Gloss & Emulsion Science (ya ya ya!!)
Science Of Paint.
When purchasing paint & apply using a brush or roller after it dries leaving it leaves behind a solid film. Paints are made up of a mixture of different components. Although paints designed for different purposes will have different formulations, they all have some key features in common.
Paints contain a pigment to give colour, including white; a film former that binds the pigment particles together and binds them to the surface to be painted; paint also contains a liquid including additives to help application & storage.
The two main types of paint are gloss and emulsion.
Gloss paint is widely used because it produces an attractive shiny surface that is so durable that it can be used outside. The binder or film former in gloss paint is called an alkyd resin. This is a long chain polymer made by reacting a vegetable oil such as soya bean or linseed oil with an alcohol and an organic acid. The resin is dissolved in an aliphatic petroleum solvent so that it can be spread easily. When the solvent evaporates, the oxygen of the air interacts with the resin which results in the formation of cross links between the polymer molecules and produces a strong, dry film.
A Typical Gloss Paint Formulation
|Component||Percentage by mass|
|Alkyd resin binder||54|
|(Additives might be driers and anti-skin agents)|
Some paints are emulsions (see Materials page 12). They are made up of tiny droplets of liquid polymer binder spread out in, rather than dissolved in water. This emulsion can be spread easily.
The polymer is made by the addition polymerisation of alkene monomers such as ethenyl ethanoate, methyl 2-methylpropenoate and 2-ethylhexyl acrylate. These monomers can be mixed in different proportions before polymerization to form a copolymer which has exactly the right properties for the purpose it is to be used for.
After an emulsion paint is applied, the water evaporates and the polymer particles pack closely and fuse together to form a continuous film. The use of water rather than an organic liquid means that emulsion paints produce fewer VOC (volatile organic compounds) when they are used.
A typical emulsion paint formulation
|Co-polymer binder||15 to 23|
|Pigment (colour)||0 to 5|
|Extenders||15 to 25|
|Water||25 to 50|
|Additives||2 to 5|
(Additives might be antifreeze, dispersing aids, wetting agents, thickeners, biocides, low-temperature drying aids, antifoam agent, coalescing solvent, ammonia)