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 laminating line operated at a line speed v, the laminated metal sheet comprising a thermoplastic polymer laminate layer comprising thermoplastic polymer,

• the method comprising the subsequent steps of:
• providing a metal sheet;
• providing the thermoplastic polymer laminate layer for laminating 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 a first incident IR-beam parallel or perpendicular to the machine direction of the laminated metal sheet and wherein the second spectrum is measured in the ATR-FTIR spectrometer with a second incident IR-beam after rotating the laminated metal sheet over an angle alpha in the plane of the laminate layer selected between 7° and 110°, and wherein the ATR-FTIR spectra are measured in the spectral range which includes the range of 1160 to 1520 cm−1,
• wherein the thermoplastic polymer laminate layer is a solid thermoplastic polymer film of:
• (I) a single thermoplastic polymer layer composed of at least 80% by mass of at least one polyester selected from the group consisting of:
• (a) polyethylene terephthalate polyester;
• (b) PETg, wherein PETg is polyethylene terephthalate (PET)-based (co)polyester modified with 1,4-Cyclohexanedimethanol (CHDM);
• (c) polyethylene terephthalate (PET)-based (co)polyester modified with isophthalic acid (IPA);
• and
• (d) polybutylene terephthalate (PBT) polyester;
• or
• (II) a plurality of thermoplastic polymer layers each composed of at least 80% by mass of at least one polyester selected from the group consisting of:
• (a) polyethylene terephthalate polyester;
• (b) PETg, wherein PETg is polyethylene terephthalate (PET)-based (co)polyester modified with 1,4-Cyclohexanedimethanol (CHDM);
• (c) polyethylene terephthalate (PET)-based (co)polyester modified with isophthalic acid (IPA);
• and
• (d) polybutylene terephthalate (PBT) polyester;
• wherein the polyesters (a)-(d) are selected from the group consisting of:
• polyester that contains at least 70% by mole of an ethylene terephthalate unit;
• polyester that contains at least 85% by mole of a butylene terephthalate unit, and polyester that 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;
• wherein the solid thermoplastic polymer film is a uniaxially oriented thermoplastic polymer film;
• wherein polymer of the thermoplastic polymer film consists of thermoplastic polymer;
• 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 thermoplastic polymer of 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 first 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 the angle alpha in the plane of the laminate layer selected between 7° and 110°, and wherein the ATR-FTIR spectra are measured in the spectral range which includes the range of 1160 to 1520 cm−1;
• wherein when measuring the first ATR FTIR spectra for the thermoplastic polymer laminate layer for coating onto at least one side of the metal sheet and when measuring the first ATR FTIR spectra for the laminate layer on the post-heated laminated metal sheet the first and second incident beams are parallel to the machine direction of the laminated metal sheet or the first and second incident beams are perpendicular to the machine direction of the laminated metal sheet;
• wherein the angle alpha for rotating the thermoplastic polymer laminate layer for laminating onto at least one side of the metal sheet and the angle alpha for rotating the laminate layer on the post-heated laminated metal sheet are the same.