A METHOD FOR MAKING SHEET LAMINATES FOR BEING PRE-PUNCHED TO A SHEET LID TO BE ATTACHED TO A CONTAINER

Abstract

A method for making a sheet laminate for being pre-punched to a sheet lid for a container, comprising the steps of providing a base sheet layer, and coextrusion coating an additional sheet layer, which comprises a tie layer comprising polyolefin and a welding layer comprising polystyrene (PS), onto said base sheet layer, so that the tie layer is disposed between the base sheet layer and the welding layer. The additional layer is coextrusion coated onto the base sheet layer. A sheet lid with a similar structure may be manufactured by punching the sheet laminate. The sheet lid may be used to close a container to form a package.

Claims

1-26. (canceled)

27. A method for making a sheet laminate for being pre-punched to a sheet lid for a container, comprising: providing a base sheet layer; and coextrusion coating an additional sheet layer onto said base sheet layer, the additional sheet layer comprising at least one tie layer comprising polyolefin and a welding layer comprising at least 80% by weight polystyrene (PS), such that the at least one tie layer is disposed between the base sheet layer and the welding layer; wherein a temperature of a welding layer material, the welding layer material being comprised in the welding layer in the sheet laminate, is kept below 275 C. during all parts of the coextrusion coating.

28. The method of claim 27, wherein the welding layer comprises at least 90% by weight polystyrene.

29. The method of claim 27, wherein the welding layer comprises at least 95% by weight polystyrene.

30. The method of claim 27, wherein the welding layer comprises substantially 100% by weight polystyrene.

31. The method of claim 27, wherein a content the polystyrene of the welding layer is at least 90% by weight.

32. The method of claim 27, wherein a temperature of the welding layer material is kept at or below a temperature of 260 C., during all parts of the coextrusion coating.

33. The method of claim 27, wherein each of the tie layer material and the welding layer material are fed into a feed block of an extruder through a respective separate feeder.

34. The method of claim 27, wherein the coextrusion coating is performed in an extruder comprising a feed zone, a transition zone, a metering/mixing zone, a feed block with a feed block zone, and a die; and in which feed zone a temperature of a tie layer material, the tie layer material being comprised in the at least one tie layer of the sheet laminate, is 120 to 160 C.; and in which feed zone a temperature of a welding layer material, the welding layer material being comprised in the welding layer in the sheet laminate, is 175 to 200 C.; and in which transition zone a temperature of a tie layer material, the tie layer material being comprised in the at least one tie layer of the sheet laminate, is 160 to 170 C.; and in which transition zone a temperature of a welding layer material, the welding layer material being comprised in the welding layer in the sheet laminate, is 230 to 250 C.; and in which metering/mixing zone a temperature of a tie layer material, the tie layer material being comprised in the at least one tie layer of the sheet laminate, is 220 to 240 C.; and in which metering/mixing zone a temperature of a welding layer material, the welding layer material being comprised in the welding layer in the sheet laminate, is 225 to 275 C.; and in which feed block zone a temperature of a tie layer material, the tie layer material being comprised in the at least one tie layer of the sheet laminate, is 225 to 275 C., and in which feed block zone a temperature of a welding layer material, the welding layer material being comprised in the welding layer in the sheet laminate, is 225 to 275 C.; and wherein a temperature of a welding layer material, the welding layer material being comprised in the welding layer in the sheet laminate, in the feed block being equal to or less than 10 C. from a temperature of a tie layer material in the die, and a temperature of a welding layer material, the welding layer material being comprised in the welding layer in the sheet laminate, in the die being equal to or less than 10 C. from a temperature of a tie layer material, the tie layer material being comprised in the at least one tie layer of the sheet laminate.

35. The method of claim 27, further comprising: punching a sheet lid from the sheet laminate.

36. The method of claim 35, further comprising: providing a container manufactured from PS or comprising an outer welding layer comprising PS; subsequent to punching the sheet lid, arranging the sheet lid with a bottom surface of the welding layer thereof facing a welding surface of the container, said welding surface surrounding an opening of the container; and welding the bottom surface of the welding layer of the punched sheet lid to the welding surface of the container.

37. A sheet laminate for being pre-punched to a sheet lid for a container, comprising: a base sheet layer; and an additional sheet layer comprising at least one tie layer comprising polyolefin and a welding layer comprising at least 80% by weight polystyrene (PS), the at least one tie layer being disposed between the base sheet layer and the welding layer; wherein the additional sheet layer has been coextrusion coated onto said base sheet layer.

38. The method according to claim 27, wherein the magnitude of curl K of the sheet laminate measured according to ISO 11556:2005(E), second edition 2005, is equal to or less than 10 m.sup.1.

