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[0001] The present invention relates to plastic containers, and more particularly to plastic containers capable of receiving positive internal pressure.
[0002] Consumers and manufacturers often prefer containers to glass containers for containing comestible products. The safety and appeal of plastic containers for such products have been enhanced by the development of hot-filling processes, in which a product is introduced into the container at an elevated temperature—typically 180 degrees to 190 degrees F.—and sealed.
[0003] Hot filling capabilities have spurred the development of related technologies to address problems of container thermal shrinkage and vacuum-induced deformation. To reduce shrinkage of polyethylene terephthalate (“PET”) containers upon exposure to hot-fill temperatures, for example, PET containers typically undergo a “head-set” process. Often, a PET container is head-set by blow molding at an elevated temperature (compared with those for conventional containers for non-hot-fill applications, such as carbonated soft drinks) for predetermined times, and held at predetermined temperatures for predetermined times. Further, heat set containers are typically formed from a plastic mix having higher intrinsic viscosity that that for bottles suitable only for non-hot-fill, PET applications, such as carbonated soft drinks.
[0004] Head-set PET containers are, thus, able to be filled at conventional hot-fill temperatures with acceptable shrinkage, such as approximately one percent, as for example taught in U.S. Pat. No. 4,863,046 (Collette). Further, heat-treating or heat-setting is taught in a number of patents, including, for example, U.S. Pat. No. 4,233,022 (Brady), U.S. Pat. No. 4,711,624 (Watson), and U.S. Pat. No. 4,219,526 (Mehnert). Each of the patents and applications referred to in the specification is incorporated herein by reference in its entirety.
[0005] Vacuum deformation of a hot-filled container occurs upon capping and cooling after filling with contents at an elevated temperature. Employing vacuum panels or others structure(s) that flex or deform in response to internal container negative pressure has been a popular approach to preventing container collapse upon vacuum deformation. Numerous approaches to vacuum panels in the container sidewalls have been developed. For example, U.S. Pat. Nos. 5,178,289, 5,092,475, and 5,054,632 teach stiffening portions or ribs to increase hoop stiffness and eliminate bulges while integral vacuum panels collapse inwardly.
[0006] Other containers include a pair of vacuum panels, each of which has an indentation or grip portion enabling the container to be gripped between a user's thumb and fingers. For example, U.S. Pat. No. 5,141,120 teaches a bottle having a hinge continuously surrounding a vacuum panel, which includes indentations for gripping. In response to cooling of the container contents, the hinge enables the entire vacuum panel in collapse inwardly. U.S. Pat. No. 5,141,121 similarly teaches a bottle having an outward bulge that inverts in response to cooling of the container contents. Further, bases for heat-set, hot-fillable containers have been developed which are capable of withstanding internal negative pressures common to hot-filling applications. Such bases typically have a continuous standing ring on which the container rests and a ribbed recess portion. For example, U.S. Pat. Nos. 5,503,283; 5,642,826; 4,993,567; 4,993,566; 4,598,831; and 4,108,324 disclose conventional base configurations.
[0007] Often, a continuous standing ring is commercially beneficial because it enables the plastic bottle to mimic the overall appearance of a glass bottle. Further, bases for heat-set, hot-fillable bottles typically have a standing ring that is substantially flat and horizontal in order to accommodate internal negative pressure. In order to promote flexing or deformation of the standing ring, and thereby relieve stress inherent upon vacuum deformation or diminish the magnitude of the corresponding stress risers, such standing rings typically are relatively large.
[0008] Because conventional hot-fillable containers are subjected to negative internal pressure, the ribs of conventional hot-fillable container bases generally are configured to control only inwardly directed forces and deformation. In this regard, the magnitude of inward deformation of a portion of the base typically is inconsequential or unimportant as long as the base is sufficiently strong. The ribs of such bases are generally spaced apart from the standing ring because stiffening proximate the standing ring is unimportant, and because ribs coupled to the standing ring may interfere with the beneficial deformation of the standing ring to compensate for the negative internal pressure. Thus, conventional ribs are typically spaced apart from the standing ring to enable the base to deflect inwardly such that the base may compensate for the negative internal pressure to supplement the vacuum panels. Moreover, if ribs were to contact the standing ring under such conditions, the standing ring would transition quickly from the inner portion that is stiffened by the ribs to the unstiffened portion, which may result in stress risers or otherwise be detrimental to the strength or other attribute of the base.
