| Résumé : |
Although the solvent component is a transient ingredient in paint, its quality and appropriateness will be apparent for the life of the coating. Film integrity, appearance, and application are significantly affected by the nature of the solvent. Thus, the solvent plays a very important role in the film formation and durability even though it is not a permanent component.
Two properties that are of the utmost importance when selecting the proper solvent for any end use are solvency and evaporation rate. In paints, the solvent must dissolve the resin and reduce its viscosity so that the paint can be applied. Evaporation is subsequently necessary, not only as part of the drying process, but to control the coating viscosity at various stages of drying.
Initial coating viscosity depends on the solubility of the resin(s) and the solvency of the solvent(s). Viscosity at various stages of drying depends, additionally, upon the sovent evaporation rate. As the solvent evaporates, film viscosity increases. The solvent must evaporate relatively quickly during initial drying to prevent excessive flow, but it must evaporate slowly enough to provide sufficient levelling and adhesion. In lacquer coatings, this is accomplished by varying the levels of fast, medium, and slow evaporating solvents.
The most widely used solvents in the coatings industry are hydrocarbons and oxygenated solvents. Their consumption in coatings is shown in Figure 1. |
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Solvents in JOURNAL OF COATINGS TECHNOLOGY (JCT), Vol. 71, N° 892 (05/1999)
