Abstract:
A molded, tamper-evident seal for a liquid container is formed with a flat end wall, a cylindrical side wall having a flared edge, and three detents spaced by 120 degrees from one another and extending inward from the side wall. Score lines extend from the edge of the side wall, and past one of the detents on both sides thereof, toward the end wall. An outwardly protruding pull tab is located between the score lines adjacent the edge of the side wall.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to closures for containers such as drums used for storage and shipment of liquids, and more particularly to a plastic bung seal which is destroyed when pried off the closure fitment or plug of a container, so that unauthorized access to the container can be detected. 
       BACKGROUND OF THE INVENTION 
       [0002]    A fluid-containing drum is typically provided with an opening formed in an end wall of the drum by a permanently attached fitment. A plug or “bung” is removably threaded into the fitment to seal the opening. 
         [0003]    Since it is desirable to prevent unauthorized access through the opening, a bung seal is commonly used to cover, and prevent access to, the fitment and bung. The seal is preferably designed so that it is destroyed in the process of removal. When this objective is achieved successfully, unauthorized removal can be readily detected. 
         [0004]    U.S. Pat. Nos. 3,122,261, 3,923,192, 3,987,929 and 4,706,836 disclose bung seals manufactured of plastic, which snap fit over the fitment and plug. A problem with plastic bung seals is that they do not always create a sufficiently tight seal, and can be removed and re-attached without detection. 
         [0005]    U.S. Pat. Nos. 2,760,671, 5,996,833, 6,360,908, 6,726,048 and 7,080,749, and U.S. patent publication 2004/0144786 disclose plastic bung seals formed with tear strips that can be torn away for removal of the seals. 
         [0006]    Most of the prior art plastic bung seals are formed with rim-engaging elements that are constituted either by a continuous circular structure, or consist of a series of teeth disposed around the perimeter of the seal. If made sufficiently flexible to be easily snapped onto a fitment or plug, these seals are often so weak as to be easily removed and replaced, sometimes without detection. 
         [0007]    An object of this invention is to provide a simple and secure seal that can be snapped onto the rim of a fitment or plug of a container, that attaches securely to the container, and that can be easily and quickly removed, but only by visible destruction of the seal. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    The tamper-evident seal according to the invention comprises a molded unit composed of plastics and having a substantially flat end wall with a circular perimeter, and a side wall extending perpendicularly from the perimeter of the end wall. The side wall has a circular edge spaced from the end wall, and a substantially cylindrical inner face. The side wall is preferably formed with a tapered outward flare at its circular edge. 
         [0009]    A plurality of detents, which are unitary with the side wall, protrude inwardly from the inner face of the side wall for locking engagement with an overhanging rim on the closure of a fluid container. Preferably, the detents protrude from said inner face of the side wall at a location spaced from said circular edge of the side wall. 
         [0010]    One of the detents is circumferentially spaced from each of the other detents by an angle of at least 90 degrees measured along an arc centered on the central axis of the cylindrical inner face of the side wall. Preferably the detents are three in number and disposed at 120 degree intervals on the inner face of the side wall. A pull tab extends outward from the side wall at a location adjacent said one of the detents, and preferably from the circular edge of the side wall. Two score lines extend from the pull tab, past said one of the detents on opposite sides thereof, toward the end wall. Optionally, the score lines can also extend across the end wall or across part of the end wall. The score lines weaken the side wall and permit a strip, defined by an area of the side wall between the score lines, and including said one of the detents, to be pulled away from the remainder of the side wall, thereby releasing the seal from the overhanging rim on the closure of the fluid container. 
         [0011]    Preferably, the side wall of the seal has sufficient resilience that the seal can be engaged with the closure by causing said one of said detents to expand away from the other detents of a fluid container as the seal is pressed onto the closure, and allowing the detents to snap into locking engagement with an overhanging rim on the closure. To this end, each of the detents is preferably formed with a rim-engaging ramp extending obliquely from said inner face of the side wall toward the end wall and a rim-engaging surface extending inward from said side wall in substantially parallel relationship to the end wall. 
         [0012]    Because the detents are arranged so that the detent between the score lines is at least 90 degrees away from the other detents, the seal can be relatively rigid compared to conventional seals, yet easily snapped onto the rim of a bung or bung fitment. Moreover, the arrangement of the detents is such that the pull tab need only be pulled far enough to release the one detent between the score lines from the rim in order to release the seal. 
