The Challenging Nitrosols: Our Latest Frontier For almost 70 years, “nitrosols” (aerosols using nitrogen or compressed air as the propellant) were almost unknown commercially. They were not seriously considered because of three major problems: gas loss if the dispenser was strongly tilted or inverted, pressure loss during product use, and coarse sprays. However, these deficiencies have now been largely resolved, allowing nitrosol technology to be used in an impressive number of both Bag-On-Valve (BOV) and single compartment aerosols. FIGURE ONE Representative Nitrosol Products BOV PRODUCTS • Shave Creams • Sun Tan, Sun Screen & Sun Block Sprays • Body Sprays • Depilatories • Insect Repellents • Bug Killers • Cookware Lubricants • Food Flavorings • Ultra-pure Water (for facial rinses) • Other “continuous” sprays SINGLE COMPARTMENT PRODUCTS • Air Fresheners • Air Fresheners & Deodorizers • Furniture Polishes (Europe) • Some Hard Surface Cleaners (Europe) • Contact Lens Flushing Sprays • Water Repellent Sprays for Shoes & Boots • Oral Refresher Sprays • Selected Lubricants • Internal Gasoline Engine Cleaners (Sludge Removers) Cheese spreads in piston cans and other examples could be mentioned. Although this technology is still in its early development, in the U.S. there are fillers who now produce nitrosols and nothing else. Some larger fillers have installed production lines for the exclusive manufacture of nitrosols. By Montfort A. Johnsen, Ph.D., Technical Ed itor Product Management Because tilting and actuating a single compartment nitrosol dispenser past the horizontal may cause a significant loss of nitrogen or air, production equipment has been developed that will orient full-diameter actuators to a directional dot on the curl of the valve mounting cup before pressing them firmly into place. The actuator orifice then lines up with the curvature of the dip tube. Also, the new actuators are very difficult for consumers to rotate, so the alignment becomes relatively permanent. For a few products, “jumbo” dip tubes may also be used. They can hold about 4–8 seconds of product, to further minimize the possibility of gas escaping from a highly tilted or inverted dispenser. The “up-down, 360 degree” valve design has been studied, but not yet commercialized for nitrosols. The second significant concern with all nitrosols is that they steadily decrease in pressure as they are used by the consumer. There are two solutions, aimed mainly at single compartment types. One is to use a high initial gas pressure, even up to 150 psi-g at 70°F. The other is to use a reduced product fill. Whereas other aerosols are often filled to about 85% of can capacity, nitrosols are usually filled to about 55% to 70%. For example, a popular nitrosol air freshener is filled to about 56% by volume, in a 59mm nominal diameter, shaped, DOT- 2Q aluminum can. The combination of a reasonably high initial pressure and reduced product volume yields the best results. In the case of foam products in BOV nitrosols, initial pressures over about 75 psi-g at 70°F may lead to product jetting and possible spattering. There may also be a slightly higher rate of gas seepage as the product ages. For aluminum cans over about 38mm in diameter, and any others where the curl or machined curl is not perfectly smooth, marketers prefer to use a 1mm thick lathe-cut buna gasket to minimize the inevitable very slight weight January 2014 Spray 19
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