The Effect of Colloidal Silicas on Water-Based Clear Coatings

Given the global warming we are experiencing today, colloidal silica usage is becoming more widespread due to its positive effects on the environment and the coatings industry. In the past, many studies have been conducted on the use of silica nanoparticles in resin-based systems. However, there is little research on the use of silane-modified water-based colloidal silica in water-based coating formulations. Nouryon is a manufacturer that produces these products, conducts the necessary technical work, and is active in 80 countries. Thanks to technical professionals like Dr. Peter Greenwood who have worked at this company for many years, the number of similar studies has increased and many positive effects of the products have been investigated. Nouryon has investigated the effects of silane-modified colloidal silicas on improved working time, block resistance, sanding, and mechanical properties of clear water-based systems. The impact of longer/improved working time and lower resin usage rates on VOC levels has been evaluated with various data. Nouryon has developed Levasil CC 301 for silane-modified colloidal silica.  

What is Colloidal Silica?

Very small amorphous silicon dioxide (SiO2) particles dispersed in water. It is safe for both the environment and humans. Due to the large number of very small particles, it has a wide surface area. Since these particles are electrically charged, they interact easily with other particles and substances. [4] The properties of colloidal silicas can be modified in many ways: Concentration: 7–50% silicon dioxide, Particle size distribution, Structure: Discrete particles (High S value) or chains (Low S value), Particle diameter: 2–100 nm, Surface area: 30–1,100 m² / g, pH: 2–12, Modifications: ammonium, aluminate, chloride, silane, deionized.  

Silane Modification

Epoxy-silane modified colloidal silica are extremely stable aqueous colloidal silica dispersions. The epoxy functional group is bonded to the particle surface with a tight (strong) covalent bond. The epoxy functional group opens and is transferred to a diol group. No aggregation occurs (the entire particle surface can work efficiently in a coating). [3]  

Levasil CC 301

A neutral aqueous colloidal silica dispersion with approximately 28% solids. Amorphous silica particles carry a negative surface charge. The SiO2 particles are discrete, flat spherical in shape. It has a narrow particle size distribution. The particles are modified with epoxy silane. For 2K systems, the "Hydroxy value" is 0.45 mole OH / kg. Its physical properties are a clear liquid dispersion more viscous than water. [2]  

Water-Based Coating Formulations Without Levasil CC 301 Addition

Different varnish formulations were examined. Clear substrate coatings formulated on 1K or 2K acrylic formulations containing resin, modified colloidal silica, and film formers and additives. [caption id="attachment_142678" align="aligncenter"] Table 1: Clear wood coating - 1K acrylic formulation[1][/caption][caption id="attachment_142679" align="aligncenter"] Table 1: Clear wood coating - 1K acrylic formulation[1][/caption][caption id="attachment_142680" align="aligncenter"] Table 2: Formulation 8 2K acrylic / industrial water-based varnish and topcoat, Formulation 9 2K
acrylic / industrial water-based high-gloss varnish and topcoat [1][/caption] 

Gloss & Haze

The gloss of aluminum sheets was measured at 20°C after drying for 30 days at ambient temperature. Dry film thickness 40–50 μm. The haze index, defined as gloss difference, was calculated from gloss measurements at 20°C and 60°C following ASTM D 4039. [1] Results are given in Table 4 and Table 5. After silica addition, there is little or no change in gloss. [1] [caption id="attachment_142681" align="aligncenter"] Table 3: Gloss 20°C [1][/caption][caption id="attachment_142682" align="aligncenter"] Table 4: Haze Index (Gloss 60°C–Gloss 20°C ) [1][/caption] 

Block Resistance

Block resistance of different systems was evaluated according to ASTM D 4946. Block resistance is defined as a coating's ability to resist adhesion to another surface. The coating was applied as two coats on oak and left to dry at room temperature for 24 hours. Dry film thickness is 65–70 μm. Wood-coated pieces were placed face to face at 60°C with a weight of 1 kg (127 g / cm²) for 30 minutes. A ranking was created based on the force to be applied to the system, as the wood did not peel. The addition of silane-modified colloidal silica to the water-based systems studied is beneficial for block resistance. [1] [caption id="attachment_142683" align="aligncenter"] Table 5 : Block resistance 1K acrylic clear formulations [1] Rating: 0=very poor, 5=best[/caption]    Eliz Türkileri Chemical Engineer Senior Technical Sales Manager Ravago Chemicals Turkey     Dr. Peter Greenwood Doctor of Chemistry Technical Development Manager Nouryon Inorganic Specialties | Technology Solutions       References : [1] P. Greenwood, "Impacts of Silane Modified Colloidal silica on Waterborne Clear formulations", 2018 [2] Nouryon Product Information, Levasil CC 301 [3] P. Greenwood, "Modified colloidal silica for enhancement of open time and dirt pick up resistance", December 1, 2018 [4] Nouryon, "Natural part of everyday life"