39. The sheet laminate according to claim 37, wherein no separate adhesive or glue layer, which includes a hardener or a hardening component, is provided between the additional sheet layer and the base sheet layer.

40. The sheet laminate of claim 37, wherein the magnitude of curl K of the sheet laminate measured according to ISO 11556:2005(E), second edition 2005, is equal to or less than 10 m.sup.1.

41. A laminated sheet lid for a container comprising: a base sheet layer; and an additional sheet layer comprising at least one tie layer comprising polyolefin and a welding layer comprising at least 80% by weight PS, the at least one tie layer being disposed between the base sheet layer and the welding layer; wherein the additional sheet layer has been coextrusion coated onto said base sheet layer.

42. A package comprising a container with a sheet lid according to claim 41, wherein the container is a PS container or comprises an outer welding layer comprising PS; the sheet lid is arranged with the welding layer facing a welding surface of the container, said welding surface surrounding an opening of the container; and a bottom welding surface of the welding layer of the punched sheet lid is welded to the welding surface of the container.

43. A method for making a sheet laminate for being pre-punched to a sheet lid for a container, comprising: providing a base sheet layer; and coextrusion coating an additional sheet layer onto said base sheet layer, the additional sheet layer comprising at least one tie layer comprising polyolefin and a welding layer comprising at least 80% by weight polystyrene (PS), such that the at least one tie layer is disposed between the base sheet layer and the welding layer; wherein a styrene content in the polystyrene of the welding layer is at least 90% by weight.

44. The method of claim 43, wherein a temperature of a welding layer material, the welding layer material being comprised in the welding layer in the sheet laminate, is kept at or below a temperature of 260 C. during all parts of the coextrusion coating.

45. The method of claim 43, wherein each of the tie layer material and the welding layer material are fed into a feed block of an extruder through a respective separate feeder.

46. The method of claim 16, wherein the coextrusion coating is performed in an extruder comprising a feed zone, a transition zone, a metering/mixing zone, a feed block with a feed block zone, and a die, and in which feed zone a temperature of a tie layer material, the tie layer material being comprised in the at least one tie layer of the sheet laminate, is 120 to 160 C.; and in which feed zone a temperature of a welding layer material, the welding layer material being comprised in the welding layer in the sheet laminate, is 175 to 200 C.; and in which transition zone a temperature of a tie layer material, the tie layer material being comprised in the at least one tie layer of the sheet laminate, is 160 to 170 C.; and in which transition zone a temperature of a welding layer material, the welding layer material being comprised in the welding layer in the sheet laminate, is 230 to 250 C.; and in which metering/mixing zone a temperature of a tie layer material, the tie layer material being comprised in the at least one tie layer of the sheet laminate, is 220 to 240 C.; and in which metering/mixing zone a temperature of a welding layer material, the welding layer material being comprised in the welding layer in the sheet laminate, is 225 to 275 C.; and in which feed block zone a temperature of a tie layer material, the tie layer material being comprised in the at least one tie layer of the sheet laminate, is 225 to 275 C., and in which feed block zone a temperature of a welding layer material, the welding layer material being comprised in the welding layer in the sheet laminate, is 225 to 275 C.; and wherein a temperature of a welding layer material, the welding layer material being comprised in the welding layer in the sheet laminate, in the feed block being equal to or less than 10 C. from a temperature of a tie layer material in the die, and a temperature of a welding layer material, the welding layer material being comprised in the welding layer in the sheet laminate, in the die being equal to or less than 10 C. from a temperature of a tie layer material, the tie layer material being comprised in the at least one tie layer of the sheet laminate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0160] Embodiments will be described in the following detailed description with reference to the drawings in which:

[0161] FIG. 1 shows a perspective view of an embodiment of a package manufactured according to an embodiment of a method for making a package, the package comprising a container and an embodiment of a sheet lid manufactured from an embodiment of a sheet laminate, the package being shown prior to welding the lid to the container,

[0162] FIG. 2 shows a detail of the package of FIG. 1 in a sectional view taken along the line II-II in FIG. 1 after the sheet lid has been torn off of the container, i.e. after delamination,

[0163] FIG. 3 shows a schematic sectional view of a sheet laminate from which the sheet lid of FIG. 1 has been cut,

[0164] FIG. 4 shows a schematic sectional view corresponding to that of FIG. 3 of an alternative embodiment of the sheet laminate,

[0165] FIG. 5 shows a schematic sectional view corresponding to that of FIG. 3 of another alternative embodiment of the sheet laminate,

