GB2528046A

GB2528046A - Sealed container, method and apparatus for sealing a container

Info

Publication number: GB2528046A
Application number: GB1412021.6A
Authority: GB
Inventors: Venkatesh Sheregar
Original assignee: Intercontinental Great Brands LLC
Current assignee: Intercontinental Great Brands LLC
Priority date: 2014-07-07
Filing date: 2014-07-07
Publication date: 2016-01-13
Also published as: WO2016005800A1; GB201412021D0

Abstract

A container body 12 has a base 14 and a side wall 16, an upper rim portion 20 of the side wall defining an opening to the interior volume of the container. The opening is closed by a membrane 42 extending across and heat sealed to the rim portion 20 to define a primary seal 46. The membrane has a peripheral skirt region extending about and heat sealed to an outer surface of the side wall adjacent the rim portion to define a secondary seal 48. The container may be a large diameter container with an opening having a maximum diameter of 150 mm or more.

Description

Sealed Container, Method and Apparatus For Sealing A Container

Technical Field of the Invention

The present invention relates to sealed containers and to methods and apparatus for sealing containers. The present invention is particularly, but not exclusively, related to large sealed containers and to methods and apparatus suitable for scaling large containers.

Background to the Invention

Containers comprising a main body having a basc and a side wall which extends upwardly about the perimeter of the base to define an interior volume in which product can he held are known. Containers of this type, which will he referred to herein as "containers of the type defined", can be made from a variety of materials including metal (e.g. tinned or coated steel and aluminium), plastics, glass and paper.

Containers of the type defined can be produced in a range of shapes and when viewed in plan may be round, oval, polygonal (including, for example. square, rectangular and hexagonal), as well as irregular shapes. Containers of the type defined can also be provided in a range of sizes having openings with a maximum dimension ranging typically from around 30mm to 250mm or more. Thc term "maximum dimcnsion" as used in relation to the opening refers to the largest dimension of the opening measured across thc containcr at the upper edge or rim of the side wall. In a round containcr thc maximum dimension will be its diameter, whilst in a square or rectangular container it wifi he a diagonal measured from corner to opposed corner. The opening can he measured internally or externally hut for convenience the dimensions stated herein will assume the opening is measured internally.

It is known to form the main body from a single component shaped to define the base and the side wall or to form it from two separate components joined together.

one forming the base and the other the side wall. When made from polymeric mater als or glass, the main body will typically be moulded or otherwise formed as a single component. It is known to make the main body from a single metal component, say by deep drawing, or from two components. In a two-piece construction, the side wall is typically formed from a generally rectangular flat metal sheet which is curved or lokied to lorm (lie side wall. The opposed ends of the sheet are connected together to form a seam which extcnds vertically up thc sidc wall. A scparatc sheet of metal forms the base and is joined to the lower edge of the side wall in the completed main body.

Containers of the type defined can be provided with a separale push-fit lid to close the opening of the main body. The lid typically has a downwarWy extending flange about its periphery which is a push-fit over an upper cnd region of the sidc wall of the main body. A ridge may be formed in the side wall parallel to and spaced downwardly from the rim against which a lower edge of the Ud flange sits when the lid is fitted. When provided with a push-fit lid, a container of the type defined is commonly referred to as a "tin" regardless of the material from which it is actually made, which may or may not contain tin.

Containers of the type defined are olien used to package confectionery and other snack foods such as biscuits and wafers that are intended for sharing and/or otherwise consumed over a perod of time. The provision of a push-fit lid means the container can be easily opened to allow some of the product to be removed and reclosed to protect the remaining product until it is consumed. Containers used for this purpose can often be quite large.

