Method for producing polymer coated steel sheet for 3-piece cans and use thereof

A method for manufacturing polymer coated tinplate for 3-piece can bodies comprising the steps of:

• providing a tinplate in the form of a strip;
• producing one or two polymer films by means of in-line extrusion forming an in-line extruded polymer film or films using an extruder;
• slitting the in-line extruded polymer film or films in a longitudinal direction into at least N separate wide polymer film strips where N is two or more and (N-1) narrow polymer film strips cut out from between the separate wide polymer film strips using slitting means;
• in-line trimming of edges of the in-line extruded polymer film or films to produce cut-off edges and to ensure that a width of the in-line extruded polymer film or films is smaller than a width of the tinplate in the form of a strip to enable edges of the polymer coated tinplate to be free from said in-line extruded polymer film or films;
• leading the narrow polymer film strips, and the cut-off edges, away from the wide polymer film strips;
• conveying the separate two or more wide polymer film strips to a nip-roll assembly;
• preheating the tinplate in the form of a strip to form a preheated tinplate and subsequently coating the separate two or more wide polymer film strips onto the preheated tinplate by means of the nip-roll assembly to obtain a polymer coated tinplate with the separate two or more wide polymer film strips separated spatially in a longitudinal direction by narrow strips free from said in-line extruded polymer film or films and wherein edges of the polymer coated tinplate remain free from said in-line extruded polymer film or films;
• post-heating the polymer coated tinplate to a post-heat treatment temperature above the melting point of the in-line extruded polymer film or films, or if the in-line extruded polymer film or films is a multilayer system, to a temperature above the melting point of a polymer film layer in the multilayer system that has the highest melting temperature forming a post-heated polymer coated tinplate;
• quenching the post-heated polymer coated tinplate forming a quenched polymer coated tinplate.