Abstract:
A container with an improved container side wall is disclosed. The improved container side wall including a top end and a bottom end, an open top and a bottom wall. The top of the container merges with the top end of the side wall and the bottom wall merges with and closes the bottom end of the side wall. The side wall also includes a plurality of ribs which protrude radially outward from an inside surface of the side wall and which are integrally displaced upon the inside surface of the side wall. These ribs cause the inside surface of the container side wall to form a varying thickness. In this manner, an improved container side wall is provided that increases the resistance of the side wall to deformation caused by internal/external positive or negative pressures without significantly increasing the overall amount of material needed to manufacturer the container. The container side wall may assume a cylindrical, rectangle, oval, or square geometry.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates generally to hollow plastic containers and, more particularly, to an injection stretch-blow-molded plastic container with an improved side wall design.  
           [0002]    Plastic containers for use in storing and transporting a variety of materials are well known in the art and hundreds of millions of plastic containers are used each year to distribute goods to consumers. The large number of plastic containers being shipped to consumers has resulted in increased competition and the need for plastic containers capable of being shipped in large quantities. Thus, the plastic container industry has been faced with the challenge of producing cheaper plastic containers that are structurally sound and that are capable of meeting the filling line, distribution system and consumer performance requirements. In order to be competitive within the container industry, manufacturers have continued to reduce the cost of plastic containers. Many manufacturers have determined that the best way to accomplish that goal is by using thinner walls and therefore, less material per container. However, since the thickness of the container walls directly affects the structural integrity of the container, manufacturers are limited in their ability to reduce the thickness of the container walls.  
           [0003]    There are various factors that need to be considered and which ultimately define the limits on any variance in the thickness of container side walls. For example, in addition to the actual load conditions that the container is subjected to and the physical properties of the material, the production process must also be considered in combination with the performance requirements.  
           [0004]    While it is common for the container wall thickness to vary in plastic articles, the magnitude of the variations is different dependent upon the process and the size of the article. Injection molding generally produces containers with the least amount of dimensional variation in the side walls. However, since injection stretch blow molded containers consist of generally uniform, but thin side walls, it is not uncommon to observe variations in the side wall thickness of plus or minus 30% of the nominal or average side wall thickness. For example, an 18 oz. cylindrical stock container for hot or vacuum filled products typically requires an average wall thickness of 0.025 in. Thus, the side wall thickness can vary from 0.0175 in. to 0.0325 in. This variance in the side wall thickness may result from either a one step or two step multi-cavity injection stretch blow process.  
           [0005]    To achieve the goal of producing containers with the requisite degree of structural integrity, while also minimizing the amount of material included therein, manufacturers have designed containers with different shapes and structures. These different designs allow manufacturers to produce stronger plastic containers. Typically, the design of the uniform side wall is altered in order to incorporate different shapes that, through geometry alone, will increase the strength of the container with respect to certain load conditions. These geometric changes may vary in shape, location and design to meet the actual load conditions that are to be addressed, such as internal or external pressures versus direct mechanical axial loads, also commonly referred to as top load in the container industry.  
           [0006]    For example, U.S. Pat. No. 4,892,205 to Powers et al., which is incorporated herein by reference in its entirety, describes an improved plastic container comprised of a base that includes a plurality of concentric ribs on the inner surface of the base. The concentric ribs are of decreasing thickness as they move radially outward from the center of the base. A concentric ribbed preform is used to manufacture that container. This improved plastic container design was intended to provide a container with improved base strength.  
           [0007]    While the container disclosed in the &#39;205 patent provides a stronger and more economical container base, it does not allow a manufacturer to reduce the thickness of the container side wall, which makes up the majority of the plastic container while also increasing the strength of the side wall. For improving side wall strength in containers for certain load conditions, without significantly increasing the thickness of the side wall, it is known to form beads or other similar shapes on the container side wall. This method, however, suffers the disadvantage of causing the side walls to form uneven inner and outer surfaces which, in turn, creates unacceptable problems with regard to removal of the product from the container and the application/aesthetics of labeling.  
         SUMMARY OF THE INVENTION  
         [0008]    To overcome the disadvantages noted above, the present invention is directed to a container with an improved container side wall. More specifically, the improved container in a preferred embodiment includes a side wall with a top end and a bottom end, an open top and a bottom wall. The open top merges with the top end of the side wall and the bottom wall merges with and closes the bottom end of the side wall. The side wall also includes a plurality of inwardly protruding ribs integrally disposed upon the interior surface of the side wall between thinner intermediate side wall sections. These ribs and intermediate side wall sections cause the side wall to exhibit a generally smooth exterior surface, while also producing a side wall cross section of a varying thickness. In this manner, an improved container side wall is provided that increases the strength of the side wall with respect to internal and external pressures, without substantially increasing the overall amount of material needed to manufacturer the container. Therefore, an objective of the invention is to generally redistribute the material, which defines the side wall, to localized thicker sections, or ribs, interspersed between localized thinner sections, or intermediate side wall sections.  
