Now, inside the can, there’s more than just paint. There is a delicate balance of pressurized gases.
The Head Space: When the can is filled, there is space left at the top to allow for some of the propellant to remain a gas.
The Gaseous Propellant: The same chemical propellant which is in liquid form mixed with the product, but at the top the propellant remains is gaseous form, which maintains a constant pressure inside the can (until you press the button).
Some propellants used today include propane, butane, which are naturally occurring hydrocarbons. Other propellants include compressed gasses such as nitrogen or carbon dioxide. Only a minuscule minority of modern aerosols uses CFC propellants, and this only because an appropriate substitute as not yet been found. These products, which are exempt from the EPAs ban, are primarily pharmaceutical products, which account for less than one percent of all aerosol products in consumer use. Soon, even these products will no longer use CFCs, once a proper alternative has been determined.
The Product: The liquid part is a combination of propellant, product and inert ingredients. The product, also known as the “active ingredient” you see on the label, is dissolved in the liquid form of the propellant, using a combination of inert ingredients which are used to suspend the product in the liquid propellant. Once sealed inside the can, the product is completely sterile, safe from evaporation or contamination.
The Curved Base: It’s not just for looks. The unusual concave bottom of the can helps to counteract the high pressure inside the can, and also conveniently ensures that the dip tube you see pictured can reach every last drop of the product.
The Head Space: When the can is filled, there is space left at the top to allow for some of the propellant to remain a gas.
