Abstract:
A reclosable container includes a container having an opening defined by a rim, a reclosable lid having a rim-engaging portion and a recessed portion inwardly of the rim-engaging portion, and a sealing sheet material separate from the lid, the sealing sheet material extending across the opening and being removably secured to the container rim beneath the lid, wherein the recessed portion of the lid projects into the container opening and the sealing sheet material has a recessed portion which accommodates the recessed portion of the lid.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to the field of containers, particularly reclosable containers, that is containers having a lid, and to a method of forming a sealed container package.  
           [0002]    Reclosable containers are desirable for a variety of reasons. For example, the contents may be subject to contamination, or spillage, if a container is not reclosed after first being opened.  
           [0003]    Conventional containers with lids which can be opened and reclosed are not usually airtight, in which case they will not possess any sealing properties. Many products require a sealed environment prior to first being opened, not only to alleviate the risk of oxidation prior to the product being sold, but also to resist other contamination. Such products are commonly sold in containers with a sheet of film or foil sealed across the opening. If such products are unlikely to all be consumed immediately following removal of the sealing sheet material, a reclosable lid is commonly supplied with the container.  
           [0004]    Many different forms of sealed reclosable containers have been proposed. By way of example, AU 58499/80 proposes a lid for a container comprising a panel of sheet material for covering the container opening, and a moulded plastic rim for engaging the rim of the container, the sheet material being bonded to the plastic rim of the lid during an injection moulding process in which the plastic rim is formed. The sheet material is a laminate and the bottom layer is sealed to the container rim when the lid is fitted to the container. Subsequently, when the lid is removed, the bottom layer separates from the remainder of the sheet material and remains bonded to the container. The bottom layer can be ruptured, peeled or cut away, for access to the contents. However, the lid can then be replaced to give protection to any remaining contents.  
           [0005]    In this proposal, the formation of a specially adapted lid as well as the requirement of a panel of sheet material in laminate form adds complexity and cost to the manufacture of the container.  
           [0006]    A sealed container is also disclosed in AU 63912/90. This disclosure addresses the problem of bonding the sealing sheet material to a narrow cylindrical upper edge of a container. This problem is overcome by bonding the sealing sheet material not only to the upper edge but also to an annular inner surface of the container rim which is inclined downwardly and inwardly, thereby increasing the bonded surface area and allowing for tolerances in the diameter of the container rim. It is further proposed that a container closed in such a way can additionally be covered with a reclosable cover.  
           [0007]    Thermoformed or thin-walled injection moulded lids for containers such as the well known thermoformed or thin-walled containers used, for example, for butter or margarine commonly are shaped to increase the strength and/or flexibility of the lid at the container rim-engaging portion. Generally, this shaping involves recessing the central or inner portion of the lid so that when the lid is engaged with the container rim the recessed inner portion projects into the container opening. The recessed inner portion of the lid is connected to an inner wall of the rim-engaging portion which increases the flexibility of the rim-engaging portion and the overall strength of the lid.  
           [0008]    Containers of the type described in the immediately preceding paragraph have been sealed with a sealing sheet material that is bonded to the upper edge of the container rim and extends in a planar manner across the container opening. Since such a sealing sheet material interferes with a lid of the type described in the immediately preceding paragraph, a different lid has been used. This lid is modified by forming the material of the lid into an annular inverted channel in the rim engaging portion which channel overlies the container rim. The inner portion of the lid extends from the bottom of an inner wall of the inverted channel across the container opening at the level of the upper edge of the container rim and overlies the sealing sheet material.  
           [0009]    One such prior art sealed container and lid assembly  110  is illustrated in FIGS. 1 and 2. A conventional container  112  has a base  114  and continuous side wall  116  upstanding from the base. Adjacent the rim  118  of the container, the sidewall has an annular reinforcing flange  120 . The rim  118 , which defines the container opening  122 , is in the form of an inverted channel  124  an inner wall  126  of which projects upwardly from the reinforcing flange  120 . An annular base  128  of the inverted channel extends outwardly from the inner wall  126 , generally transversely to the axis of the container, and an annular skirt  130  depends from the outer edge of the base  128 . Such a container is of thin-walled plastics and is formed by injection moulding or thermoforming.  
