Process for producing a polymer-coated metal strip and a polymer-coated metal strip produced thereby

A laminate produced according to a process for producing the laminate in a coating line comprising the subsequent steps of:

• providing a metal strip;
• pre-heating the metal strip to a temperature of at least 100° C. suitable for lamination on one major surface of the strip with a first thermoplastic polymer coating layer which comprises a layer comprising polymer with a melting point below 200° C. and lamination on the other major surface of the strip with a second thermoplastic polymer coating layer;
• producing a laminate by adhering the first thermoplastic polymer coating layer on the one major surface of the pre-heated strip and the second thermoplastic polymer coating layer on the other major surface of the pre-heated strip, wherein the first thermoplastic polymer coating layer comprises the polymer with a melting point below 200° C.;
• heating the laminate in a non-oxidising gas atmosphere in a post-heating step to temperature that is at least the melting point of the polymer or polymers in the second polymer coating layer but no less than 220° C.;
• rapidly cooling or quenching the laminate to a temperature of below 50° C.,
• wherein the first polymer coating layer comprises a polyolefin with the melting point below 200° C. selected from polyethylene, polypropylene, or copolymers of ethylene and propylene, or blends of polyethylene and polypropylene;
• wherein the second polymer coating layer comprises a thermoplastic polymer with the melting point above 200° C., and
• a crystallinity of less than 20 wt. % after said heating of the laminate in a non-oxidising gas atmosphere in a post-heating step to the temperature that is at least the melting point of the polymer or polymers in the second polymer coating layer but no less than 220° C. and said rapidly cooling or quenching the laminate to the temperature of below 50° C. the second polymer coating layer, and
• which is selected from the group consisting of an aromatic polyester;
• acid-modified poly(ethylene terephthalate) copolyesters comprising isophthalate;
• glycol-modified poly(ethylene terephthalate) copolyesters comprising cyclohexanedimethanol, 2,2,4,4-tetramethyl-1,3-cyclobutanediol or isosorbide;
• and blends comprising two or more of the above listed homo- or copolymers,
• wherein the second thermoplastic polymer coating layer has a higher melting point than the first thermoplastic polymer coating layer,
• wherein said aromatic polyester is selected from the group consisting of poly(ethylene terephthalate), poly(trimethylene terephthalate), poly(butylene terephthalate), poly(ethylene naphthalate) and poly(butylene naphthalate);
• and
• wherein the ratio Mw, after postheat/Mw, before postheat of the polyolefin coating layer is at least 0.9.