How Does Spray Paint Work?
Spray paint is a very convenient way to paint. It enables a very smooth finish without the need to own - or clean - expensive spray equipment. Spray paint is also a fantastic way to cover hard to paint surfaces like railings, hard to reach places, wicker and other intricate surfaces.
The paint is forced through a spray tip (actuator) that atomizes the paint into a fine mist as it is forced through the tip. The mist settles onto the surface as small drops which coalesce into a smooth coating as it dries.
But how does spray paint work? We all know what a spray paint can looks like, but beyond the cylindrical can and the depressable nozzle, what is happening inside a can of aerosol spray paint to make it work?
An aerosol can of spray paint has several components:
- Actuator (aka nozzle or tip)
- Spray can - usually tin or steel
- Actuated valve
- Shaker ball (usually glass)
The paint used in spray paint is usually a fast-drying paint that atomizes well. Most common types of paint used in spray applications are lacquer or acrylic enamels which air dry (single component) as well as two-component paint such as urethane or epoxy that starts to dry when mixed together. This article covers the single-component air dry types of spray paint.
The solvent is usually a blend of materials to reduce the paint to its optimal viscosity for spraying. If the paint is too thick it won’t atomize or spray well.
The propellant is usually a compressed gas that stays liquid while under pressure in the can. The most common propellants are hydrocarbons like propane.
The spray can, while held upright, will have the paint at the bottom of the can where it can enter the bottom of the tube. The propellant and solvent, in liquid form, mix with the paint. To the extent there is room in the can, the propellant turns to gas and maintains the pressure. Once the nozzle is depressed and opens the valve, the paint is then pushed up the tube and out the nozzle. As the material leaves the can the pressure is reduced allowing more liquid propellant to change to gas, thus maintaining the pressure and pushing more paint out of the can.
This explains why spray paint only works when held upright. If the paint isn’t at the bottom of the can where the tube is, then the paint doesn’t get pushed out. If you depress the tip while holding the spray paint can upside down, you’ll get a little paint since some is already in the tube, but once that is gone only gas will come out. The liquid is at the other end of the can away from the tip. (Tip: Whenever you are done spray painting you should always spray the can upside down for a few seconds because it clears any paint out of the tube so it remains clear for the next time you want to use it. Otherwise that paint can dry in the tube and permanently clog the can.)
MyPerfectColor offers the largest selection of colors anywhere including difficult to match industry standard colors such as Pantone, RAL, Federal Standard and Munsell, matches of many powder coats including Tiger Drylac and IFS Coatings as well as matches of any major paint brands including Sherwin Williams, Benjamin Moore, Behr and much more.
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