Abstract:
A plastic container includes an upper portion having a mouth defining an opening into the container. A shoulder region extends from the upper portion. A sidewall portion extends from the shoulder region to a base portion. The base portion closes off an end of the container. The sidewall portion is defined in part by at least one arcuately formed rib having a body portion and opposite ends. The body portion curves from a central portion toward the base portion at each of the opposite ends.

Description:
TECHNICAL FIELD 
       [0001]    This disclosure generally relates to plastic containers for retaining a commodity, and in particular a liquid or semi solid commodity. More specifically, this disclosure relates to a plastic container having a sidewall portion defining arcuate ribs that promote improved material distribution during container formation. 
       BACKGROUND 
       [0002]    The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
         [0003]    As a result of environmental and other concerns, plastic containers, more specifically polyester and even more specifically polyethylene terephthalate (PET) containers are now being used more than ever to package numerous commodities previously supplied in glass containers. Manufacturers and fillers, as well as consumers, have recognized that PET containers are lightweight, inexpensive, recyclable and manufacturable in large quantities. 
         [0004]    Blow-molded plastic containers have become commonplace in packaging numerous commodities. 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 relates to the percentage of the PET container in crystalline form, also known as the “crystallinity” of the PET container. The following equation defines the percentage of crystallinity as a volume fraction: 
         [0000]    
       
         
           
             
               % 
                
               
                   
               
                
               Crystallinity 
             
             = 
             
               
                 ( 
                 
                   
                     ρ 
                     - 
                     
                       ρ 
                       a 
                     
                   
                   
                     
                       ρ 
                       c 
                     
                     - 
                     
                       ρ 
                       a 
                     
                   
                 
                 ) 
               
                
               x 
                
               
                   
               
                
               100 
             
           
         
       
     
