Aerosol spray

Aerosol spray can

Aerosol spray is a type of dispensing system which creates an aerosol mist of liquid particles. This is used

with a can or bottle that contains a liquid under pressure. When the container'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,

only 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 atomizer is a similar device that is

pressurised by a hand-operated pump rather than by stored gas.

History

The aerosol (A gaseous suspension of fine solid or liquid particles) spray canister invented by USDA researchers, Lyle Goodloe and William

Sullivan.

Perfume spray.

The concepts of aerosol probably goes as far back as 1790.[1] The first aerosol spray can patent was

granted in Oslo in 1926 to Erik Rotheim, a Norwegianchemical engineer,[1][2] and a United States patent was

granted for the invention in 1931.[3] The patent rights were sold to a United States company for

100,000Norwegian kroner.[4] The Norwegian Post Office celebrated the invention by issuing a stamp in

1998.

In 1939, American Julian S. Kahn received a patent for a disposable spray can,[5][6] but the product

remained largely undeveloped. 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.[7] 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.[dubious – discuss]Pressurized by liquefied gas, which gave

it propellant qualities, the small, portable can enabled soldiers to defend against malaria-

carrying mosquitoes by spraying inside tents in the Pacific during World War II.[8] In 1948, three companies

were granted licenses by the United States government to manufacture aerosols. Two of the three

companies, Chase Products Company and Claire Manufacturing, still manufacture aerosols to this day.

The "crimp-on valve", used to control the spray was developed in 1949 by Bronx machine shop

proprietor Robert H. Abplanalp.[9][7]

Aerosol propellants

If aerosol cans were simply filled with compressed gas, it would either need to be at a dangerously high

pressure and require special pressure vessel design (like in gas cylinders), or the amount of gas in the can

would be small, and would rapidly deplete. Usually the gas is the vapor of a liquid with boiling point slightly

lower than room temperature. This means that inside the pressurized can, the vapor can exist

in equilibrium with its bulk liquid at a pressure that is higher thanatmospheric pressure (and able to expel

the payload), but not dangerously high. As gas escapes, it is immediately replaced by evaporating liquid.

Since the propellant exists in liquid form in the can, it should be miscible with the payload or dissolved in

the payload. In gas dusters, the propellant itself acts as 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 andisobutane. Dimethyl ether (DME) and methyl ethyl ether are also used. All

these have the disadvantage of being 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 usehydrofluoroalkanes (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. Manual pump sprays can be used as an

alternative to a stored propellant. A UK company (42 Technology) has developed a patented technology to

generate more finely dispersed mists by using a disc of superhydrophobic material within the manual

pump.[10]

[edit]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 insta can as one piece, prior to pressure-filling. The actuator is added later.

A different drawing of the spray valve assembly

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 two or three 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, and 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.

Packaging that uses a piston barrier system is often used for highly viscous products such as post-

foaming hair gels, thick creams and lotions, food spreads and industrial products and sealants. The main

benefit of the piston barrier system is that is assures separation of the product from the propellant,

maintaining the purity and integrity of the formulation throughout its consumer lifespan. The piston barrier

system also provides a controlled and uniform product discharge rate with minimal product retention and is

economical.

Another type of dispensing system is the bag-in-can system (or BOV “bag on valve”). This system

separates the product from the pressurizing agent with a hermetically sealed, multi-layered laminated

pouch, which maintains complete formulation integrity so only pure product is dispensed. Among its many

benefits, the bag-in-can system extends a product’s shelf life. The bag-on-valve, or ABS, is widely used

by sun care marketers for its benefits: all-attitude (360-degree) dispensing, quiet and non-chilling

discharge. This bag-in-can system is also used in the packaging of pharmaceutical, industrial, household,

pet care and other products that require complete separation between the product and the propellant.

A new development is the 2K (two component) aerosol. A 2K aerosol device has main component stored in

main chamber and a second component stored in an accessory container. When applicator activates the

2K aerosol by breaking the accessory container, the two components mix. The 2K aerosol can has the

advantage for delivery of reactive mixtures. For example, 2K reactive mixture can use low molecular

weight monomer, oligomer, and functionalized low molecularpolymer to make final cross-linked high

molecular weight polymer. 2K aerosol can increase solid contents and deliver high performance polymer

products, such ascurable paints, foams, and adhesives.

[edit]Health concerns

Canned air / spray dusters are dangerous to inhale. They do not use compressed air, but rather other inert gases.

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

Deliberate inhalation of the contents to achieve intoxication from the propellant, also known as inhalant

abuse or "huffing".

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

Aerosol burn  injuries can be caused by the spraying of aerosol directly onto the skin, in a practice

sometimes called "frosting". Adiabatic expansion causes the aerosol contents to cool rapidly on exiting

the can.[11]