Abstract:
A champagne type base for a molded polymeric container has an annular step immediately inside an annular contact ring. A push-up area is a central portion of the base immediately surrounding the container longitudinal axis. A transition region between the push-up area and the annular step provides for outstanding base stabilization. The transition region includes an upwardly arching surface extending between the annular step and the push-up area with a plurality of integrally molded, spaced apart, radially extending and downwardly projecting hollow ribs. Each of the ribs has a lower curved surface extending substantially continuously from the push-up area to the inner margin of the annular step.

Description:
BACKGROUND  
       [0001]     1. Technical Field  
         [0002]     The present invention is directed to molded plastic bottles having a champagne style bottom structure closing the container lower end. The phrase champagne style is used in reference to a base having an outside surface rotationally symmetric about a longitudinal axis of the bottle including a convex heel having an upper margin integrally formed with the lower end portion of the bottle sidewall, and a central concavity separated from the convex heel by a continuous standing ring that supports the bottle on any underlying planar surface.  
         [0003]     The present invention particularly relates to blow-molded containers of biaxially oriented thermoplastic materials such as polyethylene terephthalate that are designed to be filled with a hot liquid or semi-liquid product and hermetically sealed, generally referred to as thin-walled, hot-fill containers. The invention pertains to improvements in the design of such containers intended to achieve a container base that, despite the low weight of polymer used to form the container, resists the hydraulic and thermal shock of the entering hot product during a filing operation, yet when cooled, retains the desired container configuration despite the development of a partial vacuum within the container.  
         [0004]     2. General Background  
         [0005]     It is well recognized that the exposure of any plastic container to elevated temperatures tends to soften the plastic material and make the container less resistant to deformation. Thin-walled, hot-fill containers are typically used for packaging beverages and other food products that must be placed in the container while hot, the container being quickly capped to preserve the quality of the contents. During the filling process, the container is subjected to temperatures from the hot product on the order of about 85° C. The interior of the container base is also subjected to a hydraulic force from the fast flowing hot product as it enters the container. The combination of the thermal and hydraulic forces can easily cause deformation of the container base, which if insufficiently controlled can lead to failure during the immediately subsequent capping operation.  
         [0006]     The desire for stability of base configuration is not limited to hot-filled containers. Plastic containers used for beverages and other food products that are subjected to a post-capping pasteurization process are also subjected to considerable internal pressures that can lead to base deformation. During a typical pasteurization process, the contents of the container are heated, to a temperature that is within the general range of about 62° to 67° C. As the temperature rises during the pasteurization process, the internal pressure also rises, sometimes to a level of about 2 to 2½ times higher than what occurs during the packaging of non pasteurized beverages. Under these circumstances, the base of the molded plastic container is vulnerable to outward deformation due to the internal pressures, which can affect the continued serviceability of the container.  
         [0007]     Dimensional stability in the base region of molded plastic containers is most important, and particularly in the portions of the base region that are designed to support the container with respect to any underlying surface. In the case of a champagne type base, the dimensional stability of the areas adjacent to the annular support ring is particularly important. Thus, there is a continuing need for an improved molded plastic container having a base that exhibits outstanding dimensional stability under conditions of relatively high pressure and/or temperature and, in particular, that is designed to be particularly resistant to deformation in areas of the base that are designed to support the container with respect to any underlying surface.  
       BRIEF SUMMARY  
       [0008]     A molded polymeric container of the present invention satisfies such needs by providing a champagne type base having an annular contact ring for supporting the container with respect to an underlying surface. An annular step is situated immediately radially inward of the annular contact ring, the annular step having a substantially vertical outer wall and a substantially horizontal inner wall. A push-up area is provided at a central portion of the base that is immediately adjacent to and surrounds the longitudinal axis of the container. A transition region is interposed between the push-up area and the annular step that provides for outstanding base stabilization. The transition region includes an upwardly arching surface extending between the annular step and the push-up area with a plurality of integrally molded, spaced apart, radially extending and downwardly projecting hollow ribs. Each of the ribs has a lower curved surface extending substantially continuously from the push-up area to the inner margin of the annular step.  
         [0009]     The upwardly arching surface of the container base of the present invention can have a radius of curvature R S  that is greater than the radius of curvature of the rib lower surface R R . The radius of curvature R S  can be between about 1.5 R R  and 2.0 R R , and in a preferred embodiment the radius of curvature R S  can be about 1.7 R R . The ratio of the height to base width of each rib can be less than 1.0 down to at least about 0.7. Each of the ribs can have two sides diverging from the lower curved surface to an adjacent portion of the upwardly arching surface. The angle of divergence of the two sides can be between about 25° and about 35°. The contact ring can be defined by a horizontal planar annulus that can be several times the width of the horizontal inner wall of the annular step. The push-up area of the base can include a horizontal planar ring with a central depending nib aligned with the longitudinal axis of the container.  
         [0010]     The champagne type base of the present invention exhibits exceptionally stable geometry from manufacture through typical hot-fill conditions and subsequent storage despite the use of a modest amount of polymer. This base can be combined with a variety of side wall structures to provide a remarkably satisfactory container for hot-fill operations. The scope of the containers that can be constructed with a champagne type base of the present invention will become more apparent from the following description and accompanying drawings detailing an illustrative example of the present invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is a side elevation view of a molded polymeric container that can incorporate a champagne type base of the present invention.  
         [0012]      FIG. 2  is a bottom plan view of the container shown in  FIG. 1 .  
         [0013]      FIG. 3  is another bottom plan view of the same container.  
         [0014]      FIG. 4  is a sectional view taken along line A-A of  FIG. 2 .  
