Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing
Reexamination Certificate
1998-10-30
2002-04-16
Dye, Rena L. (Department: 1772)
Stock material or miscellaneous articles
Hollow or container type article
Polymer or resin containing
C428S036600, C428S036700, C428S036900, C428S036920, C428S910000, C215S375000, C220S606000, C220S609000
Reexamination Certificate
active
06372318
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to new and useful improvements in containers, and more particularly to a method of forming a container having enhanced sidewall crystallinity and low base crystallinity. The container is particularly adapted for use as a refillable carbonated beverage container able to withstand higher caustic wash temperatures and exhibit reduced product flavor carryover, or as a hot fill container.
BACKGROUND OF THE INVENTION
The market for PET refillable carbonated soft drink (CSD) bottles has enjoyed significant growth worldwide since its introduction in 1987 by Continental PET Technologies. These bottles have been commercialized throughout much of Europe, Central and South America, and are now moving into the Far East market.
Refillable bottles reduce the existing landfill and recycle problems associated with disposable plastic beverage bottles. In addition, a refillable bottle provides a safer, lighter-weight plastic container in those markets, currently dominated by glass, where legislation prohibits use of non-returnable packages. The goal is to produce a refillable bottle having the necessary physical characteristics to withstand numerous refill cycles, and which is still economical to produce.
Generally, a refillable plastic bottle must maintain its functional and aesthetic features over a minimum of 10 and preferably over 20 cycles or loops to be considered economically feasible. A loop is comprised of (1) an empty hot caustic wash followed by (2) contaminant inspection and product filling/capping, (3) warehouse storage, (4) distribution to wholesale and retail locations and (5) purchase, use and empty storage by the consumer followed by eventual return to the bottler. This cycle is illustrated in FIG.
1
. In an alternative cycle, the contaminant inspection occurs prior to the caustic wash.
Refillable containers must meet several key performance criteria to achieve commercial viability, including:
1. high clarity (transparency) to permit on-line visual inspection;
2. dimensional stability over the life of the container; and
3. resistance to caustic wash induced stress cracking and leakage.
A commercially successful PET refillable CSD container is presently being distributed by The Coca-Cola Company in Europe (hereinafter “the prior art container”). This container is formed of a single layer of a polyethylene terephthalate (PET) copolymer having 3-5% comonomer, such as 1,4-cyclohexanedimethanol (CHDM) or isophthalic acid (IPA). The preform, from which this bottle is stretch blow molded, has a sidewall thickness on the order of 5-7 mm, or about 2-2.5 times that of a preform for a disposable one-way bottle. This provides a greater average bottle sidewall thickness (i.e., 0.5-0.7 mm) required for abuse resistance and dimensional stability, based on a planar stretch ratio of about 10:1. The average crystallinity in the panel (cylindrical sidewall section beneath the label) is about 15-20%. The high copolymer content prevents visual crystallization, i.e., haze, from forming in the preform during injection molding. Preform haze is undesirable because it produces bottle haze which hinders the visual on-line inspection required of commercial refill containers. Various aspects of this prior art container are described in Continental PET Technology's U.S. Pat. Nos. 4,725,464, 4,755,404, 5,066,528 and 5,198,248.
The prior art container has a demonstrated field viability in excess of 20 refill trips at caustic wash temperatures of up to 60° C. Although successful, there exists a commercial need for an improved container that permits an increase in wash temperature of greater than 60° C., along with a reduction in product flavor carryover. The latter occurs when flavor ingredients from a first product (e.g., root beer) migrate into the bottle sidewall and subsequently permeate into a second product (e.g., club soda) on a later fill cycle, thus influencing the taste of the second product. An increase in wash temperature may also be desirable in order to increase the effectiveness and/or reduce the time of the caustic wash, and may be required with certain food products such as juice or milk.
Thus, it would be desirable to increase the caustic wash temperature above 60° C. for a returnable bottle having a lifetime of at least 10 refill trips, and preferably 20 refill trips, and to reduce the product flavor carryover. These and other objects are achieved by the present invention as set forth below.
SUMMARY OF THE INVENTION
In accordance with this invention, a method of forming a container is provided having an enhanced level of sidewall crystallinity and a low level of base crystallinity. The container has improved resistance to caustic stress cracking, while maintaining a high level of transparency (clarity) and dimensional stability, and thus is particularly suitable for refillable beverage bottles. The container has a lifetime of at least 10 refill cycles and more preferably at least 20 refill cycles, at caustic washing temperatures of above 60° C. The container exhibits a reduction in flavor carryover of at least 20% over the previously described refillable CSD prior art container.
The method of forming the container includes a first expansion step in which a substantially amorphous polyester preform is at least partially expanded into an intermediate article, followed by a heat treating step in which the intermediate article is at least partially heated to contract and crystallize the same, and then a second expansion step in which the contracted intermediate article is reexpanded to form the final container.
In a first method embodiment of the invention, a base-forming section of the preform is not expanded during the first expansion step, is not heated and remains substantially unchanged in crystallinity during the heat treating step, and is expanded without significant crystallinity change during the second expansion step. In contrast, a sidewall-forming section of the preform is expanded during the first expansion step to dimensions substantially equal to or greater than the dimensions of the final container sidewall, heated to crystallize and contract the same below the dimensions of the final container during the heat treating step, and reexpanded during the second expansion step to the final dimensions of the container sidewall. The relatively thinner container sidewall thus achieves a substantially higher percent crystallinity than the thicker base, which provides enhanced resistance to caustic stress cracking in both the sidewall and base.
In a second method embodiment, the base-forming section of the preform is expanded during the first expansion step, but is not heated during the heat treating step so that it maintains a low level of crystallinity compared to the container sidewall. Again, the sidewall-forming section of the preform is expanded during the first expansion step to form an intermediate expanded sidewall with dimensions substantially equal to or greater than the dimensions of the final container sidewall, the expanded intermediate sidewall is then heated to crystallize and contract the same below the dimensions of the final container sidewall, and then the contracted intermediate sidewall is expanded during the second expansion step to the final dimensions of the container sidewall. The thinner container sidewall thus achieves a substantially higher percent crystallinity than the thicker base, which provides enhanced resistance to caustic stress cracking in both the sidewall and base.
The base-forming section of the preform is generally substantially thicker than the sidewall-forming section and thus more resistant to heating (and resultant crystallization) during the heat treating step. In addition, it is preferred to localize or confine the heat treatment to the intermediate sidewall, while the base-forming section (or base) is shielded to prevent heating thereof. In one preferred heat treating step, the intermediate container is heated by passing through a row of heating elements and shielding elements move (or incr
Collette Wayne N.
Krishnakumar Suppayan M.
Lin Chi Ching
Continental Pet Technologies, Inc.
Finnegan Henderson Farabow Garrett & Dunner
Hendricks Therese A.
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