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(11) | EP 1 061 000 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | One piece lid for a receptacle |
| (57) A lid for a receptacle includes a sealing portion which, in use, is capable of forming
a hermetic seal between the lid and an opening on the receptacle. The lid and the
sealing portion thereof are formed from the same polymer composition and the sealing
portion comprises the composition in the form of one or more foamed sections. The lid alleviates the problems of backing off and hermetic sealing and is recyclable. Furthermore, it is capable of being formed in a single injection moulding operation. |
BACKGROUND OF THE INVENTION
Field of the Invention
[0001] This invention relates to a lid for a receptacle, to a process for its production and to a container for a foodstuff which comprises the lid and a receptacle.
Description of the Related Art
[0002] In order to maximise the shelf-life of foodstuffs which are prone to atmospheric deterioration or microbiological spoilage caused by contact with air and which are offered to the consumer in screw lidded receptacles it is generally considered necessary to provide a seal, between the lid and the receptacle, which is generally hermetic (i.e., substantially or completely airtight). A hermetic seal can be difficult to achieve using a lid without an inserted wadding or liner when the receptacle is made from glass or from plastics materials formed into their final shape by a process incorporating a plastics extrusion stage and an injection moulding stage. This is because the surface of such glass or plastics receptacles, at the sealing surface of the receptacle over which the lid is applied, can be inherently rough. Thus, it is conventional in the art to use a lid which has sealing media, such as wadding or a deformable lining material inserted into the lid, to seal more effectively against surface irregularities that occur in the sealing surface of the receptacle. A further problem suffered by a lid, which has no inserted sealing media, for a receptacle onto which the lid is screw-fit is that the lid can loosen from the initial torque provided, a phenomenon known in the art as "back off". Loosening can be caused by the natural creep of the materials used or during transportation for instance by continued vibration. It is, thus, difficult, in the absence of sealing media, to maintain sufficient torque on a screw-fit lid to prevent it from unscrewing and thus weakening the seal.
[0003] Attempts to solve the problem of providing a hermetic seal between a container and a lid which is a screw-fit with the container have involved the use of a deformable insert or seal in the lid. Thus, it is known to provide sealing media, e.g., a wad of deformable material in the lid to solve the problems of sealing and to improve the maintenance of torque to reduce backing off. The incorporation of sealing media into the lid takes place after the lid has been formed, either by simply physically positioning a wad of deformable material in the lid or by injection moulding two plastics materials in a single operation into a single injection moulding cavity; one material being used to produce the load bearing cap and a further deformable material being injected into the sealing surface to form an integral deformable lining to mate with the sealing surface on the receptacle thus providing a seal. In either case, the number of steps for producing the lid is increased by the inclusion of a wad or lining and, because the wad or lining and the lid have different chemical compositions, the overall lid (i.e., the lid plus the wad or lining) cannot be recycled easily without an expensive separation operation.
[0004] Another solution to the problem of providing a hermetic seal, particularly where a metal lid is involved, involves the use of a flowed in lining composition located in the sealing area in the lid. Before the lid has been put onto the receptacle, the lining composition is softened, typically by heating the lid externally with steam, such that it flows or deforms to take up the surface roughness between the opposing surfaces of the lid and the receptacle to provide an effective seat between them. As it is tightened the softenable or deformable lining composition helps maintain torque.
[0005] In packaging for less sensitive foodstuffs, where hermetic sealing is desirable but not essential, the problem of backing off which can occur when lids of plastics material are screw-fitted to receptacles has been addressed by using a so-called tightening ring with a so-called "crab's claw" seal. The tightening ring provides a bead on the inside of the lid which allows sufficient torque to be applied to the lid to inhibit backing off and to afford protection to the "crab's claw" seal. A problem with "crab's claw" seals, however, is that they are by their very nature deformable and repeated impacts, caused by vibration and excessive top loading during transportation for example, can cause them to become damaged. Sustained damage can cause failure of the seal with the result that leakage from the receptacle may occur.
SUMMARY OF THE INVENTION
[0006] The present invention relates to a lid formed of a single material which alleviates the problems of backing off and hermetic sealing whilst at the same time being recyclable. The lid of the invention has the further advantage of being capable of being formed in a single injection moulding process and, therefore, the process for its production is as simple as the process for producing a basic lid without a wad.