           [0009]    A better understanding of the objects, advantages, features, properties and relationships of the invention will be obtained from the following detailed description and accompanying drawings which set forth an illustrative embodiment and which are indicative of the various ways in which the principles of the invention may be employed. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    For a better understanding of the invention, reference may be had to a preferred embodiment shown in the following drawings in which:  
         [0011]    [0011]FIG. 1 shows a side view of an exemplary container embodying the present invention;  
         [0012]    [0012]FIG. 2 shows a sectional view of the container shown in FIG. 1;  
         [0013]    [0013]FIG. 3 shows a side view of an exemplary injection molded preform for use in forming a blow molded plastic container which embodies the present invention;  
         [0014]    [0014]FIG. 4 shows a sectional view of the preform illustrated in FIG. 3, along line AA;  
         [0015]    [0015]FIG. 5 shows a sectional view of an injection mold, a preform and an injection core for producing the preform shown in FIG. 3; and  
         [0016]    FIGS.  6  shows an sectional view of the injection core and the preform shown in FIG. 5. 
     
    
     DETAILED DESCRIPTION  
       [0017]    Turning now to the figures, wherein like reference numerals refer to like elements, there is illustrated an improved container  20  comprised of a container side wall of varying thickness, which is capable of producing a container  20  with a stronger side wall. The improved side wall strength is particularly advantageous as it allows the container  20  to meet the need for manufacturers of containers to reduce the thickness of container side walls without negatively affecting the structural integrity of the container  20 . As will be understood by those of ordinary skill in the art, the container  20  is manufactured using standard injection blow-molding techniques.  
         [0018]    As shown in FIG. 1, the container  20  includes an open top  22  that merges with a top end  24   a  of a cylindrical side wall  24 , and a bottom wall  26  that merges with and closes a bottom end  24   b  of the side wall  24 . The top  22  of the container  20  may also include threads  28  on the outside to engage a container cap or similar means for releasably closing the open top  22  of the container  20 .  
         [0019]    For increasing the strength of the container side wall  24 , the side wall  24  includes a plurality of one or more ribs  30  that protrude radially outward from the inside surface of the container side wall  24 . These ribs  30  may be of a thickness generally between 20% and 150% greater than the thickness of the intermediate side wall sections  31 . The container side wall  24  also includes intermediate side wall sections  31  where the side wall  24  thickness is deliberately thinner than the average thickness of the side wall  24 . Thus, the thickness of the container side wall  24  varies beyond general variations associated with the production of containers.  
         [0020]    By varying the thickness of the side wall  24  in this deliberate manner, a side wall  24  is created that provides increased mechanical strength without a significant increase in the total amount of material that is used to form the side wall  24 . Moreover, by deliberately forming the ribs  30  on the inside surface of the container side wall  24 , this approach alleviates the labeling and product removal problems associated with containers that include bead designs and similar geometric variations in the shape of the container.  
         [0021]    While the overall material usage for the side wall  24  may increase slightly in cases where the container  20  size, or conditions associated with the process for forming the container  20 , limit the minimum thickness which can be utilized for the intermediate side wall sections  31 , methods will be described below where the increase in wall thickness of the improved container  20  will use significantly less material than would normally be used to produce an equivalent increase in strength in a container having a uniform side wall thickness.  
         [0022]    For producing a container  20  with a side wall  24  of varying thickness, a preform, or parison,  40  is provided that includes an open top  42  formed at a top end  44   a  of a side wall  44 , and a bottom wall  46  that merges with and closes the bottom end  44   b  of the side wall  44 . The side wall  44  of the preform also includes a plurality of ribs  48  that protrude radially outward from the inside surface of the preform side wall  44 . Interspersed between the ribs are intermediate side wall sections  47  where the side wall thickness is deliberately thinner than the average thickness of the side wall  44 . The combination of these features will cause the preform side wall  44  to be of a varying thickness. Since these features of the preform side wall  44  are generally maintained during the stretching process associated with stretch-blow molding plastic containers, the side wall  24  of the finished container  20  will maintain a varying thickness.  