[0166] FIG. 6 is a schematic view of an extruder for coextrusion of an additional layer of the sheet laminate according to any one of FIGS. 3 to 4,

[0167] FIG. 7 is a flow diagram illustrating a coextrusion process carried out in the extruder of FIG. 6, showing temperature zones in the different parts of the extruder,

[0168] FIG. 6a is a view similar to that of FIG. 6, showing an extruder for coextrusion of an additional layer of the sheet laminate according to any one of FIG. 5,

[0169] FIG. 7a is a flow diagram similar to that of FIG. 7 and illustrating a coextrusion process carried out in the extruder of FIG. 6a, showing temperature zones in the different parts of the extruder,

[0170] FIG. 8 shows a schematic side view of an apparatus for a coating process following the coextrusion process of FIG. 7 for coating the coextruded additional layer onto a base sheet layer, and

[0171] FIG. 9 shows a schematic side view of a test sample of a sheet laminate for measuring curl,

[0172] FIG. 10 shows a photographic representation of a melt curtain during manufacture of a first sample sheet laminate,

[0173] FIG. 11 shows a photographic representation of a melt curtain during manufacture of a second sample sheet laminate,

[0174] FIG. 12 shows a photographic representation of a coating distribution on the second sample sheet laminate,

[0175] FIG. 13 shows a photographic representation of a melt curtain during manufacture of a third sample sheet laminate,

[0176] FIG. 14 shows a photographic representation of a melt curtain during manufacture of a fourth sample sheet laminate, and

[0177] FIG. 15 shows IR scans of the sealing zone after separation of a sample sheet laminate and a thick PS-film.

DETAILED DESCRIPTION

[0178] In this specification, generally, when terms such as thickness (measured in m) and distribution (measured in g/m.sup.2) are used, unless otherwise indicated it is to be understood that the layer in question has a substantially or essentially uniform thickness across the planar extent of the layer or sheet or laminate according to the stated value.

[0179] The package shown in FIGS. 1 and 2 is an embodiment of the packages according to this disclosure and is manufactured according to an embodiment of the methods according to this disclosure for making a package.

[0180] The package comprises a container 1 and an embodiment of the sheet lids according to this disclosure, denoted 2, which sheet lid 2 is manufactured from the embodiment of a sheet laminate, which sheet laminate is denoted S and is illustrated in FIG. 3.

[0181] In FIG. 1 the package is shown before welding the lid 2 to the container 1.

[0182] FIG. 2 shows a detail of the package of FIG. 1 in a sectional view taken along the line II-II in FIG. 1 after the sheet lid 2 has been torn off of the container 1, i.e. after delamination.

[0183] The container 1 is manufactured of thermoformed polystyrene (PS).

[0184] The container 1 is provided with an upper welding rim 3, which is plane on an upper surface facing the sheet lid 2 to enable welding of the sheet lid 2 onto the upper surface of the rim 3 to produce the closed and sealed package. The rim 3 is a flange projecting in an outwards direction along an opening of the container 1.

[0185] When the container 1 has been filled with its contents, which may be foodstuff, such as a dairy product, it is closed with the sheet lid 2. The sheet lid 2 has been pre-punched, i.e. punched in advance of closing the container, from the sheet laminate S shown in FIG. 3 and is thus adapted in shape and size to the opening of the container 1, specifically the rim 3, before welding.

[0186] Referring to FIG. 3, the sheet laminate S and thus the punched sheet lid 2 comprise a base sheet layer 4, the base sheet layer 4 in the shown embodiment comprising a polyester top layer 4a, which has a thickness of about 36 m. This thickness is adapted to the need for strength, barrier properties, and other functional requirements of the container 1. The polyester layer 4a consists of polyester, specifically OPET. The base sheet layer 4 also comprises a barrier coating 4b, specifically a SiOx coating coated onto a first major surface of the OPET layer 4a and having a thickness of less than 1 m, whereby an oxygen transmission rate of the sheet laminate of less than 3 cm.sup.3/m.sup.2/24 h/bar and a water vapour transmission rate of less than 3 g/m.sup.2/24 h is achieved.

[0187] The base sheet layer 4 can in an alternative embodiment additionally be metallized on its second major surface, the metal layer being provided with an outer protective lacquer to prevent the metal layer from being scratched or damaged.

[0188] An additional sheet layer 5 comprising a tie layer 5a, essentially consisting of an EVA copolymer resin, specifically Escorene Ultra UL 00728EL, and a PS welding layer, specifically a HIPS layer 5b, has been coextrusion coated onto the base sheet layer 4. Thus, the additional sheet layer 5 is provided by coextrusion coating of the two layers 5a and 5b onto a first major surface 4c of the base sheet layer 4. The welding layer 5b is intended to be welded to the upper surface of the rim portion 3 of the container 1.

