Abstract:
A container and a method for making a container having inwardly formed threads are provided. The container includes a body portion having a bottom portion and a sidewall portion. A neck portion is formed above the body portion and defines an opening at a top of the container. The neck portion includes a vertical cylinder portion extending vertically upward from the body portion, the vertical cylinder portion having a thread portion formed as a concave profile around the vertical cylinder portion.

Description:
[0001]    This application claims the benefit of U.S. Provisional Patent Application No. 61/765,419 filed on Feb. 15, 2013 in the U.S. Patent Trademark Office, the disclosure of which is incorporated herein in its entirety by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    Apparatuses and methods consistent with the present invention relate to a polyethylene terephythalate (PET) container and a method for making the same by forming an inward thread finish. 
         [0004]    2. Description of the Related Art 
         [0005]    The current state of art for container finishes on blow and trim style containers consist of a cylinder with the threads projecting outward from that cylinder for engagement with the threads of the closure. The threads must be large enough in cross section to allow the plastic to form into them completely. 
         [0006]    In order to fully form the threads of the finish, enough material, heat and air pressure must be applied to the finish for proper closure application. This condition causes more attention to the finish and less to the body of the container sometimes resulting in limited process capabilities. The seal surface of the blow-trim type of finish also protrudes into the opening of the container and blocks the flow of product both into and out of the container. The radius between the seal surface and vertical cylinder that forms the body of the finish is large enough at times to cause less than desirable sealing. 
         [0007]      FIG. 12  shows a conventional thread on a container top. The thread is formed as a projection projecting outwardly from a vertical cylindrical surface. 
       SUMMARY OF THE INVENTION 
       [0008]    Aspects of the invention relate to a blow-molded PET container having an inward thread finish. 
         [0009]    Aspects of the present invention solve the aforementioned problems by (1) moving the vertical cylinder of the finish body outward to what would have been the outer diameter of the threads in a conventional design and (2) forming the threads inwardly from the vertical cylinder of the finish body. This enables one to form, by blowing molding a container, threads having a smaller thread cross section. Thus, the threads can be formed with less material, heat and air pressure. This allows more attention to be paid to design of the rest of the container for a better processing. 
         [0010]    According to one aspect, provided is a method of making a blow-molded PET plastic container having an inward thread finish, the method includes providing a mold having a neck forming surface comprising a first surface configured to form a vertical cylinder portion of a bottle and a projecting portions projecting outward from the first surface that are configured to form helical threads, and stretching the preform against the mold surface to form a neck portion of the container, the neck portion comprising a vertical cylinder portion having helical threads formed radially inward of the vertical cylinder portion. 
         [0011]    According to another aspect, portions of the preform forming the vertical cylinder portions are stretched to a greater length than portions forming an inner surface of the helical threads, the inner surface being radially inward of the vertical cylinder portion. 
         [0012]    According to another aspect, a container is provided. The container includes a body portion having a bottom portion and a sidewall portion. The container also includes a neck portion formed above the body portion and defining an opening at a top of the container. The neck portion further includes a vertical cylinder portion extending vertically upward from the body portion, the vertical cylinder portion having a thread portion formed therein, the thread portion formed as a concave profile around the vertical cylinder portion. The container also includes a top portion formed at an uppermost part of the vertical cylinder portion and extending in a horizontal direction. 
         [0013]    According to another aspect, the thread portion includes a helical groove that is formed radially inward of and around the vertical cylinder portion. the top portion of the container joins the vertical cylindrical wall at a position that is radially outward of the thread portion. 
         [0014]    According to another aspect, the thread portion comprises multiple non-intersecting grooves. 
         [0015]    According to another aspect, the thread portion comprises an inner surface, an upper surface and a lower surface, the inner surface joining the upper surface and the lower surface, the upper surface and the lower surface extending from different portions of the vertical cylindrical portion. Further, a maximum width between the upper surface and the lower surface is ranges from 0.084 to 0.120 inches. 
         [0016]    According to another aspect, a depth of the thread portion from the vertical cylindrical surfaces ranges from 0.042 to 0.060 inches. 
         [0017]    According to another aspect, the width of the helical groove is less than a width of a portion of the vertical cylindrical portion between adjacent grooves. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    The above and other aspects and features of the various aspects of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
           [0019]      FIGS. 1A-1D  show inward threads formed on a top portion of a bottle. 
           [0020]      FIGS. 2A-2D  show another embodiment of a container top having inwardly formed threads. 
           [0021]      FIGS. 3A-3D  show another embodiment of a container top having inwardly formed threads. 
           [0022]      FIGS. 4A-4D  show another embodiment of a container top having inwardly formed threads. 
           [0023]      FIGS. 5A-5D  show another embodiment of a container top having inwardly formed threads. 
           [0024]      FIGS. 6A-6D  show another embodiment of a container top having inwardly formed threads. 
           [0025]      FIGS. 7A-7C  show another embodiment of a container top having inwardly formed threads having a two lead finish. 
           [0026]      FIGS. 8A-8C  show an embodiment of a container top having inwardly formed threads having a four lead finish. 
           [0027]      FIGS. 9A-9C  show a blown up view of the thread entrance ramps in accord with the various embodiments. 
           [0028]      FIG. 10  is a flowchart showing a method of making a blow molded container. 
           [0029]      FIG. 11  shows a preform used to form a container using blow molding. 
