Abstract:
A closure for covering an opening of a container. The closure includes an inverted U-shaped peripheral channel for receiving the rim of a container therein. A tear strip is formed with the skirt of the closure via a tear line that circumscribes the skirt. A breakaway pull tab having an inner surface with U-shaped ribs, the combination of the surface and ribs being such as to provide a concavity which assists in gripping the tab to pull the strip away. Linear vertical ribs may be provided on the outer surface to provide further assistance in the gripping function. The skirt includes a recessed area underlying the pull tab for providing access to the pull tab. An alternative embodiment uses a zig-zag structure of strengthening ribs in the skirt to reduce the amount of material necessary to provide the undercut. This reduces the probability of warpage in the closure structure.

Description:
RELATED APPLICATION  
       [0001]     This application is a continuation of U.S. application Ser. No. 10/752,756 filed under attorney docket no. LTC-114-A on Jan. 7, 2004, currently pending and claims priority thereto. The content of the U.S. patent Ser. No. 10/752,756 is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention relates to plastic container/closure combinations and more particularly to an improved closure structure.  
       BACKGROUND OF THE INVENTION  
       [0003]     Injection molded plastic containers and lock-on closures are in popular use for packaging a wide variety of products in quantities of one to six gallons. Examples include asphalt sealant, paint, drywall putty and food products. The “lock-on” feature is typically provided by an undercut in the closure which snaps around a peripheral edge flange in the open top of the container. The hoop strength of the closure is such that means must be designed into the closure to facilitate its removal. The two most common such means include (1) tear strips which are removed to reduce the force of the locking mechanism and (2) windows or apertures in the closure skirt which permit the skirt to be fractured at several circumferentially spaced locations. These mechanisms can also be used in combination.  
         [0004]     Prior art tear strips can be difficult for a user to access and to grip as the tab is broken away and the tear strip is removed from the outer periphery of the closure. To solve this problem, some prior art closures have been designed to provide a tab that protrudes outwardly from the skirt of the closure for easier access. However, this method prevents efficient stacking of closures for storage.  
         [0005]     Efforts to design strength into the closure generally involve adding thickness to the closure skirt. This approach uses additional plastic material, adds weight and can give rise to warpage problems in critical areas of the closure.  
       SUMMARY OF THE INVENTION  
       [0006]     The present invention provides an improved closure for an open top container which solves the problems found in the prior art. The closure includes an integral skirted rim which receives the upper edge of the container therein. In one form, a tear strip is formed with and in the skirt but can be separated therefrom via a tear line that extends around the skirt. An essentially flush pull tab is positioned on the end of the strip directly over a recess in the skirt wall which provides room to grasp the tab.  
         [0007]     In the preferred embodiment of the tear strip aspect of the invention, the pull tab includes an inner gripping surface having ribs formed therein in such a way as to form a concavity which adds to the effectiveness of the grip. An outer surface of the pull tab includes one or more substantially linear ribs protruding in a substantially vertical arrangement therefrom. The combination of ribs and the recessed grip area provides a more secure grip for tearing the pull tab away from a frangible connection. Once the pull tab has been broken away, the ribs provide a gripping feature to facilitate the removal of the tear strip from the closure skirt. The recessed area further includes an opening formed in the skirt wall around the perimeter of the pull tab. The opening forms an arrow shaped element indicating the direction for pulling and removing the tear strip from the skirt.  
         [0008]     Another aspect of the invention involves the design of a zig-zag rib structure into the interior of the closure to reduce material, add strength, and minimize warpage.  