         [0000]    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). 
         [0005]    Container manufacturers use mechanical processing and thermal processing to increase the PET polymer crystallinity of a container. Mechanical processing involves orienting the amorphous material to achieve strain hardening. This processing commonly involves stretching an injection molded PET preform along a longitudinal axis and expanding the PET preform along a transverse or radial axis to form a PET container. The combination promotes what manufacturers define as biaxial orientation of the molecular structure in the container. Manufacturers of PET containers currently use mechanical processing to produce PET containers having approximately 20% crystallinity in the container&#39;s sidewall. 
         [0006]    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 thus, generally undesirable. Used after mechanical processing, however, thermal processing results in higher crystallinity and excellent clarity for those portions of the container having biaxial molecular orientation. The thermal processing of an oriented PET container, which is known as heat setting, typically includes blow molding a PET preform against a mold heated to a temperature of approximately 250° F.-350° F. (approximately 121° C.-177° C.), and holding the blown container against the heated mold for approximately two (2) to five (5) seconds. Manufacturers of PET juice bottles, which must be hot-filled at approximately 185° F. (85° C.), currently use heat setting to produce PET bottles having an overall crystallinity in the range of approximately 25%-35%. 
         [0007]    Food and juice suppliers often fill these products into the containers while the product is at an elevated temperature, typically between 155° F.-205° F. (68° C.-96° C.) and usually at approximately 185° F. (85° C.). When packaged in this manner, the hot temperature of the commodity sterilizes the container at the time of filling. The bottling industry refers to this process as hot filling, and the containers designed to withstand the process as hot-fill or heat-set containers. 
         [0008]    One challenge associated with thermal processing of an oriented PET container is the ability to direct material throughout the critical areas of the container during formation. One approach includes preferential heating of the preform to control material distribution wherein different portions of the preform are heated to different temperatures to encourage material distribution in critical areas of the container. However, such as with formation of some rectangular or oval containers, this approach is costly and does not always yield satisfactory material distribution throughout the container. Additionally, in some instances it may be desirable to incorporate ribs at various locations on the container to improve structural integrity of the container as a whole. While such ribs may provide improved durability to the container, the ribs may make it more difficult to successfully distribute the material throughout the container during formation. Explained further, containers incorporating horizontal ribs (i.e., in a direction generally parallel to a container base), may result in material being trapped at the ribs thereby inhibiting material distribution in the heel or base of the container during formation. Similarly, containers incorporating vertical ribs (i.e. in a direction generally transverse to a container base), may result in material being trapped at the ribs thereby causing an uneven distribution of material throughout the sides of the container during formation. 
         [0009]    After being hot-filled, the heat-set containers may be capped and allowed to reside at generally the filling temperature for approximately five (5) minutes at which point the container, along with the product, is then actively cooled prior to transferring to labeling, packaging, and shipping operations. The cooling reduces the volume of the commodity in the container. This product shrinkage phenomenon results in the creation of a vacuum within the container. Generally, vacuum pressures within the container range from 1-380 mm Hg less than atmospheric pressure (i.e., 759 mm Hg-380 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 that is unstable. Hot-fillable plastic containers must provide sufficient flexure to compensate for the changes of pressure and temperature, while maintaining structural integrity and aesthetic appearance. Typically, the industry accommodates vacuum related pressures with sidewall structures or vacuum panels formed within the sidewall of the container. Such vacuum panels generally distort inwardly under vacuum pressures in a controlled manner to eliminate undesirable deformation. 
         [0010]    While such vacuum panels allow containers to withstand the rigors of a hot-fill procedure, the panels have limitations and drawbacks. First, such panels formed within the sidewall of a container do not create a generally smooth glass-like appearance. Second, packagers often apply a label to the container over these panels. The appearance of these labels over the vacuum panels is such that the label often becomes wrinkled and not smooth. Additionally, one grasping the container generally feels the vacuum panels beneath the label and often pushes the label into various panel crevasses and recesses. 
         [0011]    Thus, there is a need for an improved plastic container, which allows for improved material distribution during formation and accommodates the vacuum pressures which result from hot filling. 
       SUMMARY 
       [0012]    Accordingly, the present disclosure provides a plastic container including an upper portion having a mouth defining an opening into the container. A shoulder region extends from the upper portion. A sidewall portion extends from the shoulder region to a base portion. The base portion closes off an end of the container. The sidewall portion is defined in part by at least one arcuately formed rib having a body portion and opposite ends. The body portion curves from a central portion toward the base portion of the container at each of the opposite ends. 
