Ingredients

• Pigments, which are materials that change the color of reflected or transmitted light, provide color when added to the paint mixture. Liquid solvents are added to carry the remaining paint ingredients. Hydroflourocarbons (HFCs) are a type of propellant or gas used in spray paint to force the paint out of the can by rapidly expanding when the valve is opened.
  
  

Packaging

• A spray paint can is typically made of tin-plated steel or aluminum. The inner components of the can consist of a valve, dip tube and an agitator, which moves throughout the can as it is shaken, mixing and combining the pigments and propellant with the solvent. The valve seals the can and controls how the paint is dispensed; the dip tube is attached to the valve to bring paint upward from the bottom of the can.
  
  

Mixing

• The first step in manufacturing a spray paint can involves mixing the liquid components of the paint such as the pigments, solvents, pH and viscosity (resistance to flow) control substances and corrosion inhibitors with large, electric motor-driven mixers. The liquid concentrate is prepared in large glass or metal tanks.
  
  

Dispersing

• A crucial step in the manufacturing process is making certain the solid pigment particles are appropriately dispersed. Simply mixing the ingredients in the large mixers is not adequate, so mixing equipment such as a ball mill must be used. A ball mill is a circular drum-like container filled with stainless steel or ceramic balls. Dry pigments are mixed with some of the liquid paint concentrate to form slurry (mixture of water with an insoluble solid), which is poured into the ball mill. The ball mill is then placed on a pair of spinning metal rollers that spin the container around so the balls inside tumble, breaking apart the pigment particles.
  
  

Stirring

• When the pigments have been appropriately dispersed, the slurry can be added to the remaining liquid concentrate in the mixing tank; it is stirred until homogeneous (having uniform composition). A sample of the paint concentrate is taken to check for proper color and consistency; adjustments can be made by adding pigment to increase color or more solvent to dilute it. Once the batch meets the required specifications, it gets transferred to a filling tank.
  
  

Filling

• The filling process is highly automated; as the empty cans travel down a conveyor belt to the filling equipment, compressed air is blasted at the cans to remove any dust or dirt before they are filled with the liquid concentrate. The filling heads are a series of nozzles connected to tubes that take the paint from the filling tank and inject it into the empty cans. A piston mechanism controls how much liquid paint concentrate is injected into each can.
  
  

Gassing

• Once filled, the cans move along the assembly line to a gassing device, where liquefied propellant is injected into the cans, and then the valve is immediately crimped against the rim of the can to seal it shut. The sealed cans then move through a hot-water "bath" to check for leaks. If there are holes or the valves are not properly sealed, a stream of bubbles will be visible in the water; faulty cans are discarded. The cans are dried with compressed air; a cap is fitted over the valve to prevent accidental activation of the aerosol; and the cans are packed into cartons and loaded onto pallets for shipping.