PLASTIC CONTAINER HAVING A DEEP-SET INVERTIBLE BASE AND RELATED METHODS

Abstract

In one embodiment, a method of processing a plastic container having a longitudinal axis is disclosed. The method includes: blow-molding a plastic container having an upper portion including a finish, a sidewall, a lower portion including a base defining a standing surface, and a substantially transversely-oriented pressure panel having an inner annular wall and a central push-up portion located in the base, wherein a base mold portion is displaced longitudinally with respect to first and second side mold portions to form the pressure panel set above the standing surface; introducing heated liquid contents into the plastic container with the pressure panel located in an outwardly-inclined position entirely between the standing surface and the upper portion; capping the plastic container; and, moving the pressure panel to an inwardly-inclined position entirely between the standing surface and the upper portion.

Claims

1. A method of processing a plastic container having a longitudinal axis, the method comprising: (a) blow-molding a plastic container having an upper portion including a finish, a sidewall, a lower portion including a base portion defining a standing surface, the base portion comprising: a plurality of footed or support portions having a downwardly inclined outer annular wall portion to form a discontinuous or footed contact surface for supporting the container, a substantially transversely-oriented pressure panel having an inner annular wall, the inner annular wall comprising radially displaced regions of lesser and greater angular extent, a central push-up portion located in the base portion, and a plurality of webs extending radially along the base portion away from the inner annular wall along a horizontal or transverse axis, substantially perpendicular to the longitudinal axis, each one of the webs having a surface that is radially displaced between the footed or support portions and longitudinally displaced upwardly from the footed contact surface, wherein a base mold portion is displaced longitudinally with respect to first and second side mold portions to form the pressure panel set above the standing surface; (b) introducing heated liquid contents into the plastic container with the pressure panel or plurality of webs located in an outwardly-inclined position entirely between the standing surface and the upper portion; (c) capping the plastic container; and (d) moving the pressure panel or plurality of webs to an inwardly-inclined position entirely between the standing surface and the upper portion.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The foregoing and other features and advantages of the invention will be apparent from the following, more particular description of a preferred embodiment of the invention, as illustrated in the accompanying drawings wherein like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements.

[0015] FIG. 1 is a perspective view of an exemplary embodiment of a plastic container according to the present invention, shown with a pressure panel in an initial, outwardly-inclined position;

[0016] FIG. 2 is a side, sectional view of the plastic container of FIG. 1, shown with the pressure panel in the initial, outwardly-inclined position;

[0017] FIG. 3 is a side, sectional view of the plastic container of FIG. 1, shown with the pressure panel in an inverted, inwardly-inclined position;

[0018] FIG. 4 is a bottom view of the plastic container of FIG. 1;

[0019] FIG. 5 is a perspective view of another exemplary embodiment of a plastic container according to the present invention, shown with the pressure panel in the initial, outwardly-inclined position;

[0020] FIG. 6 is a bottom view of the plastic container of FIG. 5;

[0021] FIG. 7 is a perspective view of a portion of a plastic container according to yet another exemplary embodiment of the present invention, shown with the pressure panel in an initial, outwardly-inclined position;

[0022] FIG. 8 is a bottom view of the plastic container of FIG. 7;

[0023] FIG. 9 is a side, sectional view of a portion of the plastic container of FIG. 7, shown with the pressure panel in the initial, outwardly-inclined position;

[0024] FIG. 10 is a side, sectional view of a portion of the plastic container of FIG. 7, shown with the pressure panel in the inverted, inwardly-inclined position;

[0025] FIGS. 11A-E schematically illustrate an exemplary method of processing a plastic container according to the present invention;

[0026] FIGS. 12A-C schematically illustrate an exemplary method of forming a plastic container according to the present invention;

[0027] FIG. 13 illustrates a lower portion of a container similar to that shown in FIG. 7 according to an alternate embodiment;

[0028] FIG. 14 illustrates a lower portion of the container of FIG. 13 similar to the view shown in FIG. 8 according to an alternate embodiment;

