The customary practice is to neglect any very slight gas solubility in the liquid product, and then determine what the pressure would be when 95% of the product has been discharged. Tables or graphs can be developed for any initial gas pressure, using various percentage product fill volumes. This is illustrated in the following table: FIGURE SIX NITROSOL PRESSURE DECREASES DURING CONSUMER USE (For an initial pressure of 140 psi-g at 70°F) Initial Fill Pressure Pressure (% of can capacity) (50% dispensed) (95% dispensed) 72.5 51.4 psi-g 29.5 psi-g 70.0 56.8 33.1 67.5 61.0 37.4 65.0 65.7 41.4 62.5 69.8 45.3 The use of pressures in the 130 to 150 psi-g range for single compartment dispensers makes it necessary to consider DOT-2Q cans, valve stem height controls, heavier download springs in the crimper and so forth. The DOT-2Q cans will always tolerate at least 180 psi-g without any permanent deformation. Marketers have the option of specifying lower pressures, in which case smaller product fill volumes will be required in order to maintain good dispensing characteristics near the end of can life. For example, with an initial pressure of 100 psi-g and a 55 volume-% fill, the 95%-out pressure will become about 38.4 psi-g at 70°F. This much pressure fill easily produce good sprays, without such detractions as hotspots or streaming tendencies. The BOV nitrosols are dispensed as foams, lotions or sprays. The initial pressures, created by inflating the bag with product, are typically in the 70 psi-g area at 70°F. Final pressures as low as about 10 to 15 psi-g are sufficient to dispense foams and lotions through the large valve orifices at satisfactory delivery rates. By formulating anhydrous products with ethanol, and sometimes more volatile ingredients, they can also be sprayed down to this low pressure range. With an initial pressure of 75 psi-g at 70°F, a BOV, filled to 70% of the net container volume will have a pressure of about 13.2 psi-g when 95% is dispensed. This is often considered as too marginal for comfort. In such cases, a 60% fill might be used, which would provide a pressure of about 22.3 psi-g at incipient emptiness. To Wrap up… Nitrosol technology is now providing still another chapter in the continuing development of new and useful aerosol products. They probably accounted for about 200 million units per year in the U.S. in 2013. The leading product is the BOV shaving cream. While nitrosols represent only about 5% of U.S. total aerosol production and are technically restricted to certain types of products, still, they should grow in importance, propelled by CARB regulations, environmental concerns, safety aspects and sometimes by economics. Like many new developments, there are advantages and disadvantages. Our scientists are already mitigating the challenges, opening the way to further marketing successes. SPRAY January 2014 Spray 21
SprayJan14
To see the actual publication please follow the link above