Abuse resistant preform and container neck finish

Abstract

A neck finish of a preform or container having a crystallized top sealing surface (TSS) for withstanding deformation from multiple use cycles. In a returnable and fillable container, the improved TSS has enhanced caustic stress crack resistance resulting in a more secure finish-closure seal and an extended container life (number of refill cycles).

Description

TECHNICAL FIELD[0001]The present invention is directed generally to plastic preforms and containers, and more specifically to a preform and container neck finish able to withstand the mechanical abuse and rigors of multiple use cycles, while maintaining a secure seal with a closure.BACKGROUND OF THE INVENTION[0002]Conventional manufacture of plastic (e.g., polyethylene terephthalate (PET)) containers employs an initial step of forming a substantially amorphous and unoriented parison or preform by an injection molding process. The process of crystallizing the finish of such preforms is sometimes used to thermally stabilize the dimensions of the finish, and in particular the finish threads, for high temperature applications such as hot filling and pasteurization.[0003]In hot filling and pasteurization applications, the sealed container undergoes significant pressure changes, i.e., the pressure increase due to filling with a heated liquid and immediate capping or the exposure to a high...

AI Technical Summary

Benefits of technology

[0007]The neck finish may be for a pressurized returnable and refillable container. The crystallized TSS provides a more secure finish-closure seal, thus increasing the service life of the container. Preferably, the container can withstand at least 10 refill cycles, including a hot caustic wash at a temperature of at least 60° C. and pressurized filling of at least 3 atmospheres, while maintaining a secure seal with the closure. More preferably, the container can withstand at least 20, and still more preferably at least 25 refill cycles.

Problems solved by technology

These internal pressure changes cause the threads on the cap to push up or down on the warm threads of the finish, distorting the finish threads.

If the warm finish threads distort, the cap becomes loose and there is a loss of product quality (e.g., exposure to the atmosphere and possible contamination) and / or leakage.

However, refill containers are subjected to greater opportunities for mechanical abuse.

Not only must they typically withstand at least ten cycles of re-use to be commercially viable as refillable containers, but after each use they are potentially subject to unintended conditions of storage, handling and misuse by the consumer (e.g., filling with other liquids, crushing, and / or use for other purposes, such as a candle holder) which can seriously affect their ability to survive the intended number of commercial re-use cycles.

In particular, refill containers have a substantially unoriented and amorphous neck finish of relatively low mechanical strength.

As such, the finish can easily be nicked or dented during such uncontrolled handling by the consumer prior to their return to the manufacture for cleaning and re-use.

This denting of the neck finish is a particular problem because the neck finish is one area of the container with particularly tight dimensional tolerances necessary to ensure a tight seal with the closure.

For these reasons, refillable containers are subject to a leakage test after refilling and a substantial number of refillable containers are rejected for failure to withstand the leakage test.

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