[0189] All of the base sheet layer 4, the tie layer 5a, the welding layer 5b, the sheet laminate S and the sheet lid 2 are transparent, but somewhat milky due to the somewhat milky HIPS used in the welding layer, and allow substantially 50% of visible light to pass through them.

[0190] An extruder used in the coextrusion process of the coextrusion coating step of the method for making of the sheet laminate S is shown in FIG. 6. The coextrusion process of the coextrusion coating step is schematically illustrated in the diagram of FIG. 7. The coating process of the coextrusion coating step is illustrated in FIG. 8, which schematically shows the coating process carried out on an apparatus for the coating step.

[0191] Referring to FIG. 6, the extruder or coextruder shown is a conventional apparatus for coextruding sheet laminates comprising thermoplastic polymer materials. It comprises two respective feeders I and II, where a PE tie layer granulate is fed into feeder I, and a PS welding layer granulate is fed into feeder II at the arrows in the figure. Each feeder I, II comprise a worm for transporting the respective material through the feeder I, II and into a feed block F via an adapter/melt pipe A/M.

[0192] Referring now also to FIG. 7, each feeder I, II comprise an initial feed zone I1, II1, respectively, followed by a transition zone I2; II2 (which may in other embodiments comprise two or more subzones), followed by a metering/mixing zone with subzones I3, II3; I4, II4; I5, II5, respectively. The metering/mixing zone is followed by an adapter/melt pipe A/M zone, which leads into the feed block F. In the respective feed zone I1, II1 the respective material fed into the respective feeder I, II is softened and heated almost to the melting point. In the transition zone I2, II2 the material is melted and pressure is built up. In the metering/mixing subzones I3, II3; I4, II4; I5, II5 a respective uniform melt of the respective material is created. In the A/M zone the two melts are transferred to meet in the feed block F. In a feed block upper zone F1 and a feed block lower zone F2, structure is built up in the two melts to be coextruded. The two melts are then coextruded from a die D with a nozzle width of 1550 mm to form the additional layer 5, see FIG. 6. Generally, the nozzle width of the Die D usually may vary from 1000 mm to 2500 mm. The feeders I, II, the adapter/melt pipe A/M, the feed block F and/or the die D comprise a number of not shown conventional heaters that are temperature regulated by a not shown conventional regulator or controller. The regulator sets the heaters to heat the materials within the extruder to a given temperature in each of the zones. Temperature measurements in one or more of the temperature zones are provided to the regulator to allow the regulator to regulate the zone temperatures according to the set temperatures. The heaters take the form of one or more mantles or casings that surround or encase part or all of each of the apparatus parts I, II, A/M, F and D, Heat energy is also created due to friction inside the extruder, especially within the feeders I, II. When referring to a temperature within a zone in the following, reference is made to the set temperature of the heater in that zone.

[0193] As mentioned, the feed block F comprises an upper zone F1 and a lower zone F2, the upper zone F1 being positioned subsequent to the adapter and melt pipe NM zone, and the lower zone F2 leading into the die D from which the coextruded melt is extruded. The die D comprises three interior zones D1, D2, D3 in a transverse direction, each interior zone having three subzones (not shown). The melts or extrudates of the materials merge and weld together into a laminar structure within and/or when exiting the die D to form the coextruded additional layer 5 that is applied onto the base sheet layer 4 before chilling as described below.

[0194] The feed zones I1, II1 extend from about 0 to about of an entire transport length from beginning to end of the respective feeder I, II, the transition zone I2, II2 extends from about to of the length, the respective subzone I3, II3 of the metering/mixing zone from about to of the length, the second subzone I4, II4 from about to of the length, and the third subzone I5, II5 from about to 5/5 of the length.

[0195] The set temperatures of the heaters of the extruder are shown below in C. for each zone/subzone:

TABLE-US-00009 Zone Metering/ Metering/ Metering/ Feed Transition mixing mixing mixing zone 1 zone 2 zone 3 zone 4 zone 5 Tie layer 120 170 220 220 220 (I) Welding 180 240 240 240 240 layer (II)

TABLE-US-00010 Zone Feed block Feed block Die 1 Die 2 Die 3 upper F1 lower F2 D1 D2 D3 Both 240 240 240 240 240 layers (I, II)