           [0010]    The lid  132  of the assembly  110  is modified from a conventional lid (illustrated in FIGS. 3 and 5) to accommodate a planar sealing sheet material  134  extending across the container opening  122  and bonded to the base  128  of the inverted channel  124  defining the container rim. The lid  132  has a container rim engaging portion  136  and a planar inner or central portion  138  which overlies the sealing sheet material  134 . The rim engaging portion  136  includes an annular skirt  140  which cooperates with the depending skirt  130  of the container rim by snap engagement to hold the lid on the container  112 .  
           [0011]    Between the annular skirt  140  and the inner portion  138  of the lid, the rim engaging portion  136  includes an annular inverted channel portion  142  which substantially overlies and projects up from the base  128  of the container rim when the lid is engaged with the container. The lid  132  is thermoformed or injection moulded in thin-walled plastics material and the inverted channel portion  142  increases the overall rigidity of the lid while enhancing the flexibility of the annular skirt. The inverted channel portion also defines with the inner portion  138  a recess capable of receiving the base  114  of another container  112  so as to facilitate stacking of the container and lid assemblies  110 .  
         SUMMARY OF THE INVENTION  
         [0012]    According to the present invention there is provided a reclosable container comprising:  
           [0013]    a container having an opening defined by a rim;  
           [0014]    a reclosable lid having a rim-engaging portion and a recessed portion inwardly of the rim-engaging portion; and  
           [0015]    sealing sheet material separate from the lid, the sealing sheet material extending across the opening and being removably secured to the container rim beneath the lid;  
           [0016]    wherein the recessed portion of the lid projects into the container opening and the sealing sheet material has a recessed portion which accommodates the recessed portion of the lid.  
           [0017]    By the present invention, the cost and other disadvantages of providing a different lid when it is desired to provide sealing sheet material across a container opening are alleviated.  
           [0018]    The lid is therefore preferably essentially conventional, wherein the rim-engaging portion of the lid has an inverted channel-shaped cross-section with an annular base which overlies the container rim, an outer skirt depending from the base outwardly of the container and an inner wall depending from the base within the container opening, with the recessed portion of the lid extending from a distal edge of the inner wall. The outer skirt of the lid will generally make an interference fit with the rim to engage the lid with the container, for example by screw-threaded engagement or, preferably, snap engagement. The base of the rim engaging portion of the lid preferably overlies the container rim adjacent thereto with the sealing sheet material therebetween.  
           [0019]    The lid is preferably thermoformed or injection moulded, advantageously with a thin-walled construction. By thin-walled as used throughout this specification is meant a wall thickness of no greater than about 1 mm, more preferably between 0.2 and 0.6 mm. The lid may be of any suitable plastics material, whether in mono- or multilayer form, selected for example from one or more of PET, polypropylene (PP), high impact polystyrene (HIPS), all types of polyethylene (PE), nylon and, in a multilayer structure, ethylene/vinyl acetate (EVA). In a preferred embodiment, the lid is thermoformed in PP.  
           [0020]    The container may also be essentially conventional, for example a thermoformed or injection moulded container, particularly an injection moulded thin walled container formed from, for example, any of the materials mentioned above for the lid, whether with a mono- or multi-layer structure. The container may have a circular, oval or any other desired cross-section.  
           [0021]    In a preferred embodiment the rim of the container comprises an upper end face supported at an inner edge by a wall of the container and a skirt depending from the upper end face. Generally the lid will cooperate with the skirt of the container rim to removably engage the lid with the container. Preferably, the upper end face of the rim extends substantially transversely to the axis of the container.  
