Driers for Paints & Coatings

Driers are heavy metal salts of organic acids used to accelerate the conversion of liquid paint film to dry film. Oil based paint need driers if the oils are oxidizing in nature or paint dry in presence of air by auto oxidative polymerization for example alkyd resin-based paints (enamels) or architectural paints or paints for houses and building. Not all the air-drying paint need drier for example plastic or acrylic emulsion paint, lacquers etc.

As the name indicates, the paint drier will help in drying ability of the paint over the surface. It contains oxidizable or drying oil components. The formulation of solid film at the ambient temperature will quickly dry up paint.

  • There are some drier used in baking or stoving paints also for example iron drier used in baking type paints.
  • Heavy metals used in drier are generally: lead, cobalt, manganese, calcium, zirconium, iron, zinc, vanadium, lithium, strontium, cerium etc.

Basic rules for selecting Heavy metals are-

  • Polyvalence
  • Difference in free energy of different oxidation states should be small (of the order 3-5 Kcal/g mole)
  • If difference is high, metal will not work at low temperature but can function as drier at elevated temperature.
Pigments
Resins
Extenders
Solvents
Additives

Introduction & synthesis of Driers

Driers are one of the most important additives in paints that speed up the autoxidation process, improve the aesthetics and performance of the final product. 

The paint drier is the compound to be used with the paint when you are about to use the paint. As soon as drier is added to paint, it will start doing its action as a catalyst immediately. It will lead to the hardening of paint, decreasing workability.

please watch the given lecture to know more—>

CLASSIFICATION OF DRIERS

Primary/active driers- Active driers at ambient temperatures promote oxygen uptake, peroxide formation, and peroxide decomposition. Primary driers when used without through driers would simply dry the upper surface of the film, while the coating underneath would remain wet.

secondary/auxiliary/ through driers- Auxiliary driers do not show catalytic activity themselves at ambient temperatures, but enhance the activity of the active drier metals, especially regarding the through drying and are also referred to as “through driers “. This category of dries ensure that the drying process occurs at a uniform rate throughout the film body and not just at the surface.

Organic acid used for manufacturing driers are linoleic, rosin, naphthenic, octoic. The most popular is octoic acid also known as 2-ethyl hexoic acid.