[0196] Now referring also to FIG. 8, in the coating process of the coextrusion coating step the base sheet layer 4 is continuously rolled off from a feed roll to be moved between two rollers, specifically a cooling roller 50 and a counter roller or pressure roller 51. The cooling roller has a chilled or cooled outer surface onto which a melt 5c of the material eventually forming the additional layer 5 is applied from the extruder die D of FIGS. 6 and 7 (which is seen from a lateral side in FIG. 8 as opposed to FIG. 6 where it is seen in a plane view) so as to be positioned between a base sheet 4d, which eventually forms the base sheet layer 4, and the cooling roller 50. The coextrusion coating step shown in FIGS. 6 to 8 is thus a continuous process, the rollers 50, 51 rotating along the arrows in FIG. 8 to continuously pull the base sheet 4d off the not shown feed roll. Upon contact with the base sheet 4d at or right before a nip 52 between the rollers 50, 51, the melt 5c adheres to the base sheet 4d. Subsequently or at the same time, upon contact with the cooling roller 50, the melt 5c is chilled to solidify.

[0197] The result is the laminate sheet S comprising the base sheet layer 4 coated with the additional layer 5, which is then rolled up on a not shown collecting roller. The additional layer melt 5c comprises the two melts of the materials of the layers 5a and 5b that are coextruded, i.e. extruded together through the single die D of the extruder shown in FIG. 6. Thus, the two coextruded melts of the additional layer melt 5c are coextruded onto the base sheet 4d so that the coextruded additional layer 5 adheres to the base sheet layer 4 so as to form the sheet laminate S shown in FIG. 3. The additional layer melt 5c and the base sheet layer 4 are guided through the nip 52 between the cooling roller 50 and the opposed pressure roller 51 so that the additional layer melt 5c faces and contacts the cooling roller 50 and the base sheet 4d faces and contacts the pressure roller 51.

[0198] The tie layer 5a essentially consists of a copolymer of PE, specifically an acrylate-containing copolymer of PE or an ethyl vinyl acetate (EVA) containing PE. Use of any one of these copolymers or a combination of these may ensure that delamination between the welding layer 5b and the polyethylene layer 5a only occurs in the welding area, i.e. at the upper surface of the rim 3 and may ensure sufficient welding strength.

[0199] The two layers 5a and 5b are distributed in an accumulated amount of 15 g/m.sup.2. The tie layer 5a is distributed in an amount of about 10 g/m.sup.2 or has a thickness of about 11 m. The welding layer 5b is distributed in an amount of about 5 g/m.sup.2 or has a thickness of about 5 m.

[0200] The base sheet layer 4 may alternatively be extruded immediately before the additional layer 5 is coextrusion coated onto it.

[0201] Referring also to FIG. 3, an extrusion primer is applied to the base sheet 4 to form a primer layer 6 before the coextruded melt 5c is applied onto the base sheet 4 to form the sheet laminate S. The primer layer 6 provides enhanced adhesion between the first major surface 4c of the base sheet layer 4 and the polyethylene tie layer 5a. This primer layer can be avoided if a less strong adherence is desired.

[0202] The primer layer 6 is applied to the base sheet 4d immediately before, i.e. 0 to 20, 1 to 10, 2 to 7 seconds before, the step of coextrusion coating. The primer layer 6 essentially consists of a polyethyleneimin based primer.

[0203] The resultant sheet laminate S shown in FIG. 3 is weldable in its full planar extent. Thereby, any lid shape and dimension may be punched from a roll of the sheet laminate S the resultant sheet lid 2 being adapted to the size and shape of the container 1 and being weldable thereto without the need for applying a welding lacquer. The lid sheet S is supplied from the collecting roll of the sheet laminate S and is punched into its final shape of the sheet lid 2 prior to being applied to the container 1.

[0204] The container or cup 1 is filled with foodstuff in a filling machine, and the sheet lid 2, pre-punched to its final shape, is applied to the container 1 subsequently and welded to the rim portion 3 to seal the container 1.

[0205] When the container 1 has thus been filled with the foodstuff and closed with the sheet lid 2, a user may pull off the lid 2 by pulling in a periphery of the sheet lid 2, specifically in a peripheral lid flap or lid tap 2a visible in FIG. 1. Hereby, the tie layer 5a and the welding layer 5b will be separated or delaminated from each other in such a manner that the pulling-off or opening of the package along the rim portion 3 is controlled and precise, the welding layer 5b essentially remaining on the container 1 in the welding area, i.e. on the rim portion 3 thereof, and remain on the lid 2 in the non-welded area, see FIG. 2.

[0206] Optionally, an additional print or colour layer may be applied in a generally known manner on for example a top surface or a bottom surface of the sheet lid 2 either before or after the punching of the lid 2, and/or an additional barrier coating may optionally be applied to the sheet laminate before or after the punching.

