Corporate sustainability, commonly understood as a business approach that creates long-term value to financial, environmental and societal stakeholders, is absolutely essential for commercial success in the coatings industry. As the global economy cycles through downturns, the consequences of low sustainability are rapid and unforgiving, leaving many companies unable to survive.
Counter intuitively, there is perhaps no better time to innovate than when economic conditions are challenging. This can be likened to a foot race – does one get further ahead by sprinting when all of the competition is sprinting, or by sprinting when the competition is resting? In general, large, sustainable companies not only survive bleak economies, they actually grow stronger by relying on their technical and financial strengths to fund innovation when their competitors cannot. This will certainly be the case for coatings producers during the current economic conditions. We can expect that during these times the gap will widen between marginally sustainable paint producers and those manufacturers who have the resources and vision to position themselves now for better times in the future. By teaming with the right raw material partners, coatings manufacturers can improve both their short-term and long-term business health.
Corporate sustainability of the coatings market sector is achieved through a balance of often-conflicting priorities. Above we focused on financial sustainability, but environmental stewardship continues to be a growing issue with consumers, and the two aspects of sustainability are becoming more interdependent as time goes on.
Recently, environmental sustainability in the coatings industry has mainly focused on formulating paints for which the level of volatile organic solvents, co-solvents and additives is minimized. While the focus on VOC is understandable, there are additional ways that coatings producers can reduce their environmental footprint. One way is to consider the environmental footprint of their raw material suppliers. A good example of this is titanium dioxide pigment. TiO2 is made by two processes, the batch sulfate route and the continuous chloride route. The sulfate route is the older of the two, and produces many times more waste products than the more modern chloride route, making it less preferred. Even within the chloride manufacturing process, different TiO2 producers produce different amounts of waste per tonne of product because of differences in their operational details. Not surprisingly, the largest producers are able to invest the time and resources necessary to minimize waste generation and environmental impact.
The conventional wisdom in the coatings industry is that the actions that improve environmental sustainability will hurt financial sustainability, because environmental stewardship comes at a cost, either in terms of product quality or cost of manufacture. But better environmental sustainability does not always have to lead to higher costs. As shown below, there are opportunities to improve environmental sustainability that actually result in improved product quality and lower cost of manufacture.
Discussion
Perhaps the best way of reducing the environmental impact of paints is to make paint films that last longer. For example, by doubling the service life of a coating, the amount of paint used over the long run will be cut in half. With no other changes in the process, this alone amounts to a 50% reduction in pollution.There are other ways of satisfying consumer needs by using less paint for a given application and at the same time financially benefit the coatings manufacturer. For example, better opacity can lead to thinner films, something that powder coatings producers can readily take advantage of. Opacity improvements can also lead to reductions in the amount of opacifying pigment used, which is a direct benefit to most coatings producers.
Another financial sustainability strategy that is often employed is to develop a less-costly way to make a coating, without any change in paint performance. Careful choice of TiO2 grade based on dispersibility is an example of how this can be done. Some grades are extremely easy to disperse, allowing the coatings manufacturer to grind-in the pigment in less time. Since most TiO2 grades are priced the same, this saves on electricity cost and improves throughput rates, without affecting the performance or raw material cost of the paint.
One type of TiO2 for which all three of these beneficial strategies – greater service life, higher opacity and easier dispersion – enter into play is superdurable pigment. Superdurable pigments have historically been among the most difficult TiO2 grades to disperse. This difficulty leads to more expensive processing and, in many instances, lower opacity (opacity is negatively impacted by poor pigment dispersion). Recent work in our laboratories has resulted in the development of DuPont™ TS
Superdurability
The term “TiO2 pigment durability” is somewhat misleading, as it implies that the TiO2 itself is not normally durable. In fact, TiO2 pigments are thermodynamically extremely favored and do not change on exposure to the elements. What does change, however, is the organic binder holding the paint film together. Binders are almost exclusively organic polymers, and, like all organic molecules, are unstable in air because the reaction products of organics and oxygen are CO2 and H2O, both of which are thermodynamically extremely favored.While the binder molecules are unstable to oxygen, the rate of oxidation is slow because there is a significant energy barrier that must be overcome to initiate these reactions. During exterior exposure, UV light photons from the sun supply the energy needed to overcome this reaction barrier. This is, in fact, the main mechanism by which resin degrades when exposed to the elements.
