Retort container with thermally fused double-seamed or crimp-seamed metal end

(56) References cited:

CH-A- 422 690 US-A- 3 868 917 US-A- 4 948 006 US-A1-2011 226 787

GB-A-2 067 158 US-A- 3 978 232 US-A- 5 257 709

ΕΡ 2 750 980 Β1

Note: Within nine months ofthe publication ofthe mention ofthe grant ofthe European patent in the European Patent Bulletin, any person may give notice to the European Patent Office of opposition to that patent, in accordance with the Implementing Regulations. Notice of opposition shall nőt be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).

Printed by Jouve, 75001 PARIS (FR)

ΕΡ 2 750 980 Β1

Description

BACKGROUND OF THE INVENTION [0001] The present disclosure relates to containers, particularly to containers having one or two metál ends applied to one or both ends of the Container body and crimp-seamed or double-seamed onto the Container body, and most particularly to such containers used fór retort Processing and in which the Container body is formed substantially of thermoplastic.

[0002] Traditionally, retort containers have been constructed substantially of metál. Fór many decades the standard retort food containers have been three-piece or two-piece metál cans. In a three-piece metál can, a metál can body is closed by a pair of metál ends that are typically double-seamed onto the ends of the can body. A two-piece metál can eliminates one of the metál ends because the can body is a deep-drawn body with an integrál bottom wall. The metál ends of such typical retort containers have an outer peripheral portion forming a curl that receives the end of the can body, and afterthe end is applied the curl and the wall of the can body are rolled up together to form a double seam. This construction has the great advantage that it readily withstands retort Processing withouttheseams being compromised, because the plastically deformed metál of the can body in the seam area tends to hold its deformed shape despite the high pressure and temperature during retort.

[0003] More recently there has been a desire to construct retort containers that use less metál, motivated by the potential cost reduction and improved aesthetics that such a construction can offer. The development described in the present disclosure at least in somé aspects is aimed at addressing this desire.

[0004] US Patent 4,948,006 (Okabe et al.) relates to a Container with a metallic cover, including a Container body having a plasticflanged portion and a metallic cover provided with a peripheral edge, according to the preamble of claim 1.

BRIEF SUMMARY OF THE INVENTION [0005] In particular, the present disclosure describes a retort Container having one or two metál ends attached to a substantially thermoplastic Container body in such a way that there is an improvement in blow-off resistance when the inside of the Container is pressurized relatíve to outside ambient pressure fór any reason (e.g., during retort Processing, or as a result of changes in altitude of the Container, such as when a Container is fiiled and sealed at sea level and is subsequently transported to a high-altitude location).

[0006] In accordance with the invention in one embodiment, a retort Container comprises:

a Container body constructed substantially of thermoplastic and having a sídé wall extending about a

Container body axis, the sídé wall having a lower end and an upper end, the upper end defining an upper edge that extends about a top opening of the Container body, the sídé wall having an inner surface and an outer surface;

a metál end closing the top opening of the Container body, the metál end having at least a metál layer and comprising a Central portion and an outer peripheral portion extending generally radially outwardly from the Central portion and extending circumferentially about the Central portion, the peripheral portion having a radially outer part and a radially inner part, a first heat-sealable matéria! being present on at least one of (a) a lower surface of at least the peripheral portion of the metál end and (b) the inner surface of the sídé wall adjacent the upper end thereof, the radially outer part of the peripheral portion defining a curl, the radially inner part of the peripheral portion defining a chuck wall that extends generally downward from the curl and has a radially outer surface forming an interface with the inner surface of the sídé wall of the Container body;

a seam connecting the metál end to the upper end of the sídé wall, the seam having the curl of the metál end and the upper end of the sídé wall interlocked via a biting interface between a földed peripheral edge of the curl and the sídé wall; and the interface between the chuck wall and the sídé wall being fused by heat-sealing of the first heatsealable matéria! between the radially outer surface of the chuck wall and the inner surface of the sídé wall, the interface being oriented along a direction such that stress on the interface caused by internál pressure inside the Container exerted on the metál end is predominantly shear stress.

[0007] The retort Container in accordance with a further embodiment can include a second heat-sealable matéria! present on the other of (a) the lower surface of at least the peripheral portion of the metál end and (b) the inner surface of the sídé wall adjacent the upper end thereof. In this embodiment, the second heat-sealable matéria! and thefirst heat-sealable matéria! are in contact with each other and are thermally fused together such that the interface between the chuck wall and the sídé wall is fused. Advantageously, bút nőt essentially, the second heat-sealable matéria! and thefirst heat-sealable matéria! are thermally fused together in the seam as well. [0008] Heat-sealable materials useful in the practice of the present invention can comprise any known heatsealable materials. The metál end can have an interior coating, and optionally an exteriőr coating as well. [0009] The seam between the metál end and the sídé wall can be a crimp seam or a double seam. In the case of a double seam, the upper end of the sídé wall forms a body hook and the curl of the metál end forms an end hook interlocked with the body hook.