[0207] The punched sheet lid 2 essentially does not curl after the punching, specifically even when it is not attached to the container 2, see also the examples below.

[0208] In an alternative embodiment of FIG. 3, the barrier coating 4b instead is positioned to face away from the tie layer 5a.

[0209] FIGS. 4 and 5 show views similar to that of FIG. 3, but of two respective alternative embodiments of the sheet laminate. These sheet laminates S are generally identical to the embodiment of the sheet laminate S shown in FIGS. 1 to 3 and made by an identical method, except for the differences mentioned in the following for each of the alternative embodiments.

[0210] In the embodiment of FIG. 4, the barrier coating 4b is applied to the second or outer major surface of the polyester layer 4a so that the tie layer 5a is in direct contact with the first major surface 4c of the polyester layer 4a of the base sheet layer 4, The tie layer 5a is made from an acrylate containing PE polymer with sufficient adherence to both PET and PS so that the additional sheet layer 5 can be coextrusion coated directly onto the base sheet layer 4 without the use of a primer layer 6.

[0211] In an alternative embodiment of FIG. 4, the barrier coating 4b instead is positioned to face the tie layer 5a.

[0212] FIG. 5 shows another embodiment of the sheet laminate, which is similar to and made by an identical method as that of FIGS. 3 and 4 except for the following differences.

[0213] In FIG. 5, a metallization 4b of the base sheet layer, i.e. a metal layer 4b including Al, faces the tie layer, in this case an upper tie layer 5a. No primer layer 6 as in FIG. 3 is present in the embodiment of FIG. 5. The additional sheet layer 5 includes two tie layers 5a and 5a, these two tie layers corresponding to the tie layers 1 and 2, respectively, as described in the general description above. The two tie layers 5a, 5a comprise respective polymers which have sufficiently high adherence to their respective adjacent layers for the sheet laminate S to not unintentionally delaminate, i.e. the sublayer 5a adjacent to the base sheet layer 4 adheres to the PET of the base sheet layer 4 and the adjacent tie layer 5a, the latter in turn adhering to the welding layer 5b.

[0214] FIGS. 6a and 7a show views similar to those of FIGS. 6 and 7, respectively, but including not only two feeders I and II, but three I, II and III. The feeder I feeds the tie layer 5a material, feeder II feeds the tie layer 5a material, and feeder Ill feeds the welding layer 5b material. The process of manufacture is otherwise similar to as described in connection with FIGS. 6 and 7.

[0215] Referring to FIGS. 6a and 7a, the temperatures applied in the process of manufacture of the Sheet S of FIG. 5 are the following:

TABLE-US-00011 Zone Metering/ Metering/ Metering/ Feed Transition mixing mixing mixing zone (1) zone (2) zone (3) zone (4) zone (5) Tie layer 140 220 240 240 240 1, 5a (I) Tie layer 120 170 220 220 220 2, 5a (II) Welding 180 240 240 240 240 layer 5b (III)

TABLE-US-00012 Zone Feed block Feed block Die 1 Die 2 Die 3 upper (F1) lower, (F2) (D1) (D2) (D3) All layers 240 240 240 240 240 (I, II, III)

[0216] The thickness of the welding layer 5b is about 3 m. The thickness of the tie layer 5a is about 3 m. The thickness of the tie layer 5a is 6 m. No primer layer is present. The thickness of the polyester base sheet layer is about 36 m.

[0217] The tie layer 5a essentially consists of Escor 5110, and the tie layer 5a essentially consists of Escorene Ultra UL 00728EL, mentioned above. The welding layer 5b essentially consists of HIPS.

[0218] In an alternative embodiment of FIG. 5, the metal layer 4b is not present or is present on the opposite surface of the base sheet layer 4a.

[0219] The sheet laminate S shown in FIGS. 4 and 5 may be applied to the container 1 as shown in FIGS. 1 and 2 in a similar manner as described above.

[0220] Generally, in the sheet laminates S and the sheet lids 2 described above the layers are preferably provided extending substantially along the entire area of the adjacent layer so that the area sizes of major surfaces of all layers are similar to each other.

Example 1

[0221] A sample of the sheet laminate S according to FIG. 5 was manufactured in a coextrusion coating process as described above with reference to FIGS. 6a and 7a.

[0222] No significant bubbles (due to production of gases), material degradation or burns were detected in the welding layer 5b of the sample.

[0223] A test sample was punched from the sheet laminate sample, and the value h of the test sample was measured according to ISO 11556:2005(E), second edition 2005, in the manner described in the above with reference to FIG. 9. The value h for the test sample was measured to less than 3 mm, and the value C was measured to 112.7 mm, the K value accordingly being calculated to be less than 0.002 m.sup.1. The test sample of the sheet laminate thus had no or only very small curl.

