What is the technology behind spraying technique in deodorant?

Aerosol cans can't be simply filled with compressed gas. If it is so the deodorant can should be strong like a gas cylinder or the amount of active ingredient will be very less. The gas used is the vapor of a liquid with its boiling point slightly lower than room temperature. Inside the pressurized can, the vapor will be in equilibrium with its bulk liquid at a higher pressure than atmospheric pressure. When you press the can the gas escapes. The area vacated by the gas coming out will be occupied by evaporating liquid. This liquid may be propellant and in some cases, the propellant itself will get vaporized.

The spraying system consists of two parts one is the container in which the spray material is kept and other is the spring loaded valve on the top of the container which opens when pushed and comes back to closed condition due to the spring action. This valve is a vital part of the system as it allows the container material to escape out in a controlled manner. Pushing the valve creates a low pressure area and the material (under pressure) from the inside of container comes out.

Now coming to the container it contains the liquid material that is deodorant or any other such item which needs to be sprayed and a propellent gas is also added to it so that when the valve is pushed the gas moves out taking fine droplets of the deodorant liquid along with it and a mist or cloud or aerosol type of spray is created by it which can be directed to the required part of the body or the room itself. The purpose of propellent gas is very important as it helps in creating sufficiently forceful way for the liquid to escape out in form of a fine mist. To make the process easier, one can also shake the container a little before use.

Earlier CFC (chlorofluorocarbons) was used in these containers as propellent but due to environmental concerns (threat to ozone layer), it was discontinued and now a days other gases like propane, butane etc are used.