[0029] FIG. 15 is a bottom plan view of FIG. 8 with planes C-C and D-D indicated;

[0030] FIG. 16 is a side section view of FIG. 15 taken along C-C;

[0031] FIG. 17 is a side section view of FIG. 15 taken along D-D;

[0032] FIG. 18 is a schematic representation of a system for handling plastic containers;

[0033] FIG. 19 is a flowchart of a method of handling plastic containers;

[0034] FIG. 20A is a side view of the plastic container of FIG. 5;

[0035] FIGS. 20B and 20E are side sectional views of the plastic container of FIG. 6 through plane B-B; and,

[0036] FIGS. 20C and 20D are side sectional views of the plastic container of FIG. 6 through plane C-C.

DETAILED DESCRIPTION OF THE INVENTION

[0037] Embodiments of the invention are discussed in detail below. In describing embodiments, specific terminology is employed for the sake of clarity. However, the invention is not intended to be limited to the specific terminology so selected. While specific exemplary embodiments are discussed, it should be understood that this is done for illustration purposes only. A person skilled in the relevant art will recognize that other components and configurations can be used without departing from the spirit and scope of the invention. All references cited herein are incorporated by reference as if each had been individually incorporated.

[0038] As discussed above, to accommodate vacuum forces during cooling of the liquid contents within a hot-fill container, plastic containers have typically included a series of vacuum panels located around the sidewall and/or in the base portion. The vacuum panels deform inwardly, and the base deforms upwardly, under the influence of the vacuum forces. This configuration attempts to prevent unwanted distortion elsewhere in the container. However, the container is still subjected to internal vacuum forces. The sidewalls and base merely provide a suitably resistant structure against that force. Additionally, the vacuum panels in the sidewall can undesirably detract from the appearance and feel of the container, and limit the design possibilities for the container.

[0039] Typically at a bottling plant, the containers are filled with a hot liquid and then capped before being subjected to a cold water spray, resulting in the formation of a vacuum within the container. The container structure needs to be able to cope with this vacuum force. U.S. patent application Ser. No. 10/529,198, filed on Dec. 15, 2005, the entire content of which is incorporated herein by reference, discloses hot-fill containers that provide for the substantial removal or substantial negation of the vacuum pressure within the containers. The disclosed containers include a transversely-oriented pressure panel located in the container base. The pressure panel is movable between an initial, outwardly inclined position, and an inverted, inwardly inclined position, in order to reduce the volume of the container and accommodate for vacuum forces within the container, The present invention relates to additional embodiments of this concept in which the pressure panel is set deeply into the base of the container, such that no portion of the pressure panel extends beyond the standing ring, regardless of whether the pressure panel is in the initial position or in the inverted position. This configuration can allow the container to be supported by the standing ring regardless of whether the pressure panel is in the initial position or the inverted position.

[0040] Referring to FIGS. 1-4, an exemplary embodiment of a plastic container 10 according to the present invention is shown. The container 10 can include an upper portion 12 including a finish 14 that defines an opening into the interior of the container 10. As shown, the finish 14 can include threads 16 or other structures adapted to secure a closure (not shown) onto the container 10. The container 10 can also include a lower portion 18 having a base 20, and a sidewall 22 extending between the upper portion 12 and the lower portion 18. The base 20 can define a standing surface 21 that is substantially flat and adapted to support the container 10 in a substantially upright position (e.g., with longitudinal axis A substantially perpendicular to the surface on which container 10 is resting).