         [0013]    According to additional features, a series of arcuately formed ribs are defined on the sidewall portion. Each of the ribs define an inboard depression along the sidewall portion. The sidewall portion may be defined in part by at least two vacuum panels formed therein. The vacuum panels are movable to accommodate vacuum forces generated within the container resulting from heating and cooling of its contents. The sidewall portion may define a label panel area on an area across the vacuum panels. The label panel area may be adapted to accept a label over the series of ribs. 
         [0014]    A method of making a blow-molded PET plastic container includes disposing a preform into a mold cavity. The mold cavity has a surface defining a shoulder forming region, a sidewall forming region and a base forming region. The sidewall forming region defines at least one arcuate extension rib having a body portion and opposite ends. The opposite ends of each extension rib curve from a central portion toward the base forming region at each of the opposite ends. The preform is blown against the mold surface to form a resultant container having a shoulder, a sidewall and a base. The sidewall defines at least one arcuate depression rib corresponding to the at least one arcuate extension rib of the mold cavity. 
         [0015]    The configuration of the arcuate extension ribs in the mold cavity are consistent with the directional flow of material during container formation thus facilitating consistent material flow during formation of the container. Moreover, the arcuate extension ribs are generally curved from a central portion at an upstream area to opposite ends at a downstream area. In this way, material may flow smoothly around the arcuate surfaces without becoming substantially impeded or trapped at the ribs. 
         [0016]    Additional benefits and advantages of the present disclosure will become apparent to those skilled in the art to which the present disclosure relates from the subsequent description and the appended claims, taken in conjunction with the accompanying drawings. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a perspective view of a plastic container constructed in accordance with the teachings of the present disclosure; 
           [0018]      FIG. 2  is a front view of the container of  FIG. 1 ; 
           [0019]      FIG. 3  is a side view of the container of  FIG. 1 ; 
           [0020]      FIG. 4  is a cross-sectional view of the plastic container, taken generally along line  4 - 4  of  FIG. 2 ; and 
           [0021]      FIG. 5  is a sectional view of an exemplary mold cavity used during formation of the container of  FIG. 1  and shown with a preform positioned therein. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    The following description is merely exemplary in nature, and is in no way intended to limit the disclosure or its application or uses. 
         [0023]      FIGS. 1-4  show one example of the present container. In the figures, reference number  10  designates a plastic, e.g. polyethylene terephthalate (PET), hot-fillable container. As shown in  FIG. 2 , the container  10  has an overall height A of about 8.15 inch (207 mm), and a sidewall and base portion height B of about 4.50 inch (114 mm). The height A may be selected so that the container  10  fits on the shelves of a supermarket or store. As shown in the figures, the container  10  is substantially oval in cross sectional shape including opposing longer sides  14  each having a width C of about 3.00 inch (76.4 mm), and opposing shorter, parting line sides  15  ( FIG. 3 ) each having a width D of about 1.65 inch (42.0 mm). The widths C and D are selected so that the container  10  can fit within the door shelf of a refrigerator. As with typical prior art bottles, opposing longer sides  14  of the container  10  of the present disclosure are oriented at approximately 90 degree angles to the shorter, parting line sides  15  of the container  10  so as to form a generally oval cross section as best shown in  FIG. 4 . As such, the container  10  further includes a diagonal width G of about 3.04 inch (77.3 mm). In this particular example, the container  10  has a volume capacity of about 14 fl. oz. (414 cc). Those of ordinary skill in the art would appreciate that the following teachings of the present disclosure are applicable to other containers, such as round, square or rectangular shaped containers, which may have different dimensions and volume capacities. It is also contemplated that other modifications can be made depending on the specific application and environmental requirements. 
         [0024]    As shown in  FIGS. 1-3 , the plastic container  10  of the invention includes a finish  12 , a shoulder region  16 , a sidewall portion  18  and a base  20 . Those skilled in the art know and understand that a neck may also be included having an extremely short height, that is, becoming a short extension from the finish  12 , or an elongated height, extending between the finish  12  and the shoulder region  16 . The plastic container  10  has been designed to retain a commodity during a thermal process, typically a hot-fill process. For hot-fill bottling applications, bottlers generally fill the container  10  with a liquid or product at an elevated temperature between approximately 155° F. to 205° F. (approximately 68° C. to 96° C.) and seal the container  10  with a closure (not illustrated) before cooling. As the sealed container  10  cools, a slight vacuum, or negative pressure, forms inside causing the container  10 , in particular, the sidewall portion  18 , as will be described, to change shape. In addition, the plastic container  10  may be suitable for other high-temperature pasteurization or retort filling processes, or other thermal processes as well. 
         [0025]    The finish  12  of the plastic container  10  includes a portion defining an aperture or mouth  22 , a threaded region  24  having threads  25 , and a support ring  26 . The aperture  22  allows the plastic container  10  to receive a commodity while the threaded region  24  provides a means for attachment of a similarly threaded closure or cap (not illustrated). Alternatives may include other suitable devices that engage the finish  12  of the plastic container  10 . Accordingly, the closure or cap (not illustrated) engages the finish  12  to preferably provide a hermetical seal of the plastic container  10 . The closure or cap (not illustrated) is preferably of a plastic or metal material conventional to the closure industry and suitable for subsequent thermal processing, including high temperature pasteurization and retort. The support ring  26  may be used to carry or orient a preform  28  (the precursor to the plastic container  10 , shown in  FIG. 5 ) through and at various stages of manufacture. For example, the preform  28  may be carried by the support ring  26 , the support ring  26  may be used to aid in positioning the preform  28  in the mold, or an end consumer may use the support ring  26  to carry the plastic container  10  once manufactured. 