[0010] The Container body can be made and config2

ΕΡ 2 750 980 Β1 ured in various ways. Fór example, the Container body can be a blow-molded, thermoformed, or injection-molded Container body having a bottom wall integrally joined to the side wall. Alternatively, the Container body can be an extruded Container body having an open lower end, in which case the lower end is closed by a second metál end similar to that closing the top end.

[0011] In somé embodiments, the metál end is an easy-open end having a severable panel defined by a score line in the metál layer. Alternatively, the metál end can be a sanitary end, or the metál end can comprise a membráné sealed to an annular metál ring.

[0012] The presentdisclosure alsó describes methods fór making containers. In one embodiment a method fór making a Container comprises the steps of:

providing a Container body constructed substantially of thermoplastic and having a side wall extending about a Container body axis, the side wall having a lower end and an upper end, the upper end defining an upper edge that extends about a top opening of the Container body, the side wall having an innersurface and an outer surface;

providing a metál end fór closing the top opening of the Container body, the metál end having at least a metál layer and comprising a Central portion and an outer peripheral portion extending generally radially outwardly from the Central portion and extending circumferentially about the Central portion, the peripheral portion having a radially outer part and a radially inner part, a first heat-sealable matériái being present on one of (a) a lower surface of at least the peripheral portion of the metál end and (b) the inner surface ofthe side wall adjacentthe upper end thereof, the radially outer part of the peripheral portion defining a curl, the radially inner part ofthe peripheral portion defining a chuck wall that extends generally downward from the curl and has a radially outer surface;

applying the metál end to the Container body such that the metál end closes the top opening and the radially outer surface ofthe chuck wall and the inner surface ofthe side wall have an intimately contacting interface therebetween; forming a seam connecting the metál end to the upper end of the side wall, the seam being formed by interlocking the curl of the metál end with the upper end of the side wall via a biting interface between a földed peripheral edge of the curl and the side wall;

afterformation ofthe seam is completed, heating the first heat-sealable matéria! to a temperature sufficient to cause the first heat-sealable matéria! to be softened or melted and to wet the radially outer surface of the chuck wall and the inner surface of the side wall; and allowing the first heat-sealable matéria! to cool and harden such that the interface between the chuck wall and the side wall is fused, the interface being oriented along a direction such that stress on the interface caused by internál pressure inside the Container exerted on the metál end is predominantly shear stress.

[0013] The step of forming a seam can comprise forming a crimp seam, or it can comprise forming a double seam by rolling the curl ofthe metál end and the upper end of the side wall together so as to form the upper end of the side wall intő a body hook and to form the curl intő an end hook and to interlock the body hook and the end hook.

[0014] The heating step can be carried out in any of various ways, including heating by conduction, heating by induction, frictional heating, etc.

[0015] In somé embodiments the method can further comprise providing a second heat-sealable matéria! present on the other of (a) the lower surface of at least the peripheral portion ofthe metál end and (b) the inner surface ofthe side wall adjacent the upper end thereof. Thus, the metál end and the side wall both have respective heat-sealable materials thereon. The method entails piacing the second heat-sealable matéria! and the first heat-sealable matéria! in contact with each other at the interface between the chuck wall and the side wall, and heating the first and second heat-sealable materials to a temperature sufficient to cause the first and second heatsealable materials to be softened or melted and to flow together, after which cooling ofthe first and second heatsealable materials is allowed to occur so as to fuse the chuck wall to the inner surface of the side wall.

[0016] The second heat-sealable matéria! and the first heat-sealable matéria! can be thermally fused together in the seam as well.

[0017] The Container body can be made by various processes, including, fór example, blow molding, thermoforming, orextrusion. In the case of a blow-molded or thermoformed Container body, the Container body indudes a bottom wall integrally joined to the side wall. In the case of an extruded Container body, the Container body has an open lower end and therefore a second metál end is attached to the lower end. The second metál end and its attachment to the Container body can be substantially identicalto the first metál end and its attachment to the Container body.

[0018] The method can further comprise the steps of fii ling the Container with a food product prior to the step of applying the metál end to the Container body, and, after the interface between the chuck wall and the side wall is fused, retorting the Container. During the retorting step the thermoplastic Container body is radially unconstrained such that the Container body is allowed to expand radially as internál pressure is exerted on the side wall. Notably, the Container body is free of any special expansion panels, whereby the radial expansion of the Container body occurs substantially uniformly about a circumference ofthe Container body.

[0019] In somé embodiments, the chuck wall extends

ΕΡ 2 750 980 Β1 at a non-zero acute angle relatíve to a longitudinal axis of the Container body and is configured such that a lower end of the chuck wall is smaller in diameterthan the inner surface of the side wall, while an upper end of the chuck wall is larger in diameter than the inner surface of the side wall. The step of applying the metál end to the Container body results in the side wall of the Container body moving relatively upward from the lower end to the upper end of the chuck wall such that an interference fit is created between the chuck wall and the side wall, thereby creating the intimately contacting interface therebetween.