         [0013]    Other objects, details and advantages of the invention will be apparent from the following detailed description when read in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a perspective view showing the underside of a seal according to the invention; 
           [0015]      FIG. 2  is a cross-sectional view of the seal, taken on section plane  2 - 2  in  FIG. 1 , and showing the manner in which the seal is fitted onto the rim of the closure of a container; 
           [0016]      FIG. 3  is a bottom plan view of the seal; and 
           [0017]      FIG. 4  is a perspective view of the closure showing a strip defined by the score lines partially pulled away to release the seal from the container. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0018]    As shown in  FIGS. 1 and 2 , the seal  10  according to the invention is molded unit formed form a suitable resilient plastics material such as polyethylene or the like. The seal is formed with a substantially flat end wall  12  having a circular perimeter  14 . A side wall  16  extends perpendicularly from the perimeter of the end wall. The connection between the side wall and the end wall can be rounded, as shown in  FIGS. 1 and 2 . 
         [0019]    The side wall  16  has a substantially cylindrical inner face  18 , and is flared at  20 , forming a circular edge  22  that has a diameter slightly larger than the outer diameter of side wall  16 . Preferably, the side wall is tapered at the location of the flare to ensure that attempts to pry the seal away from the container will either tear or deform the circular edge  22 . 
         [0020]    Three detents  24 ,  26  and  28  (see  FIG. 3 ) are molded as a unit with the seal, and are formed on the inner face  18  of the side wall  16 . The detents can be, and preferably are, identical. As seen in  FIG. 2 , detent  24  extends inward from face  18 , and has a flat upper surface  30  that is substantially parallel to end wall  12 . This flat upper surface  30 , and corresponding flat upper surfaces of the other detents  26  and  28 , are adapted to engage the underside  32  of the overhanging rim  34  of a bung-receiving fitment formed on a container, or the underside of a rim formed on a bung. For the purpose of this description, the term “closure” should be understood as referring to the combination of the fitment and the bung or plug, and the rim of the closure can be either a rim on the fitment or a rim on the bung or plug. 
         [0021]    As shown in  FIG. 2 , the underside of detent  24  is formed with a ramp  36  that extends obliquely upward from the inner face  18  of the side wall  16  toward the end wall  12 . As seen in  FIG. 1 , the ramp is preferably composed of three triangular elements  38 ,  40  and  42 . However, the detent can be a single wedge-shaped element, in which case the ramp will be a continuous surface. Each of the other detents,  26  and  28  is similar to detent  24 . The ramp engages the upper part of rim of the closure as the seal is applied to the container, and produces a camming action, forcing the side wall  16  outward until the detents snap over the rim, and their upper surfaces (e.g., surface  30 ) are situated underneath the rim to hold the seal in place. Although the ramp surfaces shown are straight, they can be curved, if desired, to modify their camming properties. 
         [0022]    The detents  26  and  28  are both spaced at least 90 degrees from detent  24  along arcs centered on the axis of the cylindrical inner face  18  of the side wall. Preferably each of the detents itself subtends an arc of not more than 30 degrees centered on the same axis. Even if each of three detents subtends 30 degrees, the detents can still be positioned at uniform intervals and 90 degrees apart from one another. 
         [0023]    As shown in  FIG. 1 , the seal is formed with two, preferably parallel, score lines  44  and  46 , which extend from edge  22  upward, on opposite sides of detent  24 , toward the end wall  12 . These score lines are preferably formed on the inside face  18  of the side wall, and weaken the side wall so that a strip of side wall material can be removed from the side wall. The score lines can, but do not need to, extend across the underside of end wall  12 , as shown in  FIG. 3 . Detent  24 , and the other detents  26  and  28  are disposed at intermediate positions between the edge  22  of the side wall and the end wall  12 , and the score lines should extend from the edge  22  at least to a location beyond the upper surface  30  of detent  24 . 
         [0024]    A tab  48 , which is also a part of the molded unit, protrudes outward from the lower part of side wall  16  between the score lines  44  and  46 , and preferably from the edge  22  of the sidewall. A through hole  50  is preferably provided in the tab for insertion of a tool, such as a screwdriver, for exerting a pulling force on the tab sufficient to break the seal along the score lines and peel back a strip  52  as shown in  FIG. 4 . When the strip  52  is peeled back, the detent  24  is pulled out from underneath the rim  32  ( FIG. 2 ) of the closure. Since the other detents  26  and  28  are both more than 90 degrees away from detent  24 , when the detent  24  clears the rim, the portions of the seal adjacent the opening left by the peeled-away strip  52  can be easily lifted, and the other detents  26  and  28  can be moved out from underneath the rim of the closure so that the entire seal can be removed and discarded. The peeling of the strip  52  destroys the seal, preventing its re-use. 
         [0025]    Various modifications can be made to the seal described. For example, the locations and number of the detents can be modified, so long as the detent adjacent the pull tab is at least 90 degrees away from each of the other detents. The pull tab can be positioned on the side wall at a location remote from edge  22 . 
         [0026]    Still other modifications may be made to the apparatus and method described above without departing from the scope of the invention as defined in the following claims.