METHOD OF PRODUCING A LAMINATED METAL SHEET FOR PACKAGING APPLICATIONS AND LAMINATED METAL SHEET FOR PACKAGING APPLICATIONS PRODUCED THEREBY

Abstract

A method of producing a laminated metal sheet for packaging applications and laminated metal sheet for packaging applications produced thereby.

Claims

1. A method for producing a laminated metal sheet in a continuous coating line operated at a line speed v, the laminated metal sheet comprising a laminate layer, the method comprising the subsequent steps of: providing a metal sheet; providing a laminate layer for coating onto at least one side of the metal sheet with a value for the Euclidean distance matrix D between a first and a second ATR FTIR spectrum of the laminate layer of 0.20 or higher, wherein the first spectrum is measured in an ATR-FTIR spectrometer with the incident IR-beam parallel or perpendicular to the machine direction of the laminated metal sheet and wherein the second spectrum is measured in the spectrometer after rotating the laminated metal sheet over an angle alpha in the plane of the laminate layer selected between 70 and 110°, and wherein the ATR-FTIR spectra are measured in the spectral range which includes the range of 1160 to 1520 cm.sup.-1; laminating the laminate layer onto the metal sheet to produce a laminated metal sheet; post-heating the laminated metal sheet to a post-heat set-point T2 sufficiently high to melt the laminate layer; cooling the post-heated laminated metal sheet to produce a laminated metal sheet with an Euclidean distance matrix D between a first and a second ATR FTIR spectrum of the laminate layer having a value in the range of 0.10 or lower, wherein the first spectrum is measured in an ATR-FTIR spectrometer with the incident IR-beam parallel or perpendicular to the machine direction of the laminated metal sheet and wherein the second spectrum is measured in the spectrometer after rotating the laminated metal sheet over an angle alpha in the plane of the laminate layer selected between 70 and 110°, and wherein the ATR-FTIR spectra are measured in the spectral range which includes the range of 1160 to 1520 cm.sup.-1.

2. The method according to claim 1, wherein the laminate layer for coating onto the metal sheet consists of one or more layers and is provided by: melting thermoplastic polymer granules in one or more extruders to form the one or more layers; forming the thermoplastic polymer film consisting of the two or more layers by passing the molten polymer or polymers through a flat (co-)extrusion die and/or two or more calendering rolls; optionally followed by: cooling the thermoplastic polymer film to form a solid thermoplastic polymer film; optionally trimming the edges of the thermoplastic polymer film; reducing the thickness of the solid thermoplastic polymer film by stretching the solid polymer film in a stretching unit by exerting a stretching force only in the longitudinal direction;optionally trimming the edges of the stretched thermoplastic polymer film.

3. The method according to claim 1, wherein the post-heat set-point (T2) or the line speed (v) of the continuous coating line or both the heat set-point and the line speed is or are adjusted if the Euclidean distance matrix D of the laminate layer after post-heating and cooling has a value of above 0.10.

4. The method according to claim 1, wherein alpha is selected between 80 and 100.

5. The method according to claim 1, wherein the metal sheet is a steel.

6. The method-according to claim 1, wherein the thermoplastic polymer film is a single layer or multilayer polyester or polyolefin polymer film.

7. The method according to claim 1, wherein the thermoplastic polymer film is a biaxially oriented polymer film.

8. The method according to claim 1, wherein the thermoplastic polymer film is a uniaxially oriented polymer film.

9. The method according to claim 1, wherein the laminate layer is laminated onto the metal sheet to produce a laminated metal sheet without interruption in a continuous process.

10. The method according to claim 1, wherein the laminate layer is applied at least to the side of the metal sheet that becomes the inside of a packaging and the polyester in the laminate layer contains at least 70% by mole of an ethylene terephthalate unit.

11. The method according to claim 1, wherein the laminate layer is applied at least to the side of the metal sheet that becomes the inside of a packaging and the polyester in the laminate layer contains at least 85% by mole of a butylene terephthalate unit.

12. The method according to claim 1, wherein the laminate layer is applied at least to the side of the metal sheet that becomes the inside of a packaging, such as a container or can, and the polyester in the laminate layer contains a blend of a polyethylene terephthalate and polybutylene terephthalate, preferably wherein the ratio of PET to PBT is 60:40 or higher.

13. The method according to claim 1, wherein the laminate layer is applied at least to the side of the metal sheet that becomes the inside of a packaging and the polyester in the laminate layer contains at least 85% by mole of an blend of a polyester containing 85% by mole of an ethylene terephthalate unit and a polyester containing at least 85% by mole of a butylene terephthalate unit.

14. The method according to claim 1, wherein the laminate layer contains a single layer containing 50% by mass or more of polyester or a plurality of layers containing 50% by mass or more of polyester, wherein the laminate layer prior to being laminated onto the metal sheet has a preferred molecular orientation in one direction and wherein an Euclidean distance matrix D between a first and a second ATR FTIR spectrum of the laminate layer is 0.20 or higher, and wherein the laminate after lamination onto the metal sheet has a value of D between the first and the second ATR FTIR spectrum of the laminate layer of 0.10 or lower.

15. A laminated metal sheet for packaging applications obtainable or obtained by the method according to claim 1, the laminated metal sheet comprising a metal sheet and a laminate layer that covers at least one side of the metal sheet, wherein 5 the laminate layer contains a single layer containing 50% by mass or more of polyester or a plurality of layers containing 50% by mass or more of polyester, wherein the laminate layer after lamination onto the metal sheet has a value of D between the first and the second ATR-FTIR spectrum of the laminate layer of at most 0.10, and wherein the first spectrum is measured in an ATR-FTIR spectrometer with the incident IR-beam parallel or perpendicular to the machine direction of the laminated metal sheet and wherein the second spectrum is measured in the spectrometer after rotating the laminated metal sheet over an angle alpha in the plane of the laminate layer selected between 70 and 110°, and wherein the ATR-FTIR spectra are measured in the spectral range which includes the range of 1160 to 1520 cm.sup.-1.

