Patent Publication Number: US-2005133508-A1

Title: Tamper evident lid welded to a container

Description:
FIELD OF THE INVENTION  
      This invention relates to a tamper-evident plastic lid and to the combination of the lid welded to a rim of a plastic container.  
     BACKGROUND OF THE INVENTION  
      The present invention is directed to a one-piece plastic lid which is often applied to a plastic container to provide a tamper-evident replaceable lid such that when it is removed it is apparent to the user that the lid has been tampered with. The lid is replaceable in the sense that after using some of the contents or accessing the contents, the lid may be repositioned back onto container in a retained or a generally sealed position to protect the contents against contamination or the like.  
      Lids of this general type are usually lightweight, inexpensive and stackable such that they can be stacked in lid applying machines which feed the lids and automatically apply them to filled containers.  
      The present invention will be described in conjunction with a preferred and illustrated use, which is that of a lid of the so-called recessed central plug kind which fits into the container and is replaceable to have a friction interfit with the container after the lid has been initially removed from the container. The illustrated container is that commonly used in dairy applications for dairy products such as cottage cheese and involves a lightweight plastic tub-like container with an annular rim into which is fitted the plug-fit lid. To provide a tamper-evident feature to this plug-fit lid and container, a thin, clear discrete band of clear plastic is wrapped about the container rim and lid skirt and this thin, frangible band must be broken and removed before the lid can be removed from the container. The attaching of this clear band and the cost of this clear band are desired to be eliminated. Thus, there is a need for a new, improved lid and container construction.  
     SUMMARY OF THE INVENTION  
      In accordance with the preferred embodiment, there is provided a new and improved tamper-evident lid for attachment to a plastic container which is welded to the plastic container to provide a permanent interconnection with the container to prevent tampering with the container contents. A frangible portion is provided on the lid which can be broken to allow detachment of a replaceable lid portion while leaving a welded portion of the lid welded to the skirt of the container which shows that the lid has been removed.  
      In accordance with the preferred embodiment, there is provided a plug-type lid which has a central, recessed panel and an upstanding skirt with a horizontally extending rim portion which is welded to the rim of the container. The frangible portion on the skirt is located radially inward of the welded portion and is fractured to allow removal of the replaceable lid from the outer skirt portion of the lid which remains permanently attached to the rim of the container. The plug lid may be fitted and pressed back in place, that is replaced to cover the contents after they have been accessed and it is desired to replace the lid. This plug lid portion has a friction interfit with the container rim to retain the lid portion on the container. The frangible portion is preferably a very thin web of reduced cross-sectional thickness which when is subjected to a pulling force fractures and disconnects the detachable lid from the welded lid portion which remains on the container rim.  
      A pull tab may be connected to the detachable lid portion to assist in starting and in fracturing the frangible portion. The preferred welding is achieved by the use of a energy director such as a depending bead on the underside of the skirt which is welded to the horizontal portion of the rim of the container. Also, a pry slot may be provided on the lid to locate and to indicate where and how the lid portion is detached from the welded portion. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a perspective view of a lid and a container and constructed in accordance with one embodiment of the invention;  
       FIG. 2  is a plan view of the lid of  FIG. 3 ;  
       FIG. 3  is another perspective view of another embodiment of a lid and a container;  
       FIG. 4  is an enlarged cross-sectional view of a lid skirt having an energy director and a frangible portion;  
       FIG. 5  is a cross-sectional view taken along the line  5 - 5  of  FIG. 2 ;  
       FIG. 6  is an enlarged cross-sectional view of a skirt portion of the lid;  
       FIG. 7  is an enlarged cross-sectional view of the lid showing an internal rib in the lid;  
       FIG. 8  is a cross-sectional view showing the lid welded to a rim of the container; and  
       FIG. 9  is a side elevational view of a container used with a weldable lid.  
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
      As shown in the drawings for purposes of illustration, a container and lid assembly  10  is illustrated as comprising a container  11  of plastic material and a lid  12  of plastic such as polypropylene. The container may also be made of a suitable plastic. Both the lid and the container may be made of various plastic materials, although polypropylene is preferably selected for the lid because it is lightweight and inexpensive and has good properties when subjected to extreme cold as may be the case with various dairy products.  
      The lid  12  herein is an injection molded plastic lid that is welded to an injection molded plastic container  11 . To provide a lightweight and low cost injection molded lid and container, they are each preferably made of polypropylene plastic. It is to be understood that the lid and/or container may be made by a thermoforming technique rather than an injection molding technique and still fall within the purview of this invention. Also, the present invention is not limited to use of polypropylene as the plastic for either the lid and the container as they made be made of polyethylene or other plastics and still fall within the purview of this invention.  
      The illustrated lid  12  is of the plug type in that it has a depending recessed, plug portion  14  which has an outer, encircling upper skirt  16  integrally joined at its lower end to a flat, wide circular central panel portion  18  which is located at the center of the lid. The skirt  16  is joined to the central panel  18  by an annular, vertical sidewall  20 . Although the invention is described herein as a tamper-evident plug-fit lid that is welded to the container, it is to be understood that the invention is not limited to a plug kind of lid. Manifestly, the lid could have a replaceable portion that is not in the shape of a plug and falls within the purview of the claims defining this invention.  
      The illustrated container  11 , as shown in  FIGS. 1 and 8 , has an encircling radially outwardly extending rim portion  22  projecting outwardly from the top of an inclined sidewall  24  which is integrally joined at its lower end to a bottom wall  26  for the container. The illustrated container is also injected molded of a plastic material. The rim portion  22  has a flat, annular horizontally disposed rim wall  22   a  which extends radially outward of the inclined sidewall and terminates in a depending flange  22   b  which fits within a depending flange  34  on the skirt of the lid.  
