According to EN 13523-0, a prepainted metal is a ‘metal on which a coating material (e.g. paint, film…) has been applied by coil coating’. When applied onto the metallic substrate, the coating material (in liquid, in paste or powder form) forms a film possessing protective, decorative and/or other specific properties.
The choice of metallic substrate is determined by the dimensional, mechanical and corrosion resistance properties required of the coated product in use. The most common metallic substrates that are organically coated are:
- Hot dip galvanised steel (HDG) which consists of a cold reduced steel substrate onto which a layer of zinc is coated via a hot dip process to impart enhanced corrosion properties onto the base steel.
- Galvanized mild steel (GMS) can be used as balustrade and handrail of staircase, pipe and etc.
- Other zinc-based alloys are coated onto steel and used as a substrate for coil coating, giving different properties. They give improved corrosion resistance in particular conditions.
- Electro-galvanised (EG) coated steel consists of a cold reduced substrate onto which a layer of zinc is coated by an electrolytic process.
- Cold reduced steel (CR) without any zinc coating
- Wrought aluminium alloys
- Many other substrates are organically coated: zinc/iron, stainless steel, tinplate, brass, zinc and copper.
A wide range of organic coatings are in use for prepainted metal, developed in order to provide different levels of durability and performance, or to satisfy different aesthetic requirements. The most commonly applied coatings are based upon liquid paints, although films (also known as laminates) and powder coatings are used in smaller quantities. These are liquid paints (e.g. primers, finishes/backing coats, polyesters, plastisols, polyurethanes, polyvinylidene fluorides (PVDF), epoxies), powder coatings and laminate films.
Liquid paints account for more than 90% of the coatings used for prepainted metal. Films are often used where very high aesthetic quality is required. Variations in film thickness, colours and finish (smooth, structured or printed) can be achieved. Powder coatings can be described as "solid paint" which can be melted to form a continuous film over the substrate. Each type of coating has its own specific advantages, be it thickness, gloss, hardness, flexibility, durability in harsh weather or resistance to chemical attack. The choice of the most suitable system must be based on its usage and expected performance.
The Coil coating process is a continuous, high-volume process that produces a consistent product in comparison to batch post-coating methods. Coil coating provides for controls that are virtually impossible to attain with most other painting processes. Dealing with a flat sheet enables excellent control of coating weights of both the pretreatment and the paint.
In one continuous process, a coil of metal, up to 2.6m wide moving at up to 200m/min, is unwound and both the top and bottom sides are cleaned, chemically treated, primed, oven cured, top coated, oven cured again, rewound and packaged for shipment.
The output of the coil coating industry is a prepainted metal strip. This has numerous applications in various industries, including in:
- The European market for prepainted metal, ECCA Academy, http://www.prepaintedmetalacademy.eu/prg/selfware.pl?id_sitemap=197&language=EN
- British Standards Institution, BS EN 10169:2010, http://shop.bsigroup.com/ProductDetail/?pid=000000000030251498
- Lars Courage, Architect, "Archived copy". Archived from the original on 2013-06-22. Retrieved 2012-03-08.CS1 maint: archived copy as title (link)