Whilst push-fit lids are a close fit, they do not provide a hermetic seal. In order to protect perishable product prior to first opening, it is known to close the opening of a containcr of thc typc defined by means of a mcmbranc which is hermetically scaled to the rim of the main body. However, the known membrane sealing arrangements are typically only suitable for use with smaller containers and have not been used for large containers. In this regards, a container is regarded as "large" if it has a main body with an opening having a maximum dimension of 150 mm or more, and more particularly a maximum dimension of 175 mm or more, and even more particularly a maximum dimension of 190mm or more. Gencrafly, with large containcrs it is known to hermetically seal the product within an inner packaging, which may comprise a scalcd plastic hag or othcr flexihlc sealed wrappcr in which the product is containcd, insidc thc containcr. hi ordcr to first gain acccss to thc product casc, it is necessary to remove the lid and to open the inner packaging. which is often removed. This may require that the whole of the contents are completely removed from the container.

Once the inner packaging as been removed, any remaining product is replaced in the container and the lid reclosed.

Whilst inner packaging has been found to be effective, it has disadvantages and is not always popular with consumers.

It is desirable to provide an alternative container of the type defined which overcomes or at least mitigates some or all of the disadvantages of the known containers.

It is desirable to provide an alternative membrane sealing arrangement for a container of the type defined which is also suitable for large containers.

It is desirable to provide a method of sealing the opening of a container of the type defined which can be used to seal a large container.

It is also desirable to provide alternative apparatus for sealing a container of the type defined which can he used to seal a large container.

Summary of the Invention

According to a first aspect of the invention, there is provided a container as set out in claim 1. Further optional features of the first aspect of the invention are set out in the claims dependent on claim I. According to a second aspect of the invention, there is provided a method of sealing a container of the type defined as set out in claim 22. Further optional features of the second aspect of the invention are set out in the claims dependent on claim 22.

According to a third aspect of the invention, there is provided apparatus for heat sealing a membrane to the rim portion of a container main body as set out in claim 40. Further optional features of the third aspect of the invention are set out in the claims dependent on claim 40.

A Detailed Description of the Invention

In order that the invention may be more clearly understood, embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings. of which: Figure 1 is a plan view from above of the main body of a container of the type defined in accordance with the invention; Figure 2 is an exploded, partial cross sectional view taken on line A-A of Figure 1 but also showing the main body sealed by means of a membrane in accordance with the invention and a push-fit lid for mounting to the main body; Figure 3 is a perspective view of the main body of the container of Figure 2; Figure 4 is a plan view from above of a membrane for sealing the main body of a container of the type defined in accordance with the invention; Figure 5 is a schematic cross sectional view on an enlarged scale through the membrane of Figure 4 illustrating a laminated construction in accordance with one embodiment of the membrane; Figure 6 is a partial sectional view of the sealed main body of Figure 4 showing a primary seal and a secondary side seal between the membrane and the main body; Figure 7 is a view similar to that of Figure 6 but showing the assembly after formation of the primary seal and prior to formation of the secondary side seal; Figures 8a to 8d am a series of plan views of different embodiments of a sheet of material suitable for forming the side wall of the main body of the container of Figures 1 and 2; Figure 9 is a perspective view of apparatus for sealing a container of the type defined in accordance with an aspect of the invention; Figure 10 is a perspective view of a sealing unit forming part of the apparatus of Figure 9; Figure 11 is a perspective view of a crimping unit also forming part of the apparatus of Figure 9; and Figure 12 is a partial cross sectional view of a crimping head forming part of the crimping unit of Figure 11.

Figures 1 and 2 show a container 10 of the type defined in accordance with the invention. The container has a main body 12 comprising a base 14 and a side wall 16 which extends upwardly about the pcnphcry of the base 14. An internal volume 18 in which product can be received is defined between the side wall 16 and the base 14. In the embodiment shown. the container is round when viewed in p'an having a cylindrical side wall. However, the invention is not limited to containers that are round but can be applied to containers of any suitable shape including oval, polygonal or irregularly shape containers.

The upper edge of the side wall 16 is curled to form a rim 20 with a convex curved upper surface. In the present embodiment, the side wall is curled inwardly hut in an alternative embodiment it can be curled outwardly. The side wall is shaped to define an external ridge 22 which extends about the side wall parallel to but spaced below the rim 20. The upper edge region of the side wall between the ridge 22 and the rim defines a lip 24 for receiving a push-fit lid 26. The lid 26 has a substantially p'anar upper surface 28, although this could he embossed or otherwise profiled, which curves downwardly about its periphery to a radially outwardly extending flange 30. A further flange 32 extends downwardly form the outer periphery of the radial flange 30 for engagement about the lip 24 on the main body. The lower end of the downward flange 30 is curled outwardly to form a rolled end 34. When the lid 26 is fufly fitted, the curled end 34 abuts the ridge 22 whilst the rim 20 abuts the radial flange 30 to provide a firm fit. The rolled end 34 on the lid 26 provides a surface which can be gripped by the fingers to help remove the lid.

