Abstract:
A plastic container having a base portion adapted for vacuum absorption. The base portion including a ring upon which the container is supported, an upstanding wall and a recessed portion. The upstanding wall being adjacent to and generally circumscribing the contact ring. The recessed portion being defined in at least part by a flat base region and a central base region. The flat base region extending from the upstanding wall toward a longitudinal axis of the container. The flat base region defining a projected surface area of at least 45% of a total projected surface area of the container. The flat base region being moveable to accommodate vacuum forces within said container.

Description:
REFERENCE TO PRIOR PROVISIONAL APPLICATION 
     This application claims the benefit of prior provisional application No. 60/220,326 filed Jul. 24, 2000. 
    
    
     TECHNICAL FIELD OF THE INVENTION 
     This invention generally relates to plastic containers for retaining a commodity, and in particular a liquid commodity. More specifically, this invention relates to a plastic container base structure that allows for significant absorption of vacuum pressures by the base without unwanted deformation in other portions of the container. 
     BACKGROUND 
     Numerous commodities previously supplied in glass containers are now being supplied in plastic, more specifically polyester and even more specifically polyethylene terephthalate (PET) containers. The manufacturers and fillers, as well as consumers, have recognized that PET containers are lightweight, inexpensive, recyclable, and manufacturable in large quantities. 
     Manufacturers currently supply PET containers for various liquid commodities, such as beverages. Often these liquid products, such as juices and isotonics, are filled into the containers while the liquid product is at an elevated temperature, typically 68° C.-96° C. (155° F.-205° F.) and usually about 85° C. (185° F.). When packaged in this manner, the hot temperature of the liquid commodity is used to sterilize the container at the time of filling. This process and the containers designed to withstand it are respectively known as hot filling, and hot fill or heat set containers. 
     Hot filling works, and is an acceptable process, with commodities having a high acid content. Non-high acid content commodities, however, must be processed in a different manner. Nonetheless, manufacturers and fillers of non-high acid content commodities desire to supply PET containers for these commodities as well. 
     For non-high acid commodities, pasteurization and retort are the preferred sterilization methods. Pasteurization and retort both present an enormous challenge for manufactures of PET containers in that heat set containers cannot withstand the temperature and time demands of pasteurization and retort. 
     Pasteurization and retort are both methods for cooking or sterilizing the contents of a container after it has been filled. Both processes include the heating of the contents of the container to a specified temperature, usually above about 70° C. (about 155° F.), for a specified length of time (20-60 minutes). Retort differs from pasteurization in that higher temperatures are used, as is an application of pressure externally to the container. The pressure is necessary because a hot water bath is often used and the overpressure keeps the water, as well as liquid in the product, in liquid form above its boiling point temperature. 
     The present invention will find particular utility in hot fill applications, vacuum seal applications and applications where water loss through the container is a concern. It may also find utility in pasteurization and retort applications. 
     PET is a crystallizable polymer, meaning that it is available in an amorphous form or a semi-crystalline form. The ability of a PET container to maintain its material integrity is related to the percentage of the PET container in crystalline form, also known as the “crystallinity” of the PET container. Crystallinity is characterized as a volume fraction by the equation:        Crystallinity   =       ρ   -     ρ   a           ρ   c     -     ρ   a                                
     where ρ is the density of the PET material; ρ a  is the density of pure amorphous PET material (1.333 g/cc); and ρ c  is the density of pure crystalline material (1.455 g/cc). 
     The crystallinity of a PET container can be increased by mechanical processing and by thermal processing. 
     Mechanical processing involves orienting the amorphous material to achieve strain hardening. This processing commonly involves stretching a PET container along a longitudinal axis and expanding the PET container along a transverse or radial axis. The combination promotes what is known as biaxial orientation in the container. Manufacturers of PET bottles currently use mechanical processing to produce PET bottles having about 20% crystallinity in the container&#39;s sidewall. 
     Thermal processing involves heating the material (either amorphous or semi-crystalline) to promote crystal growth. On amorphous material, thermal processing of PET material results in a spherulitic morphology that interferes with the transmission of light. In other words, the resulting crystalline material is opaque (and generally undesirable). Used after mechanical processing, however, thermal processing results in higher crystallinity and excellent clarity. The thermal processing of an oriented PET container, which is known as heat setting, typically includes blow molding a PET preform against a mold heat to a temperature of about 120° C.-130° C. (about 100° F.-105° F.), and holding the blown container for about 3 seconds. Manufacturers of PET juice bottles, which must be hot filled at about 85° C., currently use heat setting to produce PET bottles having a crystallinity range of 25-30%. 
     After being hot filled, the heat set containers are capped and allowed to reside at generally about the filling temperature for approximately five minutes. The container along with the product is then actively cooled so that the container may be transferred to labeling, packaging and shipping operations. Upon cooling, the volume of the liquid in the container is reduced. This reduction in volume results in the creation of a vacuum within the container. Generally, vacuum pressures within the container range from 1-300 mm/Hg. If not controlled or otherwise accommodated, these vacuum pressures result in deformation of the container which leads to either an aesthetically unacceptable container or one which is unstable. Typically, vacuum pressures have been accommodated by the incorporation of structures in the sidewall of the container. These structures are commonly known as vacuum panels. Vacuum panels are designed to distort inwardly under the vacuum pressures in a controlled manner so as to eliminate undesirable deformation in the sidewall of the container. 
     While vacuum panels have allowed the containers to withstand the rigors of a hot fill procedure, they do present some limitations and drawbacks. First, during labeling, a wrap-around or sleeve label is applied to the container over the vacuum panels. Often, the appearance of these labels over the sidewall and vacuum panels is such that the label is wrinkled and not smooth. Additionally, when grasping the container, the vacuum panels are felt beneath the label resulting in the label being pushed into the various crevasses and recesses of the vacuum panels. 
     It would therefore be desirable to have a container which could accommodate the vacuum pressures which result from hot filling yet which has or is capable of having smooth sidewalls. 
     In view of the above, it is an object of the present invention to provide a plastic container which principally accommodates vacuum pressure through a mechanism other than vacuum panels in the sidewalls of the container. 
