Recent trends

In the 1960s, priming by electrodeposition of paint was introduced. These systems were anodic, i.e. the car body formed the anode. Taubmans supplied Ford with a system based on a maleinised oleo-resin, and Dulux supplied other manufacturers with an epoxy ester based product. When a cathodic system was developed by Pittsburgh Plate Glass in the USA, Dulux and Taubmans took licences to this technology and the first cathodic electrocoat tank in Australia was filled by Taubmans at Ford Broadmeadows in the late 1970s. Deposition at the cathode reduces metal dissolution which, together with inherently greater corrosion resistance of the aminated epoxy resins used, results in much improved underbody corrosion resistance.

Dulux[143] devised a cathddic electrocoat in the 1970s, based on an aminated epoxy resin crosslinked with a nitrogen resin. After further development in the UK it found widespread use in industrial applications.

Rollercoating of paint on continuous metal strip in Australia was introduced by Hunter Douglas in Sydney in the mid 1950s. During the late 1960s and 1970s Lysaght (now BHP Coated Products) installed lines which run at speeds up to 180 metres/minute and coat metal at widths up to 1.2 m. End-uses include metal cladding for industrial and domestic buildings, caravans, white-ware, metal shelving and roofing. The new cladding and roofing soon largely displaced the traditional corrugated galvanised iron which had characterised many an old mining town. While some might have regretted the gradual disappearance of what almost qualified as an 'Australianum', the more aesthetically minded welcomed the transformation and architects soon used the new materials as an effective tool.

For all these uses the metal is painted first and only afterwards fabricated to its final shape. This heightened demands on durability, flexibility and stoving conditions of typically 20 secs. for the primer and 40 secs. for the topcoat at very high temperatures. A completely new approach to paint formulation was necessary.

Much of the initial technology came from the USA, but progressively local development enhanced performance to meet the stringent Australian weathering conditions. In the mid-sixties, Taubmans commissioned the first line for BHP with vinyl copolymers. In 1968, Dulux and Taubmans introduced silicone modified polyesters crosslinked during stoving with melamine formaldehyde and in the 1970s, Anzol and Dulux followed with a polyvinylfluoride polymer. In due course all major paint companies produced saturated polyester recipes, crosslinkable with melamine formaldehyde and finally Dulux and Berger provided yet another recipe based on thermosetting acrylics.

A significant development occurred in the early 1970s, when Robert Bryce and Dulux set up plants to manufacture powder coatings. These powders, based on thermosetting epoxy, polyester or acrylic technology, are electrostatically sprayed. For general industrial metal finishing they offer advantages in film toughness as well as eliminating solvent emission. A subsequent outlet was for the coating of natural gas/oil transmission pipelines. They are manufactured by a mix/melt/extrusion/pulverisation technique which is completely different from the milling/dispersion procedures used for liquid paints.

Australian Academy of Technological Sciences and Engineering