           [0022]    Depending upon the material of the sealing sheet material and of the container, the sealing sheet material may be heat sealed and/or adhesively engaged with the container rim, preferably with an upper end face of the container rim. Possible materials for the sealing sheet material include a metal foil such as aluminium, a polymer/metal laminate, a polymer film and a multi-layer polymer film. Suitable polymer films include polyethylene terephthalate (PET), nylon, polypropylene, polyethylene in any of its forms such as LDPE, LLDPE and HDPE, and polystyrene alone or in a variety of multilayer combinations. Many different types of multi-layer polymer films are known and may be suitable depending upon the container contents, the gas permeability and other desired characteristics of the film, the method of forming the recessed portion in the sealing sheet material and the method of bonding the sealing sheet material to the container rim. A simple multi-layer structure might be PET with a sealant layer of modified EVA. If it were desired to print the sealing sheet material a top layer of PE may be provided, bonded to the PET with an adhesive such as EVA.  
           [0023]    A polymeric film may incorporate desirable additives such as oxygen scavenging materials.  
           [0024]    Further according to the present invention, there is provided a method of forming a sealed container package which comprises providing a container having a container opening defined by a rim of the container;  
           [0025]    providing a sealing sheet material across the container opening and removably securing the sealing sheet material to the container rim;  
           [0026]    forming a recessed portion in the sealing sheet material whereby at least after the sealing sheet material has been secured to the container rim the recessed portion projects into the container opening; and  
           [0027]    attaching a reclosable lid to the container rim, the lid projecting into the recessed portion of the sealing sheet material within the container opening.  
           [0028]    Also depending upon the material of the sealing sheet material, the recessed portion in the sealing sheet material may be cold-formed, for example by deep drawing, or thermoformed. Thermoforming may be carried out with a vacuum or fluid pressure, but preferably a former is engaged with the sealing sheet material to form the recessed portion therein. The sealing sheet material, or part of it, may be heated before, at the same time as and/or after the former is engaged with the sealing sheet material.  
           [0029]    The recessed portion in the sealing sheet material need be substantially no deeper than the recessed inner portion of the lid. The recessed portion of the sealing sheet material may be at least partly formed before the sealing sheet material is secured to the container rim; for example, it may be preformed, that is before the sealing sheet material is provided across the container opening. However, preferably the recessed portion of the sealing sheet material is formed at the same time as and/or after the sealing sheet material is secured to the container rim.  
           [0030]    Most preferably, the recessed portion of the sealing sheet material is formed after the sealing sheet material has been secured to the container rim, at least to the extent that the sealing sheet material is not drawn across the container rim as the recessed portion is formed. This is especially advantageous in a forming station in which multiple lines of containers are having the sealing sheet material secured thereto and the recessed portions formed simultaneously from a single sheet of the sealing sheet material, since it alleviates puckering caused when sealing sheet material is drawn across or from one container rim as the recessed portion is formed in the sealing sheet material on an adjacent container.  
           [0031]    In a preferred embodiment, the sheet sealing material is a thermoformable film or foil and the action of heating the film for the thermoforming procedure also initiates securing of the film to the container rim. For a polymeric film, the heating of the film may soften it such that it can be heat sealed to the container rim or to a surface layer on the container rim. Alternatively, the heating may activate an adhesive or sealing layer on the sheet sealing material. Polyethylenes and modified EVAs are examples of adhesives or sealing materials which may have a similar sealing temperature range as the thermoforming temperature range of at least one of PET, polypropylene, nylon and polystyrene.  
           [0032]    The thermoformable film or foil may be heated by contact heaters, induction, infra red, hot air or any other commonly used heating method. In the aforementioned preferred embodiment, the thermoformable film or foil is advantageously heated for the thermoforming process by means for holding the sealing sheet material on the container rim as it is bonded thereto.  