In the present embodiment, the main body 12 is made from metal and is a two-piece construction including a first component or end 36 which forms the base 14 and a second component 38 which forms the side wall 16 in a known manner. The first.

component 36 is a circular sheet of metal having a substantially pInnar central region which defines the majority of the base. The edge of the sheet 36 and the lower end of the side wall 16 are folded about each other to form a joint 40 in a known manner. It will be appreciated that (he central region of the base need not be wholly planer but it couki he shaped to provide additional rigidity. Also, the precise manner by which the base 14 and the side wall 16 are joined is not essential to the invention and any of the known arrangements used in the manufacture of tins and cans can he adopted.

The second component 38 is conventionally formed from a substantially rectangular sheet of metal which is folded around to form the desired shape. which in this embodiment is a cylinder. and the ends joined by means of a vertical seam 41 shown in Figure 3. The vertical seam may be a folded seam and/or may be soldered or welded, in a known manner.

The container 10 is a large container in which the opening of the main body has an internal diameter B of 150 mm or more and a rim with a width of 2 to 6 mm. In a non-limiting example, the opening of the main body has an internal diameter 0 199 mm and the rim has a width X 2.5 mm.

In accordance with the invention, the opening of the main body 12 is sealed by means of a membrane 42 as illustrated in Figures 2, 3. 6 and 7. The membrane 42 as illustrated in Figure 4 is circular in shape for use with the circular main body 12 and has a diameter larger than that of the rim 20 of the main body so that when positioned centrally across the opening, a peripheral portion 44 of the membrane (the inner cxtent of which is schematically indicatcd by thc solid line 45 in Figure 4) extends beyond the rim 20 to form a skirt 44 that is folded down about the outside of the lip 24. In the non-limiting embodiment, the membrane has a diameler of 210 mm providing a skirt of 3-4 mm. The membrane 42 is heat scaled to the upper surface of the rim 20 to form a primary seal 46 and the skirt 44 is hot crimped to the outside surface of the lip 24 of the side wall 16 to form a secondary seal 48. The membrane 42 has a pair of tabs 50 on opposite sides which arc not sealed to the sidewall and which can be used to remove the membrane 42 on first opening. The membrane 42 when attached to the main body 12 hermetically closes the main body 12 to protect the contents and when renioved will leave marks on the main body 12 to provide tamper evidence.

The membrane 42 in this embodiment is circular for use with the circular main body 12. However, it will be appreciated that the shape and size of the membrane 42 can be adapted for use with a container main body having a different shape and/or size. Furthermore, whilst a hermetic seal is preferable for many applications, in some situations the seal need not need to be hermetic, for example where only a simple seal or tamper evidence is required.

As illustrated in Figure 5, in one embodiment the membrane is a laminate comprising an outer aluminium foil layer 52 and an inner layer of polyethylene terephthalate (PET) layer 54. The inner layer 54 is coated with a heat sealing compound layer 56 on its exposed lower/inner surface. In tile non-limiting embodiment, the aluminium foil ayer may he 9 to 25 micron in thickness and the PET layer may be 8 to 18 micron in thickness. The exposed upper surface of the aluminium foil layer 52, which is outer most when the membrane is affixed to the main body. niay be printed on and/or covered with a high temperature resistant varnish 58. Any suitable varnish can be used such as an acrylic varnish, an ailcyd varnish or PET.

hi an alternative embodiment, the aluminium foil and the PET layers are replaced by a paper substrate to provide different print effects. In this case, in the non-limiting embodiment the paper substrate may he 9 gsm to 120 gsm paper.