[0041] In the exemplary embodiment shown, the sidewall 22 is substantially tubular and has a substantially circular transverse cross-sectional shape. Alternative cross-sectional shapes can include, for example, an oval transverse cross-section; a substantially square transverse cross-section; other substantially polygonal transverse cross-sectional shapes such as triangular, pentagonal, etc.; or combinations of curved and arced shapes with linear shapes. As will be understood by one of ordinary skill in the art, when the container 10 has a substantially polygonal transverse cross-sectional shape, the corners of the polygon are typically rounded or chamfered. Although the container 10 is shown as having reinforcing ribs or rings 23 in the sidewall 22 to resist paneling, dents and other unwanted deformation of the sidewall, particularly under vacuum force, other embodiments are possible where the sidewall 22 is substantially devoid of such features (e.g., the sidewall 22 can be smooth like that of a conventional glass container).

[0042] As best seen in FIG. 4, a portion of the base 20 can include a plurality of reinforcing ribs 24, however other embodiments with or without the reinforcing ribs 24 are possible.

[0043] The lower portion 18 of the container 10, and particularly the base 20, can include a substantially transversely-oriented pressure panel 26. The pressure panel 26 can be moved between an outwardly-inclined position (shown in FIGS. 1 and 2) and an inwardly-inclined position (shown in FIG. 3) in order to reduce the internal volume of the container 10 and compensate for any vacuum forces created within the container, for example, during the filling process. For example, the pressure panel 26 may substantially remove the internal vacuum that develops within the container 10 during a hot-fill process once the container 10 has been hot-filled, capped, and cooled.

[0044] As best seen in the sectional views of FIGS. 2 and 3, the pressure panel 26 can be deeply set into the container 10 in order to facilitate standing of the container 10 on its standing surface 21 regardless of whether the pressure panel 26 is located in the outwardly-inclined position (FIG. 2) or the inwardly-inclined position (FIG. 3). In other words, the entire pressure panel 26 structure can be located between the plane P of the standing surface 21 and the upper portion 12 of the container 10 when the pressure panel 26 is in the outwardly-inclined position (FIG. 2) and also when the pressure panel 26 is in the inwardly-inclined position (FIG. 3).

[0045] According to the exemplary embodiment shown in FIGS. 1-4, the lower portion 18 of the container 10 includes a concave outer wall portion 30 that extends from the lower end of the sidewall 22 to the standing surface 21. The standing surface may be a ring or annular portion as shown in FIG. 1, or may be discontinuous as shown in FIG. 5. The pressure panel 26 is deeply set into the lower portion 18 of the container 10 via an inner wall 32 that extends from the standing surface 21 to the pressure panel 26. The inner wall may therefore comprise an instep or hollow recessed portion between the pressure panel 26 and the standing surface 21. In the exemplary embodiment shown, the inner wall 32 is parallel or nearly parallel to the longitudinal axis A of the container 10, and provides the recessed portion with a concave annular ring shape; however, other configurations and/or inclinations of the inner wall 32 are possible that are not concave annular ring structures. In addition, one of ordinary skill in the art will know that other configurations besides the inner wall 32 may be implemented to set the pressure panel 26 deeply into the lower portion 18. An annular, recessed channel 34 can be provided in the inner wall 32 adjacent the standing surface 21 to provide a further recessed concave ring structure in the inner wall 32. In the exemplary embodiment shown, the annular recessed channel 34 has a substantially square or annular cross-section, however, other shapes are possible for the channel to be inwardly stepped. Channel 34 can act as a rib member and reinforce the foot portion or standing surface 21 and/or facilitate stacking of multiple containers on top of one another, depending on the shape and size of the finish 14 and/or closure.

[0046] In the exemplary embodiment of FIGS. 1-4, the standing surface 21, inner wall 32, and outer wall 30 are substantially continuous about the circumference of the container 10 (see FIG. 4). However, as shown in the alternative embodiment of FIGS. 5 and 6 and FIGS. 20A-E, the container 10′ can have a standing surface 21′, inner wall 32′, and outer wall 30′ that are discontinuous.