[0020] During the heating step there is a substantial absence of external pressure exerted on the chuck wall and side wall; rather, pressure between the chuck wall and side wall comes from the interference fit that already exists between them when the end is applied and seamed to the side wall. Thus, there is no need fór sealing jaws to create pressure during the heating step in order to form a secure thermal bond between the metál end and the Container body. Indeed, in somé embodiments the heating step can be carried outwith induction heating in which there can bean absenceofcontact between the induction tool and the metál end.

[0021] The present disclosure alsó describes a packaging and retorting process fór packaging and sterilizing a food product. In one embodiment, a method fór packaging and retort-processing a food product comprises the steps of:

providing a Container assembly that includes a substantially thermoplastic Container body having a side wall and further includes an end wall closing a lower end of the Container body, an opposite upper end of the Container body being open;

providing a metál end having at least a metál layer and comprising a Central portion and an outer peripheral portion extending generally radiallyoutwardly from the Central portion and extending circumferentially about the Central portion, the peripheral portion having a curl and a chuck wall that extends generally downward and radially inwardlyfrom the curl; providing at least one heat-sealable matéria! on at least one of (a) a lower surface of the peripheral portion ofthe metál end and (b) an inner surface ofthe Container body adjacent the upper end thereof; piacing the food product intő the Container assembly through the open end ofthe Container body; forming a crimp seam between the metál end onto the Container body to close the open end thereof, the forming step causing the side wall ofthe Container body to be compressed between the chuck wall on an inner side ofthe side wall and a permanently deformed portion ofthe metál end formed bydeforming the curl on an outer side of the side wall; thermally fusing the metál end to the Container body by causing the heat-sealable material(s) to be melted where the metál end compresses the side wall and then allowing the melted heat-sealable material(s) to cool and harden, thereby completing a fiiled Container; and retort-processing the fiiled Container to sterilize the food product and interior ofthe Container.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) [0022] Having thus described the invention in generál terms, reference will now be made to the accompanying drawings, which are nőt necessarily drawn to scale, and wherein:

FIG. 1 is a diagrammatic depiction of several steps of a process fór making containers in accordance with one embodiment ofthe invention;

FIG. 2 is a photomicrograph of a sectioned Container in the region of the metál end’s seam with the Container body, in accordance with an embodiment of the invention;

FIG. 3 is a schematic depiction of a further step of the process fór making containers, wherein the seamed metál end is induction sealed to the Container body, in accordance with an embodiment of the invention;

FIG. 4 is a cross-sectional view through the region of the metál end’s seam with the Container body, after the induction sealing step, in accordance with an embodiment ofthe invention;

FIG. 5 is a cross-sectional view through the region of the metál end’s seam with the Container body, after the induction sealing step, in accordance with another embodiment of the invention;

FIG. 6 is a cross-sectional view through the region of the metál end’s seam with the Container body, after the induction sealing step, in accordance with a further embodiment ofthe invention;

FIG. 7 is a diagrammatic depiction of a test retort apparátus fortesting containers made in accordance with embodiments ofthe invention;

FIG. 8 is a graph of differential pressure (= can pressure - retort pressure) and retort temperature versus time, showing test results fór a conventional metál can and fór a Container in accordance with an embodiment ofthe invention;

FIG. 9 is a chart of finite element analysis results fór a Container in accordance with an embodiment of the invention, showing critical pressure (defined as the pressure above which permanent deformation

ΕΡ 2 750 980 Β1 of the Container body occurs) as a function of retort temperature;

FIG. 10 is a graph of differential pressure and retort temperature versus time, showing test results fór a Container in accordance with an embodiment of the invention, wherein the differential pressure was allowed to increase until a failure of the Container occurred; and

FIG. 11 is a cross-sectional view of a Container having a double-seamed and sealed end in accordance with another embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS [0023] The present invention now will be described more fully hereinafter with reference to the accompanying drawings in which somé bút nőt all embodiments of the inventions are shown. Indeed, these inventions may be embodied in many different forms and should nőt be construed as limited to the embodiments setforth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers referto like elements throughout. The drawings are nőt necessarily to scale, and thus the relatíve proportions of various elements (e.g., thicknesses of layers in multi-layer structures) suggested by the drawings is nőt necessarily indicative of the actual relatíve proportions.

