Formulating Paint
Paints generally contain three types of material, which are resin, pigments and solvents. The resins are a mixture that forms the paint film, also called as blinder, which provides a clear film. The kind of resin used could vary to allow the paint to have whatever ultimate properties are necessary. The pigments are nothing but the colors. It provides colors to the paint film and allows the coat of the paint to cover what is below. Solvents are useful to provide right consistency (viscosity) for easy application. They dissolve in the paint film or suspend the binder. They should also evaporate after application in order to allow the paint to dry.
A mixture of solvent and resin is the 'vehicle' for the pigment. Many of the paints also include small quantities of several additives, such as driers in order to speed up the drying procedure, materials to adjust pH of the paint, and so on.
This part describes the method the paint chemist uses to mix the pigment and "vehicle" together to make paint.
Why Disperse Pigments?
Pigments are available through the industry in dry powder forms. These consist of "primary particles" that are sized to provide the best outcome in the paint films. For instance, white pigments (TiO2 Titanium dioxide) spreads out light most effectively (opacity and whiteness) when the element size is about 0.22 microns. A few pigments are very small, while some are bigger. The small main particles of the pigment clump together while the powder is in the process of drying and storage, in order to form comparatively large clumps. A ‘clump’ of TiO2 might contain 5,000,000 main particles. These clumps or aggregates are the combined form in which the pigments are available. To make good paints, it is essential for the pigment to be at its primary particle size while being mixed with the vehicle. If not, one cannot use most of the classy colored pigment, and the dry film would not be glossy, smooth, opaque or have the right color.
Pigment Dispersion
It is thus essential to break down the aggregates of the pigment particles in the presence of the vehicle and to stop them from re-aggregating. For this cause, it is not usually possible just to mix the pigment in the vehicle. Instead, the job has to be completed on the mixture to break down the aggregates and make sure that the resin coats the little particle surfaces. This procedure is called as pigment dispersion and the following procedures must occur:
A resin that is to perform well with a pigment dispersant should thus be composed of molecules comprising of two parts, such as anchor group and stabilizing chain. Anchor group wets the pigment surface and combines with it. The stabilizing chain is soluble in the solvent used and stretches out into it.