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Alternatives to the Venerable Hot Water Bath Johnsen, Ph.DBy Montfort A. technical editor Thas taken many shapes (linear, serpentine, drum) but almost by alternative methodologies for these products. At the presentAdministration of the DOT) develop a comprehensive generalpermit exemption that will allow the hot water bath to be replacedhe hot water bath has been an integral fixture in virtuallyevery U.S. aerosol production line for the last 64 years. It always with the goal of submerging aerosols in hot water and heating time, at least 19 Special Permits have been issued to 14 firms for them until they reach a pressure equal to their equilibrium pressure exemptions to aerosol water bath requirements, starting in 2007. at 55°C (131°F). Meanwhile, an operator monitors the tank, looking They are somewhat cumbersome for firms to obtain, are limited for leakers, cans that may permanently deform or those extremely in scope, must be renewed every two to four years and have other rare dispensers that may burst. detractions. For those interested in reviewing them, these U.S. During the 1990s, the U.S. Dept. of Transportation (DOT) DOT PHMSA Special Permits include those numbered 14440, modified the heating requirements in their paragraphs 173.306(a) 13577, 14842, 14723, 14627, 14953, 14,205, 12,995, 14544, (3)(v) and (5)(v) to be reduced to 50°C (122°F), provided the 14,724, 14623, 14786, 13,292, 14429, 14427, 15135, 14097, 14887, liquid content does not exceed 95 volume-% of the net can and 14625. They can be accessed by searching the DOT web site at capacity at 50°C (122°F). This was designed to harmonize with http://phmsa.dot.gov/. European directives. Because of legal concerns (possible torts), nearly all marketers have elected to require the 55°C (131°F) The BOV Dispensing System testing parameter. For completeness, the DOT has permitted The BOV unit consists of a multi-layered, often gusseted bag (or aerosols with temperature sensitive contents to be passed extruded plastic bag), hermetically attached to the tailpiece of a through water maintained between 20°C (68°F) and 30°C (86°F), valve that has a uniquely large inner orifice. The valve, sometimes although one dispenser must be successfully tested at the higher called the “EP valve” after the Swiss developer, utilizes this large temperature. Finally, under paragraph 173.306(a)(5)(vi), plastic orifice for rapid filling of even fairly viscous products, such as aerosols pressurized with Division 2.2 (non-flammable) gases are thickened emulsions or gels. The typical bag consists of a laminate approved for shipment, provided they are given a pressure and leak of PE-Nylon-aluminum-PET and is 0.125mm (0.005") thick. test before and after filling. The innermost layer of PE is required to facilitate welding at the Over 30 years ago, a major filler in Germany developed an seams and to the valve tailpiece. The bag is rolled into a “double interesting alternative to the practice of hot water bathing. Using a S” shape, giving it a cigar-like appearance. It is customized to the rotary pressure tester, empty cans were pressurized with compressed can diameter and length. Two paper bands keep the bag from air to at least the equilibrium 50°C (122°F) pressure of the product unwinding. They break easily, at perforated or rouletted lines when to be filled. Any failed units were discarded. Then, after filling the product is pressure filled into the bag during production. The and gassing, the cans were tested by another rotary machine bags are usually designed to extend nearly to the bottom of the can. which briefly isolated them and then “sniffed” the miniscule In practice, they are filled to about 72% of their capacity. Larger atmosphere in the enclosure for gas leakage. The firm claimed that fills will result in higher initial gas pressures and enhance the this alternative was less costly, more reliable and left a decidedly possibility of product jetting in the initial emissions. smaller footprint than the large water bath, hot water source and accumulation table for drying emergent dispensers. The quality of BOV Production Aspects leak detection was said to increase over that provided by the water A BOV production line is quite different from the usual aerosol bath operator, also noting that a barely discernible gas bubble every line. The BOV unit is inserted into the empty can, which is then meter (39") or so in the water bath would calculate to a weight conveyed into an Under-the-Cap (U-t-C) gasser where the space loss of roughly 10 to 15 grams per year, which would be intolerable around the bag (exo-space) is pressurized with from about 1.7 to for some aerosol products. The German aerosol association and 2.8 bars (25 to 40 psi-g.) of either nitrogen or purified compressed government approved the alternative, so that today most German air (CAIR). A second machine then inserts the product into the aerosols are produced without hot water bathing. bag, generally expanding it so that it fills about 65 volume-% of With the advent of the “Bag-In-Can” or “Bag-On-Valve” the can. This acts to reduce the volume of the exo-space and (by (BOV) aerosol dispenser as a significant packaging option, Boyle’s Law) causes a significant pressure increase; sometimes to as several rationales have been advanced proposing that the DOT high as 8 bars (116 psi-g.). (actually, the PMHSA—Pipeline & Hazardous Materials Safety After a rinsing station and check-weigher, the cans are 100% December 2012 Spray 25


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