The purpose of this blog post is to provide a throrough answer to this basic question, "what are waterborne coatings?".
Waterborne coating is a general term used to describe any surface coating or finish that uses water as a solvent to disperse the resin added to it to create the coating. Composition varies and may include as much as 80% water with small amounts of other solvents such as glycol ethers. High water content makes waterborne coatings both environmentally friendly and easy to apply.
What Makes A Waterborne Coating Different?
Waterborne finishes are very like their solvent–based counterparts in terms of curing mechanism, polymer makeup, and film integrity. Chemical composition is also similar as water plays an identical role in the production of waterborne finishes as that played by thinners, such as mineral spirits or Toluol, in solvent–based finishes.
Waterborne Coating Applications
Waterborne finishes offer a broad variety of application, including automobiles, concrete, furniture, plastic, wood, and even printing inks, and are compatible with both conventional and electrostatic application equipment.
Resin types with waterborne finishes cover a broad range including acrylic, alkyd, epoxy, fluoropolymer, polyester, urethane, and waterborne powder. Similarly, they work under a variety of curing chemistries, including air dry thermoplastic, aminoplast, epoxy–polyamide, oxidative, urethane, and UV cure.
The Primary Categories of Waterborne Coatings
There are three primary categories of coatings designated as waterborne: water–soluble or water–reducible, water–dispersible or colloidal, and emulsion or latex.
Water–soluble refers to coatings in which individual molecules of resins dissolve completely in water. Creation of water–soluble coatings takes place in an organic medium through a process of polycondensation or polymerization reaction; accordingly, these typically contain organic co–solvents such as alcohol or glycol ethers. These types of waterborne coatings contain only 30–40% solid content by weight, and most baked coatings fall under this heading.
Water–dispersible refers to resins first made in solvent and later reduced in water resulting in small particles of insoluble resin dispersed in water. This type of waterborne coating also involves the use of organic solvents as coalescing agents, but these are in small amounts that evaporate on drying. Colloidal dispersions are used primarily for applications on porous material such as leather or paper.
Emulsions (more commonly referred to as latex) are not dissimilar to water–dispersible coatings. Resin particles in emulsions tend to cluster in larger groups and require the presence of an emulsifier to remain suspended throughout the water base. Emulsions are more permeable than other waterborne coatings allowing them to “breathe” and reducing the risk for blistering or peeling. Architectural coatings, such as interior and exterior paints, fall under this heading.
Several features of waterborne coatings contribute to their environmental advantages. These coatings meet the US and European regulations governing VOC (volatile organic compound) emissions, producing VOC content of less than 3.5 pounds per gallon.
In addition to their low toxicity, their high water content also makes waterborne coatings less flammable and results in reduction or elimination of hazardous waste disposal. Containers and paint guns used during the application of waterborne coatings can be easily cleaned with water or water–based cleaners disposing of the need for cleaners such as acetone, methyl acetate, or paint thinner.
Another advantage to waterborne coatings above solvent–based counterparts is the relatively lower cost of production since they do not require additives, hardeners, or thinners. Less product covers more surface area with waterborne coatings relative to solvent–based coatings, and they are the better choice than solvent–based finishes for applications in which there is a risk of reaction with existing substrates and/or finishes.
Waterborne coatings provide excellent surface properties such as anti–sealing effects and non–yellowing film, high gloss, and rub resistance. Due to their resistance to heat and abrasion, waterborne coatings make excellent primers. They create strong adhesion, can be applied in thick or thin coats, and allow for easy color blending and change.
Waterborne coatings represent the largest category of coating or finish technology used globally today. Estimates suggest that their global market share will grow to more than $146 billion USD by 2022. A driving force behind this predicted growth is the increase in both construction and automotive markets that utilize acrylic finishes. Acrylic coatings constitute more than 80% of the market for waterborne coatings.
Another factor in market growth is government regulatory support for these eco–friendly products. Government regulations on VOC and other emissions may be a key factor in Asia and the Pacific, where demand for waterborne finishes continues to rise steadily.
Some market analysis suggests a split in analytics between architectural and industrial sectors. Technology around waterborne coatings in both market sectors has surged with the trend in environmentally–friendly building materials and methods. For many years, waterborne technologies have dominated the architectural market. The industrial market, by contrast, has continued to demand and develop alternate solvent–based technologies to meet a broader range of performance standards
Waterborne coatings represent a versatile, high quality, and environmentally–sound choice for a variety of finish applications.