[0024] With referenceto FIG. 1,severalstepsofaprocess fór making containers in accordance with an embodiment of the invention are schematically depicted. In a first step, an extruder 10 is employed to extrude a substantially thermoplastic tűbe 12 as a continuous extrusion. The extruder 10 includes a screw 14 orthe like that feeds a molten substantially thermoplastic matéria! under pressure through a die 16 such that the continuous tűbe 12 is extruded through an annulardie orifice 18. The extruded tűbe 12 can have a monolayer or multi-layer construction. As an example of a multi-layer construction, the tűbe wall can have the structure (from ID to OD): heat-sealable layer / tie layer / barrier layer / tie layer / heat-sealable layer.

[0025] The continuously extruded tűbe 12 is cooled sufficiently (via known cooling means, nőt ilIustrated) and is then cut intő parent tubes 20 of a convenient length. Typically each parent tűbe 20 will be of sufficient length to provide a plurality of Container bodies 22 cut from the parent tűbe as shown. Each Container body 22 is then mated with a pair of metál ends 30.

[0026] The metál end 30 and Container body 22 in somé embodiments can be constructed to mate with each other as described in Applicant’s co-pending Application Serial No. 13/161,713 filed on June 16, 2011, the entire disclosure of which is hereby incorporated herein by reference.

[0027] The metál end 30 includes a Central portion 32 and an outer peripheral portion 34 extending generally radially outwardly from the Central portion 32 and extending circumferentially about the Central portion 32. The peripheral portion 34 has a radially outer part and a radially inner part. The radially outer part defines a curl 36 having a lower surface that is generally concave downward in an axial direction of the metál end. The radially inner part defines a chuck wall 38 that extends generally downward and radially inward from the curl 36. The chuck wall 38 can be a compound-angle chuck wall, as described in the above-noted ’713 application, having an upper part adjacent the curl 36 and a lower part joined to and positioned below the upper part. The upper part of the chuck wall is substantially linear and oriented relatíve to the axial direction at a relatively smaller non-zero angle and the lower part of the chuck wall is substantially linear and oriented relatíve to the axial direction at a relatively larger angle compared to the upper part of the chuck wall.

[0028] The metál end 30 is configured such that at least a bottom edge of the lower part of the chuck wall has an outside diameter that is smaller than the inside diameter of the Container body sídé wall 24 at the upper edge thereof. Additionally, the chuck wall 38 is configured such that it becomes somewhat larger in diameter than the inside diameter of the Container body sídé wall 24 as the top edge of the sídé wall progresses up toward the curl 36 during mate-up of the metál end 30 with the Container body 22. In other words, the sídé wall’s ID is undersized in relation to the OD of the chuck wall adjacent the curl. This has the effect of wiping the inner surface of the sídé wall 24 with the metál end during mate-up, which has the benefit of cleaning the inner surface prior to seaming. This alsó results in an interference fit between the chuck wall 38 and the sídé wall 24.

[0029] Once the metál end 30 is mated with the Container body 22, a seaming operation is performed in order to seam the metál end onto the Container body. In the illustrated embodiment, the Container body is a straightwalled (non-flanged) Container body, and a crimp seam 40 is formed between the metál end and the Container body, in which the sídé wall 24 remains substantially straight and is compressed between the chuck wall 38 and a deformed portion of the curl 36. Alternatively, in other embodiments, a double seam can be formed (see, fór example, FIG. 11), in which case the Container body can be flanged. The crimp seam 40 has the advantage of being usable with non-flanged Container bodies and yet providing a positive locking of the metál end 30 onto the Container body 22 even before the metál end is heatsealed to the Container body. This can be seen in FIG. 2, which is a photomicrograph of a sectioned Container in the region of the crimp seam 40. A nub or interlocking portion of the Container body sídé wall is formed by the földed peripheral edge of the curl biting intő the sídé wall. The nub and the földed edge effectively interlock, thereby locking the metál end onto the Container body. [0030] It will be understood, of course, that a second

ΕΡ 2 750 980 Β1 metál end is attached to the opposite end of the Container body 22 in the same fashion described above. Alternatively, in the case of a Container body having an integrál bottom wall (as may be the case with, fór example, a blow-molded, thermoformed, or injection-molded Container body), the second metál end is nőt required. [0031] The above-described interlocking of the metál end 30 and Container body 22 alone, however, is nőt sufficient to enable the Container to withstand a retort process. In order to be able to withstand retort intact, the Container is subjected to a heat-sealing operation to fuse portions of the metál end 30 to the Container body side wall 24. In this regard, at leastone ofthe respective surfaces ofthe metál end and side wall that are intimately contacting each other in the region ofthe crimp seam 40 is formed by a heat-sealable matériái, and the two surfaces are such that heating ofthe crimp seam to soften or melt this heat-sealable matériái, followed by cooling ofthe matériái, causes the two surfaces to be thermally fused to each other. More specifically, it is important to the attainment of adequate blow-off resistance during retort (or other high-internal-pressure condition of the Container) that at least the chuck wall 38 ofthe metál end 30 be thermally fused to the innersurface ofthe side wall 24 ofthe Container body, and preferably both the chuck wall 38 should be thermally fused at the ID and a portion ofthe curl 36 (or, more accurately, what was the curl prior to the seaming operation) should be thermally fused at the OD of the Container body side wall 24.

