Curing Mechanisms-Nonconvertible Coatings
Curing is the mechanism that a specific coating uses to transform from the liquid state found in the bucket to a solid coating film. There are two broad classifications of curing mechanisms: Convertible and Nonconvertible. Understanding the curing mechanism is very important for the proper installation of the coatings and a guide to observe those factors that will affect the cure and ultimately the service life of the coating.
Nonconvertible coatings cure by evaporation of the solvent. There is no chemical change to the resins in nonconvertible coatings as they transform from the liquid to the solid state. Once applied, nonconvertible coatings can be redissolved in the original solvent or one with similar solvency power. Because of that, these types of coatings are sometimes referred to as thermoplastic materials. Since it requires a large amount of solvent to dissolve the resin, in many parts of the world use of nonconvertible coatings has been limited by VOC regulations. Examples include vinyl and chlorinated rubber.
Areas of concern for the coatings that cure by evaporation are:
- High surface temperature during application
- High wind flow over freshly coated surface
- Excessive film build
- Drying times (typically short)
- Freezing temperatures
- Ventilation in the area being painted
- Overcoating these materials can be problematic since the solvents in the overcoating material may soften or dissolve it.
Coalescence cure is a specialized case of evaporation cure. In these coatings, tiny particles of resin are dispersed in water with the aid of specialized additives called surfactants. When the water evaporates, the resin particles fuse (coalesce) together to form the film. Particle fusion is assisted by small quantities of organic solvents (coalescing solvents). These types of coatings are also known as latex or acrylic latex, and are being used more and more.
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