         [0015]      FIG. 5  is a sectional view taken along line B-B of  FIG. 3 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0016]     A container  10  of the present invention is shown in  FIG. 1  to be generally symmetric about a vertical axis Y, and has an open mouth  12  surrounded by a lip  14  intended to cooperate with a cap, not shown, to seal the container and contents. A cap-engaging finish  16  is located below the lip  14 , which is illustrated to have the form of a spiral thread  18 . The particular form of the finish  16  can be varied to include a range of thread styles or even be replaced with any number of non-threaded finishes designed to accept a crown type or other cap. A pilfer ring  20  can be located immediately below the finish  16  to engage a pilfer-indicating band of a cap. A support ring  22  can be provided below the pilfer ring  20  that facilitates handling of the container  10  as well as the handling of the parison or preform from which the container  10  is formed. A neck portion  24  is located immediately below the support ring.  
         [0017]     A shoulder portion  26  extends outward and downward from a lower margin of the neck portion  24 . The shoulder portion  26  can include an indented hoop ring  28  to provide added strength to the container  10 . A bumper ring  30  can be provided at a lower margin of the shoulder portion  26  that can define the maximum radius R of the container sidewall  32  measured from the axis Y. A lower margin of the bumper ring  30  can also define the upper margin  34  of a label receiving portion  36  that is intended to receive a separate label, not shown. The label can be a sheet of plastic, paper, or other similar material of suitable dimension that can surround the entire sidewall  32  of the container  10 . The label typically covers the container  10  from the upper margin  34  down to the lower margin  38  of the label receiving portion  36 . The label receiving portion  36  can also include one or more reinforcing hoop rings  40 . A plurality of vacuum compensation panels  42  can also be provided within the label receiving portion  36  of the sidewall  32 . A convex heel portion  44  extends downward from the container sidewall  32  to an annular contact ring  46  that supports the container  10  with respect to any underlying surface.  
         [0018]     The convex heel portion  44  and annular contact ring  46  form the outer margin of the base  48  of container  10  shown in FIGS.  2  to  5 . When viewed in a vertical section as shown in  FIG. 4 , the convex heel portion  44  is arcuate, generally having a vertical radius of curvature R H  that is less than R. The vertical radius of curvature R H  of the convex heel portion  44  can be about 0.5 R. The annular contact ring  46  can have a generally planar bottom surface  50  that extends from a point of merger  52  with the convex heel portion  44  inward to a small annular step  54 . The distance between the point of merger  52  and the annular step  54  can be about 0.15 R. The annular step  54  is formed by a substantially vertical, inwardly facing, outer wall  56  that extends upward to a substantially horizontal band  58 . The band  58  extends inwardly from the vertical outer wall  56  to an inner margin  60  of the annular step  54 .  
         [0019]     A transition region  62  extends radially inward from the inner margin  60  of the annular step  54 . The transition region  62  includes a plurality of upwardly arching segments  64  that are spaced from each other by a plurality of ribs  66 . When viewed in a vertical section as shown in  FIG. 4 , the upwardly arching segments  64  can be defined by a single radius of curvature R S  extending substantially continuously from the annular step inner margin  60  to a margin  72  that defines the outer perimeter of a central push-up area  74 . The radius of curvature R S  of the upwardly arching segments  64  can be about 0.5 R. Each of the ribs  66  has two sides  68  diverging from adjacent portions of the upwardly arching segments  64  to merge with a lower curved surface  70  of the rib  66 . The sides  68  of the ribs  66  diverge from each other at an angle θ that can be between about 25° and 35° as shown in  FIG. 5 . Due to the differences in curvature of the surfaces  64  and  70  the ribs achieve a maximum height H about half way between the annular step inner margin  60  and the central push-up area margin  72  as shown in  FIG. 4 . As seen in  FIG. 5 , each rib  66  has a base width W at the point of maximum height H, ratio of H/W being less than 1 and can be about 0.7. When viewed in a vertical section, as shown in  FIG. 4 , the lower curved surface  70  of the ribs  66  is defined by a radius of curvature R R  extending over a major portion of the rib lower surface  70 . The radius of curvature R S  of the upwardly arching segments  64  is generally greater than the radius of curvature R R  of the rib lower surfaces  70 . The radius of curvature R S  can be between about 1.5 and 2.0 times the radius of curvature R R . The radius of curvature R S  is preferably about 1.7 times the radius of curvature R R .  
         [0020]     Both the upwardly arching segments  64  and ribs  66  converge to an inner margin  72  that defines the outer perimeter of a central push-up area  74  immediately surrounding the longitudinal axis Y of the container  10 . The central push-up area  74  is generally horizontally planar, but can contain a spru artifact  76 . The central push-up area is maintained in position relative to the annular contact ring  46  by virtue of the stress created in the sides  68  of the ribs  66  in the event of any downward displacement of the central push-up area  74 . As a result, the champagne type base  48  exhibits exceptionally stable geometry from manufacture through typical hot-fill conditions.  
         [0021]     During the blow-molding of a container to have a base of the present invention, the plastic forming the base  48  more intimately contacts the mold interior and is thus subjected to better heat transfer from the plastic forming the base to the cooled mold. This more intimate contact is established because of the previously described special geometric relationships in the base  48  which reduce or eliminate any extreme angles and tapers that commonly are present in similar contemporary base designs. As a result, the plastic forming the base  48  of the present invention cools more completely during a molding cycle of a given length of time. The more thorough cooling results in less post molding creep of the base structure. The more thorough cooling may be used to increase the bottle production rate. The base  48  can be combined with a variety of side walls  32  to provide a remarkably satisfactory container for hot-fill operations.  
         [0022]     The foregoing detailed description of the embodiment shown in the Figures should be regarded as merely illustrative rather than limiting, and the following claims, including all equivalents, are intended to define the spirit and scope of this invention.