[0032] The thermal fusing operation is diagrammatically depicted in FIG. 3, and the resulting thermally fused seam 40 is shown, greatly enlarged, in FIG. 4. As indicated in FIG. 3, the thermal fusing operation can be accomplished using an induction heater 50. The induction heater 50 includes a coil through which a high-frequency alternating current is passed, thereby creating a highfrequency alternating electromagnetic field. The metál layer ofthe end 30 is exposed to this alternating electromagnetic field, which induces eddy currents (alsó called Foucault currents) within the metál so as to cause Joule heating because ofthe resistance ofthe metál. This heating ofthe metál then causes heat transfer by conduction to anything in contact with the metál, including the heatsealable material(s) on the end 30 and/or side wall 24. [0033] Thus, as an example, FIG. 4 illustrates the metál end 30 as having a metál layer 42 and an interior layer or coating of a heat-sealable matéria! 44. Any suitable heat-sealable matéria! can be usedforthe layer 44, nonlimiting examples of which include: acrylonitrile butadiene styrene (ABS), acrylic (PMMA), celluloid, cellulose acetate, cyclic olefin copolymer (COC), ethylene-vinyl acetate (ÉVA), ethylene vinyl alcohol (EVOH), fluoroplastics (PTFE, alongside with FEP, PFA, CTFE, ECTFE, ETFE), ionomers, liquid crystal polymer (LCP), polyoxymethylene (POM or acetal), polyacrylates (acrylic), polyacrylonitrile (PAN or acrylonitrile), polyamide (PA or Nylon), polyamide-imide (PAI), polyaryletherketone (PAEK or Ketone), polybutadiene (PBD), polybutylene (PB), polybutylene terephthalate (PBT), polycaprolactone (PCL), polychlorotrifluoroethylene (PCTFE), polyethylene naphthalate (PEN), polyethylene terephthalate (PÉT), polycyclohexylene dimethylene terephthalate (PCT), polycarbonate (PC), polyhydroxyalkanoates (PHAs), polyketone (PK), polyester, polyethylene (PE), polyetheretherketone (PEEK), polyetherketoneketone (PEKK), polyetherimide (PEI), polyethersulfone (PES), chlorinated polyethylene (CPE), polyimide(PI), polylactic acid (PLA), polymethylpentene (PMP), polyphenylene oxide (PPO), polyphenylene suliidé (PPS), polyphthalamide (PPA), polypropylene (PP), polystyrene (PS), polysulfone (PSU), polytrimethylene terephthalate (PTT), polyurethane (PU), polyvinyl acetate (PVA), polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), styrene-acrylonitrile (SAN). Where the Container is to be retort-processed, a suitable heat-sealable matéria! able to withstand the retort-processing conditions should be selected.

[0034] When the metál layer 42 is heated by induction heating, the heat-sealable layer 44 is heated by conduction, which causes the heat-sealable matéria! to be softened or melted. Because the electromagnetic field’s strength obeys the inverse square law, Joule heating of the metál end is greatest in the parts ofthe end closest to the coil ofthe induction heater and decreases proportional to the inverse square ofthe distance írom the coil. Thus, only localized heating ofthe metál end occurswith a great enough magnitude to cause melting of the heatsealable layer 44. More particularly, the melting of the heat-sealable layer 44 is confined essentially to the region ofthe seam 40.

[0035] As FIG. 4 indicates, the induction heating ofthe seam 40, followed by cooling (which occurs rapidly upon cessation of the electromagnetic field or movement of the Container away from the coil), results in two areas of thermal fusing between the metál end 30 and Container body side wall 24: there is an inner seal S,· between the innersurface ofthe side wall 24 and a portion ofthe chuck wall 38 that lies parallel to and intimately contacts the side wall, and there is an outerseal S_o between the outer surface ofthe side wall 24 and a portion of what was the curl of the metál end prior to seaming. The seals S,· and S_o in FIG. 4 (and in FIGS. 5 and 6) are depicted fór illustrative purposes as if they were each a distinct layer between the metál end 30 and the side wall 24, bút it is to be understood that in reality the seals are formed by a melding of the heat-sealable layer 44 of the metál end and the thermoplastic matéria! on the surface ofthe side wall 24 (or, in the case of FIG. 5 where the metál end does nőt have a heat-sealable layer, by a fusing of the thermoplastic surfaces of the side wall 24 to the metál end).

[0036] It is important to the attainment of adequate blow-off resistance that the chuck wall 38 include a portion that is parallel to and intimately contacting the inner surface of the side wall 24, and that this portion be thermally fused as described above. This results in the inter6

ΕΡ 2 750 980 Β1 face between the chuck wall 38 and the side wall 24 being oriented along a direction substantially parallel to the axis ofthe Container, such that stress on the interface caused by internál pressure inside the Container exerted on the metál end 30 is predominantly shear stress in the pláne ofthe interface (as opposed to out-of-plane stress tending to peel one part from the other).

