As the public become more environmentally conscious and health-focused, and with stricter regulations on Volatile Organic Compounds (VOCs) in national environmental laws, traditional solvent-based coatings are encountering unprecedented challenges. Instead, waterborne paints are gaining increasing attention.
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What is waterborne paints?
Waterborne paints refer to coatings with water as the dispersing medium, generally divided into two main categories: water emulsion and water-soluble. Among them, water emulsion is more widely used. The main types of water emulsion include Polyurethane Dispersions (PUD), Pure Acrylic Emulsions (PA), Acrylic-Polyurethane Modified Emulsions (PUA), etc. The packaging forms include single-component and two-component.
Currently, the resins commonly used in waterborne wood paints include waterborne alkyds, acrylic emulsions or dispersions, waterborne polyurethane dispersions, waterborne acrylic-polyurethane dispersions, and two-component waterborne polyurethane dispersions. These resins are mixed with water, thickeners, and additives to prepare coatings.
How does waterborne paints work?
The film-forming mechanism of waterborne paints is theoretically consistent with that of solvent-based coatings and is closely related to the resin system selected for the coatings. It involves processes such as volatile drying, cross-linking curing, heat curing, UV curing, etc. However, the presence of the special solvent "water" in waterborne paints makes their curing mechanism more complex. For example, in the film-forming process of water-soluble two-component polyurethane coatings, it includes the evaporation of volatile components (solvents, water), co-condensation of polyols and polyisocyanate particles, reaction between polyisocyanate and water, and reaction between polyols and polyisocyanate. These reactions accompany the entire drying process of the coating.
Unlike solvent-based coatings where film formation is primarily driven by the evaporation of solvents, waterborne paints achieve film formation through interactions and bonding between emulsion particles.
Film-forming mechanism of waterborne paints
Pros of waterborne paints
Environmental-friendly. Waterborne paints use water as solvents instead of volatile organic solvents. And thus, waterborne paints typically have lower Volatile Organic Compound (VOC) content compared to traditional solvent-based paints with reduced emission of harmful pollutants into the air. This reduces the environmental impact and eliminate the risk of fire during application.
Excellent adaptability. Waterborne paints can be directly applied on wet surfaces and in humid environments, which ensuring a strong adhesion.
Easy to clean.Tools used for waterborne coatings can be cleaned with water, significantly reducing solvent consumption.
Cons of waterborne paints
Weaker Performance.Waterborne paints generally have lower solid content, and a single application may not achieve a high film thickness. There are certain differences in solvent resistance, chemical resistance, heat resistance, hardness, and feel of the coating film compared to traditional Nitrocellulose (NC) and Polyurethane (PU).
Expansive. The unit price of coatings is also relatively high. The manufacturing process of waterborne paints requires advanced technology and equipment, which increase the cost of raw material.
Corrode the metal. Waterborne paints can corrode most metal materials. And thus it require the use of corrosion-resistant linings or stainless steel that raises equipment costs. Also, in transportation pipelines, these paints may cause metal dissolution, particle precipitation, and coating defects like pinholes, requiring the use of stainless steel pipes and adding to expenses.
Poor water resistance.This affects the stability of both the coating and the liquid solution, resulting in a weaker ability of the coating to withstand water exposure. Another factor is that the medium in waterborne coatings is usually a bit alkaline (with a pH ranging from 7.5 to 8.5). This alkalinity makes the resin's ester bonds prone to breaking down in water, causing the molecular structure to degrade. This, in turn, affects how stable the coating and liquid solution are and impacts the performance of the coated film.