[0007] According to the present invention, there is provided a lid for a receptacle which lid includes a sealing portion which, in use, is capable of forming a hermetic seal between the lid and an opening on the receptacle, wherein the lid and the sealing portion thereof are formed from the same polymer composition and wherein the sealing portion comprises the composition in the form of one or more foamed sections and wherein, in use, the one or more foamed sections are capable of coming into direct contact with the opening and/or a sealing surface of the receptacle.
[0008] Forming the sealing portion as an integral part of the lid simplifies the process for producing a lid with a seal. Also, forming the lid as a onepiece article from a single polymer composition means that the lid can be readily recycled or recovered. The sealing portion of the lid which comprises the same polymer composition as the non-sealing portion of the lid comprises a foamed section which, in use, takes up surface imperfections (for example by being resiliently deformable) like a wad as used in the prior art and maintains torque. In one embodiment, the sealing portion of the lid is positioned around all or part of an edge region of the lid, for example in an annular manner.
[0009] Preferably, the sealing portion is adapted to compress against a specific sealing surface on the receptacle. Thus, the sealing portion provides a seal against a sealing surface of the receptacle which may be on, outside of and/or inside of the rim of a receptacle such as a bottle or jar whilst allowing application of the appropriate amount of torque to inhibit backing off and to maintain a seal.
[0010] The receptacle is preferably a bottle or jar formed of glass or of a suitable plastics material.
[0011] The lid preferably has means for releasable attachment to the receptacle. Thus, although the lid may be intended to be permanently attached to the receptacle such that the lid remains associated with the receptacle even when it does not cover the opening on the receptacle, it is preferred that it is completely detachable from the receptacle. The means for releasable attachment preferably comprises a portion on the lid having a profile adapted for interengagement with a complimentary profile provided at or near the neck and/or mouth of the opening on the receptacle. This may comprise a screw-threaded arrangement, for instance using a multi-start thread or a continuous thread, between the receptacle and the lid involving a screw-thread on the receptacle and a corresponding screw thread and/or lugs on the lid. The screw thread may have a relatively steep angle such that less than one complete rotation of the lid relative to the mouth or neck of the receptacle is required to attach or remove it from the receptacle.
[0012] The lid of the invention is produced by a process comprising injection moulding. The sealing portion of the lid is formed by selective blowing of the polymer composition in predetermined regions of the lid to cause those regions of the lid to become foamed. The remaining parts of the lid, thus, remain essentially unexpanded. This means that the profile formed for interengagement with the receptacle to provide a screw-fit will remain strong to enable torque to be applied and maintained. Selective blowing of thermoplastic polymer compositions is a,known technique.
[0013] In another embodiment, the present invention provides a process for producing the lid of the invention comprising injection moulding a polymer composition to form an intermediate moulded body and then subjecting one or more predetermined regions of the intermediate moulded body to selective blowing to cause said predetermined regions to undergo foaming to form the sealing portion of the lid.
[0014] One way of selectively blowing the predetermined regions of the intermediate moulded body is achieved by forming the said regions at a greater thickness than the remainder of the body. Thus, if a blowing agent is incorporated into the whole of the polymer composition, on release of the moulded body from the mould, the thicker parts of the moulded body which are still soft are expanded by gas in the polymer composition. Parts of the moulded body where the skin of the polymer composition has solidified maintain a packed structure and are, thus, not expanded. In this way, the polymer composition in the relatively thicker softer parts of the moulded body becomes foamed by the gas when the moulded body is released from the mould. The thinner sections are hard when released from the mould and these sections do not undergo expansion. The structure of the foam in the predetermined sections is preserved as the moulded body cools.
[0016] In a further embodiment, the invention relates to a container for a foodstuff comprising a receptacle for the foodstuff and a lid of the invention.
[0017] The invention will now be described, by way of example only, with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018]
Figure 1 shows a cross-sectional side view of a container for a foodstuff which comprises a receptacle and a lid according to the invention;
Figure 2 is a cross-sectional side view of part of a lid according to the invention;
Figure 3 is a cross-sectional side view of part of another lid according to the invention; and
Figure 4 is an underplan view of a lid of the invention.
