Water-Based Architectural Coatings

    The use of water-based coatings for interior and exterior architectural applications is popular due to ease of use and fast drying times compared to oil based paints.  In addition, latex paints typically have a mild odor and produce films that are highly flexible and resistant to cracking.
Water-based architectural coatings do have their fair share of drawbacks as well.  The high surface tension of the aqueous medium can lead to poor surface wetting and sub-optimal adhesion.  In addition, the films produced by latex paints are inherently soft and susceptible to abrasion, blocking, and soiling.

LUDOX® Performance Additives for Architectural Coatings

The addition of a small amount of LUDOX® colloidal silica, typically around 5% solids, to latex paint formulations drastically improves the adhesion of the paint and the properties of the resulting film formed during drying and coagulation of the coating.  The benefits of using LUDOX® colloidal silica in water-based coatings is further explained in the sections below.

Adhesion

LUDOX® colloidal silica improves the molecular interactions and increases attraction of water-based coatings with substrates.  The silanol functional groups on the surface of the silica particles are highly reactive with other functional groups and essentially work to "cross-link" the latex polymers and the substrate.  In addition, the incorporation of LUDOX® into latex films reduces shrinkage upon drying that can lead to early adhesion failure.

Abrasion / Scrub Resistance

The ability of LUDOX® to cross-link functional groups on organic polymers leads to films with a higher density that are more resistant to abrasion and hold up to scrubbing.  In addition, LUDOX® colloidal silica particles remain an integral part of latex films and increase the overall hardness of the film leading to a tougher coating with a longer service life.

Anti-Blocking

Surfaces coated with a latex paint have high degree of tack and a tendency to stick or "block" when brought into contact with another surface.  LUDOX® colloidal silica  remains discrete particles within latex films and adds a degree of "roughness" to the film and prevents blocking.

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 surface of the coating and easily remove dirt resulting in coatings that are easier to keep clean.

How LUDOX® Functions in Water-Based Coatings

The silanol groups on the surface of the silica particles orient on the surface of polymer speheres and upon coalescence, become an integral part of the polyer matrix.  Upon further drying of the matrix, the coloidal silica particles concentrate the point where they begin to cross-link with themselves and the polymers resulting in a highly durable film.  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.
    Grade
    SiO2
    Description
    LUDOX® HS-30
    30%
    General purpose grade for alkaline paint formulations
    LUDOX® HS-40
    40%
    General purpose grade for alkaline paint formulations
    LUDOX® AM
    30%
    Broad pH stability for use in acidic & neutral paint formulations
    LUDOX® AS-30
    30%
    Ammonium stabilized for use in paint formulations sensitive to sodium
    LUDOX® AS-40
    40%
    Ammonium stabilized for use in paint formulations sensitive to sodium

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.

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