Method for manufacturing polymer coated tinplate for 3-piece can bodies comprising the steps of: - providing tinplate in the form of a strip; - producing one or two polymer films by means of in-line extrusion; - slitting the in-line extruded polymer film or films in the longitudinal direction into at least N wide polymer film strips (3a-3d) where N is at least 2 and (N-1) narrow polymer film strips (4a-4c) cut out from between the wide polymer film strips (3a-3d) using slitting means; - in-line trimming of the edges of the polymer film to ensure that the width of the polymer film is smaller than the width of the tinplate to enable the edges of the polymer coated tinplate to be free from polymer film; - leading the narrow polymer film strips (4a-4c), and the cut-off edges, away from the wide polymer film strips (3a-3d) by discharging means; - conveying the separate two or more wide polymer film strips (3a-3d) to a nip-roll assembly; - preheating the tinplate and subsequently coating the two or more wide polymer film strips (3a-3d) onto the preheated tinplate by means of the nip-roll assembly to obtain a polymer coated tinplate with the two or more wide polymer film strips (8a-8d) separated spatially in the longitudinal direction by narrow strips (9a-9c) free from said polymer film and wherein the edges (10a, 10b) of the polymer coated tinplate remain free from said polymer film; - post-heating the polymer coated tinplate in a post-heat device to a temperature above the melting point of the polymer film or films, or if the polymer film is a multilayer system, to a temperature above the melting point of that polymer film layer in the multilayer system that has the highest melting temperature; - quenching the post-heated polymer coated tinplate. - providing tinplate in the form of a strip; - producing one or two polymer films by means of in-line extrusion; - slitting the in-line extruded polymer film or films in the longitudinal direction into at least N wide polymer film strips (3a-3d) where N is at least 2 and (N-1) narrow polymer film strips (4a-4c) cut out from between the wide polymer film strips (3a-3d) using slitting means; - in-line trimming of the edges of the polymer film to ensure that the width of the polymer film is smaller than the width of the tinplate to enable the edges of the polymer coated tinplate to be free from polymer film; - leading the narrow polymer film strips (4a-4c), and the cut-off edges, away from the wide polymer film strips (3a-3d) by discharging means; - conveying the separate two or more wide polymer film strips (3a-3d) to a nip-roll assembly; - preheating the tinplate and subsequently coating the two or more wide polymer film strips (3a-3d) onto the preheated tinplate by means of the nip-roll assembly to obtain a polymer coated tinplate with the two or more wide polymer film strips (8a-8d) separated spatially in the longitudinal direction by narrow strips (9a-9c) free from said polymer film and wherein the edges (10a, 10b) of the polymer coated tinplate remain free from said polymer film; - post-heating the polymer coated tinplate in a post-heat device to a temperature above the melting point of the polymer film or films, or if the polymer film is a multilayer system, to a temperature above the melting point of that polymer film layer in the multilayer system that has the highest melting temperature; - quenching the post-heated polymer coated tinplate.