         [0009]     Other applications of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the invention is read in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views, and wherein:  
         [0011]      FIG. 1  is a perspective view of a resealable closure attached to a container;  
         [0012]      FIG. 2  is a top plan view of the resealable closure of  FIG. 1 ;  
         [0013]      FIG. 3  is a bottom plan view of the resealable closure of  FIG. 1 ;  
         [0014]      FIG. 4  is an enlarged partial perspective view showing a pull tab on the resealable closure of  FIG. 1 ;  
         [0015]      FIG. 5  is an enlarged perspective view showing the inner surface of the pull tab of  FIG. 4 ;  
         [0016]      FIG. 6  is a cross-sectional view taken along lines  6 - 6  in  FIG. 3 ;  
         [0017]      FIG. 7  is a section through the pull tab;  
         [0018]      FIG. 8  is an interior view of another embodiment of the invention showing the anti-warpage pattern in the interior of the closure;  
         [0019]      FIG. 9  is a cross-section showing the container and closure in combination; and  
         [0020]      FIG. 10  is a detail of the closure interior. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0021]      FIGS. 1-6  illustrate a first embodiment of the invention as the combination of an injection molded plastic closure  10  and an open top cylindrical container  12  of three to six gallon capacity. In such capacity, the closure is about 12 inches in outside diameter; these size and capacity numbers are given by way of example only. The material is preferably polyethylene but may also be polypropylene and/or other moldable polymers. The closure  10  includes a substantially planar deck portion  14  peripherally bounded by an inverted U-shaped channel  16 , to receive the upper rim  15  of container  12 , and a peripheral skirt  18  which overlies the upper wall of the container when installed. A tear strip  20  is formed integrally with the skirt  18  in the injection molding process. The tear strip  20  is removable from the skirt  18  via a tear line  22  of substantially reduced thickness and tensile strength relative to the rest of the skirt  18 . A breakaway pull tab  24  is positioned substantially flush with an outer portion  26  of the skirt  18 . The pull tab  24  is integral with the tear strip  20  and is operable to facilitate removing the tear strip  20  from the skirt  18  such that the closure  10  becomes more easily removed from the container  12 . Once the tear strip  20  has been removed, the locking strength between the closure  10  and the container  12  is reduced but not to zero; therefore, the closure  10  can be reapplied to the container  12 . A recessed area  28  is formed in the skirt  18  adjacent an inner portion of the pull tab  24  for providing access to the pull tab  24 . The recessed area  28  is formed from an area of reduced wall thickness relative to the remainder of the skirt  18  as best shown in  FIG. 4 .  
         [0022]     Both embodiments of the invention are shown with cylindrical designs. It is to be understood that the improvements disclosed herein can also be used with non-cylindrical designs including oval, square and rectangular.  
         [0023]     In the present embodiment, the outer wall of the container  12  is configured to provide an undercut  52  which provides the primary lock between the closure  10  and container  12  in conventional fashion both before and after removal of the tear strip.  
         [0024]     A circumferential rib  53  may be formed in the container wall below the undercut  52  to protrude into the interior groove formed by the tear lid  22  to provide a second, supplemental lock which is operable only until such time as the tear strip  20  is removed. A second rib  55  may be formed on the container  12  to immediately underlie the closure skirt  18  to impede access to the lower edge of the skirt with a tool or one&#39;s fingers before the tear strip is removed.  
         [0025]     Those skilled in the art will appreciate that the tear strip  20  is not limited to use with double lock closures but may also be used with single lock closures simply to reduce the hoop strength of the closure skirt  18  to facilitate post-tearing removal of the closure  12 . In this regard, windows or apertures  58  are provided at 45 degree intervals around the skirt  18  to facilitate lifting and bending of the skirt  18  after removal of the strip  20 .  
         [0026]     The pull tab  24  includes a concave inner surface  62  best seen in  FIGS. 5 and 7 , having several parallel U-shaped ribs  30  protruding therefrom. The U-shaped ribs  30  in combination with the concave shape provide a gripping surface for breaking the tab  24  away from frangible area  32  of the skirt  18 . Concavity may be provided in one of three ways: either the inner surface can be concave and the ribs of equal height, or the inner surface flat and the ribs of increasing height from inside to outside, or a combination of the two can be used. The pull tab  24  includes an outer gripping surface (best seen in  FIG. 4 ) having at least one but preferably three or more substantially linear shaped ribs  34  protruding in a substantially vertical arrangement therefrom. The vertical ribs  34  provide a gripping surface to pull the pull tab  24  around the periphery of the closure  10  to remove the tear strip  20  from the skirt  18 . The recessed area  28  includes an opening  36  formed in the skirt  18  around the perimeter of the pull tab  24 . The opening  36  has an arrow shape  37  formed on one end thereof for defining the direction of pull to remove the tear strip  20  from the skirt  18 .  
