Prepainted metal is produced by adding paint or film coating to strip metals, primarily steel and aluminium, on a continuous basis. This process is called coil coating. The definition of a coil coating process according to EN-10169:2012-06 is:
‘A method in which an organic coating material is applied on rolled metal strip in a continuous process. This process includes cleaning if necessary and chemical pre-treatment of the metal surface and either one side or two side, single or multiple application of (liquid) paints or coating powders which are subsequently cured or laminated with plastic films.’
The substrate is normally either steel or aluminium, although other metals can be coil-coated too. In the case of steel, it is usually cold-reduced and generally with a zinc or zinc alloy metallic coating to provide galvanic corrosion protection. About 95% of the organic coatings are paints with 5% being plastic films, laminated to the surface.
The coated surface can have a wide range of colours, gloss levels and surface textures. What dictates the choice of coating is the end use of the finished product. The user may require non-stick properties, great flexibility or high chemical resistance. Modern developments have provided many new coating types to meet the increasing demands of users.
Coated coil can be slit for narrow widths, cut to required lengths, bent, profiled or deep drawn, without damaging the organic coating. It can be processed into any number of shapes, depending on the end use.
The prepainted metal industry is a well developed, worldwide industry with over 40 years of history. Output of the global prepainted metal industry is nearly 15 million tonnes per annum of prepainted steel and nearly 1 million tonnes per annum of prepainted aluminium. The European industry represents 32% of this total, with over 150 production lines situated within the EU-28 countries producing over 1,500 million m² of prepainted metal per year – enough to clad 25 million homes. In over 40 years since prepainted metal started in Europe, an area of metal almost the size of Belgium has been coated using this technique. The European prepainted metal industry is now worth over €10bn in turnover of coil coaters alone.