           [0033]    The sheet sealing material may be cut or otherwise shaped to the desired size at any time, prior to, during or after it is secured to the container rim. In the preferred embodiment it is cut after being secured to the container rim. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0034]    One embodiment of a reclosable container and a method of forming same in accordance with the invention will now be described, by way of example only, with reference to the accompanying drawings in which:  
         [0035]    [0035]FIG. 1 is a cross-sectional view of a prior art sealed container and lid assembly;  
         [0036]    [0036]FIG. 2 is an enlargement of the circled portion of FIG. 1;  
         [0037]    [0037]FIG. 3 is a cross-sectional view similar to that of FIG. 1 but of a reclosable container in accordance with the invention;  
         [0038]    [0038]FIG. 4 is an enlargement of the circled portion of FIG. 3;  
         [0039]    [0039]FIG. 5 is a view similar to FIG. 4 but with the container lid omitted; and  
         [0040]    [0040]FIGS. 6A to C show three successive stages of one method of forming the sealed container, without the lid, of FIGS.  3  to  5 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0041]    Referring to FIGS.  3  to  5 , the sealed container and lid assembly  10  has a conventional thin-walled injection moulded or thermoformed container  12  which is identical to the container  112  described with reference to FIGS. 1 and 2. For convenience only, the container  12  will not be described again in detail and any subsequent reference to its component parts will be followed by a reference numeral corresponding to the reference numeral given to the same part of the container  112  but at one order of magnitude less (e.g., the base of the container  12  is designated by reference numeral  14  instead of  114  as in FIG. 1).  
         [0042]    The lid  32  of the assembly  10  is also a conventional thermoformed or injection moulded thin-walled lid, but is of a type which hitherto has only been used with a container  12  without sealing sheet material extending across the container opening  22  and bonded to the container rim  18 . The lid  32  has a container rim-engaging portion  34  and a central or inner portion  36  which is recessed and which, with reference to FIGS. 1 and 2, would interfere with the planar sealing sheet material  134  extending across the container opening  122 . However, in accordance with the present invention, the lid  32  can be used because a sealing sheet material  38  extending across the container opening  22  and bonded to the container rim  18  is recessed from adjacent the container rim and projects into the container opening to accommodate the recessed portion  36  of the lid.  
         [0043]    The rim-engaging portion  34  of the lid  32  also has an inverted channel-shaped cross section with a generally upright inner wall  40  from the lower edge of which the recessed inner portion  36  of the lid extends. A base  42  of the inverted channel extends from the upper edge-of the inner wall  40  and closely overlies the base  28  of the container rim  18  with the sealing sheet material  38  bonded to the container rim therebetween. An annular skirt  44  depends from the outer edge of the base  42  of the rim-engaging portion  34  to cooperate by snap engagement with the annular skirt  30  of the container rim to remove and engage the lid  32  with the container  12 .  
         [0044]    Comparing the engaged lid  32  illustrated in FIGS. 3 and 4 with the lid  132  of FIGS. 1 and 2, it may be seen that the engaged lid  32  does not project upwardly substantially above the container and that the recessed inner portion  36  is within the container opening  22  so that a stack of container and lid assemblies  10  have a reduced height compared to the same number of stacked container and lid assemblies  110  using an identical container  112 . One method of forming the recessed sealing sheet material  38 , which permits the use of the recessed lid  32 , is described with reference to FIGS. 6 a  to  c.    
         [0045]    In FIG. 6 a , the container  12  having the desired contents (not shown) therein is disposed at a sealing and thermoforming station  50  with a thermoformable sheet  52  which will form the recessed sealing sheet material  38  supported across the opening  22  of the container. The sheet  52  may be supported between a supply roll and a take-up roll (not shown), or it may be pre-cut substantially to size in which case it may be supported between spaced grippers (not shown). In any event, the sheet  52  overlies the base  28  of the container rim  18  around the full periphery of the container.  
         [0046]    Supported above the container  12  and sheet  52  in the sealing and thermoforming station  50  is a sealing and thermoforming platten  54  which is advanceable towards and withdrawable away from the container by any of a variety of known arrangements (not shown) including pneumatically hydraulically or by means of a servo motor. The platten  54  supports an annular sealing bar  56  on its underside. The shape of the annular sealing bar corresponds to that of the base  28  of the container rim  18  and the sealing bar  56  overlies the rim  18  so as to press the sheet  52  onto the upper face of the base  28  when the platten  54  is advanced.  
         [0047]    Also supported from the underside of the platten  54 , within the annular sealing bar  56 , is a thermoforming plug  58 . The plug  58  is shown suspended from the platten  54  by means of a plurality of springs  60 , but these schematically represent any suitable means for permitting the plug  58  to be advanced away from and withdrawn towards the platten. Such means may comprise one or more springs, pneumatic or hydraulic means or a servo motor device.  