The heat scaling compound 56, is a blend of polymers comprising 70% to 85% hot melt polyethylene (PE). 10% to 15% Surlyn iRTM) which is an ionomer comprising a metal salt. of an ethylene-methacrylic acid co-polymer, and 5%-l0% low IS density pcAyethylene (LDPE). In a particularly preferred embodiment the heat sealing compound is a blend of 78% hot melt PE, 12% Surlyn iRTM). and 10% LDPE.

SURLYN (RTM) is sold by E.I. DuPont Nemours and Co. USA.

This heat sealing compound 56 has been found to be particularly effective in hermetically sealing large containers and has a ow temperature seal initiation with an easy peel for removal of the sheet. The seal initiation may start from about 90 Deg.

C. The highest temperature the heat sealing compound can be subjected to is about 315 Deg. C at 40gsm of coating. However, the temperature range may vary depending on the weight of the coating. Use of this heat sealing compound 56 does not require any treatment to be applied to the rim of the container and can be used to seal containers made of a range of materials including metal, glass and plastics awl will seal on a range of finishes including tin, PET varnish, acrylic varnish, mixed varnish and alkyd varnish.

The primary seal 46 is a thin, line or point seal having a width Y of about 0.9- 1.3 mm and more preferably 1-1.25 mm. The secondary seal 48 has a depth Z of ahout 2 to 4 mm depending on the size of the skirt 44. The secondary seal 48 helps to ensure that the container main body 12 is fully sealed and makes it more difficult for the membrane 42 to be removed without leaving marks providing tamper evidence.

Effective sealing of a membrane 42 to the rim 20 of a large container is difficult as any imperfections in the rim can affect the seal quality more significantly than would he the ease with a smaller container. Also, the side wall 16 tends not to he as rgid as with smaller containers. Furthermore, the width of the rim 20 on large containers is very small relative to the size of the opening which makes an effective seal difficult to form. This is a particular issue where the rim 20 is convex as the area in which the primary seal can be formed is further reduced. hi contrast, for example, glass jars tend to have relatively thick side walls and wide rims relative to the dimension of (lie opening.

In order to be able to seal the membrane 42 to a main body 12 of a large container, very precise tooling and manufacturing processes are required to produce the main body 12 so as to minimise irregularities in the rim 20. For example, where the main body 12 is a two-piece construction, the formation of the vertical seam 41 where the ends of a conventional rectangular sheet forming the side walls are joined 1 I will usually create a ridge on the rim 20 which cm prevent effective sealing.

Particular care then needs to be taken in forming the vertical seam to keep any ridging to a minimum.

Figures 8a to 8d illustrate different embodiments of a modified plate 38a -38d that can be used to form the side wall of a two-piece main body and which are adapted to reduce or eliminate ndging on the rim 20 resulting from the longitudinal ends 60, 62 of the plates being joined to form the vertical seam 41. As can he seen, in each of these plates at least one of the corners 64. 66 where a vertical end 60. 62 meets the upper edge 68 of the plate, this being the edge which forms the rim 20, has its apex 70 removed. lii other words, at the at least one corner 64, 66, the material does not extend to flU the right angle subtended by extrapcAation of the vertical end and the upper edge. as illustrated by dashed lines in Figure 8a. The reduction of material at one or both of the upper corners 64, 66 reduces the amount of ridging in the rim when the vertical seam is produced. As illustrated in Figure 8c. both of the upper corners 64. 66 could have their apices removed. hideed. as illustrated in Figure Sd, aU the corners couM have their apices removed so that die plate 38h can he used either way up for ease of manufacture. As illustrated, the apex could be removed by means of a chamfer or angled cut at the corner or corners, however the corner or corners could be curved or otherwise shaped so that the apex is removed. The size of the chamfer or other profiling should be sufficient to reduce the formation of a ridge on the rim 20 to a minimum but without adversely affecting the vertical seam. It will he appreciated that the apex can he removed from one or more corners either by starting with a rectangular plate and physically removing the apex or by producing the plate with the apex already removed. Reference to the apex being removed is intended to cover both possibilities.

