Materiality and technology
8
the coloured powder and for bonding it permanently to the substrate by fusing it or letting it harden. In a previous step, the powder is processed specially with a view to the optical and mechanical requirements (Fig. 7). The choice of pigments depends on the requirements of the processing method, but also on how expensive and time- consuming it is to produce the powder. This means that its use might be limited for financial reasons. Powder coatings are very durable and are used in furniture, bicycle frames, household appliances and facade cladding. Applying varnishes and paints
There are many different methods for applying the wide range of varnishes and paints. Rollers and brushes Varnishes and paints can be applied to a surface using a paintbrush or a roller. This is usually done manually. Special additives and solvents have a significant impact on the application properties and make it possible to apply the paint evenly, without dripping while working overhead, or with a lower risk of sagging or running. Plastering Thick, pasty paint or plaster can be applied using a trowel or a spray. Particularly absorbent substrates should be moistened beforehand so that the plaster adheres well and does not set too quickly. Spray painting In addition to the paintbrush and roller methods mentioned above, spraying is one of the most common coating methods for flat and even surfaces, and
9
a very effective one. When working with small, complex components with a large number of openings, only a small percentage of the paint remains on the surface during conventional spraying, and paint loss (overspray) can be up to 90 per cent. When working with electrically conductive surfaces, this effect can be reduced by charging the component and the paint electrostatically, thus reducing paint loss to as little as 15 per cent. Electrostatic spray painting The principle of electrostatic painting is not only suited to spray painting, e.g. for bicycle frames, wheel rims and casings, but also for dip coating (Fig. 8). This method is also used on car bodies and ensures that the coating adheres well in areas that are difficult to reach. Baked and powder coatings Once they have been applied, special varnishes can also be baked on using a thermal treatment to make them more resilient. Particularly hard-wearing and resistant coatings can be achieved using the powder-coating method (Fig. 9). In this method, powder coatings containing plastic duroplastic or thermoplastic bonding agents are applied so that the coating hardens due to a chemical reaction or when it cools after being fused. Fluidised bed coating Using a similar principle, fluidised bed coating involves heating components above the melting point of the thermoplastic powder coating and placing them in a sealed chamber with a cloud of plastic powder. The powder fuses with the surface of the component, thus forming a solid plastic coating. Wire baskets in dishwashers or wire fences are among the products coated in this way.
Enamelling The enamelling process makes it possible to produce extremely hard, scratchproof and weather-resistant coatings. Powdered glass is mixed with water and applied to a surface in multiple layers. It is then dried and fired at temperatures above 800 °C to form a vitreous enamel coating. Due to the high temperatures involved in the process, usually only metals with a higher melting point, such as those used in baths, pots and baking trays, are subjected to this process. Monochrome and uniform coatings can be applied using the methods described above. In order to produce decorative and artistic surfaces, methods such as screen printing, hydrographics or pad printing can be used. Screen printing A wide spatula (squeegee) is used in screen printing to push thick, pasty ink through a fine mesh onto the surface to be printed. Blank areas of the fabric are coated with an impermeable substance, thus making it possible to print very detailed patterns, fonts and gradients. The print resolution is determined by the mesh size of the fabric and is still lower than in offset printing. In general, screen printing can be used on all solid materials, such as drinks cans, advertising signs, traffic signs, product labels, clothing and glass facades.
6
7 8 9
ilicone resin paints are particularly well suited S to facades in both old and new buildings. Because of their resistance to weathering, as well as to fungal and algae growth and their flaking impact, these paints protect the valuable building fabric. Colour-coated steel profiles, hotel at BerlinBrandenburg Airport (D) 2012, PETERSEN ARCHITEKTEN. Priming car bodies using electrostatic dip coating. Powder-coated MDF panels.
25