         [0023]    It should also be understood that the thinner intermediate side wall sections  31 ,  47  and the corresponding thicker ribs  30 ,  48  can have different angular relationships with respect to the side wall  24 ,  44 . For example, angular displacement of up to approximately 45° will provide usable strength increases for internal or external pressure applications. To address internal or external pressure resistance ribs  30 ,  48  and intermediate side wall sections  31 ,  47  will be generally disposed in a horizontal manner.  
         [0024]    To improve top load or direct axial strength performance it is possible to utilize ribs  30 ,  48  and intermediate side wall sections  31 ,  47 , such that the ribs  30 ,  48  and intermediate side wall sections  31 ,  47  are generally vertically disposed or assume an angular relationship which is greater than 45° from the horizontal.  
         [0025]    As shown in FIG. 5, for manufacturing a container side wall  24  with ribs  30  a mold  60  is provided that is comprised of a first half  62 , a second half  64  and a core  65 . The first half  62  and the second half  64  of the mold  60  cooperate to form a cavity  66  and a mold shell  67 . The cavity  66  is used to form the preform  40  for the container  20 . The cavity  66  is used to form the outside surface of the preform  40  and includes an open top  68   a , a side wall  70   a , a bottom wall  72   a  and an aperture  74 , the aperture  74  being capable of receiving molten plastic. In the preferred embodiment of the present invention, the cavity  66  may also include threaded grooves  76  at its top  68   a  for forming threads  28 ,  50  on the outer portion of the top  22 ,  42  of the container  20  and the preform  40 , respectively. The top  68   a  merges with the top end  71   a  of the side wall  70   a  and the bottom wall  72   a  merges with and closes the bottom end  73   a  of the side wall  70   a . The molten plastic can be injected into the cavity  66  using standard techniques such as ram feeding or screw feeding.  
         [0026]    The mold  60  further includes a core  65 . The core  65  cooperates with the mold shell  67  to form the preform  40  for the container  20 . More specifically, the core  65  is used to form/mold the inside surface of the preform  40 , including an open top  68   b , a side wall  70   b  and a bottom wall  72   b  and the mold shell  67  and the core  65  may have a cooperating diameter and length ratio such that the ribs  48  do not generate a point of interference that prevents the preform  40  from being removed from the mold  60 . The top  68   b  merges with the top end  71   b  of the side wall  70   b  and the bottom wall  72   b  merges with and closes off the bottom end  73   b  of the side wall  70   b . The side wall  70   b  of the core further includes a plurality of channels  78 . The channels  78  vary in depth generally between 5% and 50% of the greatest distance between the core  65  and mold shell  67 . Thus, the channels  78  are used to form the ribs  30 ,  48  on the container  20  and preform  40 , respectively.  
         [0027]    For producing a hollow container  20  with an improved side wall  24  using a single-step method, a preform  40  may be injection molded, the preform being comprised of a side wall  44  with an open top  42  and a closed bottom end  46 , the side wall  44  also including a plurality of ribs  48  protruding radially outward from the inside surface of the preform side wall  44  thereby causing the side wall  44  to assume a varying thickness. Once the preform  40  has been produced, the preform  40  must be cooled to a predetermined temperature. Typically, this predetermined temperature is between 95° C. and 120° C. degrees. The preform  40  can be cooled in a variety of manners. For example, as is generally known in the art, the preform  40  may be cooled by conductive cooling through the side walls  68   a ,  68   b  of the core  65  and cavity  66  using chilled fluids.  
         [0028]    After the preform  40  has reached the predetermined temperature, the preform  40  is stretched to a desired length. The preform  40  may be stretched by using a stretch rod to mechanically stretch the preform  40 . More specifically, the stretch rod is inserted into the open top  42  of the preform  40  and then pressure is applied at the bottom end  44   b  of the preform  40  in a direction away from the top end  44   a  of the preform  40 . Since the intermediate side wall sections  47  have a thinner cross-section than the ribs  48  of the preform side wall  44 , the intermediate side wall sections  47  will cool at a faster rate. Since these intermediate side wall sections  47  are colder than the rest of the preform  40 , the intermediate side wall section  47  will stretch less. Thus, the intermediate side wall sections  47  will retain the majority of their thickness during the stretching of the preform  40 ; hence, the intermediate side wall sections  47  of the preform  40  will be transferred into the ribs  30  on the container side wall  24  as a result of the stretching process. This will produce a container side wall  24  of a varying thickness.  
         [0029]    Meanwhile the ribs  48  on the preform  40 , or the thicker regions, will retain more heat and will be more pliable. As a result, the ribs  48  will stretch and thin to a greater extent, as compared to the intermediate side wall sections  47 , and be transformed into the thinner intermediate side wall sections  31  on the container  20 , as described above.  