16. The method according to claim 4, wherein alpha is about 90°.

17. The method according to claim 5, wherein the steel is uncoated cold-rolled steel, tinplate, ECCS (aka TFS), TCCT, galvanised steel or aluminised steel.

18. The method according to claim 10, wherein the packaging is a container or a can.

19. The method according to claim 11, wherein the packaging is a container or a can.

20. The method according to claim 12, wherein the packaging is a container or a can.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0083] The invention will now be explained by means of the following, non-limiting figures.

[0084] FIG. 1 shows a schematic drawing of an industrial continuous coating line.

[0085] FIG. 2 shows a schematic drawing of the distance between two spectra.

[0086] FIG. 3 Spectra with a bad sample for CS1 - top.

[0087] FIG. 4 Spectra with a good sample for TS1 - top.

[0088] FIG. 5 Spectra with a bad sample for CS2 - top.

[0089] FIG. 6 Spectra with a good sample for TS2 - top.

[0090] FIG. 7 Spectra with a bad sample for CS2 - bottom.

[0091] FIG. 8 Spectra with a good sample for TS2 - bottom.

[0092] FIG. 9 Spectra with a machine direction oriented film PET5 before lamination.

[0093] FIG. 10 Spectra with a good sample for TS3 - top.

[0094] FIG. 11 Build-up of the laminated metal sheet.

[0095] FIG. 12 Schematic interpretation of the method according to the invention.

[0096] The laminate layers are laminated to the metal strip by a process schematically shown in FIG. 1. The metal strip (1) is passed through first heating device (2) where temperature of the metal strip is raised to pre-heat temperature suitable for lamination, T1. In the present examples T1 was chosen to be 200° C. for lamination of pure PET films, 220° C. for lamination of films containing 25% PBT and 225° C. for lamination of film based on pure PBT. A coil of film PET1, PET3 or PET5 (3a) and PET2, PET4 or PET6 (3b) are simultaneously unwound and passed, together with the pre-heated metal strip, through a pair of laminating rollers (4a, 4b). The laminated metal sheet (5) is passed through a second heating device (6) where the temperature of the laminated metal sheet is raised to a post-heat set-point, T2. After the second heating device, the laminated metal sheet is immediately cooled by passing through a quenching device (7) to reach room temperature. The method of pre-heating the metal strip in the first heating device is not particularly limited and may include passing the strip over heated rolls, conductive heating, inductive heating, radiative heating, etc. The method of post-heating the laminated metal sheet in the second heating device is preferably a contactless method, such as heating in a hot gas environment or inductive heating. The method of immediate cooling in the quenching device is not particularly limited and may include applying cold air or passing through a cold-water bath etc.

[0097] The spectral distance D is proportional to the area between two curves. In FIG. 2 two model sine curves are depicted. The spectral distance is proportional to the grey area between the two sine curves.

[0098] FIG. 11 shows the schematic build-up of a laminated metal sheet. The top drawing shows the simplest form of laminated metal sheet 9 with the metal sheet 1 provided with one laminate layer 3a. The bottom figure shows a more complicated embodiment according to the invention where the metal sheet 1 is provided with a multilayer laminate layer 3a on top, wherein the multilayer (in this example) comprises three separate layers 3a', 3a" and 3a"', for instance serving as a top layer, bulk layer and adhesion layer respectively, each potentially having a different composition tailored to the requirements posed to the individual separate layer, and a second laminate layer on the bottom of the metal sheet, which may be the same in terms of composition, build-up or thickness to the laminate layer on the top in case of a symmetrical laminated metal sheet, or different in case of an asymmetrical laminated metal sheet.

[0099] FIG. 12 shows a schematic interpretation of the preparation of a sample taken from a laminated metal sheet and the subsequent measurements in the ATR-FTIR spectrometer. The first spectrum is measured with the direction of the incident IR-beam parallel to the machine direction (MD), which is the same as the rolling direction (RD), and the second spectrum is measured with the direction of the incident IR-beam more or less perpendicular (angle of rotation a) to the machine direction. The Euclidean distance matrix D is determined between these two spectra, and after post heating and cooling the value of D according to the invention is at most 0.10.

TABLE-US-00004 Characterisation data of comparative (CS) and inventive (TS) laminated metal sheet samples. Sample .fwdarw. TS1 CS1 TS2 CS2 TS3 PET5 (before lamination) Side .fwdarw. Top Top Top Bottom Top Bottom Top Film .fwdarw. PET1 PET1 PET3 PET4 PET3 PET4 PET5 T1 (°C) 200 200 220 220 225 n.d. T2 (°C) 260 200 270 No post-heat 275 n.d. X (%) 5.4 36.2 8 2.6 32.6 37.1 37 38 Modulus MD (Mpa) 2830 8188 2823 3101 8392 9875 2756 3912 Modulus TD (Mpa) 3006 4097 2814 3012 3745 3787 2391 2680 Gitterschnitt (Bouillon Plasmal) 1 0 1 122 000 000 444 555 001 n.d. D 0.016 0.482 0.046 0.006 0.480 0.482 0.010 0.416 Sample quality Good Bad Good Bad Good Bad