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, films produced by latex paints are inherently soft and susceptible to abrasion, blocking, and soiling.  To help remedy these drawbacks, a specific additive is recommended for latex paint compositions.

LUDOX® Performance Additives for Architectural Coatings

LUDOX® colloidal silica is an aqueous dispersion of silica nanoparticles.  Adding a small amount of LUDOX®, typically around 5% solids, to latex paint formulations drastically improves the adhesion, abrasion resistance, antiblocking, and antisoiling properties of the resulting film, which is formed after drying and coagulation 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.

Anti-Soiling

Films formed by latex paints are highly susceptible to soiling and staining due to their hydrophobic nature.  When LUDOX® is incorporated into latex films, the silanol groups on the surface of the silica particles allow for water to form a film on the coating’s surface.  This allows dirt to be easily removed, resulting in coatings that are easier to keep clean. LUDOX® also helps to fill the small voids present in latex paint films, preventing soil from being deposited and promoting anti-soiling properties. These functions enable LUDOX® to impart paints with the highest classification for dirt-pickup resistance according to UNI 10792.

Abrasion / 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 web scrub resistance is highly valuable. In addition, LUDOX® colloidal silica particles remain an integral part of latex films and increase the overall hardness of the film, resulting in a tougher coating with a longer service life.

Adhesion

LUDOX® colloidal silica improves the molecular attraction 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 essentially work to "cross-link" formulation components, such as latex polymers and organic pigments, with the substrate.  Incorporation of LUDOX® into latex films also reduces shrinkage upon drying, which can lead to early adhesion failure.

Anti-Blocking

Surfaces coated with latex paint have a high degree of tack and a tendency to stick or "block" when brought into contact with another surface.  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 escape of moisture of 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 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 a colloidal silica with an average particle size of 12nm is recommended and 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 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 to 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 summarized the common grades used in latex paint and when each should be utilized.

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 provide long lasting protection to the substrate.  LUDOX® colloidal silica is recommended as an additive for water-based architectural coatings to improve adhesion, abrasion resistance, anti- blocking, and anti-soiling properties.