Abstract:
Conventional adhesive and contact welding methods for holding the paperboard and plastic components of a composite closure together present a number disadvantages and do not lend themselves easily to mass production. The present invention describes two novel approaches, firstly the pre-assembly heating of the closure components with directed hot air to partially melt the thermoplastic surfaces and allow the parts to be immediately assembled sealingly and, secondly, a novel construction of plastic and paperboard composite closure in which the plastic rim is of a two-piece snap-fit constructions which firmly grips the top panel of the paperboard lid.

Description:
RELATED APPLICATION 
     This application replaces and claims priority from U.S. provisional patent application No. 60/656,408 filed on Feb. 28, 2005 and entitled COMPOSITE CLOSURE FOR CONTAINERS, incorporated by reference. 
    
    
     FIELD OF INVENTION 
     This invention relates generally to composite lids for containers and particularly to tamper-resistant, tamper-evident composite lids for containers for products that present significant concerns for the consumer about unauthorized tampering with the product (e.g. food products and other consumables). 
     By a “composite” lid, is intended a lid composed of a sheet of printed matter (e.g. paperboard) serving as a top panel cover and a molded plastic rim secured to and compatible with the panel material to form the means for engaging the lid to a container. Where they are capable of being used in place of wholly plastic lids, composite lids allow for reduced material costs and superior lid-top graphics. 
     A composite container closure of this general kind is exemplified by the tamper resistant composite lids for food containers which are the subject of U.S. Pat. No. 6,772,901 (Witt), owned by the assignee of rights in the present application. In the Witt composite closure member, a cover panel formed from generally flexible sheet material is peripherally sealed to an annular ledge formation which joins two cylindrical ring portions of a closure member having a rupturable line of weakness which breaks upon any attempt to prise the lid off, thereby providing evidence of tampering. The entire specification of U.S. Pat. No. 6,772,901 is expressly incorporated herein by reference for its teaching of tamper-evident closures. 
     BACKGROUND OF THE INVENTION 
     In the ice cream packaging industry, a variety of closure arrangements are used to hold a paperboard, plastic or composite lid in place on the paperboard container or tub holding the ice cream. An example of the combining of paper and plastic in the design of a container closure of this general kind is afforded by U.S. Pat. No. 6,053,353 (Helms), in which the composite lid includes a blank of sheet material and a peripheral molding, with a marginal portion of the blank being displaced out of the general plane of the central panel. The peripheral molding includes the marginal portion of the blank bonded to a portion of the rim on an exterior surface, in order to control longitudinal shrinkage and provide a printed surface on the marginal section. 
     In the composite lid of aforementioned U.S. Pat. No. 6,772,901, the top portion of the lid consists of a polymeric layer for moisture resistance attached to a paper disk suitable for the application of product identification printing on the top side. A poly-layer on the underside of the paper disk keeps moisture from the product from entering the paper and enables the disk to be bonded to the plastic ring. The top and bottom portions of the ring are bonded together by fusing the poly-layer of the paper to a landing on the plastic ring by conduction, ultrasonic or spin welding. Alternatively, a coating of adhesive applied to either surface before insertion of the disk may be used. Once joined together, the upper and lower portions form a composite-closure. 
     SUMMARY OF THE INVENTION 
     It is a general object of the present invention to provide composite container closure members, comprising a plastic rim and paperboard lid, in which the lid is sealingly secured to inwardly directed peripheral means on the rim, without the requirement for any adhesives or any contact welding treatment such as conduction, ultrasonic or spin welding. 
     It is a further object of the present invention to provide composite container closure members of this kind, including tamper-resistant, tamper-evident features. 
     According to a first embodiment of the invention, the plastic rim comprises a lower, inner ring portion and an upper, outer ring portion, both made of a fusible thermoplastic material such as low density polyethylene (LDPE). The lower ring portion includes an upper peripheral edge formation adapted to fit matingly within a cylindrical trough formed within the upper ring portion, and an inner ledge formation to support a paperboard lid. That lid has at least its upper surface coated with a film of the same thermoplastic material as the rings. 
     The upper ring portion includes an inwardly projecting annular flange parallel to the outer periphery of the lid. In a pre-sealing position, the upper ring and the lower ring holding the paperboard disk lid are maintained slightly apart. Hot air is directed into the trough portion of the upper ring and at the underside of the annular flange. When the lower surface of the flange and the inner-side wall of the trough of the upper ring become molten, the upper ring is vertically lowered into its mating position with the lower ring and the upper ring adheres to the thermoplastic layer on the paperboard and to the outer side-wall of the lower ring. 
