Method of producing a laminated metal sheet for packaging applications and laminated metal sheet for packaging applications produced thereby

A method for producing a laminated metal sheet in a continuous coating line operating at a line speed v, the laminated metal sheet comprising a laminate layer, the method comprising the subsequent steps of:

• a. providing a metal sheet;
• b. providing a predominantly or solely uniaxially oriented laminate layer for coating onto at least one side of the metal sheet, the laminate layer comprising at least an adhesion layer (A) and a bulk layer (B) and optionally one or more additional top layers (TL) on top of the bulk layer, wherein the adhesion layer (A) is intended for bonding to the metal sheet and either i). contains or comprises a copolyester having 5-30 wt. % ethylene-isophthalate units, 70-95 wt. % ethylene-terephthalate units and 0-5 wt. % other components, or ii) contains or comprises 60-100 wt. % of a non-crystallisable copolyester, 0-40 wt. % of a crystallisable polyester or copolyester or a blend thereof and 0-10 wt. % other components, and wherein the bulk layer (B) and the optional one or more additional top layers (TL) on top of the bulk layer consist essentially of poly(ethylene terephthalate) having at least 90% ethylene-terephthalate units, wherein the adhesion layer (A), the bulk layer (B) and the optional one or more additional top layers (TL) on top of the bulk layer each optionally contain(s) additives, and wherein the bulk layer optionally contains colouring agents, dyes, toners, or pigment particles;
• c. pre-heating the metal sheet to a pre-heat set-point temperature T1 wherein T1 is sufficiently high to provide initial adhesion to the laminate layer but not so high as to melt the bulk layer (B) nor any of the optional additional top layers (TL) in the laminate layer;
• d. laminating the laminate layer onto the metal sheet to produce a laminated metal sheet;
• e. post-heating the laminated metal sheet to a post-heat set-point temperature T2 without melting the bulk layer (B) nor any of the optionally present additional top layers (TL) in the laminate layer and wherein T2 is sufficiently high to produce a value of Dadh dh in the range of 0 to 0.10 after cooling the post-heated laminated metal sheet;
• f. cooling the post-heated laminated metal sheet to produce a laminated metal sheet with a value for the Euclidean distance Dadh of the adhesion layer (A) between a first and a second ATR FTIR spectrum of the adhesion layer (A) having a value in the range of 0 to 0.10, and a value for the Euclidean distance Dbulk of the bulk layer (B) between a first and a second ATR FTIR spectrum of the bulk layer (B) having a value in the range of 0.10 or higher, and wherein the first ATR FTIR spectrum is measured in an ATR-FTIR spectrometer with the incident IR-beam in a first in-plane orientation to the machine direction of the laminated metal sheet or corresponding free-standing laminate layer and wherein the second ATR FTIR spectrum is measured in the ATR-FTIR spectrometer after rotating the laminated metal sheet or corresponding free-standing laminate layer over an angle alpha (α) in the plane of the laminate layer selected between 70° and 110° to a second in-plane orientation, and wherein the ATR-FTIR spectra are measured in the spectral range which includes the range of 1160 to 1520 cm−1.