DETAILED DESCRIPTION OF THE DRAWINGS
[0019] Referring to Figure 1, a container 1 comprises a receptacle 2 and a lid 3. Receptacle 2, which may be made of any suitable material (e.g., glass or plastics material) comprises a main body 4 in which, in use, the foodstuff is stored and neck portion 5 having a screw-thread 6 for releasable attachment to lid 3 to be attached or removed from receptacle 2 by manual rotation of lid 3 relative to receptacle 2. According to a different embodiment the neck portion 5 may be formed with a continuous helical rib and lid 3 with a complimentary helical thread adapted to interengage with the rib on the neck portion. Lid 3 is of plastics material typically of a thermoplastic polymer such as polypropylene, optionally together with conventional additives for polymer compositions such as plasticisers, fillers, colouring agents and stabilisers.
[0020] Lid 3 comprises sealing portion 8 (shaded in the figures) which, in use, abuts the sealing surface of neck portion 5 of receptacle 2 to provide a hermetic seal between lid 3 and receptacle 2. Thus, sealing portion 8 prevents anything which is stored in main body 4 of the receptacle 2 from coming into contact with the atmosphere. Sealing portion 8 is of the same polymer composition as the remainder of lid 3 but, unlike the remainder of lid 3, it is foamed and can thus be resiliently deformed when lid 3 is screwed onto receptacle 2. This deformation of sealing portion 8 creates the hermetic seal as well as providing a force between screw-thread 6 and lugs 7. The compressible nature of the foamed section in relation to the main lid body reduces the tendency of lid 3 to "back off".
[0021] In Figure 2, an alternative version of lid 3 is depicted in which sealing portion 8a is present only towards the outermost edge of lid 3a. Sealing portion 8a abuts the neck of a receptacle to form a hermetic seal but the region of contact between sealing portion 8a and the neck of the receptacle is now towards the outside of the mouth of the receptacle.
[0022] A further variation of the lid 3 is shown in Figure 3. In this embodiment, sealing portion 8b is displaced towards the centre of lid 3b and, in use, abuts the inside edge of the mouth of the receptacle to form a hermetic seal.
[0023] The lid illustrated in Figure 1 is also shown, this time as an underplan view, in Figure 4. Lid 3 is generally disc-shaped and sealing portion 8 takes the form of a ring which passes circumferentially around the inside rim of lid 3 to ensure a complete seal around the edge of the mouth of a circular opening on a receptacle. Lugs 7 are substantially evenly disposed about the edge of lid 3 in the case of a multi-start thread. Alternatively, a profile corresponding to a continuous thread can be used.
1. Lid for a receptacle which lid includes a sealing portion which, in use, is capable
of forming a hermetic seal between the lid and an opening on the receptacle, wherein
the lid and the sealing portion thereof are formed from the same polymer composition
and wherein the sealing portion comprises the composition in the form of one or more
foamed sections and wherein, in use, the one or more foamed sections are capable of
coming into direct contact with the opening and/or a sealing surface of the receptacle.
2. Lid as claimed in claim 1, wherein the sealing portion is adapted to abut the sealing
surface of the receptacle.
3. Lid as claimed in claim 1 or claim 2, wherein the receptacle is a bottle or jar formed
from glass or a plastics material.
4. Lid as claimed in any one of claims 1 to 3, further comprising means for releasable
attachment to the receptacle.
5. Lid as claimed in claim 4, wherein said means for releasable attachment comprises
a portion on the lid which is adapted for corresponding engagement with a formed portion
at the neck and/or mouth of the opening on the receptacle.
6. Lid as claimed in any one of claims 1 to 5, which is produced by a process comprising
injection moulding of the composition.
7. Lid as claimed in claim 6, wherein the sealing portion is formed by selective blowing
of the composition at predetermined locations of the lid.
8. Process for producing the lid of any one of claims 1 to 7, comprising injection moulding
a polymeric composition to form an intermediate moulded body and then selectively
blowing a part or parts of the intermediate moulded body to form the sealing portion
of the lid.
9. Process as claimed in claim 8, wherein the selective blowing of the part or parts
of the moulded body is achieved by forming the said part or parts at a greater thickness
than the remainder of the body such that the composition in those parts is soft when
the moulded body is released from the mould.
10. Process as claimed in claim 9, wherein the part or parts are selectively blown by
introducing a gas into the composition and then reducing the pressure on the moulded
body to allow the gas to expand the composition in those parts which are soft.
11. Process as claimed in claim 9, wherein the gas comprises carbon dioxide.
12. Container for a foodstuff comprising a receptacle for the foodstuff and a lid according
to any one of claims 1 to 7.