     According to a second embodiment of the invention, the plastic rim is of a two-piece snap-fit construction including an inwardly directed peripheral means which grips the top panel of the paperboard lid securely when assembled. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top perspective view of an ice cream container with closure means according to either of the embodiments of the present invention, including tamper-resistant, tamper-evident features; 
         FIG. 2  is an exploded view of the ice cream container of  FIG. 1 , with lid components according to the first embodiment of the invention; 
         FIG. 3  is a vertical cross-sectional view taken along the long axis X of  FIG. 1  of an ice cream container which includes closure means according to the first embodiment of the invention; 
         FIGS. 4   a ,  4   b  and  4   c  are respectively perspective, side elevational, and top plan views of assembled closure means according to either embodiment of the invention; 
         FIG. 5  is an enlarged sectional view along line A-A in  FIG. 4   a  of the mutually engaging components of the container and lid when assembled according to the first embodiment of the invention; 
         FIG. 6  schematically illustrates means for heating the lid components prior to assembly, according to the first embodiment of the invention; 
         FIG. 7  schematically illustrates the set position of the heated composite lid components immediately prior to assembly, according to the first embodiment of the invention; 
         FIG. 8  schematically illustrates the contacting and final assembly of the components of the composite closure according to the first embodiment of the invention; and 
         FIG. 9  is an enlarged sectional view along line A-A in  FIG. 4   c  of the mutually engaging components of a container and lid according to the second embodiment of the invention, when assembled. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As best seen in  FIGS. 1-3 ,  5  and  9 , a composite closure  10  according to the present invention and adapted to seal a conventional ice cream container  12 , comprises an upper cylindrical ring  14  and a lower cylindrical ring  16 , both made of resilient-plastic, which fit together to hold a paper lid cover portion  18  flat in the horizontal plane, perpendicular to the axis of the container when the closure is in place. As best seen in  FIG. 5 , upper ring  14  presents at its upper end a concave trough  15  adapted to closely receive an elongate bead  16   a  integral with lower ring  16 . Lower ring  16  also features regularly spaced ledge formations  16   b  for peripheral seating of the paperboard disk  18 . 
     Integral with upper ring  14  is an annular flange  14   a  which contacts the upper surface of lid  18  when outer ring  14  is fitted closely over lower ring  16  as illustrated in  FIG. 5 . 
     Upper ring  14  and lower ring  16  are fabricated of a meltable thermoplastic such as low-density polyethylene (LDPE) and at least the upper layer of disk  18  is coated with a fusible poly-layer. Optionally and advantageously, a poly-layer is also applied to the underside of paper disk  18  to keep moisture from the product from entering the paper. 
     The upper and lower ring portions of the closure are bonded together and to the top poly-layer of the paper by a novel hot-air welding method which will be described below and which is simpler and more efficient than conventional laser or ultrasonic welding of the components of a composite lid. 
     In the particular embodiments of the invention illustrated in the drawings, the lower ring is also a tamper-evident closure component. As best seen in  FIGS. 5 and 9 , lower cylindrical ring  16  [ 16 ′] includes a lower portion  16   c  [ 16 ′ e ] which joins the upper portion of wall  16  [ 16 ′] along a ring which is thinned and weakened by means of a circumferential notch  16   d  [ 16 ′ f ]. Legitimate opening of the container by a consumer starts by separating the upper and lower portions of cylindrical ring  16  [ 16 ′] by tearing away the lower part  16   c  [ 16 ′ e ] thereof along the line of weakness  16   d  [ 16 ′ f ]. Alternatively, the tear-away portion may be joined to the rest of the closure by separate frangible tabs. 
     Extending upwardly and inwardly from the lower portion  16   c  [ 16 ′ e ] of lower ring  16  [ 16 ′] are a circumferentially spaced plurality of teeth  20  which lock under the rim  12   a  of container  12  when the lid is first pushed downwardly to seal the container. 
     For convenience in legitimately opening the container, the lower part  16   c  [ 16 ′ e ] of the lower cylindrical ring portion  16  [ 16 ′] may be provided with gripping means such as a thumb notch  21  disposed at a location on the lower periphery, as best seen in  FIGS. 1 and 2 . By exerting moderate force on the accessible edge portion  22  (here shown serrated for easy gripping), that part of ring  16  [ 16 ′] which is below the line of weakness  16   d  [ 16 ′ f ] is readily removed as a tear-away strip, taking with it the circumferential line of teeth  20 , for easy removal from the closure and from the container. 
     Method of Hot Air Sealing of Composite Lid Components 
     In connection with this first embodiment of the present invention, special reference may be made to drawing  FIGS. 1-8 . The hot-air welded surfaces joining upper ring  14  to lower ring  16  and upper ring annular flange  14   a  to the plasticized upper surface of paperboard lid  18  are indicated in  FIG. 5  by arrows  24 . 
     The essential process of the invention comprises maintaining upper ring  14  spaced slightly above lower ring  16  in which paperboard disk has already been seated flat on ledge formations  16   b . Hot air is then injected into the trough  15  in direction toward flange  14   a  and the inner side-wall  14   b  immediately connecting to flange  14   a.    