[0009] U.S. Pat. No. 5,251,424 (ZENGER), which is incorporated herein by reference in its entirety, discloses another approach to enabling a container to accommodate negative internal pressure from a hot-filling application. The '424 patent discloses introducing liquefied gas into the container upon hot-filling to provide a positive internal pressure. Thus, the internal positive pressure counteracts the negative pressure induced by the shrinkage of the contents upon cooling.
[0010] It is a goal of the present invention to provide a base, and corresponding container, that is suitable for a heat-set container that is capable of withstanding positive internal pressure.
[0011] A base is provided for a heat-set container that is suitable for withstanding internal pressurization without everting. The base includes a standing ring on which the container rests, a recess that extends inwardly and upwardly relative to the standing ring; and plural ribs extending substantially inwardly from the recess. Each one of the plural ribs includes a lower portion that includes a draft surface extending inwardly and upwardly from the standing ring.
[0012] Preferably, the draft surface is directly connected to the standing ring such that the draft surface extends down to a lowermost surface of the container. The angle of the draft surface preferably is approximately five degrees, although the present invention encompasses other ranges, as explained more fully herein. Various geometric relationships are employed to describe the configuration of bases, and it is understood that an independent claim may rely on any single one of the geometric relationships and/or structure described herein, as well as any combination thereof.
[0013] The draft surface deforms substantially downwardly in response to internal pressurization of the container, such as that created upon internal pressurization of the container by introducing liquefied gas upon filling. The container rests on the standing ring even after internal pressurization of the container. The ribs resist eversion of the recessed base surface such that the container is capable of withstanding internal positive pressure. A corresponding method is also provided.
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[0026] A heat-set container
[0027] Container upper portion
[0028] Base
[0029] Recess
[0030]
[0031] Each one of ribs
[0032] As best shown in
[0033] It is preferred that draft surface
[0034] The present invention encompasses any draft angle θ (theta), although some angles provide particular advantages. For example, a draft angleθ (theta) approximately equal to zero provides a substantially horizontal surface that may enhance plastic flow during blow molding and that is pushed downwardly relative to standing ring
[0035] It has also been determined that draft angle θ (theta) preferably is less than 45 degrees to facilitate plastic flow during blow molding. Further, angles of 40 degrees, 30 degrees, and 15 degrees have also been determined to be beneficial in this regard. The width of standing ring
[0036] The magnitude of the variables provided herein may apply to a container of any size, and especially to a container having a base that is consistent with a single serving container, such as about 10 to 16 ounces. Because base
[0037] The relationship of diameters A and C is helpful, among other things, to indicate a beneficial geometry of heel
[0038] A point E is defined at the juncture between draft surface
[0039] The depth of rib
[0040]
[0041] Alternatively, the sidewall of rib
[0042] The present invention is not limited to employing ribs having straight sidewalls. For illustration,
[0043] The present invention is not limited to bases with ribs having the angle ranges disclosed herein, but rather encompasses ribs of any configuration. The geometry of the ribs
[0044] Container
[0045] Upon introduction of the contents into container
[0046] Co-pending U.S. patent application Ser. No. ______ (Attorney Docket Number CC-3412), entitled “Method For Diminishing Delamination Of A Multilayer Plastic Container,” and co-pending U.S. patent application Ser. No. ______ (Attorney Docket Number CC-3449), entitled “Method For Extending The Effective Life Of An Oxygen Scavenger In A Container Wall,” describe nitrogen dosing techniques with which the container according to any aspect of the present invention may be employed. Further, U.S. Pat. Nos. 5,955,527; 5,639,815; 5,049,624; and/or 5,021,515 disclose an oxygen scavenging material that is suitable for use in bottles in hot-fillable and other containers, and that may be employed in container
[0047] Techniques for introducing liquefied gas into container
[0048] The internal positive pressure within container
[0049] Conventional bases often fail under such conditions either by complete eversion, which is a complete failure mode in which much of recess
[0050] Standing ring
[0051] Thus, the stiffening of standing ring
[0052] Upon pressurization of container
[0053] Preferably, draft surface
[0054] Persons familiar with preform and blow molding processes and technology in light of the present disclosure will be enabled to configure a container that employs the present invention(s), such as a container base in which its draft surface deforms as described above.
[0055] Further, a method is provided in which hot-fillable container base
[0056] The geometry of draft surface