[0224] A lid sample was pre-punched from the sheet laminate sample to correspond in size to an opening or rim of a thermoformed PS cup similar to the container 1 shown in FIG. 1 with an opening diameter of about 100 mm. The lid sample had no detectible curl and welded well to the respective container, the welding strength being above 5 N per 15 mm. The welding between lid sample and container resisted 0.3 atmosphere overpressure in the container for over 30 seconds.

[0225] The container was subsequently opened by pulling in a peripheral lid flap of the lid sample. The welding layer 5b of the lid sample essentially remained on the container in the welding area, i.e. on a rim portion of the container, and remained on the lid sample in the non-welded area, similar to as shown in FIG. 2.

Example 2

[0226] An initial explorative screening of different sheet laminate material combinations was carried out.

[0227] The sheet laminates according to the embodiments above were manufactured according to embodiments of the present disclosure with the following layers in succession: [0228] a base sheet layer of metallized PET (MET-PET) with a layer thickness of 36 m, and [0229] an additional sheet layer, which comprised two tie layers and a welding layer, the two tie layers being disposed between the base sheet layer and the welding layer, the first tie layer being adjacent to the base sheet layer, the second tie layer being adjacent to the welding layer, the additional sheet layer being coextrusion coated onto the base sheet layer.

[0230] The following two sheet laminate material combinations were selected for further tests. The respective layers essentially consisted of the material provided in the tables below for each respective sheet laminate.

TABLE-US-00013 Sheet laminate #1 Layer Material Layer thickness/distribution Base sheet layer Metallized PET 36 m First tie layer Nucrel 0609 HSA 3 g/m.sup.2 Second tie layer Lotader 4503 6 g/m.sup.2 Welding layer HIPS 3630 3 g/m.sup.2

TABLE-US-00014 Sheet laminate #2 Layer Material Layer thickness/distribution Base sheet layer Metallized PET 36 m First tie layer Escor 5110 3 g/m.sup.2 Second tie layer Escorene FL00728EL 6 g/m.sup.2 Welding layer HIPS 3630 3 g/m.sup.2

[0231] Nucrel 0609 HSA is a trade name as marketed by Dupont and consists essentially of a copolymer of ethylene and methacrylic acid made with nominally 6.5 wt % methacrylic acid.

[0232] Lotader 4503 is a trade name as marketed by Lotader and consists essentially of a random terpolymer of ethylene, acrylic ester and maleic anhydride, polymerized by high-pressure autoclave process.

[0233] HIPS 3630 is a polystyrene grade as marketed by Total and consists essentially of an easy flowing, medium impact polystyrene.

[0234] Escor 5110 and Escorene FL00728EL are as described previously.

[0235] Each sheet laminate was then subjected to qualitative tests including a friction test, a vacuum test, and a peel test. Sheet laminate #1 and #2 were manufactured with success and have almost similar properties; however, sheet laminate #2 appeared to perform slightly better. Further tests with sheet laminate #2 were conducted as outlined in the following.

[0236] Five sample sheet laminates #1 to #5 were produced using different temperature profiles with the material combination of sheet laminate #2 above. The below table shows the temperatures in C. that were applied during manufacture of the respective sample sheet laminate. The temperatures of the tie layer and the welding layer in the feed block and in the nozzle were the same, as seen from the tables below.

Sample Sheet Laminate #1

[0237]

TABLE-US-00015 Tie layer Welding layer Feed zone 115 160 Transition zone 160 220 Metering/Mixing zone 190 220 Feed block 220 Nozzle 220

Sample Sheet Laminate #2

[0238]

TABLE-US-00016 Tie layer Welding layer Feed zone 115 160 Transition zone 140 200 Metering/Mixing zone 170 200 Feed block 200 Nozzle 200

Sample Sheet Laminate #3

[0239]

TABLE-US-00017 Tie layer Welding layer Feed zone 160 200 Transition zone 190 250 Metering/Mixing zone 240 260 Feed block 260 Nozzle 260

Sample Sheet Laminate #4

[0240]

TABLE-US-00018 Tie layer Welding layer Feed zone 160 200 Transition zone 190 250 Metering/Mixing zone 260 280 Feed block 280 Nozzle 280

Sample Sheet Laminate #5

[0241]

TABLE-US-00019 Tie layer Welding layer Feed zone 120 175 Transition zone 170 230 Metering/Mixing zone 220 240 Feed block 240 Nozzle 240

[0242] Each sample sheet laminate was subjected to three tests to examine the feasibility for production: a run-ability (or manufacturability) test, a sealing strength test and a vacuum test.

