Nanotechnology, microencapsulation, conductive materials, self-healing and self-assembling systems are among a number of technologies which are expanding the capabilities of coatings well beyond the conventions of aesthetics and protection.
The widening functionality of coatings is already boosting paint sales for industrial applications. The introduction of smart technologies should expand industrial coatings demand even further.
David Rickerby, chief of surface engineering at Rolls-Royce, the UK-based aircraft engines manufacturer, told the Materials Congress 2006 in London in April that coatings now accounted for over 30% of the company's production costs against five percent 45 years ago. Surface coatings are now crucial to the effective operation of an aircraft component throughout its designed lifetime, he said.
Nonetheless, experts are warning that some smart technologies could take much longer to establish themselves in the coating sector than expected because of the problems of transferring inventions from the laboratory to the marketplace.
"Virtually every coatings company and materials suppliers are conducting some sort of research into smart technologies because potentially there is so much added value in them," explained an executive at one European coatings company. "But a formulation that works well in the lab will not necessarily be possible to make on an industrial scale and, most important of all, may not be able to provide what the customer wants."
Professor Joergen Rassing, a consultant to Akzo Nobel, pinpointed in a paper presented to the Boya 2006 coatings conference held in Istanbul in May some of the problems facing smart coatings based on materials in the 0.1-100 nanometer size. The coatings formulations incorporating the materials would themselves have to contain nanostructures and compatible polymeric binders and other components.
Rassing pointed out the "question marks" hanging over the dispersion of nano-sized polymers with different surface features. These dispersants are a matter of "art and science." The effectiveness of the dispersions would depend on their total energy content, which could be influenced by stirring speeds, temperature profiles and the addition of difference components, Rassing explained.
Coatings formulators have also been raising the issue of the high costs of smart materials, which in some cases is hampering the development of intelligent paints. "Mass production will drive down the costs," Mike Hicks, a scientist at Rolls-Royce, told the Materials Congress. But some coatings producers argue that costs need to come down in order to make mass production economically viable.
With conductive polymers, which offer the opportunity for introducing electronics into coatings, most are considered to be far too expensive at the moment by formulators, even though their prices have been coming down over the past year.
Nonetheless there are exceptions. A few conductive polymers already have a big market because they are being used for functions other than electronics. Panipol, a Finnish company specializing in the production of the conductive polymer polyaniline has been able to bring down the price of the material to that of conventional polymers because of its wide use in packaging coatings as a protection against electro static discharge (ESD). In the rapidly growing ESD coatings segment, polyaniline is now a strong competitor to carbon black-based compounds.
The relatively low cost of titanium dioxide because of its mass use as a white pigment has opened the way for the exploitation of its photocatalytic characteristics. As a result, coatings with suitable prepared TiO2 particles, can be given a wide range of functions, including ones which are smart.
With the help of nanotechnology, which can dramatically increase the surface area of TiO2 particles, energy from ambient light can be used as an energy source for photocatalysis. This chemical reaction can cause the breakdown of organic toxins and odors. Hence it gives coatings capabilities such as deodorization, water purification and removal of environmental pollutants like nitrogen and sulphur dioxides. TiO2-sourced photocatalysis is also being utilized to make surfaces superhydrophilic with self-cleaning properties and antimicrobial capabilities.
European coating companies and their suppliers of materials are now tentatively taking advantage of some of the new technologies to give their products active as well as the conventional passive functions. To be smart a coating has to be able to be active by responding to changes in the conditions of its environment.
Akzo Nobel's International marine coatings business has a self-polishing copolymer system for antifouling applications. It reacts with ions in the seawater to produce a thin soluble layer on the surface of the coating which self-polishes at a predetermined rate to maintain a continuous controlled release of biocides.
The company has also been extending its range of intumescent fire proofing materials for steel coatings. These react to the heat generated during a fire and intumesce, or swell up, to provide a tough and stable insulating layer of the steel which can prevent it from buckling for at least one hour.
Material and chemical suppliers have not surprisingly been the most active in developing components for smart coatings formulations, particularly in the area of nanotechnology.
Altana Chemie, the German-based maker of coatings chemicals which formed a partnership with U.S.-based Nanophase Technologies Corporation two years ago, has already introduced a number of nano-scale materials to improve the scratch and abrasion resistance of coatings.
Clariant has extended its capabilities in polysilazanes, which it already utilizes in its anti-grafitti coating tutoProm. The company has developed nanoparticles which can be bound into polysilazane matrices to give them photocatalytic properties.
Last year Clariant formed a partnership with U.S.-based Starfire Systems Inc., a leader in nanostructured ceramics, and recently acquired Kion Corp of Pennsylvania, a manufacture of polysilazane resins and compounds.
The company has also been working on nanoparticles which self-organize or self-assemble on surfaces to give them intelligent capabilities.
Bayer MaterialScience has also been focused on developing new applications for smart processes for coatings. Among these are a range of conductive polymers which can provide electro-conductivity and luminescence.