Apparatus 100 for applying the membrane 42 to the main body 12 is shown in Figures 9 to 11. The apparatus 100 comprises a carousel unit 110 having a central turntable 112 with a plurality of arcuatc indentations 114 in its outer diameter, in each of which a main body 12 can be inserted and retained for incremental movement.

between a number of discrete work stations 116-120 located about the unit as the turntable 112 is rotated. The carousel unit 110 has a loading area 111 at which an unsealed main body can be loaded into one of the indentations 114. The main body 12 is loaded in an upright position with the rim 20 uppermost and is pre-filled with product. The turntable 112 rotates in a clockwise direction as shown and a first work station 116 is located adjacent the loading area and comprises a pick and place unit 122 which is configured to pick a membrane 42 from a stock of membranes (not shown) and to position the membrane centrally on the rim 20 of a main body 12 at that work station. The pick and place unit 122 will not be described in detail but those skilled in the art will have no difficulty in selecting an appropriate unit for this task.

Also located at the first work station 116 is a tacking unit 124 which tacks the picked and placed membrane 42 in position on the rim 20. The membrane 42 can be tacked at a number of discreet locations about the rim 20, say three or four. The tacking unit may apply heat and pressure to the membrane 42 at the discreet locations in order to melt the sealing compound 56 to form a bond between the membrane 42 and the rim 20. Each tack may have a length in the region of 8-12 mm. The degree of tacking should be sufficient to hold the membrane 42 in position while main body 12 is moved in the turntable to a second work station 118 where the primary seal 46 is produced.

The second work station 118 comprises a heat sealing unit 126 which forms the primary seal 46 as will be descried in more detail below. From the second work station 118, thc main body 12 is movcd to a third work station 120 which comprises a hot crimping unit. 128 which crimps the skirt 44 of the membrane 42 to the side wall to form the secondary seal 48. The crimping unit 128 also applies further heat and pressure to the rim 20 to ensure the primary seal is fully formed. From the third work station 120, the sealed main body is moved to an unloading area 130 where it is removed from (he carousel unit 110 for further processing and packaging. This will typically include placing a lid on the sealed main body 12 with the lid 26 being a close push-fit over the sealed and crimped skirt 44 of the membrane 42 and the lip 24 on the main body. However, lid placement could also he effected on the carousel unit by the addition of a further work station.

The heat sealing unit 126 is illustrated in more detail in Figure 10 and includes a sealing head 130 having an electronically hcated metal hcad portion 132, which may be made of brass or any other suitable material. The sealing head is 130 is mounted to a plate 134 which is attached to the pistcn 136 of a hydraulic actuator 138. The body of the actuator is fixedly mounted to the carousel unit 110 by means of a mounting plate 142. The arrangement is such that the actuator 138 can be actuated to bring the heated sealing head 130 into contact with the membrane 42 on the upper rim of a main body when positioned below the heat sealing unit 126 at the second work station 118. The heat and pressure applied by the sealing head causes the sealing compound 56 to melt so as to bond the membrane 42 to the rim 20 and form the primary seal 46. The lower face of the sealing head which contacts the membrane 42 has a soft resilient layer 144 which conforms to non-uniformities of the rim 20 so that.

an effective primary seal 46 is produced all about the rim 20. The soft resilient layer 144 can be made from any suitable material, such as silicon, and has a shore A hardness of 80 or less and preferable between 60 to 20. Preferably, the soft, resilient layer 144 should be configured so as to be capable of confirming to irregularities of up to 3 mm or more. A soft resilient layer with a thickness of 3mm to 10mm has been found to he effect with a thickness of 6mm being particularly advantageous.

The heat crimping unit 128 is illustrated in more detail in Figures 11 and 12. It is very similar to the heat sealing unit 126 as described above except that the lower end face of the crimping/sealing head 146 is profiled and shaped to press the skirt 44 in to contact with the outer surface of the side wall 16. The head 146 has a coated, metallic main body 147 with a circular plate portion 147A and a downwardly depending cylindncal rim portion 147B which engages about the outer surface of the lip 24 of the main body 12. The inner surface of the rim portion 147B is flared outwardly relative to the plate portion 147A at an angle a of about 4 to 6 degrees, preferably S degrees. This helps to press the skirt 44 of membrane 42 against the outer surface of the lip 24 on the main body without damaging the membrane 42. The plate portion 147A is mounted to an electronically heated metal head portion 148, which may be made of brass or any other suitable material.

