A method for producing a polymer coated metal strip in a continuous coating line, including the subsequent steps of:



laminating a thermoplastic polymer film onto at least one side of a metal strip to produce a polymer coated metal strip;
post-heating the polymer coated metal strip to temperature sufficiently high to melt the thermoplastic polymer film to reduce orientation and crystallinity of the thermoplastic polymer film to target value;
cooling the post-heated polymer coated metal strip;
in-line illuminating the laminated polymer film with near-infrared light having one or more or all wavenumbers between 3500 and 9000 cm−1;
in-line acquiring back-scattered near-infrared light with a near-infrared spectroscopy detector;
calculating near-infrared spectrum from the back-scattered near-infrared light;
comparing the calculated near-infrared spectrum to a reference material near-infrared spectrum to determine Conformity Index as measure of the laminated polymer film degree of crystallinity and/or molecular orientation.