         [0030]    After the preform  40  has been stretched to the desired length, the preform  40  may be blow molded to a desired shape. The side wall  44  will continue, however, to maintain a varying thickness on the inside surface of the side wall. The varying thickness of the side wall  44  will allow the container side wall  44  to achieve greater structural integrity without requiring a significant amount of additional material to be added to the container side wall  44 .  
         [0031]    For producing a hollow container  20  with an improved side wall  24  using the two-step method, a preform  40  may be injection molded, the preform  40  being comprised of a side wall  44  with an open top  42  and a closed bottom end  46 . The side wall  44  also includes a plurality of ribs  48  which protrude radially outward from the inside surface of the preform side wall  44 , which cause the side wall  44  to assume a varying thickness. Once the preform  40  has been produced, the preform  40  may be allowed to cool to the ambient room temperature, generally between 8° C. to 50° C. After the preform  40  has reached room temperature, the preform  40  may be re-heated to a designated temperature. As is known in the art, the preform  40  may be re-heated using electrical means, hot-air heating techniques or other similar methods. This occurs because the two-step process utilizes two independent pieces of equipment, one for forming the preform and a separate independent machine for stretch blow molding.  
         [0032]    After the preform  40  is heated to the designated temperature, the preform  40  may be stretched to a desired length and the blow molding process may be initiated. The designated temperature used to stretch the preform  40  is generally between 95° C. and 120° C. A stretch rod may be used to mechanically stretch the preform  40 . More specifically, the stretch rod is inserted into the open top  42  of the preform  40  and then pressure is applied at the bottom wall  46  of the preform  44  and in a direction away from the top end  42   a  of the preform  44 . The ribs  48  in the two-step preform  40  have a thicker cross-section than the other portions of the preform side wall  44  and therefore, the ribs  48  will remain at a lower temperature than the rest of the side wall  44  during the reheating process. Further, since these ribs  48  are colder than the rest of the preform  40 , the ribs  48  will stretch less. Thus, the ribs  48  on the stretched preform  40  will maintain their thicker cross-section as compared to the rest of the preform  40 . This will produce a container side wall  24  of a varying thickness.  
         [0033]    As the preform  40  is being stretched to the desired length, the blow molding process may begin and the preform  40  may be blow molded to a desired shape. Again, the side wall  44  will continue to maintain a varying thickness. The varying thickness of the side wall  44  will allow the container side wall  24  to achieve greater structural integrity without requiring a significant amount of additional material to be added to the container side wall  24 .  
         [0034]    When employing injection stretch blow molding techniques, a container side wall  24  of a varying thickness can be produced by several methods. This feature can be molded into the preform  40  by selectively shaping specific regions of the mold  60  for forming the preform  40 . The design of these regions will vary depending upon the process that is employed. For example, to produce ribs  30 ,  48  that extend radially outward from the inner surface of the container side wall  24 , the core  65  will include specifically shaped regions. On the other hand, to produce ribs  30 ,  48  that extend radially outward from the outer surface of the container side wall  24 , the mold cavity  66  will include specifically shaped regions.  
         [0035]    It is also possible to produce a container side wall  24  with a varying thickness by employing localized heating/cooling techniques. In this approach, after the preform  40  is molded but before stretching, the preform  40  is brought into contact with a shaped cooling/heating tool. This tool will have regions that will only contact specific areas of the preform for the purpose of producing a localized cooling/heating effect on the preform side wall  44 . Therefore, sections with substantially colder or hotter temperatures than the average preform side wall temperature may be generated. As mentioned before, the hotter regions will stretch and thin at a greater rate than the colder. By the use of this zoned heating/cooling approach, a conventional preform can produce articles exhibiting features similar to those obtained by using a preform  40  comprised of ribs  30 ,  48  and intermediate side wall sections  31 ,  47 , as described above. Since narrow diameter containers, such as water and beverage bottles have smaller tapers, or shallower draft angles, use of localized cooling/heating techniques would be particularly advantageous in forming ribs in narrow diameter containers.  
         [0036]    It should be understood by those skilled in the art that the order of all steps disclosed in the figures and discussed above need not be performed in the exact order set forth and the measurements relating to the thickness of the side wall and the temperature ranges listed for the preform and container are provided for exemplary purposes only. In addition, it should be understood that including ribs and intermediate side wall sections and varying the side wall thickness as described herein can be employed in a variety of containers, including non-cylindrical containers. It should also be appreciated that, as an alternative embodiment of the present invention, the ribs may protrude radially outward from and be disposed on the outside surface of the preform and the container side walls. All patents discussed in this document are to be incorporated herein by reference in their entirety.  
         [0037]    While specific embodiments of the present invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangement disclosed is meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any equivalents thereof.