Paints: gloss and emulsion

Using materials

1. Paints

Interactive graphic of matt and gloss effect.

Picture 2 Paints can give a matt or gloss finish.

page 2

Gloss or emulsion

When we buy a can of paint we expect to be able to apply it with a brush or roller and for it to dry leaving behind a solid film. To achieve this 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; a liquid that makes it easier to apply the paint and additives to make the basic paint better to store and to use.

The two main types of paint are gloss and emulsion.

Picture 3 Gloss paint drying. You can watch a Flash animation of this.

	Gloss Paint
		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
Pigment	25
Solvent	17
Additives	4

(Additives might be driers and anti-skin agents)

Picture 4 Emulsion paint drying.You can watch a Flash animation of this.


	Emulsion Paint
		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 polymerisation to form a co-polymer 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

Component	Percentage by mass
Co-polymer binder	15 to 23
Pigment (white)	20
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)

Question 1
Look at the sentences below. There are some words missing. In each case choose the best word from the drop down list. Then click on the ‘show answers’ button to see how well you did.
In gloss paint, the alkyd resin binder dissolves in the aliphatic petroleum solvent to form a . In emulsion paint, the liquid polymer binder spreads out in water to form a . In both gloss paint and emulsion paint, the solid pigment spreads out in the liquid paint to form a . After paint is applied, the aliphatic petroleum solvent in gloss paint and the water in emulsion paint are lost due to . When gloss paint dries, the alkyd resin binder reacts with in the air