“TiO2 pigment durability” refers to the impact of TiO2 on resin durability. TiO2 pigments affect resin degradation reactions in two ways. First, TiO2 is an excellent UV light absorber and increases the life of the binder by removing destructive UV photons from the paint film. However, some of the photon energy that is absorbed by the TiO2 can catalyze the degradation reactions at the pigment’s surface. While the rate of TiO2 photocatalysis is slow, exposure times are quite long (years), the TiO2 can do significant damage to the binder under natural exposure conditions.
Pigment producers can decrease the photocatalytic degradation rate by completely encapsulating the TiO2 particles in a continuous layer of inert material. This physically prevents the TiO2 surface from coming in contact with the binder molecules, separating these two reactants from one another. In practice, the material used for this encapsulation is either hydrous silica or amorphous alumina. For superdurable TiO2 pigments, a thick layer of inert material is used to ensure that there are very few gaps in surface coverage. Superdurable TiO2, like all other coatings-grade TiO2 pigments, are further covered with nano-crystalline hydrous alumina particles to improve dispersion.
The “durability” of the TiO2 can be determined by one of two end-use tests: gloss retention, and chalking (also known as fading). In these tests the pigment is incorporated into a paint, which is then exposed to the elements (typically in Florida or Arizona). As the film is exposed, its gloss decreases and the color of the paint lightens. Of course, both of these changes are undesirable. Performance is typically measured relative to one or more pigment standards that are included in an exposure series.
We have found that coating TiO2 particles with a combination of hydrous silica and amorphous alumina gives them higher durability than a thick coating of either oxide alone. This is because the surfaces of a TiO2 particle are not all the same – some areas of the surface are basic, and others acidic. Since silica is an acidic solid, it selectively coats the basic surfaces on the pigment. Similarly, amorphous alumina, which is slightly basic, preferentially coats the acid surfaces of the pigment. The overall result is more complete coverage when both oxides are used.
The durability advantage of TS
Opacity
Titanium dioxide pigments are used in coatings because of their unsurpassed opacity. No other white pigment can approach the light scattering strength of TiO2. That said, coatings formulators have long known that the scattering ability of TiO2 can change from one coating system to another. This is because high refractive index is not enough to get optimal scattering – good pigment dispersion in the final paint film is also essential. That is because when particles crowd against one another they interfere with the mechanism of light scattering. For reference, particles touching one another scatter light at less than 80% efficiency relative to particles that are well separated.TS
Wet-in and Dispersibility
While TiO2 pigments are, as a rule, easier to disperse than other pigments, there are still some significant grade-to-grade differences in dispersion performance. As a general rule, superdurable pigments are the most difficult-to-disperse grades. There are several reasons for this that are perhaps best summarized by saying that these pigments are optimized for durability performance at the expense of other properties.This is not the case with TS
Conclusion
As is true for all manufacturing industries, coatings producers can increase their rate of success by teaming with innovative and sustainable raw materials suppliers. Raw material sustainability encompasses not only environmental and regulatory issues, but also includes having the financial and technical resources, and the vision needed to innovate regardless of whether economic conditions are good or bad. In this paper we consider one area that shows the benefits of innovation – the development of higher-performing, superdurable TiO2. In this example we see that the recognition of a growing problem and the development of a cost-effective solution to this problem can lead to a solution that both lessens the coatings producers cost and enhances product performance.For more information, visit www.dupont.com.
