Abstract:
A method for forming a plastic container in which a heated end product is introduced into a heated preform to expand the preform into at least partial conform with the cavity surfaces of a mold, thereby forming a resultant container, of a first size, with a heated end product. The resultant container is then capped and shrunk to a second size, which is less than the first size. The shrinkage of the reluctant container is greater than the shrinkage of the end product thereby creating a positive pressure within the capped container.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. provisional patent application No. 61/794,775, filed on Mar. 15, 2013, the entire contents of which is herein incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    The present the invention relates to the molding of containers for liquid and viscous products. 
         [0004]    2. Description of Related Art 
         [0005]    Plastic containers are commonly used for the packaging of various products, including liquid products and viscous products. One of the most common forms of plastic container is the blow molded plastic container, which are often formed of polyester materials and, more specifically, of polyethylene terephthalate (PET). Blow molded plastic containers are generally formed by placing a heated preform into a blow mold and then inflating the preform with air until the preform contacts the interior surfaces of the mold cavity, which define the final shape of the desired container. Once the inflated preform has been positively held against the interior surfaces of the mold cavity for a length of time sufficient to “freeze” the plastic, the molded container is removed from the mold. 
         [0006]    Molded containers are then transported to a location where the container will be filled with the intended product and labeled. This post-molding process may include the packaging and shipping of the container to a different physical location or may involve the transferring of the container to another location in the manufacturing facility where these final steps are performed. 
         [0007]    In an effort to reduce costs and decrease materials ultimately entering into landfills, the amount of material in these containers has been reduced. As a consequence, the containers are less strong, and such non-carbonated containers can experience a collapsing of the container&#39;s sidewall when stacked because of the top-load applied thereto. 
         [0008]    One method to increase the top-load strength of a container is to dose the container with nitrogen immediately prior to final sealing and capping of the container. By introducing nitrogen into the headspace of the container, the content volume and internal pressure of the container is increased. The increased pressure displaces the liquid located below the headspace, which in turn results in an increase in the top-load strength of the container. 
         [0009]    Nitrogen dosing, however, is costly and therefore can negatively affect the economics of the category of the product in the container. For example, bottled water has lower profit margins than other bottled liquids, but water containers are one of the containers most impacted by light weighting due to the sheer number of water bottles that enter the product stream. Nitrogen dosing reduces that margin even further. 
         [0010]    A newer process for forming containers involves the use of the end product itself as the medium for molding the container. During this process, the container is simultaneously molded by and filled with the end product. As used herein, this molding technique is referred to as hydraulic molding. 
       SUMMARY 
       [0011]    In view of the above, the present invention provides a method for forming a plastic container in which there is a positive pressure within the container after the end product and container have been capped and cooled. According to the method, a plastic preform is heated and positioned within a mold having cavity surfaces defining a cavity shape generally corresponding to a desired shape of the container. The end product is heated to an elevated temperature above ambient temperature and injected into the heated preform. The injected end product at least partially causes the heated preformed to expand into contact with the cavity surfaces and to conform to the shape of the cavity, thereby forming a filled resultant container of a first size. The filled resultant container is capped, while generally at the first size, and thereafter shrunk to a second size, the second size being smaller than the first size. 
         [0012]    The shrinkage of the container and the shrinkage end product occur at different rates, with the shrinking of the end product being less than the shrinking of the container, thereby resulting in the final container having a positive internal pressure exhibiting good top load handling characteristics. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is diagrammatic illustration of a process, embodying the principles of the present invention, for forming a container filled with its end product. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    Referring now to the drawing, a process for forming a container filled with an end product in accordance with the principles of the present invention is illustrated therein. The process in accordance with the present invention involves the forming of a plastic container utilizing the end product as the medium that expands a heated preform within a mold cavity until the preform has been expanded into conformity with the surfaces of the mold cavity thereby defining a resultant container. As seen in the drawing, the preform is designated at  10 ; the resultant container designated at  12  and the final container designated at  14 . 
         [0015]    Generally, preforms  10  are provided to a molding system  16  at an in-feed station  18  by way of a rail or other transport mechanism (not shown). The preforms  10  are then individually placed onto a conveyor that transports the preforms  10  through a heating oven  20 . 
         [0016]    The oven  20  will typically include a plurality of heaters  22  spaced along the length of the oven  20 . The oven  20  itself may include two or more sub-zones, the purpose of which is to introduce a temperature profile into the preform  10  to facilitate the desired molding of the resultant container  12 . Such sub-zones may include a pre-heating zone, a main heating zone and a finishing heating zone. They may also include a greater or lesser number of sub- zones as well as other types of sub-zones. In the oven, the heaters  22  may be spaced not only along the length of the oven  20 , but also longitudinally relative to the length of the preforms  10 . In this manner, heaters  22  of different intensities may be utilized to define a temperature gradient over the length and or thickness of the preforms  10 . The actual heat profile employed will depend on the specific design of the preform  10 , including its shape and material composition, as well as the specific design of the final container  14 . From the heating oven  20 , the heated preforms are loaded into a mold assembly  24 , which may be one of many mold assemblies  24  and a molding machine  25 . 
