Basic Components of Paints
The exact composition of a particular paint is often complex and proprietary. In general, however, most paint contains Binder, Solvents, Pigments and Additives.
What is Binder (resin)?
The paint binder (or resin) is the solid material that forms the bulk of the paint film. It is generally a tough, amorphous polymeric material that gives the paint most of its thermal, mechanical, and weathering properties.
In a paint mixture, the binder is responsible for providing adhesion, binding the pigment, and also gives the paint resistance properties which make the final coating tough and durable. The binder itself is clear and glossy, but the presence of pigment interferes with this quality. Depending on the ratio of pigment to binder, or the PVC (pigment volume concentration) the paint can assume varying levels of glossy finish. Paints with the glossiest finish often have a typical PVC of 15 percent, while the most matte paints have a PVC anywhere from 40 to 80 percent. Paints with less gloss have more binder per unit of pigment, and tend to be more durable. There are two specific types of binder: oil-based and latex-based.
What Binder is used in Oil Based Paints?
Oil-based paint requires a binder that has similar properties to the paint—in this case, the binder oxidizes or dries when exposed to air, hardening along with the rest of the paint. Once applied, the liquid factor of an oil-based paint evaporates, and the binder then reacts with the air to harden into place with the pigment. However, sometimes this process can result in over-dry, brittle paint, and chipping can occur. Additionally, the oxidation makes the paint prone to yellowing.
What binder is used in Latex-Based (Emulsion) Paints?
Latex-based paints actually do not possess latex—rather, the binder that is used (plastic-like in nature) creates a film in the paint that resembles natural latex rubber. Almost all water-based paints have a latex-based binder. When the coating is applied, water evaporates from the paint, leaving behid a film of pigment and latex-based binder, which bind together into one continuous coating. The process by which the binder and pigment are fused is called coalescence. However, because the binding agent is thermoplastic, it cannot be applied at too low a temperature or the binder will be too hard and difficulty will arise during fusing. Common types of latex-based binder include acrylic and vinyl acrylic.
What are solvents?
Solvents adjust the viscosity of the paint to suit the method of application. Turpentine is generally used as a thinner in oil paints. In emulsion paints, water is used as a thinner. In the most basic sense, the solvent component of a paint is simply responsible for transporting the binder and pigment to the substrate surface. After the paint film has dried, usually by baking, the solvent is no longer present
What are Pigments?
A paint’s pigment plays a large role in determining color and appearance. Some pigments also provide added bulk, helping to thicken a paint when needed. In its unmixed form, a pigment is simply a powder. There are two general categories of pigments: prime and extender.
Prime pigments are mainly responsible for color or whiteness in a paint, as well as the paint’s ability to hide undesirable surface flaws. In paints that exhibit a white hue, titanium dioxide is the main ingredient. In paints the express other colors, the pigments are selected to absorb only certain kinds of light, thus yielding a given color. Organic pigments yield the brightest colors, while inorganic pigments yield less bright but more durable colors.
Extender pigments are designed to add bulk, but are not as well-suited to hiding surface flaws as prime pigments. They do, however, influence the paint’s overall sheen, color retention, and abrasion resistance. Silica and silicates, for example, are extender pigments that increase the paint’s durability. Zinc oxide helps prevent mildew and corrosion, and is especially useful in outdoor applications.
What are additives?
Additives are modifiers added to paint, usually in small quantities, to achieve special effects. They modify the properties of either the wet film or the dried paint and can affect flexibility, color fastness, gloss, solvent resistance,etc.
Depending on the type of paint and intended use, additives may include:
dispersants - to separate and stabilise pigment particles
silicones - to improve weather resistance
thixotropic agents - to give paints a jelly-like consistency that breaks down to a liquid when stirred or when a brush is dipped into it driers - to accelerate drying time
anti-settling agents - to prevent pigment settling
bactericides - to preserve water based paints in the can
fungicides and algaecides - to protect exterior paint films against disfigurement from moulds, algae and lichen