When piezoelectrically actuated aerosols are used in fast-moving consumer goods such as household and personal care products, they are often required to prevent fluid leakage from the device when it is not in use. Such applications could include, but are not limited to, fragrance dispensers, cosmetic products and household cleaning products.
In these types of applications, it is often the case that the droplets which are generated need to be sufficiently large that they will land on a surface, rather than simply evaporate into the atmosphere once they have been dispensed. Typically, these droplets will have an average droplet diameter in the region of 20 to 60 microns and a spray generator that is capable of producing such droplets will typically have nozzle diameters in the region of 10 to 20 microns. In some of the applications referred to above, the fluid to be dispensed has a relatively low surface tension and a relatively low viscosity and, as a result, fluid can easily flow through the nozzles of a membrane when the device is not in use. This fluid flow is driven by a combination of capillary action and pressure differences. This pressure difference comes from the fluid head behind the membrane and, if the chamber containing the fluid cannot maintain equilibrium with the atmosphere, differences caused by changes in atmospheric temperature or pressure.
One method of preventing fluid flow through those nozzles when the device is not in use is to apply a negative pressure to the fluid in the region directly behind the perforate membrane. However, maintaining a negative pressure behind the membrane of such a device within a sealed chamber, consisting of a fluid feed and a fluid reservoir, is not a trivial task. In particular, any mechanism for supplying a negative pressure will need to cope with pressure changes resulting from changes in ambient pressure or temperature.
Thus, an alternative method of preventing unwanted fluid flow through a perforate membrane is required.