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'Aerosol spray' is a type of canister that sprays an aerosol. This type of 'spray can' is a canister containing liquid under pressure from pressurized vapor in equilibrium with another liquid, which often also dissolves the payload (see propellant below). When the can's valve is opened, the liquid is forced out of a small hole and emerges as an aerosol or mist. As gas expands to drive out the payload, some propellant evaporates inside the can to maintain an even pressure. Outside the can, the droplets of propellant evaporate rapidly, leaving the payload suspended as very fine particles or droplets. Typical liquids dispensed in this way are insecticides, deodorants and paints. An atomiser is a similar device that is pressurised by a hand-operated pump rather than by stored gas.

Contents

History

Propellant

Packaging

Health Concerns

See also

References

History

The concepts of aerosol probably goes as far back as 1790. Bellis, Mary The History of Aerosol Spray Cans The first aerosol spray can was invented in Oslo in 1926 by Erik Rotheim, a Norwegian chemical engineer. The patent was sold to a US company for 100,000 Norwegian kroners. The Norwegian Post Office celebrated the invention by issuing a stamp in 2000.^[1]

The aerosol spray canister invented by USDA researchers, Lyle Goodhue and William Sullivan.

It was not until 1941 that the aerosol spray can was first put to good use by Americans Lyle Goodhue and William Sullivan, who are credited as the inventors of the modern spray can. World of Invention "Summary", Kimberley A. McGrath (Editor), Bridget E. Travers (Editor), , , Thomson Gale, , Their design of a refillable spray can dubbed the “bug bomb”, was patented in 1943, and is the ancestor of many popular commercial spray products. Pressurized by liquefied gas, which gave it propellant qualities, the small, portable can enabled soldiers to defend against malaria-carrying bugs by spraying inside tents in the Pacific during World War II.^[2] In 1948, three companies were granted licenses by the United States government to manufacture aerosols. Two of the three companies still manufacture aerosols to this day, Chase Products Company and Claire Manufacturing. The "crimp-on valve", used to control the spray was developed in 1949 by Bronx machine shop proprietor Robert H. Abplanalp.

Propellant

If the can was simply filled with compressed gas, either it would need to be at a dangerously high pressure, or the amount of gas in the can would be small, and it would soon run out. Hence, usually, the gas is the vapour of a liquid with boiling point slightly lower than room temperature. This means that inside the pressurised can, the vapour can exist in equilibrium with its bulk liquid at a pressure that is higher than atmospheric pressure (and able to expel the payload), but not dangerously high; yet, as gas escapes it is immediately replaced by more evaporating liquid. Since the propellant exists in liquid form in the can it is desirable that it be miscible with or dissolved in the payload.
Chlorofluorocarbons (CFCs) were once often used but since the Montreal Protocol came into force in 1989 they have been replaced, in nearly every country, due to the negative effects CFCs have on Earth's ozone layer. The most common replacements are mixtures of volatile hydrocarbons, typically propane, n-butane and isobutane. Dimethyl ether (DME) and methylethyl ether are also used. All these have the principal disadvantage of being quite flammable. Nitrous oxide and carbon dioxide are also used as propellants to deliver foodstuffs (for example, whipped cream and cooking spray). Medicinal aerosols such as asthma inhalers use hydrofluoroalkanes (HFA): either HFA 134a (1,1,1,2,-tetrafluoroethane) or HFA 227 (1,1,1,2,3,3,3-heptafluoropropane) or combinations of the two.

Packaging

A typical paint valve system will have a "female" valve, the stem being part of the top actuator. The valve can be preassembled with the valve cup and installed on the can as one piece, prior to pressure-filling. The actuator is added after.

Modern aerosol spray products have three major parts; the can, the valve and the actuator or button. The can is most commonly lacquered tinplate (steel with a layer of tin) and may be made of 2 or 3 pieces of metal crimped together. Aluminium cans are also common and are generally used for more expensive products. The valve is crimped to the rig of the can, the design of this component is important in determining the spray rate. The actuator is depressed by the user to open the valve; the shape and size of the nozzle in the actuator controls the spread of the aerosol spray.

Health Concerns

There are two main areas of health concern linked to aerosol cans:

★ Deliberate inhalation of the contents to gain a high from the propellant

★ The piggy-backing of more dangerous particles into the respiratory tracts

See also

★ Aerosol paint

★ Air pollution

★ Freon

★ Ozone Depletion

★ Nitrous oxide

References

1. Image of the Norway Postage stamp
2. Core, Jim, Rosalie Marion Bliss, and Alfredo Flores. (September 2005) "ARS Partners With Defense Department To Protect Troops From Insect Vectors". ''Agricultural Research Magazine''Vol. 53, No. 9 .