      In accordance with the illustrated embodiment, the lid is sealed and is attached to the rim of the container by a weldable portion  28  which is permanently welded to the container rim  22  as shown in  FIG. 8  substantially all the way around the lid and the container to make a sealed connection therewith. The preferred welded portion includes an energy director  30  ( FIGS. 4 and 6 ) in the form of an encircling annular, bead  32  of plastic depending from a lower surface of an annular, horizontal skirt wall  33  on the lid, as best seen in  FIG. 6 . The bead  32  has a pointed lower tip  35  which concentrates the ultrasonic welding energy at the tip to quickly raise its temperature of the pointed bead to a melting temperature to aid in initiating the plastic flow of the bead into softened plastic being melted on the encircling, horizontal flange  34  of the container rim  22 .  
      When opening the container to access the contents therein, the lid is lifted and pulled upwardly to fracture a frangible portion  40  which is preferably in the form of a thin web  42  ( FIG. 4 ) having a reduced cross-section from the remainder of the skirt  16  of the lid. By way of example only, the horizontal extending flange of the lid carrying the lid may be about 0.018 inch thick with the bead about 0.025 inch thick and with the frangible groove portion  40  being several thousandths of an inch less than 0.018 inch in cross-sectional thickness of the skirt wall  33 . The welded portion  28  is radially outward of the frangible groove  42  in the skirt wall  33  so that it remains welded to the rim of a container as the frangible web is broken. This leaves the central detachable, and replaceable lid portion  50  having an annular outer edge having once been a portion of the groove  42  at the location of the thin web in the skirt wall  33 . Manifestly, the breaking and tearing of the frangible web provides a tamper-evident feature to the user so that it is evident when the lid has been removed and the contents of the container accessed by someone. After accessing the contents, the user may reapply the lid merely by setting it back with the central plug having its vertical sidewall  20 ; and then pushing the lid down into frictional engagement with the vertical sidewall  24  of the container. Herein, the lid vertical sidewall  20  is slightly inclined or tapered by about 0.005 inch from its upper end at the lid skirt to a smaller diameter at its lower end  20   b  which is joined to a reduced diameter section  20   a  which is integrally joined to the central panel  18 .  
      In the embodiment illustrated in  FIG. 1 , the substantially annular channel or fracturable portion  40  and the thin web  42  are formed to extend and to be located downwardly within the skirt wall  33  and then are attached to a separate pull tab  55  as best seen in  FIG. 1 . By grasping the pull tab and pulling it upward, the frangible web will be fractured and torn continually along the substantially annular thin web  42  so that the replaceable lid portion, after it is detached from the welded portion on the container, has an integral pull portion  55  thereon.  
      In the embodiment shown in  FIGS. 2 and 3 , the pry slot  62  has been formed in the lid skirt  16 . Thereby making it more obvious to the user as to where to start to separate the lid portion from the container. As shown in  FIGS. 2 and 3 , the pry slot  62  is formed at the skirt and at the pull strip  55  which can be lifted by placing a screwdriver or finger or some other implement into the pry slot and exerting an upward force until the thin channel frangible portion  40  tears around the perimeter of the lid. Once the tear has been completed, the skirt outer annular portion outward of the frangible groove would be retained and attached to the container while the replaceable central panel lid would be detached. Later the plug central panel lid portion can be reapplied by inserting it back into place and pushing down on it.  
      The illustrated lids are stacked and nested, one within another, with a corner  20   e  ( FIG. 6 ) at the juncture of the lid sidewall  20  and the central panel resting on stacking ribs  70  formed at spaced locations on the lid sidewall  20 . In order to prevent a vacuum from forming between adjacent stacked lids as interferes with feeding automatically, the ribs  70  also serve as an internal venting facilities. The preferred venting and stacking ribs  70  are preferably located at 45° spacing about the circumference of the skirt wall  20  and projected radially inwardly about the interior of the lid sidewall  20 , as shown in  FIG. 7 . The illustrated ribs extend downwardly to the lid central panel  18  and extending upwardly above a radius shoulder  20   c  as shown in  FIG. 7  between the upper portion  20   b  of the lid sidewall  20  and the lower portion  20   a  of the lid sidewall  20  as shown in  FIGS. 5 and 7 . With the lids nested for feeding by an automatic lid applying machine, the smaller diameter central panel  18  of an upper lid is seated on a top edge  76  of the spaced ribs  70  in a nested position. The top edge  76  of the venting facility rib  70  is located at a height such that it seats a nested lid thereabove with its lower outer edge  78  on its depending skirt flange  66  spaced from the horizontal skirt wall  33  of a lid therebelow to provide a slot or space to allow the insertion of a finger of a lid removing and lid applying equipment for such lids. It is most desirable and necessary that the lid be machine useable with conventional existing package and machinery.  
      Although the energy direction has been shown and described as being on the lid, it is to be understood that the energy director could be on the container rim and still fall within the purview of the claims of the invention. The frangible portion is described and illustrated as a thin web in the skirt wall, but is to be understood that a scored portion or other weakened portion on the lid may be the frangible portion and that the frangible portion could be repositioned to a location other than that on the horizontally extending skirt wall as illustrated in the embodiments herein described.  
      From the foregoing, it will be seen that there has been provided a new and improved lid and container which have a welded portion retained while the reapplied, tamper-evident lid portion is free to be reapplied after the contents of the container accessed to protect the container contents until it is desired to access again the contents.