           [0030]      FIG. 12  shows a conventional thread on a container top. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0031]    According to a first non-limiting embodiment of the invention, provided is a container having a top portion  10  having inwardly formed threads  20 . The top portion  10  comprises an outer vertical cylinder portion  15  that has a horizontal flange  30  used as a sealing surface at the top thereof. The thread is comprised of a helical groove that is formed radially inward of and around the outer vertical cylinder portion  15 . This results in a thread  20  formed into the vertical cylinder portion  15  to allow engagement with the closure. Each thread has an inner surface  70 , an upper surface  50  and a lower surface  60 . In this embodiment, both the upper surface  50  and the lower surface  60  are inclined at the same angle with respect to the inner surface  70 . These surfaces define the thread profile of the thread  20 . Thus, the outermost part of the thread forming region is comprised of the vertical cylinder portion  15 , not threads as in a conventional design. 
         [0032]    The forming occurs by expanding a pre-form outwardly. Thus, when details, such as threads, are to be formed, there is a limit to how small the cross-section (in vertical direction) of the detail can be, while still be correctly formed. Thus, by forming the thread  20  inwardly of the vertical cylinder portion  15 , a smaller thread profile can be used and accurately formed. This is beneficial when finishes using thread helixes having shallow slopes or multiple thread leads, which tend to crowd together, are formed. Additionally, as the thread is formed inwardly, the top portion  10  can be made of a larger diameter then the case when the thread is formed outwardly from the vertical wall. This moves the sealing surface of the top portion  10  (outward diametrically) into a better position to match the seal beads on the closure (lid). 
         [0033]    While the present invention is described with regard to blow molding method, the container may also be injection molded. 
         [0034]    An open portion  40  where the thread  20  opens to the horizontal flange  30  (sealing surface) can run out or extend for a minimum distance based on the length of the thread root divided by the pitch of the thread helix. This embodiment uses a minimum thread run out into the sealing surface, but the present invention is not limited to this minimum distance. Variations of the finish are shown in the  FIGS. 2A-8C . 
         [0035]    In the embodiment of  FIGS. 2A-2D , the open portion  40  defining the thread run out extends 96 degrees around the periphery of the circular top portion  10 . The thread profile is defined by a vertically extending inner surface  70 , an upper surface  50  and a lower surface  60 . The upper surface  50  and the lower surface  60  extend at angles θ u  and  0   l , respectively. These angles are measured with respect to a normal to the inner surface  70 . The value of θ u  is 10 degrees and the value of θ l  is 30 degrees. 
         [0036]    The lower surface  60  of the thread  20  terminates at a ramp portion  80  adjacent the top portion  10 . In this embodiment, the ramp portion  80  comprises a straight entrance ramp. 
         [0037]    The embodiment depicted in  FIGS. 3A-3D  has dimensions similar to the embodiment of  FIGS. 2A-2D  with the exception of the ramp portion  80 . In this embodiment, the ramp portion comprises a 60 degree ramp portion. 
         [0038]    The embodiment depicted in  FIGS. 4A-4D  has dimensions similar to the embodiment of  FIGS. 3A-3D  with the exception of the run out of the open portion  40 . In this embodiment, the open portion  40  extends 116 degrees around the top portion  10 . 
         [0039]    The embodiment depicted in  FIGS. 5A-5D  has dimensions similar to the embodiment of  FIGS. 3A-3D  with the exception of the ramp portion  80 . In this embodiment, the ramp portion  80  comprises a curved entrance portion. 
         [0040]    The embodiment depicted in  FIGS. 7A-7C  shows another thread  20  having a thread  20  defined by a thread profile having a curved inner surface  70 . The upper surface  50  extends at an angle of 25 degrees to a normal of the vertical cylinder portion  15 . The lower surface  60  extends at an angle of 39 degrees to the normal. This embodiment comprises a two lead finish. 
         [0041]    The embodiment depicted in  FIGS. 8A-8C  shows another thread  20  having a similar finish to the thread of  FIGS. 7A-7C  with the exception that it comprises a four lead finish. 
         [0042]      FIGS. 9A-9C  depict a blown up view of the thread entrance ramp portions  80  in accord with various embodiments.  FIG. 9A  shows a straight entrance ramp,  FIG. 9B  shows a 60 degree entrance ramp and  FIG. 9C  shows a curved entrance ramp. 
         [0043]    The width of the thread can range from 0.084 to 0.120 inches and can have a depth ranging from 0.042 to 0.060 inches. The width of the vertical wall portion defining the thread  20  (portion between threads) can range from 0.045 to 0.140 inches. However, this wall portion is generally greater in width than the thread portions. 
         [0044]    A method of making a container in accord with an exemplary embodiment is described with reference to  FIGS. 10 and 11 . First, a preform having a thread forming region  22  below the preform neck  18  is injection molded in operation S 1  and inserted into a mold having a thread forming portion configured to form an inward thread as described above. Air is blown into the preform to mold a domed container S 2  (dome above neck and thread portion). Thereafter, the domed portion is trimmed off of the container S 3  to produce as finished container as shown in the various embodiments described herein. While this invention has been particularly shown and described with reference to exemplary embodiments thereof, the above description should be considered in as illustrations of the exemplary embodiments only and are not for purposes of limitation. Therefore, the scope of the invention is defined not by the detailed description of the invention but by the appended claims, and all differences within the scope will be construed as being included in the present invention.