         [0017]    The mold assembly  24  is typically comprised of two mold halves  26  that include interior surfaces  28  which cooperatively define a mold cavity  30  in the shape of the resultant container  12 . Once positioned within the mold cavity  30 , a nozzle  32  engages the finish of the preform  10  and/or portions of the mold assembly  24  and injects a heated end product  34  into the preform  10 . As used herein, the term end product  34  is intended to mean the product ultimately retained in the final container  14  and which is intended to be sold to the purchasing consumer. Accordingly, the end product  34  may be a beverage such as water, a sports/electrolyte replenishment drink, juice or another beverage, or the end product may be a viscous food product such as a condiment or applesauce. Obviously, the above examples of end products  34  are not intended to be an exhaustive list of the possible end products  34  with which the present invention may be employed, but rather are merely presented for illustrative purposes. 
         [0018]    The end product  34  is provided from a source  36  where the end product  34  may be heated and stored under pressure. Alternatively, the end product  34  may be heated and pressurized after being withdrawn from the source  36  and en route to the nozzle  32 . 
         [0019]    The method by which the final container  14  is directly formed and filled with the end product  34  is a one step, integrated process. By heating the preform  10  to a high temperature (about 90° to 150° C.), heating the mold halves (to about 70° to 300° F.) and by utilizing a heated (warm or hot) end product (about 50° to 205° F.) to simultaneously form and fill the resultant container  12 , a process has been developed where the resultant container  12  can be induced to shrink a desired amount after its initial formation. This process therefore results in the ability to create a positive pressure within the final container  14 , such as a water filled container, without utilizing nitrogen dosing. The process also results in the ability to control or mitigate the amount of vacuum formed within the final container  14 , such as the vacuum formed within a hot-fill container. Generally, the above is believed to be achieved as a result of the temperature of the side walls of the resultant container  12  and their controlled cooling via the latent heat of the heated end product  34 . While not completely understood at this time, the temperature of the side walls of the resultant container  12  and the controlled cooling via the latent heat of the end product  34  are believed to induce low crystallinity in the plastic material forming the resultant container  12  (a crystallinity of less than 25%), which in turn allows for post-forming shrinkage of the resultant container  12  and a reduction in the internal volume of the final container  14  relative to the resultant container  12 . Volume reductions of the resultant container  12  to the final container  14  may be achieved within the range of 0.05% to 4%. 
         [0020]    As seen in the figure, after simultaneous molding/filling of the resultant container  12 , the resultant container is capped and sealed. Thereafter, the capped resultant container  12  undergoes controlled cooling to produce the final container  14  with the end product  34  located therein. By controlling the temperature of the mold halves  26 , the temperature of the preform  10  and the temperature of the end product  34  during forming of the resultant container  12 , the resulting crystallinity of the plastic forming the resultant container  12  can be controlled. Thereafter, by controlling the ambient temperature about the capped resultant container  12 , the rate at which the capped resultant container  12  cools can also be controlled. Controlling the crystallinity of the resultant container  12  and the rate at which the resultant container  12  cools results in the ability to control the shrinkage experienced by the resultant container. Additionally, by controlling the initial amount end product  34  retained within the capped resultant container  12 , the final volumes of the end product  34  and the final container  14  can be tuned to one another to achieve a specific result for a specific end product  34 , which may be different depending on the specific end product  34 . 
         [0021]    For example, if the end product  34  is water, prior water filling temperatures of about 50° to 70° F. are used with an already formed container held at ambient or room temperature. No shrinkage of the container occurs and often nitrogen dosing is utilized to increase the top load strength of the container, particularly when the container is designed as a lightweight container. With the present invention, water is heated to a temperature in the range of 70° to 120° F. and utilized in molding the heated preform (heated to about 90° to 150° C.) within optionally heated molds (70° to 300° F.) and filling the resultant container  12 . This produces crystallinity in the resulting container that is less than 25%. Upon cooling, the resultant container  12  shrinks and its internal volume decreases. The volume of the water retained within the capped resultant container  12  will shrink less than the resultant container  12  itself This is also true of the volume of air in the headspace of the capped resultant container  12 . By controlling the ratios of the respective volume decreases of these components (keeping the volume decrease of the headspace plus the volume decrease of the water as less than the volume decrease of the resultant container  12 ), one can achieve a positive pressure within the final container  14 . This positive pressure allows the bottler to provide a lightweight final container  12  with better top-load strength in a neutral pressure container without having to resort to nitrogen dosing. 
         [0022]    When the end product is a hot-fill product, such as a fruit juice, the normal filling temperature of the end product into the already formed container may be as high as 205° F. Because of this high temperature, once the container is capped and the end product cools, the volume of the end product is significantly reduced, but the volume of the container is not. This results in a vacuum being formed within the container. To accommodate this formation of vacuum without subjecting the container to undesirable deformation, various physical structures must be provided in the container. 
         [0023]    With the present invention, tuning the shrinkage of the resultant container  12  with the shrinkage of the hot-filled end product  34  allows for the significant reduction in volume of the hot-filled end product  34  to be offset by the shrinkage and volume reduction of the resultant container  12  during cooling. As a result, the formation of vacuum within the capped final container  14  may be mitigated or controlled such that the final container  14  need not employ physical structures, such as vacuum panels, to handle otherwise high vacuum formation. 
         [0024]    The end result of the inducement of positive pressure and the mitigation of vacuum formation within the final container  14  is that the process enables a wider range of resin types, preform design and container design than is possible by current techniques. 
         [0025]    As a person skilled in the art will readily appreciate, the above description is meant as an illustration of implementation of the principles of this invention. This description is not intended to limit the scope or application of this invention in that the invention is susceptible to modification, variation and change, without departing from spirit of this invention, as defined in the following claims.