       FIG. 6  schematically illustrates a holder  26  for upper ring  14  which includes a central port  28  for receiving hot air from a source of heated air and which branches into hot air channels  28   a  including peripheral hot air ports  28   b  for directing hot air at contact portions  14   a  and  14   b  of upper ring  14 . In the “heat” position illustrated in  FIG. 7 , the upper ring  14  is held so that hot air is directed into trough  15  toward the annular flange  14   a  and inner side-wall  14   b  of upper ring  14 . The lower ring is aligned in position directly beneath. After a suitable period of time in the heat position, the annular flange and inner side-wall become molten and are ready to be moved to the “marriage” position illustrated in  FIG. 8 . 
     The marriage position is effected, after sufficient heat is added to upper ring  14 , by moving the upper ring holder  26  down for mating contact of upper ring  14  with lower ring  16 . The molten annular flange  14   a  adheres to the polyethylene layer on the upper surface of paperboard  18  and the molten side-wall  14   b  adheres to the outer side-wall of lower ring  16 . A slight clamping pressure may be applied while the thermoplastic solidifies, for a stronger seal. 
     Snap-Fit Construction of Composite Lid 
     In what follows, reference may be made to drawing  FIGS. 1 ,  4   a  to  4   c  and  9 . According to this embodiment of the invention, the composite closure for sealing a conventional ice cream container  12  again comprises an upper cylindrical ring,  14 ′ and a lower cylindrical ring  16 ′, both made of resilient plastic. Upper cylindrical ring  14 ′ includes an interior recess towards its upper peripheral margin  14 ′ b , configured to receive and snap-fit over an upper peripheral integral projection  16 ′ a  on inner ring  16 ′. 
     About their respective concave inner surfaces, upper and lower cylindrical rings  14 ′ and  16 ′ present superposable annular flanges  14 ′ c  and  16 ′ c , respectively, which come together to securely hold a paper lid cover portion  18  flat in the horizontal plane perpendicular to the vertical axis of the container when the closure is in place. 
     The lower portion of rings  14 ′ and  16 ′ may be further releasably held in close contact by an arrangement of interdentate wall projections  17  which are disengaged if the lower periphery  14 ′ d  of the upper ring is manually pulled away from the corresponding bottom portion  16 ′ d  of the inner cylindrical ring. The mating surfaces of  14 ′ and  16 ′ may advantageously include a “neck” region  19  for a more secure snap-lock fit. 
     Variations on interlocking geometries which achieve the objective of the present invention in “clamping” of the periphery of the paperboard lid  18  in a single unitary closure could readily be made without departing from the spirit of the invention. 
     In the particular embodiment illustrated in the drawings, the closure including the snap-fitted cover lid is also a tamper-evident closure. Extending upwardly and inwardly from the lower peripheral margin  16 ′ e  of lower ring portion  16  are a circumferentially spaced plurality of teeth  20  which lock under the rolled rim  12   a  of container  12  when the lid is first pushed downwardly to seal the container. 
     As best seen in  FIG. 9 , a circumferential portion of the wall of lower cylindrical ring  16 ′ is thinned and weakened, here by means of a circumferential notch  16 ′ f . Legitimate opening of the container by a consumer starts by a separation of the upper and lower portions of cylindrical ring  16 ′ by tearing away the lower part thereof along the line of weakness  16 ′ f . Alternatively, the tear-away portion may be joined to the rest of the closure by separate flangeable tabs. 
     As with the tamper-evident disclosure discussed above and again as shown in  FIG. 1 , the lower cylindrical ring portion may be provided with gripping means such as a thumb notch  21  disposed at a location on the lower periphery. By exerting moderate force on the serrated accessible edge portion  22 , that part of the lower ring  16 ′ which is below the line of weakness  16 ′ f  is readily removed as a tear-away strip, taking with it the circumferential line of teeth  20 , for easy removal from the closure and from the container. 
     As noted above, disk  18 , typically made of paperboard or the like, may be printed on its upper side for product identification, marketing information, graphics, etc. For use of ice cream food products, a paper disk  18  will generally have a polymeric film permanently attached to the underside, for keeping moisture from entering through the paper. However, according to this embodiment of the invention, the securing of the paperboard lid to the plastic portion of the closure is achieved entirely by the clamping fit action of ring sections  14 ′ c  and  16 ′ c  as described above. 
     By contrast with prior art composite container closures in which the paper lid portion is moulded right into the container side-wall or is laser-welded or otherwise chemically adhered to the plastic material of the closure, the closure in this arrangement allows paper disk  18  to be completely removed from the plastic ring, making recycling a simple matter. 
     While only a single example of this embodiment of the invention has been illustrated, those of ordinary skill in the art will readily appreciate a number of modifications to the illustrated snap-fit arrangement in composite lids, within the inventive concept.