.

6. A package including a container and a plastic closure, the package comprising:

said container with an external threaded portion for threaded engagement with an internal thread formation of said closure; and

said plastic closure including a closure cap and an annular skirt portion,

said closure cap having a top wall portion, and said annular skirt portion depending from said top wall portion and extending around an axis,

said skirt portion of said closure cap having said internal thread formation for threaded engagement with said external thread formation of said container,

wherein said internal thread formation is configured to exhibit a variation in retention force which decreases in a direction away from said top wall portion of said closure cap when engaged with said external thread formation of said container, said internal thread formation being configured to define a plurality of thread profiles, including a thread profile having a relatively large cross-sectional area viewed in a plane containing the axis positioned closer to said top wall portion than another one of said thread profiles having a relatively small cross-sectional area,

wherein at least a portion of said thread formation has a continuously varying thread profile cross section, including a continuously varying depth in said thread profile extending at least 180° about a circumference of said closure cap over which the depth in said thread profile decreases in a direction away from said top wall portion.

7. The package of claim 6 , wherein said internal thread formation of said closure is continuous and wherein said continuously varying thread profile cross section varies continuously throughout the length of the thread.

8. The package of claim 6 further including a tamper-evident pilfer band at least partially detachably connected to said skirt portion.

9. The package of claim 6 , wherein said internal thread formation of said closure includes one or more discontinuous in therein to facilitate gas venting.

10. The package of claim 6 , wherein said internal thread formation of said closure includes a helical engagement surface.