The associations of steel/thermoplastic coatings

Coil coating is a metal coating technique that has been around since the 1940s. Coil coating really took off in Europe between 1960 and 1975. The technique has made great strides in terms of application and curing processes, products, appearance, properties and durability. Today, steel coils travel at speeds of over 150 m/min. Despite these advances, the vast majority of polymers used in construction, general industry, household appliances, transport and packaging are thermosets. They come in solvent phase and are deposited mainly by roll coating. The very concept of pre-painting combines the notions of appearance, aesthetics and functionality with those of formability: it is unacceptable for the shaping of pre-painted sheets, which must be carried out by bending, profiling or even stamping, to alter the characteristics of the organic coating. The competitiveness of these products stems not only from the very high productivity of the industrial lines, but also from the very low thickness of the organic paints applied. Typically, they are no thicker than 25 to 35 µm, with the exception of polyvinyl chloride (PVC) plastisols, which are 100 or even 350 µm thick. Pre-painted products are widely described at [M 1 509] . In addition to these paints for coil-coating applications, there are also solvent-free thermoplastic coatings (dry paint film).

The aim of this document is to present the various steel/thermoplastic applications. Only coatings on flat steel-based products will be considered. This excludes thermoplastic polymer applications in products such as pipes for fluid transport and piping, offshore cables (external organic coating), polyethylene cores for transport cables, plastic coating of wire mesh, etc., steel/polymer/steel sandwich systems [M 5 810] , thermosetting powders applied to steel.

The technologies presented are :

• Thermolamination of single- or multi-layer thermoplastic films;

  • heat-bonded films: a heat-activatable adhesive is applied to the sheet beforehand;

  • pre-adhesive laminated films: deposition of a film containing a layer of...