Methods and apparatus for surface preparation and dual polymeric layer coating of continuous-strip flat-rolled sheet metal, and coated product

A process for extrusion coating a metal strip, comprising the steps of:

• activating a first metallic surface of a metal strip having opposite lateral edges;
• co-extruding a maleic anhydride polypropylene thermoplastic polymer first contact layer and a thermoplastic polymer first finish-surface layer onto the activated first metallic surface and beyond the opposite lateral edges to establish overhang portions while presenting the metal strip at substantially ambient temperature for said co-extrusion, the first contact layer being co-extruded in direct surface-to-surface contact with the activated first metallic surface, and the first finish-surface layer overlying the first contact layer;
• trimming the overhang portions of the first contact layer and the first finish-surface layer extending beyond the lateral edges;
• permitting the first contact and first finish-surface layers to solidify;
• heating the metal strip and thereby melting the first contact and first finish-surface layers;
• and
• rapidly cooling the first contact and first finish-surface layers through glass transition temperatures of the thermoplastic polymers.

A process for extrusion coating a metal workpiece, comprising:

• providing a metal sheet having substantially planar, opposite-facing first and second metallic surfaces extending width-wise between longitudinally extending lateral edges;
• co-extruding a maleic anhydride polypropylene thermoplastic polymer first contact layer and a distinct thermoplastic polymer first finish-surface layer on the first metallic surface while the metal sheet is presented at a substantially ambient temperature so as to place the first contact layer into direct surface-to-surface contact with the activated first metallic surface, extending the thermoplastic polymer first contact and first finish-surface layers across the width of the metal sheet to establish a first overhang projecting beyond the lateral edges, and permitting the thermoplastic polymers to solidify into a first polymeric coating;
• co-extruding a maleic anhydride polypropylene thermoplastic polymer second contact layer and a distinct thermoplastic polymer second finish-surface layer on the second metallic surface while the metal sheet is presented at a substantially ambient temperature so as to place the second contact layer into direct surface-to-surface contact with the activated second metallic surface, extending the thermoplastic polymer second contact and finish-surface layers across the width of the metal sheet to establish a second overhang projecting beyond the lateral edges, and permitting the thermoplastic polymers to solidify into a second polymeric coating;
• trimming the solidified overhangs;
• melting the first and second polymeric coatings solidified on the metal sheet;
• and
• rapidly cooling the first and second polymeric coatings and the metal sheet through glass transition temperatures of the thermoplastic polymers to establish amorphous characteristics throughout the first and second polymeric coatings.