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White Pigment Technology



Whether the goal is pure white, better hiding power or longer-lasting exterior coatings, white pigments are critical.



By Christine Canning Esposito



Published October 13, 2005
When it comes to creating the purest white, improving hiding power or pumping up exterior performance, mastering the use of white pigments is essential for paint and coatings formulators. Titanium dioxide (TiO2) is a pricey component of the finished formulation, and with supply tight, working closely with white pigment suppliers has become even more essential.

According to TZMI, the paint and coatings sector accounts for 56% of TiO2 global demand, with 2.57 million tons expected to be consumed in this sector during 2005. In North America, the paint and coatings sector will account for 51% of demand (710,000 tons) in 2005, while in the European paint and coatings market, demand is higher at 57%, resulting in a forecast demand of 716,000 tons in 2005.

DuPont, which had declared a force majeure on Aug. 31, said on Sept. 21 that although its DeLisle, MS plant escaped major structure damage from the high winds, floodwaters inflicted significant damage on process control systems, other electrical and electronic equipment and plant infrastructure.

Severance stressed that the company is committed to the DeLisle plant's recovery. He also called previously planned improvements at the company's Kuan Yin, Taiwan and Altamira, Mexico sites and a possible new plant in China "important elements in the financial future of the business."

As a result, TZMI expects other price increases announced by other producers, effective July 1, will also "flow through" to the market, and more could be on the way. 

With rising prices and tight supply, the temptation is there to try to cut down on TiO2 usage. But, TiO2 suppliers urge caution when doing so, and say paint companies might be better served by taking a closer look at their formulations and processes.

According to Verdejo, coatings producers should look for TiO2 grades that grind quickly and are robust to the changing environment of a drying  paint. "We encourage and actively assist our customers in optimizing TiO2 efficiency, since in the long run there is nothing to be gained by wasting  good TiO2 on poor dispersion," he said. DuPont's Ti-Select family includes TS-6200, TiO2 produced with a patented technology that provides both superdurability and excellent ease of dispersion, Verdejo added.

"On the face of it, this seems very attractive, since extenders are typically less costly than TiO2 pigments," Verdejo said. "However, since the extender particles themselves don't scatter light, the only way this strategy can work is if it better distributes the TiO2 particles in the dry film. In other words, this can be thought of as an extension of the 'better dispersion' strategy. Often, this replacement improves hiding only by pushing the paint above CPVC, where air voids, rather than the extender particles, contribute to hiding. However, when the CPVC is crossed, this can lead to a decrease in performance properties."

"Up to a point, more TiO2 in paint means more hiding or covering power. Keep in mind though, that like many things in life, once a certain level of TiO2 is reached in a paint, the law of diminishing returns comes into play," said Bob Golownia, technical manager, exterior coatings R&D with ICI Paints. "Once a paint contains several pounds of  TiO2 in a gallon of the liquid paint, adding more TiO2 provides only marginally improved covering power."

"A choice of TiO2 pigment can significantly affect an exterior durability of a coating film," said Tumom Losio, technical customer service, Kemira. "On the one hand, TiO2 protects the binder from direct exposure by absorbing ultraviolet radiation. On the other hand, the ultraviolet radiation causes release of free electrons from the titanium dioxide. These electrons may migrate to the surface of the titanium dioxide crystal where they may react with oxygen and moisture in the air to form hydroxy and perhydroxy radicals which can attack the binder system, causing degradation of the paint film."

Paint makers have recognized the advancements made by suppliers. "Today's treatments are extremely effective at stopping interaction betWeen the TiO2, sunlight and the latex binder," Golownia said.

Did ICI Paint hit the TiO2 target with the This Old House formulation?  Maybe so. "TOH's superior hiding is evident as a pure, unadulterated white," Golownia said.


Web Extra

CHINA AND TITANIUM DIOXIDE

With all eyes on the China, Coatings World asked David McCoy, director of TZ Minerals International (TZMI), an Australian consulting company that specializes in titanium minerals and pigments industries, about the effect the country's appetite for raw materials is having on the titanium dioxide market in particular.

"Chinese domestic pigment production is continuing increase, with TZMI estimating TiO2 production growth by domestic producers increasing 24% year on year for the first half of 2005. Imports of higher quality rutile pigments have decreased 17% year on year over the same period, indicating a greater acceptance of domestically manufactured products," said McCoy.

According to McCoy, the rate of growth by the Chinese producers over the last five years has been incredible. "There has been an explosion of capacity, albeit using older production technologies which have resulted in a large quantity of lower quality pigment in the domestic market. Leading Chinese producers are beginning to improve quality and infiltrate Western markets with lower cost product. This is placing additional pricing pressures on larger global TiO2 producers," he said
In addition, Chinese suppliers of titanium dioxide are increasing their expertise.

"There are several leading Chinese producers who are rapidly increasing production capacity, while at the same time improving product quality. These producers are actively marketing product in markets in Europe and Asia," McCoy said.


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