[0037] It is alsó a feature of the present invention that during the heating step fór thermally fusing the end 30 to the side wall 24, there is a substantial absence of external pressure exerted on the chuck wall 38 and side wall 24. Rather, pressure between the chuck wall and side wall comes from the interference fit that exists between them, as previously described. Indeed, when an induction heater 50 is employed, it is possible fór there to be no contact between the heating element and the metál end (although it may be advantageousordesirable to provide somé type of contact with the Container, such as fór conveying it along a path beneath the induction heating element, when the heating step is carried out in a continuous conveyor-type process).

[0038] Various constructions of the metál end 30 and Container body side wall 24 can be employed in the practice of the present invention. As noted with respect to FIG. 4, in one embodiment the metál end 30 can have an interior heat-sealable layer 44. In this case, the Container body side wall 24 can be a mono-layer construction as illustrated, the substantially thermoplastic side wall 24 being heat-sealable to the heat-sealable layer 44 ofthe metál end.

[0039] Alternatively, in other embodiments, the side wall 24 can be a multi-layer construction. Fór example, the side wall 24 can comprise atleasttwo layers including an interior heat-sealable layer and a barrier layer providing moisture and gas barrier properties fór the Container body. The metál end 30 furthermore does nőt necessarily have to have an interior heat-sealable layer, as long as the interior surface is fusible to the heat-sealable layer ofthe side wall 24. FIG. 5 illustrates a possible embodiment along these lines. The metál end 30 does nőt include an interior heat-sealable layer bút rather has a bare metál surface on its interiorside. It is illustrated as having a metál layer 42 of homogeneous construction, bút it is alsó possible fór the metál end to be, fór example, ETP (electrolytic tin plate steel) consisting of a layer of steel to which an ultrathin coating of tin is electrolytically deposited, fór example on the interior product-facing surface. The Container body side wall 24 consists of five layers, in orderfrom ID to OD: an interior heat-sealable layer 25, a tie layer 26, a barrier layer 27, a tie layer 28, and an exteriőr heat-sealable layer 29. Any ofthe previously described heat-sealable materials can be used fór the heat-sealable layers 25 and 29. The barrier layer 27 can comprise any suitable matéria! providing the necessary barrier properties fór the particular application to which the Container will be pút. Non-limiting examples of such barrier materials include ethylene vinyl alcohol (EVOH), polyvinyl alcohol (PVOH), polyvinylidene chloride copolymer(PVDC), polyacrylonitrile (PAN), polyethylene terephthalate (PÉT), polyethylene naphthalate (PEN), liquid crystal polymers (LCP), amorphous nylon, nylon 6, nylon 66, nylon-MXD6, and the like. The tie layers 26 and 28 can be any suitable adhesive materials fór adhering the heat-sealable layers 25 and 29 to the barrier layer 27.

[0040] When the metál end 30 does nőt include a heatsealable layer, the heat-sealable layers 25 and 29 can be designed to thermally fuse to the bare metál surface so as to form the seals S,· and S_o. Fór example, an ionomer (e.g., SURLYN® or the like) will thermally fuse to a bare metál such as ETP.

[0041] An advantage of the seal structure shown in FIG. 5 is that the inner seal S,· and outer seal S_o together serve to isolate the barrier layer 27 of the side wall from moisture migrating either from inside the Container or from outside the Container and contacting the barrier layer 27. This is im portant when the barrier layer is a matéria! whose barrier properties are degraded by exposure to moisture. Fór example, EVOH isan excellentoxygen barrier, bút it is well known that EVOH is deleteriously affected by moisture. The usual solution would be to bury the EVOH layer between two layers that are good moisture barriers (e.g., polypropylene). In the Container ofthe present invention, however, this may nőt completely protect the EVOH layer because the EVOH layer is exposed atthe end surface ofthe Container body side wall. If moisture were able to migrate intő the seam region, it could then migrate intő the EVOH layer through the end surface. The seal structure such as shown in FIG. 5 prevents the end surface ofthe barrier layer 27 from being exposed to moisture.

[0042] FIG. 6 showsyetanotherembodiment, inwhich the metál end 30 has a metál layer 42, an interior coating 44, and an exteriőr coating 46. The side wall 24 has a construction similar to that of FIG. 5. The interior coating 44 comprises a heat-sealable matéria! that is compatible with (i.e., heat-sealable to) the interior layer 25 ofthe side wall 24 to form the seal S,· and with the exteriőr layer 29 to form the seal S_o. The exteriőr coating 46 is provided primarily fór corrosion resistance so that the visible side of the metál end 30 remains aesthetically pleasing and does nőt develop corrosion that could be a source of contamination upon opening ofthe Container. Any of various coatings can be used on the metál end, such as polyesters, vinyls, acrylics, alkyds, oleoresins, phenolics, and the like.

