Date: Apr 15, 2009 Author: Joe Singleton Source: MDA (
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by Joe Singleton/jsingleton@nttc.edu
A process and material designed originally for rocket propellants can make cars glimmer more brightly, enhance the color and stain-resistance of clothing, and reduce housing heating costs.
Sigma Technologies International, Inc. (Tucson, AZ), in its quest to improve the strength and protection of consumer products, has developed a highly adaptable nanoscopic metallic flake, or nanoflake, composite material—and a novel process to produce it. This technology, which consists of nanoscopic aluminum and polymer layers, can be used in a variety of applications from propellants to printing
to painting.
MDA-predecessor BMDO funded Sigma through a 1997 SBIR Phase II contract to produce a solid propellant formulation using nanocomposite aluminum powders. Sigma's aluminum-powder-based solid propellants are designed to improve thrust, minimize agglomeration, and reduce nozzle blockage.
Sigma produces its composite material in a vacuum environment. A layer of liquid monomer material is deposited on the surface of a rotating drum. The layer is polymerized by exposure to an electron beam. Next, aluminum vapor is introduced, depositing a very thin (200 to 3,000 angstroms) layer of aluminum on the polymer. The process is repeated while the drum is rotating at high speed, until the desired thickness is achieved. The final product is a sheet 1 to 5 millimeters thick, containing thousands of alternating layers of polymer and aluminum.
The company's manufacturing process eliminates the costly use of polyester film, conventional roll-to-roll coating, and the subsequent additional production time needed to produce aluminum flakes. To make aluminum flakes, conventional processes start with a large roll of polyester film—solvent coated with polymer layering—that is placed in a long production line incorporating drying ovens and solvent recovery systems. The coated roll is then moved into a metallizer where it is metallized with a layer of aluminum. This process is repeated several times, and then the flake is released from the polyester film, and the film is discarded.
Sigma's manufacturing process uses no solvents or water to deposit the polymer layers, making it more environmentally friendly than processes offered by competitors. The process also is energy-efficient and uses less space than required in conventional roll-to-roll processes.
Some products, such as propellants developed under the BMDO contract, require Sigma to grind sheets of multilayer material into powder. Each grain of the powder is a nano-laminate structure consisting of multiple aluminum and polymer layers in which the higher-surface-area aluminum layers are virtually oxidation free. The polymer material has a chemistry designed to enhance aluminum oxidation when chemically changed by heat.
Magazines, clothes, and cars:
After completing their BMDO contract to improve rocket propellants, Sigma researchers began to consider the characteristics and commercial potential of the aluminum-and-polymer-flake material. The researchers determined that the polymer-sealed flakes are ideal for use in special printing inks and paints. For printing and painting, the polymer is designed to dissolve in a solvent. When processed in a solvent, the nanolaminate is reduced to aluminum flakes that are nanoscopic in thickness and about 10 micrometers in diameter. Other metals such as copper, indium tin oxide, and silver can be used in place of aluminum to produce flakes that are conductive and transparent.
Because the flake-based paint never becomes dull from accumulation of aluminum oxide, the inked or painted surface has an unusually high degree of sparkle from the shiny flakes. High-end paint jobs on automobiles and glitzy magazine covers are prime examples.
To understand how such flakes can apply to printing, look no further than your billfold. The metallic look of the optically variable ink on U.S. banknotes is due to a flake similar to the one produced by Sigma. The sparkle of the flakes enhances awareness of security elements—such as color-shifting numerals—printed on the banknotes. Although the company does not provide flakes to the U.S. Bureau of Engraving and Printing, it could provide a similar metallic film to coat security inks used on certificates, awards, credit cards, and possibly even foreign currency.
Sigma's primary focus in the printing industry has been magazine publishing. Flake-enhanced ink can produce eye-catching, metallic-looking elements on glitzy magazine covers.
The company's process for depositing polymer coatings with and without metal coatings has several other applications, including consumer apparel, heat- management textiles, and radiant barrier materials for the construction industry. Fabric finishes such as anti-stain, soil-resistant coloring, antibacterial, and anti-wrinkling can be done without the use of water. The active ingredients are evaporated and injected into the fabric and then electron-beam cured at high speed. And while strong competition exists in the fabric and clothing market, Sigma believes its cost-effective, environmentally friendly process will help it gain interest from mainline clothing manufacturers.
Beyond inks, linings, and fabrics, paint proves to be a far more profitable application for Sigma. In a joint venture with the Silberline Manufacturing Company of Tamaqua, PA, Sigma produces flake-based metallic paints for use on high-end sports cars. The selling point for Sigma's automotive paint is the nonporous nature of the flakes, which will not lose luster from the accumulation of aluminum oxide, even after three or four years. Automotive companies are considering the flake-enhanced paint as an option on its high-end cars, said Sigma President Angelo Yializis.
Sigma continues to press on with commercializing its technology. The company has recently subcontracted work to a Manchester, England-based firm to build a production- scale plant for a multinational company that will use it to produce a radiant-barrier house-wrap material in which the aluminum layer is used to reflect the heat and minimize heating costs.
And considering all of Sigma's successes, Yializis said the company still experiences growing pains, namely adapting its focus from research and development to manufacturing. On a corporate level, the company has recently created a spin-off operation called Sigma Specialty Materials to deal with the many applications and joint ventures with which it is involved.