[0047] The pressure panel or inner annular wall 240 has an inner periphery 244 and an outer periphery 242, and is set, with respect to the longitudinal axis and the opening into the container, at an outward or downward angle prior to filling with a heated liquid. The outer annular wall includes support or foot portions 230 and the inner wall portions 32′ extend from the standing surfaces 21′ to the inner annular wall or pressure panel 240. Radial webs or straps 246 are uniformly spaced apart and separate each support 230. The web surface is closer to the finish than the footed contact surface, or expressed another way, the webs 246 are longitudinally displaced above the footed contact surface 21′. In addition, each support 230 has a larger arcuate extent than that of each radial web 246. The inner annular wall 240 extends within the concave outer annular wall 30′. The outer periphery 242 of the inner annular wall or pressure panel 240 merges with the inner wall 32′ of each of the supports 230, and with the plurality of spaced-apart, horizontally disposed, radial webs or straps 246 located adjacent the outer periphery 232 of the standing surface of the base. Each of the webs 246 extends between the supports 230 and connects to the container sidewall 22 in the lower portion 18 at an elevation above the horizontal plane “P” extending through the standing surface 21 to form radius 202 such that web surface 246 is visible from a side of the container. Preferably the inner annular wall 240 and the central dimple or push up 248 merge via an annular hinge 250 at the foot of the push-up, comprising radius 251.

[0048] In order to facilitate movement (e.g., folding) of the pressure panel 26 between the outwardly-inclined position of FIG. 2 and the inwardly-inclined position of FIG. 3, pressure panel 26 can include a decoupling or hinge structure 36 that is located between the inner wall 32 and the pressure panel 26. In the exemplary embodiment shown, the hinge structure 36 comprises a substantially flat, non-ribbed region, that is susceptible to folding, however, other configurations of the hinge structure, such as a crease, are possible.

[0049] Referring now particularly to FIG. 4, the pressure panel 26 can comprise an initiator portion 40 and a control portion 42. Both the initiator portion 40 and control portion 42 can comprise part of the pressure panel 26 that folds when the pressure panel 26 is moved from its initial position in FIG. 2 to its inverted position in FIG. 3. The initiator portion 40 can be adapted to move or fold before the rest of the pressure panel 26 (e.g., before the control portion 42). In the exemplary embodiment shown, the control portion 42 is at a steeper angle to the standing plane P than the initiator portion 40, thereby resisting expansion of the pressure panel from the inverted state (FIG. 3) to the initial state (FIG. 2), for example, if the container 10 were accidentally dropped.

[0050] In order to maximize the amount of vacuum compensation from the pressure panel 26, it is preferable for at least the control portion 42 to have a steep angle of inclination with respect to the standing plane P. As shown in FIG. 2, the control portion 42 can be at a first angle alpha with respect to the standing plane P. According to one exemplary embodiment, the first angle alpha can be at least 10 degrees, and preferably is between about 30 degrees and about 45 degrees. According to this embodiment, the initiator portion 1 can be at a second angle (beta with respect to standing plane P, that is at least 10 degrees less than the first angle alpha.

[0051] When the pressure panel is inverted from the outward state (FIG. 2) to the inward state (FIG. 3), it can undergo an angular change that is approximately equal to its angle of inclination. For example, if the control portion 42 is initially set at an angle alpha of about 10 degrees, it will provide an angular change of approximately 20 degrees. At such a low angle of inclination, however, it can be difficult to provide an adequate amount of vacuum compensation in a hot-filled container. Therefore it is preferable to provide the initiator portion 40 and control portion 42 with steeper angles. For example, with the control portion set at an angle alpha of about 35 degrees, the pressure panel 26 will undergo an angular change of about 70 degrees upon inversion. According to this exemplary embodiment, the initiator portion 40 can be set at an angle beta of about 20 degrees.

[0052] Referring to FIGS. 13-14, a base portion of a container according to an alternative embodiment is shown, wherein the control portion of the pressure panel comprises a substantially continuous conical area extending around the base. According to this embodiment, the initiator portion 140 and the control portion 142 are set at a common angle, such that they form a substantially uniform pressure panel 126. However, initiator portion 140 may still be configured to provide the least amount of resistance to inversion of pressure panel 126, such that it still provides an initial area of folding or inversion. For example, the initiator portion 140 may have a smaller material thickness than the control portion 142. According to the embodiment shown in FIGS. 13-14, initiator portion 140 causes the pressure panel 126 to begin inversion at its region of widest diameter, near the hinge structure 136.