     A further object of the present invention is to provide a container having a base structure which accommodates vacuum pressure while preventing undesirable distortion in other parts of the container. 
     Still another object of this invention is to provide a plastic container in which the base structure is substantially flat in cross-section in a wall portion thereof which cooperates with an upstanding shoulder wall or ridge to permit the accommodation of vacuum pressures within the base structure. 
     SUMMARY OF THE INVENTION 
     Accordingly, this invention provides for a plastic container which maintains aesthetic and mechanical integrity during any subsequent handling after being hot filled and cooled to ambient. 
     Briefly, the plastic container of the invention includes an upper portion, a body or sidewall portion and a base. The upper portion includes an opening defining the mouth of the container, a threaded portion (or other configuration) as a means to engage a closure, and a support ring that is used during handling, before, during, and after manufacturing. The upper portion further includes a shoulder extending down to the sidewall portion which generally defines the greatest diameter of the container. 
     Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which the present invention relates from the subsequent description of the preferred embodiment and the appended claims, taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a bottom perspective view of a portion of a plastic container according to the present invention; 
     FIG. 2 is a cross-sectional view of the plastic container, taken generally along line  2 — 2  of FIG. 1; 
     FIG. 3 is a cross-sectional view of the plastic container, taken generally along line  3 — 3  of FIG. 1; and 
     FIG. 4 is an elevational view of the plastic container according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The following description of the preferred embodiment is merely exemplary in nature, and is in no way intended to limit the invention or its application or uses. 
     As discussed above, to accommodate vacuum forces during cooling of the contents within a heat set container, containers have been provided with a series of vacuum panels around their sidewalls. The vacuum panels deform inwardly under the influence of the vacuum forces and prevent unwanted distortion elsewhere in the container. However, with the vacuum panels, the container sidewall can not be smooth, an overlying label is not smooth, and end users can feel the vacuum panels when grasping and picking up the containers. 
     As shown in FIGS. 1 and 4, a plastic container  10  of the invention includes a finish  12 , a base portion  14 , and a body portion  16 . The finish  12  of the plastic container  10  includes portions defining an aperture or mouth  18 , a threaded region  20 , and a support ring  21 . The aperture  18  allows the plastic container  10  to receive a commodity while the threaded region  20  provides a means for attachment of a similarly threaded closure or cap (not shown), which preferably provides a hermetical seal for the plastic container  10 . The support ring  21  may be used to carry or orient the preform (the precursor to the container  10 ) (not shown) through and at various stages of manufacture. For example, the preform may be carried by the support ring  21 , the support ring  21  may be used to aid in positioning the preform in the mold, or the support ring  21  may be used by an end consumer to carry the container  10 . 
     The base portion  14  of the plastic container  10 , which generally extends inward from the body portion  16 , includes a chime  24 , a contact ring  26 , and an inwardly recessed region  28 . The base portion  14  functions to close off the bottom of the container  10  and, together with the finish  12  and the body portion  16 , to retain the commodity. 
     In the preferred embodiment of the invention, the body portion  16 , which generally extends downward from the finish  12  to the base portion  14 , includes a shoulder region  22  providing a transition between the finish  12  and a sidewall  23 . Because of the specific construction of the base  14  of the container  10 , the sidewall  23  for the heat set container  10  may be formed without the inclusion therein of vacuum panels, and if desired, smooth. 
     The plastic container  10  of the present invention is a blow molded, biaxially oriented container with an unitary construction from a single or multi-layer material such as polyethylene terephthalate (PET) resin. Alternatively, the plastic container  10  may be formed by other methods and from other conventional materials. Plastic containers blow-molded with an unitary construction from PET materials are known and used in the art of plastic containers, and their general manufacture in the present invention will be readily understood by a person of ordinary skill in the art. 
     The plastic container  10  is preferably heat set according to the above mentioned process or other conventional heat set processes. 
     To accommodate vacuum forces and allow for the omission of vacuum panels in the body  16  of the container  10 , the base  14  of the present invention adopts a novel and innovative construction. Generally, the round base  14  is provided with an inwardly recessed region  28  having a generally “flat” area whose projected area is at least 45%, and preferably greater than 55%, of the overall projected area of the base  14 . Additionally, an upstanding circumferential wall or ridge  30  forms a transition between the contact ring  26  and the recessed region  28 . As used herein, the term “flat” does not, but may, mean precisely flat or without any curative. The term “flat” is primarily being used to differentiate between two or more portions of the recessed region  28 . 
     As shown in FIGS. 2 and 3, the recessed region  28  includes a flat base region  32  and a central base region  34 . The flat base region  32  when viewed in cross section is generally planar and slightly up sloping toward a central longitudinal axis  36  of the container  10 . The flat base region  32 , when viewed three dimensionally, defines a conical surface which lacks an apex because of the central base region  34 . In cross section, the flat base region  32  may be provided with a slight curvature (inward or outward, but preferably inward). 
     The central base region  34  is seen as being a steeply domed area. The exact shape of the central base region  34  can vary greatly depending on various design criteria. For the purposes of the present application, the central base region  34  may be of any shape which deviates significantly from the shape of the flat base region  32 . 
     When initially formed, the flat base region  32  may be substantially parallel to a horizontal plane or a support surface  40 . Upon filling, this flat base region  32  will sag or deflect toward the support surface under the temperature and weight of the product. Radial ribs  38 , starting in the central base region  34  and terminating at the ridge  30 , may be provided in the recessed region  28  to minimize sag and prevent irreversible sagging within the container  10 . Upon capping and cooling, the flat base region  32  is raised or pulled upwardly, displacing volume, as a result of the vacuum forces. In this position, the flat base region  32  may exhibit more of the conical shape of FIG.  2 . This conical shape may be defined at an angle  33  of about substantially 0° to about 10° relative to the horizontal plane or the support surface  40 . The amount or volume which the flat base region  32  displaces is dependent on the projected surface area of the flat base region  32 . As used herein, projected surface area means the relative surface area when viewing along the central longitudinal axis  36 . 
     As illustrated in FIG. 2, the relevant projected linear lengths across the base  14  are identified as A 1 , B 2 , C, B 3  and A 4 . The projected total surface area (PSA T ) of the base  14  is readily defined by the equation: 
     