The crimping head is 146 is mounted to a plate 150 which is attached to the piston 152 of a hydraulic actuator 154. The body 156 of the actuator is fixedly mounted to the carousel unit 110 by means of a mounting plate 158. The arrangement.

is such that the actuator 154 can he actuated to bring the heated crimping head 146 into contact with the membrane 42 on the upper rim 20 of a main body when positioned below the heat crimping unit 128 at the third work station 118. The heat.

and pressure applied by the crimping head 146 causes the sealing compound 56 to melt so as to foim the secondary seal 48. The crimping head 146 of the heat crimping unit 128 will also press the membrane 42 into contact with the upper surface of the rim 20 so as to ensure that the primary seal 46 is fully formed. The heat crimping head 146 does not have a resilient layer but it could be provided with one.

In each of the heat sealing and heat crimping units 126. 128, the metallic head portion 132, 148 is heated by means of electric heating elements and applies heat directly to the membrane 42. The use of a heated metallic die head to directly heat the membrane is particularly advantageous for use in sealing a container containing product, such as food products, which are sensitive the heat as the heat is focused directly in the rim and heating of the product is minimised. However, other arrangements for heating the sealing compound can be used, particularly where the products are not heat sensitive. This could include the use of hot air and pressure or induction heating. However, induction heating br a large container would present difficulties and may lead to slower production times.

It will he appreciated that whist heat sealing unit 126 and the hot crimping unit 128 as described above each use an hydraulic actuator 138. 154 for controlling movement of the sealing and crimping heads 130, 146, any suitable arrangement for moving the heads can he adopted.

The pnmary and secondary seals 46, 48 produced by the heat sealing unit 126 and the heat crimping unit 128 may be separate seals but work together to ensure the main body 12 is hermetically scaled and to provide a tamper evidence function.

The method of manufacture awl the manufacturing apparatus described herein arc particularly suitable for scaling large containers but can be used in conjunction with smaller containers having an opening of say 30 mm or more. Accordingly, the method and apparatus are very versatile.

The above embodiments are described by way of example only. Many variations are possible without departing from the scope of the invention as defined in the appended claims.

Terms such as "upper", "lower". "vertical" and the like as used herein refer to the container and its parts when positioned in a generally upright position for normal us as illustrated in the accompanying Figures. It will be appreciated however that the container can he used in other orientations and the terms should he construed accordingly.