[0043] The above-described embodiments in FIGS. 4 through 6 are nőt limiting in terms ofthe particular construction ofthe metál end 30 and side wall 24. The present invention is applicable to and includes any combination of metál end and side wall constructions in which at least one of their respective surfaces that are intimately contacting each other in the region ofthe seam 40 is formed by a heat-sealable matériái, and the two surfaces are such that heating ofthe seam to soften or melt this heatsealable matéria!, followed by cooling of the matéria!,

ΕΡ 2 750 980 Β1 causes the two surfaces to be thermally fused to each other. Additionally, as previously noted, it is importantfor at least part of the chuck wall 38 to be parallel to and intimately contacting the side wall 24 so that an interior seal S, is created that is placed predominantly in shear by internál pressure in the Container such as during retort. [0044] Containers in accordance with the present invention were manufactured and weresubjected to testing to determine whether the containers would be capable of going through a typical retort process and remaining intact, i.e., with no failure of the metál end-to-side wall seams and with no permanent deformation of the Container. The containers had crimp-seamed and induction sealed ends such as shown in FIG. 5, and had the following construction:

Container body inside diameter = 7.6 cm (3 inches) Container body length = 11.271 cm (4.4375 inches) Container body side wall structure: PP / tie /EVOH / tie/PP

Side wall thickness = 0.089 cm (0.035 inch)

Metál end structure (from interior to exteriőr): 40 micron PP / 0.019 cm (0.0075 inch) TFS tin-free steel) /15 micron PÉT [0045] The containers were tested in an apparátus shown schematically in FIG. 7. The apparátus included a closed chamber C fór enclosing a Container under test. The interior of the chamber was fed with steam via a steam pressure regulator SP and with airvia an air pressure regulator AP. The steam and airsupplies were regulated so as to maintain a substantially constant 121° C (250° F) temperature in the interior of the chamber. A manually operated pressure regulator MPRwas used in somé of the tests to allow independent control overthe air pressure within the test Container placed in the chamber. Wireless [0046] pressure and temperature transducers (data acquisition/recording devices) were used to measure pressure and temperature within the chamber and pressure within the test Container.

[0047] FIG. 8 shows the results of tests of a Container in accordance with the invention (substantially as shown in FIG. 5) as well as a conventional metál can having similar overall dimensions and configuration. The objective of this test was to measure the differential pressure (= can internál pressure - chamber internál pressure) experienced by the containers when retorted at a substantially constant 121°C (250° F) temperature. In this test series, the manual pressure regulator MPRwas nőt used, bút ratherthe pressure inside the Container was allowed to naturally respond to the retort environment in the chamber. The metál Container developed a peak differential pressure of about 130 kPa (18.9 psi). In contrast, the Container in accordance with the invention developed a peak differential pressure of only about 44 kPa (6.4 psi), nearly one-third of that of the metál Container. It is believed that the much lowerAPforthe plastic-body Container was due to the plastic body’s ability to expand radially as a result of the internál pressure, which had the effect of reducing the ΔΡ relatíve to that of the relatively rigid metál can.

[0048] This ability to expand is advantageous in terms of reducing the ΔΡ and therefore the stress exerted on the seam between the metál end and the plastic Container body. However, if the plastic body were to expand too much during retort, it could undergo a permanent deformation, which could render the Container unsuitable fór its intended purpose. To try to determine whether such permanent deformation could pose a problem, a finite element analysis was performed on the Container fór two wall thicknesses, 0.066 cm (.026 inch) and 0.089 cm (.035 inch), and over a rangé of temperatures from 21° C (70° F) to 129° C (265° F). The analysis sought to determine at each temperature the critical pressure, which is defined as the differential pressure above which permanent deformation of the plastic body occurs. The results are plotted in FIG. 9. Asexpected, the critical pressure decreases with increasing temperature. At a typical retorttemperatureof 121° C (250° F), the critical pressure was computed to be 69 kPa (10 psi) fór the 0.066 cm (.026 inch) wall thickness and 97 kPa (14 psi) fór the 0.089 cm (.035 inch) wall thickness. This analysis provides confidence that under realistic retort conditions such as those in the test summarized in FIG. 8, the ΔΡ of the containers of the present invention should be well under the critical pressure.

