Some Australian inventions

Metallic zinc-alkali silicate paints

The first significant patents for this technology were issued to Messrs. Nightingale and McDonald in the middle 1930s. These coatings were based on relatively crude zinc dusts, yet achieved outstanding resistance. They were little known outside Australia until 1941, when their use on a 380 km long water pipeline in South Australia demonstrated their exceptional durability and led to wider acceptance.

Water-based systems

In the second half of the twentieth century social considerations exerted increasing impact on paint technology. Concerns about the environment, skin contact and exposure to vapours of solvents, and fire hazards induced a trend away from solvent based systems. Water borne paints therefore became a major area of technical and commercial interest. The proverbial incompatibility between oil (or organic polymers) and water, and the instability of such systems became a challenge.

DULUX[138] conceived an imaginative combination of polymer and colloid chemistry. By dissolving a polymer in a monomer, emulsifying the latter in water in the presence of special surface active agents and then polymerising it, tiny spheres of polymer blends could be formed. The concept led to several inventions which were exploited world-wide.

'Spindrift' beads

The first development was a process for the production of hard, crosslinked polymer particles in water. These micro-spheres can be used as a flatting agent in paints to make low gloss finishes which resist marring by washing.

In later developments, a double emulsion process was employed to incorporate titaniuim dioxide and sub-microscopic air bubbles into the microspheres. Much improved light scattering and therefore paint cover was obtained, and costs were reduced. A range of house paints based on 'Spindrift' (reg. trademark) beads followed, and special plants were built in Australia and by associated paint companies around the world. In addition licences were sold to three paint companies in the USA and a pigment manufacturer in the UK. 'Sprindrift' technology extended to North and South America, Africa, Europe and New Zealand and royalties earned overseas exceeded $1.5M. In 1981 Dulux Australia won an Export Award for 'Services to Technology'.

'Compolex'

The next step made possible by the new concept was the in situ formation of composite polymers making up the film forming particles. Water borne paints are based on polymer particles which on drying coalesce and bind the pigment into the paint film. Their formulation has to meet exacting requirements. In the 'Compolex' (reg. trademark) process a preformed polymer is dissolved or dispersed in acrylic monomer which is then dispersed in water and polymerised. The new method of forming composite polymers[139] made it possible to devise a much wider range of combinations than was possible with the earlier systems, including cathodic electrocoat compositions, novel stabilisers and two pack compositions.

'Dusol'

A further benefit of the concept of stabilising polymers in water was derived in environmental protection and energy saving. Production of conventional paint leaves residues of valuable solvents which are expensive to dispose of.

The 'Dusol'[140] (reg. trademark) process recovers nearly all of the organic solvent, leaving residues which do not harm the environment. After forming fine droplets of paint-waste in water and stabilising these, solvent stripping by conventional steam distillation is facilitated by the large surface area of the droplets. The hydrocarbon fraction which contains some polar solvent separates and is recovered, while the water fraction is continuously returned to complete steam stripping of the remaining polar solvent. The result is 98-99 per cent solvent recovery. By filtration, the remaining mixture of water and paint granules is separated and the granules are suitable for disposal as landfill. A full scale plant was built and has since treated paint waste from Dulux Australia, its customers and other paint companies.

Australian Academy of Technological Sciences and Engineering