Claims

CLAIMSI. A container comprising a main hody having a base and a side wall defining an interior volume. m opening to the interior volume being defined by an upper rim portion of the side wall, the opening being closed by means of a mcmbranc cxtcnding across and hcat scaled to the rim portion to define a primary seal, the membrane having a peripheral skirt region extending about and heat sealed to an outer surface of die side wall adjacent the rim portion to define a sccondary seal.
2. A container as claimed in claim 1, wherein the primary seal is a hermetic seal.
3. A container as claimed in claim 1 or claim 2, wherein the container further comprises a push-lit lid which engages about an outside surface of the side wall.
4. A container as claimed in any one of the preceding claims, wherein the container is large container, that is to say the opening of the main body has a maximum dimension of 150 mm or more, or more preferably a maximum dimension of 175 mm or more, or even morc preferably a maximum dimension of 190 mm or more.
5. A container as claimed in any one of the preceding claims, wherein the membrane has a heat. sealant composition comprising a mixture of 70 wt% to 80 wt% polyethylene: 5 wt% to 10 wt% low density polyethylene (LDPE); and 10 wt% to 15 wt% of an ionomcr comprising a metal salt of an ethylene-methacrylic acid co-polymer.
6. A container as claimed in claim 5. wherein the metal salt of the ethylene-methacrylic acid co-polymer has the structure: Me /1-12 I-12\/I-12 c-c"c \ C00 M wherein Mc is methyl; and M is selected from zinc, lithium, sodium or potassium
7. A container as claimed in claim 5 or claim 6, wherein the sealant composition comprises 75 wt% to 80 wt% of polyethylene.
8. A container as claimed in any one of claims 5 to 7. wherein the sealant.composition comprises II wt% to 13 wt % of lonomer.
9. A container as claimed in one of claims 5 to 8 wherein the sealant composition comprises 7 wt% to 10 wt% ol LDPE.
10. A container as claimed in any one of claims 5 to 9. wherein the sealant composition comprises substantially 78 wt% polyethylene; substantially 10 wt% low density polyethylene iLDPE); and substantially 12 wt% of ionomer
11. A container as claimed in claim 5 or claim 6, wherein the sealant composition comprises 70% to 85% hot melt polyethylene (PE), 10% to 15% Surlyn (RTM). and 5%-10% low density polyethylene (LDPE).
12. A container as claimed in claim 11. wherein the heat sealant composition comprises 78% hot melt PE. 12% Surlyn (RTM). and 10% LDPE.
13. A container as claimed in any one of claims 5 to 12, wherein the membrane is a laminate comprising an outer aluminium foil layer and an inner layer of polycthylene tcrephthalate (PET) layer, the inner layer being coated with the heat sealing compound.
14. A container as claimed in claim 13, wherein the aluminium foil layer is printed on and covered with a high temperature resistant varnish.
15. A container as claimed in any one of claims 5 to 12, wherein the membrane comprises a paper substrate coated with the heat sealing compound.
16. A container as claimed in any one of the preceding claims, wherein the rim portion has a convex upper surface.
17. A container as claimed in any one of the preceding claims, wherein the primary seal has a width of 0.9 to 1.3 mm, more preferably the primary seal hasawidthofl.toL25mni
18. A container as claimed in any one of the preceding claims, wherein the main body is a two-piece construction in which the side wall is produced from by a substantially rectangular plate having opposed longitudinal ends and upper and lower edges. the plate being bent into the shape of the side wall and the opposed ends joined together in a vertical seam, wherein in at least one of the upper corners where an opposed end meets the upper edge, the apex of the corner is removed.
19. A container as claimed in claim 18, wherein the apex is removed in both of the upper corners of the plate.
20. A container as claimed in claim 18 or claim 19, wherein the apex is removed in all corners of the plate.
21. A container as claimed in any one of the preceding claims, wherein the main body is coated with any one or more of the foflowing: varnish, acrylic varnish, PET, alkyd varnish.
22. A method of sealing a container, wherein the container comprises a main body having a basc and a sidc wall dcfining an intcrior volume, an opcning to thc interior volume being defined by an upper rim portion of the side wall, the method comprising positioning a membrane extending across the upper rim so as to close the opening, the rnembnme having a peripheral skirt region extending beyond the rim, heat. sealing the membrane to the rim to form a primary seat between the membrane and the rim and subsequently crimping the peripheral skirt region of the membrane down about an outer surface of the side wall and heat sealing the skirt region to the outer surface of the side wall to form a secondary seal between the membrane and the side wall.
23. A method as claimed in claim 22, wherein the container further comprises a push-fit lid, and the nicthod comprises fitting the lid over the sealed main body so that the lid engages about an outside surface of the side wall over the crimped edge ol the membrane.
