Aerosol spray is a dispensing system that creates an aerosol mist of liquid particles. The liquid is usually contained in a bottle under liquid pressure that is released when the valve is opened. As the gas in the can expands to drive out the liquid some of the propellant evaporates to maintain an even pressure.
Erick Rotheim invented the first aerosol spray can in 1926. Lyle Goodhue and William Sullivan were the first to put it to good use and are credited as the inventors of the modern spray can. In 1943, they created the “bug bomb” which was a refillable spray can and the ancestor to many common commercial spray products. Since the pressure gave the liquid a propellant quality it was used by soldiers to defend against malaria-carrying mosquitoes by spraying inside tents during World War II. Two of the three companies that originally received patents to manufacture aerosols still do so today: Chase Products Company and Claire Manufacturing.
Normally the gas within the can is from the evaporated liquid. These liquids normally have a boiling point slightly lower than room temperature and thus liquid and vapor stay at equilibrium within the can. As gases escape it is immediately replaced by more evaporating liquid. Previously Chlorofluorobarbons were used but have been replaced nearly everywhere due to the negative effects they have on the Ozone layer. Nitrous oxide and carbon dioxide are often used as propellants to deliver food stuffs. There are also manual pump sprays which are an alternative to stored propellant.
Aerosol spray products have three parts; the can, the valve, and the actuator. Usually the can is lacquered tinplate although aluminum cans are used for more expensive products. The valve is crimped to the can and its design determines the spray rate. The actuator is pressed to release the spray. For highly viscous products the packaging employs the use of a piston barrier system. This system assures separation of the product from the propellant which maintains the integrity of the product for its consumer lifespan.
Another dispensing system is bag-in-can system. This system keeps the products separated from the pressurizing agent with hermetically-sealed layered pouch. This system extends the shelf life of the product. It is commonly used by sun care makers due to it dispensing at all angles. The newest system is the 2k which stores the main component in one chamber while the second is stored in an accessory container. By breaking the accessory container the two components mix which provides and advantage for the delivery of reactive mixtures.