[0053] Additional structures may be added to the pressure panel 126 in order to add further control over the inversion process. For example, the pressure panel 126 may be divided into fluted regions, as shown in FIGS. 7 and 8. As shown, the fluted regions 145 can be outwardly convex, resulting in inward creases 127 between each outward flute, and evenly distributed around the container's longitudinal axis to create alternating regions of greater and lesser angular inclination. Referring to FIGS. 15-17 in particular, panel portions 145 that are convex outwardly, and evenly distributed around the central axis create regions of greater angular set 19 and regions of lesser angular set 18. The angular set in the midline of each of the plurality of flutes 145 has a lesser angular set gamma than the angular set delta in the plurality of creases 18 created between each fluted panel portion 145. This may provide for greater control over inversion of the panel. Such geometry provides increased resistance to reversion of the panel, and a more even distribution of forces when in the inverted position. This type of geometry can provide increased resistance against the panel returning from the inward position (FIG. 10) to the outward position (FIG. 9), for example, if the container were dropped. The fluted configuration can also provide more even distribution of forces on the pressure panel 126. According to an alternative embodiment, the flutes can be inwardly concave. Inwardly directed flutes offer less resistance to initial inverting forces, coupled with increased resistance to reverting back to the original, outward position. In this way they behave in much the same manner as ribs to prevent the panel being forced back out to the outwardly inclined position, but allow for hinge movement from the first outwardly inclined position to the inwardly inclined position. Such inwardly or outwardly directed flutes or projections function as ribs to increase the force required to invert the panel. Further details regarding the pressure panel and fluting are disclosed in co-pending U.S. patent application Ser. No. 10/529,198, filed on Dec. 15, 2005, the entire content of which is incorporated herein by reference.

[0054] Referring to FIGS. 11A-11E, an exemplary method of processing a plastic container according to the present invention is shown. Prior to processing, the container 10 may be formed (e g., blow molded) with the pressure panel 26 in the inwardly-inclined position. According to this embodiment, a force can be applied to the pressure panel 26 in order to move the pressure panel 26 into the outwardly-inclined position. For example, as shown in FIGS. 11A and 11B, a first mechanical pusher 50 can be introduced through the opening in the container finish 14 and forced downwardly on the pressure panel 26 in order to move it to the outwardly-inclined position (shown in FIG. 11C). One of ordinary skill in the art will know that other types of mechanical or other forces can alternatively be used to move the pressure panel 26 into the outwardly-inclined position. Alternatively, the container 10 can be initially formed with the pressure panel 26 located in the outwardly-inclined position.

[0055] Referring to FIG. 11C, the container 10 can be filled with liquid contents when the pressure panel 26 is located in the outwardly-inclined position. Particularly, the container 10 can be “hot-filled” with the liquid contents at an elevated temperature, for example, 185° C. As shown in FIG. 11C, the liquid contents can be introduced into the container 10 via a filling nozzle 52 inserted through the opening in the container finish 10, although one of ordinary skill in the art will know that any number of known filling devices and techniques can be implemented. According to an alternative embodiment, the first mechanical pusher 50 and the filling nozzle 52 can be the same instrument.

[0056] Referring to FIG. 11D, once the container 10 has been filled to the desired level, the filling nozzle 52 can be removed, and a cap 54 can be applied to the container finish 14. Any number of capping techniques and devices known in the art can be used to apply the cap 54 to the container finish 14. Next the container 10 can be cooled, for example, by spraying the container 10 with cool water, or alternatively, by leaving the container 10 in ambient conditions for a sufficient amount of time. As the container 10 and its contents cool, the contents tend to contract. This volumetric change inside the sealed container 10 can create a vacuum force within the container 10.

