Water-based coatings refer to coatings that use water as the solvent, with 70%–90% water as their composition. They do not contain toxic organic solvents such as benzene, aldehydes, and halogenated hydrocarbons, nor heavy metal compounds such as formaldehyde, lead, and chromium. They are non-toxic, environmentally friendly, virtually free of volatile substances, odorless, and stable, making them a safe and pollution-free type of environmentally friendly coating.
Water-based Coating Modification
In recent years, to address some shortcomings of water-based coatings, research on their modification has emerged. The most common modifying raw materials include: nanoparticles, polyurethane, polyacrylates, organosilicon, epoxy resins, and nano-oxide modification.
Among these, fillers (extender pigments), as an important component of coatings, are a crucial approach to inorganic modification technology. Fillers are mostly white or slightly colored powders, lacking tinting strength and hiding power, but they increase film thickness, adjust rheological properties, improve mechanical strength, enhance film durability, and reduce costs. They are mainly alkaline earth metal salts, silicates, and light metal salts such as aluminum and magnesium.
Currently, commonly used fillers in water-based coatings include: carbon materials (graphene, carbon nanotubes), calcium carbonate, bentonite, kaolin, silica, mica powder, barium sulfate, and talc. Among these, calcium carbonate has a significant cost advantage and also exhibits superior leveling, suspension, and abrasion resistance.
Applications of Water-Based Coatings
Green Building Materials
Water-based inorganic building coatings commonly used in construction engineering are prepared using alkali metal-modified silicate aqueous solutions and colloidal silica aqueous dispersions as the main film-forming substances, with the addition of pigments, fillers, and additives. The resulting coatings are environmentally friendly and non-toxic, fire-retardant, non-peeling, and possess excellent weather resistance and color retention.
Wood Products
The main function of calcium carbonate in water-based wood coatings is to fill gaps. It is not required in water-based wood varnishes, is added in small amounts in water-based wood solid color paints, and is added in larger amounts in water-based wood putty.
Automotive
Currently, countries with developed automotive industries have largely replaced solvent-based coatings with water-based coatings. Currently, water-based coatings are mainly used in automobiles as primers, intermediate coats, and topcoats.
For example, acrylic anti-stone chip underbody coatings are primarily formulated with acrylic resin obtained through the copolymerization of acrylate monomers, along with fillers and additives; it is a synthetic resin emulsion. Compared to the most widely used PVC plastisol systems and polyurethane elastomer underbody coatings, styrene-acrylic emulsions use water as the main solvent, have extremely low VOC (volatile organic compound) content, avoiding the flammability and toxicity of solvents. Furthermore, they exhibit good acid and alkali resistance, water resistance, and impact resistance, making them a novel type of anti-stone chip underbody coating.
However, in practical applications, the use of water-based coatings in the automotive industry still faces some challenges. Due to the low boiling point of water, its difficulty in evaporation, its significant susceptibility to environmental humidity, high surface tension, tendency to form bubbles, and low electrical resistance, water-based coatings are prone to sagging and defects.