[0049] Additional tests of containers with crimpseamed and sealed ends in accordance with the invention were conducted in the apparátus of FIG. 7 in order to determine how much ΔΡ would be required under typical retort conditions to cause the containers to fail. As with the previously described tests, the temperature in the retort cham bér was maintained substantially constant at about 121° C (250° F). By adjusting the manual pressure regulator MPR periodically, the pressure within the Container was stepped up synchronously with the increasing pressure in the test chamberduring come-up. Once the temperature in the chamber reached a controlled 121° C (250 ° F) (having maintained minimál differential pressure to this point), the pressure in the Container was then increased progressively until failure occurred, in order to evaluate the seal burst resistance due to positive differential pressure. FIG. 7 shows the temperature and ΔΡ versus time fór one Container. The Container failed at a ΔΡ of about 151 kPa (21.9 psi), and the failure mode was a bursting of the plastic Container body. Additional repeat tests were performed with several other nominally identical containers. Over the series of tests, the ΔΡ at failure ranged from 150 to 154 kPa (21.8 to 22.4 psi), and the failure mode was always a bursting of the plastic Container body wall. The metál ends remained attached to the Container body.

[0050] Forcomparison purposes, the same typeoftest was conducted on containers made from the same Container body and metál end components, bút having the

ΕΡ 2 750 980 Β1 ends double-seamed onto the Container bodies and without induction sealing of the ends. Fór that series of tests, the ΔΡ at failure ranged írom 30 to 57 kPa (4.4 to 8.3 psi), and the failure mode was always a breach of the double seam of one of the ends (i.e., the double seam unrolled as a result of softening of the plastic sídé wall at elevated temperature and the stress applied to the seam from the internál pressure).

[0051] Thus, comparing the performance of the inventive containers with crimp-seamed and sealed ends on the one hand to that of the containers with doubleseamed and unsealed ends on the other hand, there was an approximately 250% increase in the ΔΡ at failure fór the inventive Container. This dramatic improvement was unexpected and is nőt completely understood. It is theorized, however, that the improvement in seam integrity is due in large part to the thermal fusing of the chuck wall to the innersurface of the Container body sídé wall, which results in an interface that experiences almost purely shear stress during a high internal-pressure condition such as retort. This interface, which is very strong in shear, is thought to bear the vast majority of the stress exerted on the metál end, such that the seam itself is nőt subjected to great stress.

[0052] A further advantage of the Container of the invention is its ability to undergo elastic expansion during high internal-pressure conditionssuch as retort, and then return substantially to its original configuration when the high internál pressure is relieved. As noted, this helps alleviate internál pressure and, consequently, the stresses exerted on the chuck wall/side wall interface and the seam. To realize this advantage, of course, the Container body must be relatively unconstrained so that it is able to expand radially.

[0053] The foregoing description focuses on containers having crimp-seamed and sealed metál ends. As noted, however, the invention is nőt limited to crimp seam ing. Alternatively, the metál ends can be double seamed and then sealed via an induction heating or other process. FIG. 11 shows such a Container having a double seam 40’. Apartfrom the differentseam configuration, the double-seamed containers are similar to the previously described crimp-seamed containers. The double seam 40’ is characterized by the upper end of the sídé wall 24 forming a body hook and the curl of the metál end forming an end hook that is interlocked with the body hook. [0054] In typical double-seamed containers, a seaming compound is often applied to the metál end in the region of the curl. The seaming compound flows during double seaming so as to fill up any gaps that may exist between the metál end and Container body wall in the seam area. Containers in accordance with the invention can be made either with our without conventional seaming compounds.

[0055] In the foregoing description and the appended claims, references to the Container body being substantially thermoplastic or the like mean that thermoplastic is the majority ingredient of the Container body on a volume basis, and furthermore that any non-thermoplastic ingredient(s) does (do) nőt impair the ability of the Container body to be heat-sealed to a metál end or to expand elastically during retort Processing as previously described. Forexample, a substantially thermoplastic Container body can include non-thermoplastic ingredients such as pigments (e.g., titanium dioxide), dyes, or other additives fór imparting visual characteristics (e.g., coloration, opacity, etc.) or other properties nőt provided by the thermoplastic itself. As another example, a Container body of composite construction such as paper/thermoplasticor metal/thermoplastic would nőt be substantially thermoplastic (even if the thermoplastic were the majority ingredient by volume) ifthe paper or metál component impaired the ability of the Container body to be heatsealed to a metál end and/orto expand elastically during retort Processing.

[0056] Containers in accordance with the invention can provide distinct advantages over conventional metál retort containers. Fór example, the invention enables the option of making the Container body 22 substantially transparent so that the contents of the Container can be seen by the consumer prior to purchase. Particularly fór visually attractive products (e.g., fruits and vegetables) this can provide a perception of freshness. Alternatively, the Container body can be tinted any of various colors while still remaining substantially transparent, or can be made opaque, through incorporation of suitable dyes or pigments in the thermoplastic matériái. Additionally, the Container can befree of bisphenol-A(BPA). The Container can be microwavable, unlike a conventional metál can. [0057] Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Forexample, while induction heating has been described fór causing the metál end and Container sídé wall to become thermally fused together in the seam area, other types of heating devices and processes can be used instead. Therefore, it is to be understood that the inventions are nőt to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and nőt fór purposes of limitation.