In high-solids coatings, a balance between anti-sagging and thixotropic properties can be achieved by adjusting the type and amount of fumed silica added. The specific methods are as follows:

1. Selection of Hydrophilic vs. Hydrophobic Types
Hydrophilic Fumed Silica: Contains a large number of silanol groups on its surface, easily forming a three-dimensional network structure through hydrogen bonding, providing stronger thixotropic and anti-sagging effects. For example, in acrylic coatings, adding 1.8% hydrophilic HL-200 can achieve a 275μm thick coating without sagging.

Hyphobic Fumed Silica: Modified with organosilanes, it has stronger hydrophobicity and is suitable for oily systems or scenarios requiring reduced humidity sensitivity. Its thixotropic properties are slightly weaker than the hydrophilic type, but its dispersibility is better.

2. Optimization of Addition Amount
Anti-Sagging Requirements: The amount added must be sufficient to form a adequate three-dimensional network structure. Experiments show that the anti-sagging effect is optimal when the hydrophilic additive content reaches 1.8%.

Thixotropic balance: Excessive addition (e.g., >2.0%) may lead to excessive thickening or dispersion difficulties, requiring optimization through dispersion processes (e.g., high-speed shearing, kneading) and additives (e.g., dispersants).

3. Dispersion Process and Additive Support
Dispersion Equipment: Use a high-speed shearing machine for low-viscosity systems and a kneading machine or open mill for high-viscosity systems.

Dispersion Additives: Reduce surface tension, promote wetting and form a double electric layer, prevent particle agglomeration, and improve storage stability.

4. Practical Application Recommendations
Testing Gradient: Start at 1.0% and increase in 0.2% increments, testing the thixotropy index (e.g., Thixotropy Index) and anti-sagging properties.

System Compatibility: Hydrophilic additives are preferred for aqueous systems; hydrophobic additives can be considered for oily systems.

By selecting the right type, controlling the precise amount, and optimizing the process, the anti-sagging and thixotropic properties can be effectively balanced to meet the application and performance requirements of high-solids coatings.