         [0027]     Referring now more particularly to  FIG. 6 , the channel portion  16  includes a slightly inwardly angled inner wall  40  extending upwardly from the planar deck portion  14 . The channel portion  16  is further defined by a substantially horizontal annular connector  42  integrally extending from the inner wall  40  to an outer wall  44 . An intermediate wall  46  extends downward from an inner surface of the horizontal connector  42  between the inner  40  and outer  44  walls to define an inverted U-shaped channel  48 . An O-ring gasket  50  is positionable in the inverted U-shaped channel  48  to seal the closure  10  to the container  12 .  
         [0028]     The closure  10  includes a plurality of stiffening ribs  54  located on the underside thereof (best seen in  FIGS. 3 and 5 ). The stiffening ribs  54  provide stiffness to the closure  10  so that the closure  10  has enough structural integrity to remain connected to the container  12  under stacking loads, but still allows the closure  10  to be deformed sufficiently for removal of the closure  10  from the container  12 . The closure  10  includes a plurality of through apertures  58  that can be seen in  FIGS. 1-4 . The through apertures  58  are spaced apart from one another along the perimeter of the skirt  18 . The apertures  58  are operable for separating the perimeter of the skirt  18  into eight discreet sections  60 . Other numbers from six to 12 can also be used. After the tear strip  20  is removed from the skirt  18 , the discreet sections  60  allow the user to pry upward to deform the closure  10  enough to move the projection  52  away from the rim  53  of the container  12  and thus allow removal of the closure  10 .  
         [0029]     In operation, when the closure  10  and container  12  are first attached to one another during manufacturing, the closure  10  cannot readily be manually separated from the container  12 , thus ensuring safe storage of the contents of the container  12 . The closure  10  is tamper resistant and tamper-evident because the closure  10  cannot normally be opened until the tear strip  20  has been removed from the skirt  18 . To remove the closure  10 , a user must pull the pull tab  24  away from the skirt  18  and break the pull tab  24  from the skirt  18  along a frangible portion  32  of the skirt. The U-shaped ribs  30  located on the inner surface of the pull tab  24  provides gripping to facilitate breakage from the frangible area  32 . The pull tab  24  is more easily accessed because recessed area  28  is provided to allow the user&#39;s fingers to reach behind the pull tab  24 . The recessed area  28  allows access to the inner surface where the user&#39;s fingers can grip the U-shaped ribs  30  and pull the pull tab  24  apart from the skirt  18  along frangible area  32 . Once the pull tab has been broken away, the user then pulls the pull tab  24  in the direction of the arrow  37  using the linear vertical gripping ribs  34  on the outer surface of the pull tab  24 . The pull tab  24  stays connected to the tear strip  20  as the tear strip is being removed from the skirt  18  along tear line  22 . Once the tear strip  20  has been completely removed from the skirt  18 , the closure  10  can then be removed from the container  12 . The closure  10  can also be reattached to the container  12  in a tightly sealed arrangement using the inverted U-shaped channel  48  to position the O-ring  50  seal.  
         [0030]     Referring now to  FIGS. 8-10 , a second embodiment of the invention which adds hoop strength to the closure skirt while at the same time reducing material and the probability of warpage in the closure dimensions is shown. In this embodiment, closure  64 , although similar to closure  10 , differs from closure  10  in the addition of a zig-zag rib structure  66  on the interior of the rib skirt above the tear strip  20 ′. The zig-zag rib structure  66  is interrupted by windows or apertures  68  at approximately 45° intervals, such apertures  68  corresponding generally to the apertures  58  shown in the embodiment of  FIG. 3 . The rib structure  66  preferably comprises V-shaped elements which are joined at the top but can be spaced from one another at the top if desired. The thickness of material  72  between the rib structure  66  can be kept fairly thin while still providing the undercut which extends under peripheral lip or flange  15  of the container  12  as shown in  FIG. 9 . While shown in combination with a tear strip embodiment, the zig-zag or alternating V-shaped rib structure on the interior of the closure  64  may also be used in a non-tear strip design, wherein the windows or apertures  68  are used to break or split the skirt of the closure into a number of segments which can be levered upwardly to facilitate removal of the closure from the container  12 .  
         [0031]     While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiments but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as is permitted under the law.