         [0026]    Integrally formed with the finish  12  and extending downward therefrom is the shoulder region  16 . The shoulder region  16  merges into and provides a transition between the finish  12  and the sidewall portion  18 . The sidewall portion  18  extends downward from the shoulder region  16  to the base  20 . The specific construction of the sidewall portion  18  of the heat-set container  10  allows the shoulder region  16  and the base  20  to not necessarily require additional vacuum panels and therefore, the shoulder region  16  and the base  20  are capable of providing increased rigidity and structural support to the container  10 . The base  20  functions to close off the bottom portion of the plastic container  10  and, together with the finish  12 , the shoulder region  16 , and the sidewall portion  18 , to retain the commodity. 
         [0027]    The plastic container  10  is preferably heat-set according to the above-mentioned process or other conventional heat-set processes. To accommodate vacuum forces, the sidewall portion  18  may include vacuum panels  30  formed therein. As illustrated in the figures, vacuum panels  30  may be generally rectangular in shape and are formed in the opposing longer sides  14  of the container  10 . It is appreciated that the vacuum panels  30  may define other geometrical configurations. Accordingly, the container  10  illustrated in the figures has two (2) vacuum panels  30 . The inventors however equally contemplate that more than two (2) vacuum panels  30 , such as four (4), can be provided. That is, that vacuum panels  30  can also be formed in opposing shorter, parting line sides  15  of the container  10  as well. Vacuum panels  30  may also include an underlying surface  34 . Surrounding vacuum panels  30  is land  32 . Land  32  provides structural support and rigidity to the sidewall portion  18  of the container  10 . 
         [0028]    The plastic container  10  according to the present teachings provides a series of arcuately formed ribs  40 . The ribs  40  generally define a body  42  having opposite ends  44  curved in a direction away from the finish  12 . As best illustrated in  FIG. 3 , the ribs  40  define inboard depressions on the sidewall portion  18 . As will become more appreciated from the following description, the ribs  40  facilitate an even distribution of material during formation of the container  10 . In the example shown, three ribs  40  are formed on the sidewall portion  18  on each of the vacuum panels  30 . As shown, the ribs  40  generally define a consistent radius. It is appreciated however, that the ribs  40  may alternatively define an increasing radius or a decreasing radius from a central portion. Preferably, the ribs  40  define a length L ( FIG. 2 ) that is about 50% to 90% of the width of opposing longer sides  14 , and more preferably 60% to 80%. The present disclosure is especially effective for producing containers that are substantially rectangular, oblong or oval in shape such as containers wherein the width of opposing longer sides  14  is 1.5 to 2.5 times greater than the width of opposing parting line sides  15 . It is appreciated that fewer or more ribs  40  may be incorporated on the container  10 . Furthermore, it is appreciated that the ribs  40  may define alternate configurations and/or be located elsewhere on the container  10 . 
         [0029]    The specific height and resulting radius of curvature of the ribs  40  is dependent on container design aspects that affect the amount of stretching the material undergoes during blow molding of the container  10  from the preform  28 . The preferred range of a height H ( FIG. 2 ), for a given length L of the ribs  40 , is defined by the following equations: 
         [0000]        H   MIN =[( L/C )×( SPL−FPL )]×( C/D ); 
         [0000]      and 
         [0000]        H   MAX =[( L/C )×( CPL−FPL )]×( G/D ) 
         [0000]    where CPL ( FIG. 1 ) represents the corner profile length which is the length of a vertical profile of the container  10  measured from the shoulder region  16  to the base  20  at a corner or an intersection of an opposing parting line side  15  and an opposing longer side  14 , SPL ( FIG. 2 ) represents the side profile length which is the length of a vertical profile of the container  10  measured from the shoulder region  16  to the base  20  at a midpoint of the opposing parting line sides  15 , and FPL ( FIG. 3 ) represents the front profile length which is the length of a vertical profile of the container  10  measured from the shoulder region  16  to the base  20  at a midpoint of the opposing longer sides  14 . 
         [0030]    Accordingly, by way of example, the container  10 , may have a length L of the ribs  40  measuring approximately 2.18 inch (55.3 mm), representing about 72.4% of the width C, measuring approximately 3.00 inch (76.4 mm). Similarly, the container  10  may also include a width D measuring approximately 1.65 inch (42.0 mm), a diagonal width G measuring approximately 3.04 inch (77.3 mm), a corner profile length CPL measuring approximately 9.52 inch (241.73 mm), a side profile length SPL measuring approximately 9.37 inch (237.90 mm), and a front profile length FPL measuring approximately 9.00 inch (228.74 mm). Thus, by way of example, using the above-described equations and dimensions, the preferred range of the height H for the ribs  40  generally may be approximately 0.49 inch (12.06 mm) (H MIN ) to 0.70 inch (17.31 mm) (H MAX ). The above and previously mentioned dimensions were taken from a typical 14 fl. oz. (414 cc) container. It is contemplated that comparable dimensions are attainable for containers of varying shapes and sizes. 