[0243] The run-ability test was performed by inspecting the melt curtain exiting the die when manufacturing each sample sheet laminate and the resulting distribution of coating after application. The sample laminate sheets were manufactured on a pilot line running at about 15% of a typical line speed of a production line. The line speed is the speed at which a production line produces a sheet laminate. The speed is generally given in meters per minute. The line speed of a production line may for instance be 300 meters per minute.

[0244] The melt curtain of the sample sheet laminate #1 as seen in FIG. 10 was somewhat uneven; however, the resulting coating was made successfully with uniform coating distribution on the base sheet layer.

[0245] The melt curtain of the sample sheet laminate #2 as seen in FIG. 11 was more uneven than that of sample sheet laminate #1. The resulting coating of the sample sheet laminate #2 was not produced with a uniform coating distribution on the entire surface of the base sheet layer. The uneven distribution of coating is reflected in the glossy areas on the surface of the sample sheet laminate #2 in FIG. 12. A good uniform distribution would have instead produced a uniform matt surface. It is expected that this is probably due to a too unstable melt and that with simple variations of, for instance the line speed, tie layer materials, and/or layer thickness, the a person skilled in the art would arrive at an acceptable coating distribution.

[0246] The melt curtain of the sample sheet laminates #3 and #4 as seen in FIGS. 13 to 14, respectively, appeared even, and the resulting coating distribution appeared uniform. During the manufacture of the sample sheet laminates #3 and #4 release of smoke was observed, which appeared to increase during manufacture of sample sheet laminate #4, and which may indicate degradation of the acid modified tie layer polymer. It is expected that with simple variations of, for instance the line speed, tie layer materials, and/or layer thickness, a person skilled in the art would be able to reduce the release of smoke and/or degradation to an acceptable level.

[0247] The melt curtain of the sample sheet laminate #5 appeared even and the resulting coating distribution appeared uniform without noticeable release of smoke.

[0248] The sealing strength test was performed by sealing the sample sheet laminates to a thick PS-film at 190 C. at 5 bar pressure for 0.5 seconds. The sealing strength was measured on a 15 mm wide strip and the results in Newtons are listed in the table below. The sealing strength was measured as the force needed per 15 mm to separate the layers from each other.

TABLE-US-00020 Sample sheet Sealing strength laminate # [N/15 mm] 1 7.26 2 6.53 3 6.86 4 6.83 5 6.92

[0249] As seen from the table all sample sheet laminates had a sealing strength between 6.5 to 7.5, which all considered good. Furthermore, IR scans of the sealing zone were performed and all samples were peeled off and split substantially identically. The infrared scans of the sealing zone can be seen in FIG. 15, which shows five infrared spectroscopy scans, wherein the top row is an infrared spectroscopy scan of the sample sheet laminate #5, and the next four rows are infrared spectroscopy scans of the sample sheet laminates #1 to #4, respectively.

[0250] The vacuum tests were performed by sealing the sample sheet laminates to a polystyrene (PS) cup, at 190 C. at 2 bar pressure for 0.5 seconds. The sealed cups were put under three different vacuum pressures; a strict vacuum test of 0.30 bar, a moderate test of 0.25 bar, and a lenient test of 0.20 bar, and the time lapsed until the sealing broke is shown in the table below. When the time exceeded 40 seconds, the measurement was stopped, and 40< was noted in the table below.

TABLE-US-00021 Sample sheet 0.30 bar 0.25 bar 0.20 bar laminate # Time [s] Time [s] Time [s] 1 1.2 1.5 40< 2 1.9 40< 40< 3 35.8 40< 40< 4 2.0 40< 40< 5 35.0 40< 40<

[0251] The results show that the sample sheet laminates #3 and #5 last for 35.8 and 35.0 seconds, respectively, while the sample sheet laminates #1, #2 and #4 lasts below 2 seconds for strict vacuum test of 0.30 bar. This indicates for sample sheet laminates #1 and #2 that the coextrusion coating has lower adhesion and total strength due to lack of heat and inhomogeneous melt. Sample sheet laminate #4 also did not pass the strict vacuum test, indicating breakdown and decomposition of the polymers of the tie layers. It is expected that a person skilled in the art could, by simple variations of, for instance, the line speed, tie layer materials, layer thicknesses and/or by adding additives to the base sheet layer, the welding layer and/or the tie layer, arrive at a sealed cup which withstands a desired vacuum pressure for a desired amount of time. As seen from the table, different results were achieved when the vacuum pressure was varied. When performing the vacuum test at 0.20 bar all sample sheet laminates had improved performance.