       
           PSA   T =π(½( A   1   +B   2   +C+B   3   +A   4 )) 2 . 
       
     
     The projected surface area for the flat base region  32  (PSA F ) is defined by the equation: 
     
       
           PSA   F =π(½( B   2   +C+B   3 )) 2   −PSA   C . 
       
     
     The projected surface area of the central base region  34  (PSA C ) is defined by the equation: 
     
       
           PSA   C =π(½ C ) 2 . 
       
     
     In order to eliminate the necessity of providing vacuum panels in the body  16  of the container  10 , the flat base region  32  is provided with a projected surface area (PSA F ) of at least 45%, and preferably greater than 55%, of the total projected surface area (PSA T ). The greater this percentage, the greater the amount of vacuum the container  10  can accommodate without unwanted deformation in other areas of the container  10 . 
     The ridge  30 , defining the transition between the contact ring  26  and the recessed region  28 , is an upstanding wall (approximately 0.03 inches (0.76 mm) to approximately 0.05 inches (1.27 mm) in height) and is generally seen as being parallel to the center longitudinal axis  36  of the container  10 . While the ridge  30  need not be exactly parallel to the central longitudinal axis  36 , it should be noted that the ridge  30  is a distinctly identifiable structure between the contact ring  26  and the recessed region  28 . The contact ring  26  is itself that portion of the base  14  which contacts the surface  40  upon which the container  10  is supported. As such, the contact ring  26  may be a flat surface or a line of contact generally circumscribing, continuously or intermittently, the base  14 . 
     By providing the ridge  30 , the transition between the flat base region  32  and the contact ring  26  is strengthened. This increases resistance to creasing in the base  14 . In an alternate embodiment where reduced vacuum forces are encountered, the ridge  30  may be omitted. 
     While the above description constitutes the preferred embodiment of the present invention, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope and fair meaning of the accompanying claims.