         [0031]    A label panel area  50  is defined at the sidewall portion  18 . The label panel area  50  may generally overlay the vacuum panels  30 . As is commonly known and understood by container manufacturers skilled in the art, a label may be applied to the sidewall portion  18  at the label panel area  50  using methods that are well known to those skilled in the art, including shrink-wrap labeling and adhesive methods. As applied, the label may extend around the entire body or be limited to a single side of the sidewall portion  18 . 
         [0032]    Upon filling, capping, sealing and cooling, as illustrated in  FIG. 4  in phantom, the underlying surface  34  of vacuum panels  30  is pulled radially inward, toward a central longitudinal axis  46  of the container  10 , displacing volume, as a result of vacuum forces. In this position, the underlying surface  34  of vacuum panels  30 , in cross section, illustrated in  FIG. 4  in phantom, forms an underlying surface  34 ′. The greater the inward radial movement between underlying surfaces  34  and  34 ′, the greater the achievable displacement of volume. The configuration of the sidewall portion  18 , vacuum panels  30  and ribs  40  allow the vacuum reaction to be absorbed in a controlled manner. Furthermore, the container  10  maintains its outwardly curved cross-sectional shape during vacuum absorption providing a desirable surface for applying a label. 
         [0033]    The amount of volume which vacuum panels  30  of the sidewall portion  18  displaces is also dependant on the projected surface area of vacuum panels  30  of the sidewall portion  18  as compared to the projected total surface area of the sidewall portion  18 . The generally rectangular configuration of the container  10  creates a large surface area on opposing longer sides  14  of the sidewall portion  18 , thereby promoting the use of large vacuum panels. This large surface area promotes the placing of large vacuum panels  30  in this area. Accordingly, as illustrated in  FIG. 2 , this results in vacuum panels  30  having a width E and a height F. In one example, for the container  10  having a nominal capacity of approximately 14 fl. oz. (414 cc), the width E is about 2.8 inch (71.12 mm) while the height F is about 3.74 inch (95.00 mm). 
         [0034]    Turning now to  FIG. 5 , the preform  28  used to mold the exemplary container  10  in a mold cavity  60  is shown. The plastic container  10  of the present invention is a blow molded, biaxially oriented container with a unitary construction from a single or multi-layer material. A well-known stretch-molding, heat-setting process for making the hot-fillable plastic container  10  generally involves the manufacture of the preform  28  of a polyester material, such as polyethylene terephthalate (PET), having a shape well known to those skilled in the art similar to a test-tube with a generally cylindrical cross section and a length typically approximately fifty percent (50%) that of the resultant container height. A machine (not illustrated) places the preform  28  heated to a temperature between approximately 190° F. to 250° F. (approximately 88° C. to 121° C.) into the mold cavity  60  having a shape similar to the plastic container  10 . 
         [0035]    The mold cavity  60  generally defines a shoulder forming region  62 , a sidewall forming region  64  and a base forming region  66 . The sidewall forming region  64  includes arcuate extension ribs  70  thereon corresponding to the ribs  40  formed on the resultant container  10 . The arcuate extension ribs  70  slope generally from a central portion  80  downward and away to ends (not specifically shown in  FIG. 5 ) corresponding to the ends  44  of the ribs  40 . The arcuate nature of the extension ribs  70  facilitate material flow from an area generally upstream (central portion  80 ) to an area generally downstream toward and beyond the ends of the ribs  70 . In this way, material is discouraged from being impeded or trapped at the ribs  70  during formation of the container  10 . As a result, an even material distribution is realized throughout the container  10 . 
         [0036]    During formation, the mold cavity  60  may be heated to a temperature between approximately 250° F. to 350° F. (approximately 121° C. to 177° C.). A stretch rod apparatus (not illustrated) stretches or extends the heated preform  28  within the mold cavity  60  to a length approximately that of the container  10  thereby molecularly orienting the polyester material in an axial direction generally corresponding with the central longitudinal axis  46  ( FIGS. 2 and 3 ) of the container  10 . 
         [0037]    While the stretch rod extends the preform  28 , air having a pressure between 300 PSI to 600 PSI (2.07 MPa to 4.14 MPa) assists in extending the preform  28  in the axial direction and in expanding the preform  28  in a circumferential or hoop direction thereby substantially conforming the polyester material to the shape of the mold cavity  60  and further molecularly orienting the polyester material in a direction generally perpendicular to the axial direction, thus establishing the biaxial molecular orientation of the polyester material in most of the container  10 . Typically, material within the finish  12  and a sub-portion of the base  20  are not substantially molecularly oriented. The pressurized air holds the mostly biaxial molecularly oriented polyester material against the mold cavity  60  for a period of approximately two (2) to five (5) seconds before removal of the container  10  from the mold cavity  60 . This process is known as heat setting and results in a heat-resistant container suitable for filling with a product at high temperatures. 
         [0038]    Alternatively, other manufacturing methods, such as for example, extrusion blow molding, one step injection stretch blow molding and injection blow molding, using other conventional materials including, for example, high density polyethylene, polypropylene, polyethylene naphthalate (PEN), a PET/PEN blend or copolymer, and various multilayer structures may be suitable for the manufacture of plastic container  10 . Those having ordinary skill in the art will readily know and understand plastic container manufacturing method alternatives. 
         [0039]    While the above description constitutes the present disclosure, it will be appreciated that the disclosure is susceptible to modification, variation and change without departing from the proper scope and fair meaning of the accompanying claims.