[0057] In order to alleviate all or a portion of the vacuum forces within the container 10, the pressure panel 26 can be moved from the outwardly-inclined position of FIG. 11D to the inwardly-inclined position of FIG. 11E. For example, following filling, capping, and cooling of the container 10, an external force can be applied to the pressure panel 26, for example, by a second mechanical pusher 56, as shown in FIG. 11D. Alternatively, the pressure panel 26 can be moved by the creation of relative movement of the container 10 relative to a punch or similar apparatus, in order to force the pressure panel 26 into the inwardly-inclined position. Alternatively, the pressure panel 26 can invert to the inwardly-inclined position under the internal vacuum forces within the sealed container 10. For example, all or a portion of the pressure panel 26 (e.g., the initiator portion) can be made flexible enough to cause the pressure panel 26 to invert under the internal vacuum forces.

[0058] The inversion of the pressure panel 26 from the outwardly-inclined position to the inwardly-inclined position reduces the internal volume of the container 10, and thereby increases the pressure inside the sealed container 10. This can alleviate any vacuum created within the container 10 due to the hot-fill process. This can also remedy any deformation of the container 10 that was caused as a result of the internal vacuum.

[0059] As shown in FIGS. 11A-E, the entire pressure panel 26 is above the plane P of the standing surface 21 (see FIG. 11C) of the container 10. As a result of this configuration, the containers 10 according to the present invention can be stored, transported, and capped/filled, etc., all while standing on the standing surface 21. This can eliminate the need for any adapters or other devices to stabilize the container 10 in the upright position. This can also make the containers 10 of the present invention more readily adapted for use with conventional, existing container transports, capping and filling stations, and storage facilities.

[0060] Referring to FIGS. 12A-C, an exemplary method of blow molding a plastic container according to the present invention is shown. Referring to FIG. 12A, the method includes enclosing a softened polymer material (such as PET, PEN, PP, blends thereof, and other suitable materials known in the art) within a blow mold. In the exemplary embodiment shown, the polymer material comprises a plastic container preform 60. However, according to an alternative embodiment, the polymer material can comprise a tube of extruded polymer material, for example, as used in the known process of “extrusion blow molding.”

[0061] The blow mold can comprise two or more side mold portions 62, 64, and a base mold portion 66. The side mold portions 62, 64 can move from an open position (not shown) in which the side mold portions are separated from one another, to a closed position, shown in FIGS. 12A-C. In the closed position, shown, the side mold portions 62, 64 define a mold cavity 68 having an open bottom. The mold cavity 68 corresponds to the shape of a plastic container to be molded therein. The base mold portion 66 is located in the open bottom region of the mold cavity 68 and is movable with respect to the side mold portions 62, 64 in the vertical direction (as viewed in FIGS. 12A-C) between the retracted position shown in FIGS. 12A and 12B, and the extended position shown in FIG. 12C. Mechanical, pneumatic, hydraulic, or other means known in the art can be implemented to move the base mold portion 66 between the retracted and extended positions.

[0062] A stretch rod 70 can be inserted into the neck portion of the softened preform 60, and can be used to stretch or elongate the preform 60. Air or another medium can be expelled from the stretch rod 70 or other device to at least partially inflate the preform 60 into conformity with the mold cavity 68 in what is commonly known in the art of stretch blow molding as a “pre-blow” step. Preferably, the preform 60 is inflated into substantially complete conformity with the mold cavity 68 while the base mold portion 66 is in the retracted position, as shown in FIG. 12B. In order to stretch blow mold the container from the partially inflated volume, it is commonly known in the art of stretch blow molding to increase the pressure during the final blowing step in order to force the plastic material into complete conformity with the mold cavity 68. This can eliminate the need for the polymer material to expand deeply into tight corners, narrow spaces, etc., that are associated with the deeply-set pressure panel of the present invention. This can avoid resultant thin or weak spots in the formed container.