         [0048]    As shown, in a rest state illustrated in FIG. 6 a , the plug  58  is advanced way from the platten  54  so as to project beneath the annular sealing bar  56 . Thus, as the platten  54  is advanced the plug  58  engages the sheet  52  before the sealing bar  56 . However, at least once the sheet  52  is supported on the rim  18 , the tension in the sheet will overcome the bias in the springs  60  and the plug  58  will withdraw towards the platten  54 , permitting the sealing bar  56  to press the sheet material  52  onto the rim  18  as the platten  54  is advanced further.  
         [0049]    The sealing bar  56  is heated so as to effect the bonding of the sheet  52  onto the rim  18  when they are pressed together. Bonding may be achieved by the material of sheet  52  and of the container rim  18  being compatible so that the two materials fuse when they are heated. In a multilayer film  52 , only a lowermost sealing layer need have this compatibility. Alternatively, a heat activated adhesive layer may be applied to one or both of the lower surface of the sheet  52  and the upper face of the base  28  of the container rim. This stage of the sealing and thermoforming process is shown in FIG. 6 b.    
         [0050]    The heated sealing bar  56  also causes the annular portion  62  of sheet  52  between the plug  58  and the container rim  18  and sealing bar  56  to soften. As soon as softening of the material in portion  62  is sufficient, the bias in the springs  60  urging the plug  58  to advance away from the platten  54  stretches the annular portion  62  and causes the recess in the sheet material  52  to be formed. As soon as the plug has fully advanced, the platten  54  is withdrawn leaving the sheet material  52  bonded to the container rim with a thermoformed recess in the sheet material. Advantageously, the portion of the sheet  52  inwardly of the annular portion  62  is not stretch during the thermoforming process. However, if this is desired the plug  58  may also be heated.  
         [0051]    The forming of the recess in the sheet  52  is illustrated schematically in FIG. 6 c . As will be appreciated from FIGS.  3  to  5  the recess must be of sufficient depth and cross-section to accommodate the lid  32 . It is also to be noted that the container  12  is illustrated schematically in FIG. 6, particularly in that the depending skirt  30  is omitted.  
         [0052]    As alternatives to the described processes, the plug  58  may be rigidly supported by the platten  54 , in which case the annular sealing bar  56  should be advanceable and withdrawable relative to the platten. In such an arrangement, the sealing bar would be initially advanced relative to the plug  58  and would initially press the sheet  52  onto the container rim  18  before the plug  58  engages the sheet  52 . As the platten  54  is advanced further to form the recess in the sheet, the sealing bar must withdraw relative to the platten. Alternatively, in a similar arrangement, the sealing bar  56  may be fixed and the plug  58  relatively adjustable, but the plug  58  is withdrawn initially so that the sealing bar engages the sheet  52  first. These alternatives may be useful when the sheet  52  is at least substantially pre-cut and not supported, or not adequately supported, at its periphery.  
         [0053]    The final cutting, if necessary, of the thermoformed sheet  52  may be effected by the sealing bar  56 , by separate means (not shown) at the sealing and thermoforming station  50  or at a separate station. Cutting of the sheet may be performed by any industry standard such as a hot or cold steel rule knife or forged knife, or a punch and die assembly.  
         [0054]    It will be understood that heating of the sheet  52  may be effected by other means than the sealing bar  56 . In a variation the sheet  52  may be bonded to the container rim  18 , and optionally cut, in one station, with the recess being formed in the sheet  52  in a separate station.  
         [0055]    A major advantage of the described sealing and thermoforming station is that it may be incorporated as part of a standard container filling-line process, that is filling, sealing and closing, up to 60 containers or more per minute, with other optional procedures being included if desired. For example, if a modified atmosphere packaging process is called for, the ambient air in the head space above the contents in the container  12  may be at least partly replaced by the modified atmosphere as the sheet  52  is bonded to the container rim. Parallel sealing and thermoforming stations may be used in multiple filling lines so that, for example, for four lines up to 240 or more containers may be processed per minute.  
         [0056]    Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is to be understood that the invention includes all such variations and modifications which fall within its spirit and scope.