Improve the Durability of Water-Based Coatings with LUDOX®

However, water-based architectural coatings do have a fair share of drawbacks. The high surface tension of the aqueous medium can lead to poor surface wetting and suboptimal adhesion. Also, the films produced by latex paints are inherently soft and susceptible to abrasion, blocking, and soiling. To help remedy these drawbacks, LUDOX® colloidal silica is recommended for latex paint compositions. 

LUDOX® Performance Additives for Architectural Coatings

What Is LUDOX® Colloidal Silica? 

LUDOX® colloidal silica is an aqueous dispersion of amorphous silica nanoparticles with a high surface area and reactivity as a binder and surface modifier in coating formulations. Adding a small amount of LUDOX®, typically around 5% solids by weight, to latex paint formulations drastically improves the adhesion, abrasion resistance, antiblocking, and antisoiling properties of the resulting film, which is formed by drying and coagulating LUDOX® through a special form of a sol–gel reaction. The benefits of using LUDOX® colloidal silica in water-based coatings are explained further in the sections below. 
 

Antisoiling 

Films formed by latex paints are highly susceptible to soiling and staining due to the combination of heat and humidity in the environment, which can soften the film. When this happens, dirt adheres more easily and becomes harder to clean. LUDOX® increases the hardness of coatings by forming bonds with the functional groups of latex polymers, essentially functioning as a cross-linker. LUDOX® also helps fill the small voids in latex paint films, preventing soil from being deposited and promoting antisoiling properties. These functions enable LUDOX® to impart paints with the highest classification for dirt-pickup resistance, according to UNI 10792. Also, when paints and coatings using light-colored pigments meant for reflectance become soiled, their ability to reflect light diminishes. Thus, using LUDOX® to keep these paints soil free also provides economic benefits by helping keep surfaces cooler. 
 

Below are dirt-pickup-resistance data generated from UNI 10792 tests using pure acrylic and styrene acrylic emulsion systems. LUDOX® HS-30 and LUDOX® AM were used to examine the change in the lightness of painted surfaces when exposed to dirt. As the results indicate, adding LUDOX® improves dirt-pickup resistance for both systems, with marked improvements shown in pure acrylic systems. 

Abrasion and Scrub Resistance 

The ability of LUDOX® to cross-link functional groups of organic polymers leads to films with a higher density that are more resistant to abrasion and hold up better to scrubbing. This is especially helpful for formulating paints designed for easy cleaning, where wet scrub resistance is highly valuable. As LUDOX® colloidal silica particles remain an integral part of latex films and increase the overall hardness of the film, they also contribute to formulating coatings with a longer service life. 

 

Adhesion 

LUDOX® colloidal silica improves the chemical bonding of water-based coatings to substrates, promoting better adhesion. The silanol functional groups on the surface of the LUDOX® colloidal silica particles are highly reactive with other functional groups that form bonds between formulation components, such as latex polymers and organic pigments, and functional groups on the substrate. Incorporating LUDOX® into latex films also reduces shrinkage upon drying, which can lead to early adhesion failure. 
 

Antiblocking 

Surfaces coated with latex paints have a high degree of tack and a tendency to stick when brought into contact with another surface. In the coating industry, this phenomenon is referred to as blocking. LUDOX® colloidal silica remains as discrete particles within latex films and adds a degree of surface roughness to the film that prevents blocking. 
 

Water Vapor Permeability 

Noting that LUDOX® increases the durability of latex paints, it also increases water vapor permeability. This property is important for paints to provide the escape of moisture from wood substrates, allowing better preservation of the wood and preventing mold and mildew growth. 

 

How LUDOX® Functions in Water-Based Coatings 

The silanol groups on the surface of the silica particles orient onto the surface of latex polymer spheres and become an integral part of the polymer matrix upon coalescence. After additional drying of the matrix, the silica particles concentrate to the point where they begin to cross-link with themselves, organic pigments, and latex paint polymers, resulting in a highly durable film through a special form of a sol–gel reaction. This mechanism is outlined in the diagram below.

LUDOX® Colloidal Silica for Latex Paints 

LUDOX® colloidal silica grades vary in particle size, concentration, surface charge, pH, and surface modification. In most latex paint applications, colloidal silica with an average particle size of 12 nm is recommended because it provides the optimal balance of reactivity and stability. In alkaline latex paint formulations, LUDOX® HS-30 and LUDOX® HS-40 are regularly used to increase the durability of the latex film. If the colloidal silica needs to be added to a formulation at a neutral or slightly acidic pH, LUDOX® AM is recommended, as it is designed for stability over a wider pH range than standard colloidal silica dispersions. In paint formulations where sodium is detrimental, an ammonium-stabilized grade, like LUDOX® AS-40 or LUDOX® AS-30, is recommended. The table below summarizes the common grades and conditions for latex paint. 

Summary & Conclusion

Durability is paramount in the water-based coatings market. Latex paints with a high degree of durability have a longer service life, require less maintenance, and can impart long-lasting protection to the substrate. LUDOX® colloidal silica is recommended as an additive for water-based architectural coatings because it provides the highest dirt-pickup-resistance classification in accordance with UNI 10792 while improving adhesion, abrasion resistance, and antiblocking. Click below to request a sample of LUDOX® today.