The Universal Selection Source: Coatings Ingredients

Select Driers for High Solids and Waterborne Coatings

Driers are important additives for paints & coatings as they speed up the autoxidation process. Without these drying catalysts the cross-linking process slows down, allowing the paint layer to dry only after some months post application. With driers the formation of a hard film is accomplished typically within a few hours after paint application. This guide is designed to familiarize you with the drying process, role of driers in film hardening and different types of driers used for coatings. Read on to select the right drier for your high solids and waterborne coatings.

Driers in Coatings


driers for coatings Driers, also referred to as siccatives, are organometallic compounds soluble in organic solvents and binders1.

Chemically, driers (e.g. cobalt-ethylhexanoate) belong to the class of metal soaps and they are added to air-drying coating systems to accelerate or promote the drying process after application.



The transformation from the liquid film into the solid stage within an appropriate time occurs by oxidative cross-linking of the binder system, a process which is catalyzed by the metallic cation of the drier.

The Drying Process


After application of the paint onto the substrate the solvent is released, which is the physical part of the drying process. In order to obtain a hard paint film, further polymerization of the binder is necessary.

The chemical part of the drying process involves oxidative cross-linking and starts with the reaction between unsaturated parts in the binder molecule and oxygen (air). This process is known as the "autoxidation process" and similar to the drying process in solvent-rich paints (figure below)2. This part of the drying process significantly affects film hardness.2

autoxidation film formation process of alkyd resins

Fig: The autoxidation film formation process of alkyd resins

High solids alkyd paints differ from the classical alkyd paints in having lower solvents contents as well as in resin composition. In order to reduce solution viscosity and enable higher solids contents, high solids resins typically are composed of lower molecular weight polymers and demonstrate high reactivity towards autoxidation. The high chemical reactivity is required to compensate for the low molecular weight of the resin. Waterborne alkyd paints are based on alkyd resins, either emulsified in water or aqueous (typically colloidal) solutions.

Effect of Driers on Film Hardness


  

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