24. A method as claimed in claim 22 or claim 23, wherein the container is large container, that is to say the opening of the main body has a maximum dimension of 150 mm or more, or more preferably a maximum dimension of mm or more, or even more preferably a maximum dimension of 190 mm or more.
25. A method as claimed in any one of claims 22 to 24. wherein the heat seal is formed using a heat sealant composition comprising a mixture of 70 wt% to wt% polyethylene; 5 wt% In 10 wt% low density polyethylene (LDPE); and 10 wt% to 15 wt% of an iononier comprising a metal salt of an ethylene-methacrylic acid co-polymer.
26. A method as daimed in claim 25, wherein die metal sail ol the ethylene-methacrylic acid co-polymer has the structure: Me / H2 H2\/H2______ C-C)C \ C00 M wherein Me is methyl; and M is selected from zinc. lithium, sodium or potassium
27. A method as claimed in claim 25 or claim 26, wherein the sealant composition comprises 75 wt% to 80 wt% of polyethylene
28. A method as claimed in any one of claims 25 to 27, wherein the sealant composition compnses 11 wt% to 13 wt % of ionomer.
29. A method as claimed in any one of claims 25 to 28 wherein the sealant composition comprises 7 wt% to 10 wt% of LDPE.
30. A method as claimed in any one of claims 25 to 29, wherein the sealant composition comprises substantially 78 wt% polyethylene; substantially 10 wt% low density polyethylene LDPE); and substantially 12 wt% of ionomer
31. A method as claimed in any one of claims 25 to 30, wherein the membrane is a laminate compnsing an outer aluminium foil layer and an inner layer of polyethylene terephthalate (PET) layer. the inner layer being coated with the heat sealing compound.
32. A method as claimed in claim 31, wherein the aluminium foil layer is printed on and covered with a high temperature resistant varnish.
33. A method as claimed in any one ci claims 25 to 30, wherein the membrane comprises a paper substrate coated with the heat sealing compound.
34. A method as claimed in any one of claims 22 to 33, wherein the method comprises forming the primary seal with a width of 0.9 to 1.3 mm, more preferable a width of 1.0 to 1.25 nrni.
35. A method as claimed in any one of daims 22 to 34, wherein the step of heat sealing the membrane to the rim to foim the pnmary seal is carried out using a heated sealing head having a soft, resilient surface which is brought in to contact with the membrane to press the membrane on to the nm and apply heat to melt a heat sealing compound.
36. A method as claimed in any one of claims 22 to 35, wherein the step of crimping the peripheral skirt region of the membrane down about an outer surface of the side wall and heat sealing the skirt region to the outer surface of thc sidc wall to form a secondary seal is carried out using a hcated scaling head which is brought into contact with the membrane to press the membrane on to the rim and the outside surface of the side wall and to apply heat to melt a heat sealing compound.
37. A method as claimed in any one of claims 22 to 36, the method comprising forming the main body as a two-piece construction in which the side wall is produced from a substantially rectangular plate having opposed longitudinal ends and upper and lower edges. the plate being formed into a desired shape for the side wall and the opposed longitudinal ends joined together to form a seam, wherein the method comprises forming the side wall from a sheet shaped such that the apex of the corner is removed in at Icast one of the upper corner regions where an opposed longitudinal end meets the upper edge.
38. A method as claimed in claim 37, wherein the sheet is shaped such that the apex of the corner is removed in both of the upper corner regions.
39. A method as claimed in claim 37, wherein the sheet is shaped such that the apex of the corner is removed in all of its corner regions.
40. Apparatus for heat sealing a membrane to the rim portion of a container main body, the apparatus comprising sealing unit induding a sealing head having a heated metallic head portion with a soft, resilient layer for contact with the membrane.
41. Apparatus as claimed in claim 40, wherein the soft, resilient surface layer has shore hardness A of 80 of less.
42. Apparatus as claimed in claim 40 or claim 41, wherein the soft, resilient surface layer is made of silicon.
43. Apparatus as claimed in any one of claims 40 to 42. wherein the soft, resilient surface layer is capable of conforming to irregularities in the rim of up to 3 mm or more.
44. Apparatus as claimed in any one of claims 40 to 43, wherein the sealing head is configured for use in sealing a membrane to thc rim portion of a container main body in which the rim portion defines an opening with a maximum dimension of 150 mm or more, or more preferably a maximum dimension of mm or more, or even more preferably a maximum dimension of 190 mm or more.
45. Apparatus for heat crimping a skirt region of a membrane to an outer side wall region of a container main body, the heat crimping unit comprising a crimping head having a heated metallic head portion, wherein the crimping head is recessed, having peripheral flange for location about an outcr surface of a side wall of a container main body.
46. Apparatus for sealing a container comprising a heat sealing unit as claimed in any one of claims 40 to 44 and a crimping unit as claimed in claim 45.