[0063] While the polymer material is still in a softened state, the base mold portion 66 can be displaced upwardly into the mold cavity 68 to form a transverse pressure panel deeply set within the base portion of the plastic container (see, for example, the base 20 and pressure panel 26 of FIGS. 1 -4). Air can continue to be expelled at blowing pressure into the stretch rod in the blow mold cavity during displacement of the base mold portion 66 to the extended position, or alternatively, the supply of air can be turned off. Referring to FIGS. 1-4, by “deeply set” it is meant that the pressure panel 26 is located entirely between the standing plane P and the upper portion 12 of the container when the pressure panel 26 is in the outwardly-inclined position (FIG. 2) and when it is in the inwardly-inclined position (FIG. 3). In the exemplary embodiment of FIGS. 12A-C, the base mold portion 66 moves substantially along the longitudinal axis of the plastic container being formed in the mold cavity 68, however, other orientations are possible.

[0064] Once the plastic container has been formed in the mold cavity 68, the base mold portion 66 can return to the retracted position, and the side mold portions 62, 64 can separate to release the formed container.

[0065] By utilizing the blow molding method of the present invention, it is possible to initially form the general container shape with a generally flat bottom portion, and then deflect the bottom upwardly at orientation temperature. As a result, the container base and deeply-set pressure panel can be of improved material thickness and uniformity. In addition, the base and pressure panel can be multi-axially stretch oriented to provide increased strength without the attendant thinness or weakness at the heel portion of the bottle.

[0066] The base of the plastic container according to the present invention is preferably crystallized to some extent. Some degree of crystallinity and/or biaxial orientation can be achieved normally during the blow molding process. However, crystallization can be promoted through heat setting of the container. For example, the walls and base of the mold can be held at an elevated temperature to promote crystallization. When the container is heat set at a temperature of about 180° F., the container sidewalls, base, pressure panel, etc., can be typically crystallized to about 20%. This degree of crystallinity is typical for a blow molding process and does not represent a significant amount of heat setting or increased crystallinity or orientation, as compared with a typically prepared container. However, the properties of the base and pressure panel of the present invention can be advantageously enhanced by heat setting the container, and particularly the base and pressure panel, at ever higher temperatures. Such temperatures can be, for example, greater than 250° F. and can be 325° F. or even higher. When these elevated heat set temperatures are utilized, crystallinity can be increased to greater than 20% or 25% or more. One drawback of increasing crystallinity and biaxial orientation in a plastic container is that this process introduces opacity into the normally clear material. However, unlike bases in prior art containers, which can require a crystallinity of 30% or more, utilizing crystallinities of as low as 22-25% with a base structure according to the present invention can achieve significant structural integrity, while maintaining the substantial clarity of a base that is preferred by manufacturers, packagers and consumers.

[0067] U.S. Pat. Nos. 4,465,199; 3,949,033; 4,378,328; and 5,004,109, all of which are incorporated herein by reference, disclose further details relating to blow molding methods utilizing displaceable mold portions. The methods disclosed in these references can also be implemented to form plastic containers according to the present invention. According to an alternative embodiment of the invention, the plastic container can be removed from the blow mold prior to forming the deeply-set pressure panel. Outside of the mold, the pressure-panel and related structure(s) can be formed in the base of the plastic container using a mandrel or similar device. U.S. Pat. No. 4,117,062, the entire content of which is incorporated herein by reference, provides further details on this type of post-mold processing.

[0068] The embodiments illustrated and discussed in this specification are intended only to teach those skilled in the art the best way known to the inventors to make and use the invention. Nothing in this specification should be considered as limiting the scope of the present invention. All examples presented are representative and non-limiting. The above-described embodiments of the invention may be modified or varied, without departing from the invention, as appreciated by those skilled in the art in light of the above teachings. It is therefore to be understood that, within the scope of the claims and their equivalents, the invention may be practiced otherwise than as specifically described.