The dispersion process of aluminum-silver paste in coating systems is critical, with the primary objective being to achieve uniform and stable distribution of aluminum flakes while preserving their intact lamellar structure to obtain optimal metallic luster and brilliance. Key steps include: pre-dispersion (wetting). Never directly add aluminum-silver paste to resins or powders, as this may lead to agglomeration and hinder dispersion.
Pre-dispersal (wetting)
Do not directly pour the aluminum silver paste into the resin or powder. This will cause the paste to easily clump and be difficult to disperse.
The aluminum silver paste should be pre-soaked and wetted with some of the solvents in the formula or a dedicated dispersant. It is recommended to use a ratio of aluminum silver paste to solvent of approximately 1:1, and stir at a low speed to form a uniform paste.
Select the appropriate dispersion medium and tools
Solvent selection: Use the solvent specified in the formula and compatible with the system for pre-dispersion. Avoid using strong polar solvents (such as alcohols, water) or highly acidic solvents to prevent the aluminum sheet from being corroded or oxidized.
Mixing tools: Must use low-speed, low-shear force mixing equipment, such as anchor, sawtooth or frame-type stirrers. Strictly prohibit the use of high-speed dispersing discs, sand mills or ball mills, as these high-shear devices will cut or curl the aluminum flakes, resulting in a decrease in gloss, blackening, and reduced covering power.
Low-speed stirring and dispersion
After pre-wetting the aluminum silver paste slurry, slowly add it to the diluted resin solution (base material) under low-speed stirring (usually 300-600 revolutions per minute).
This process aims to allow the aluminum sheets to be uniformly coated with the resin solution and gradually dispersed. The duration should not be too long, typically 10-20 minutes, and it should be judged by the uniformity of the system without any particles.
Subsequent blending
After the aluminum silver paste is uniformly dispersed, the remaining resins, additives, solvents, etc. in the formula are added successively under low-speed stirring, and the viscosity is adjusted to the desired level.
All subsequent additions should be carried out under low shear conditions.
Key Considerations
“Slow First, Then Adjust” Principle: Always follow the sequence of “first slowly disperse the aluminum silver paste, then adjust the entire system”.
Control the Acid Value: Ensure that the acid value of the entire coating system is kept at a low level (typically recommended <7) to prevent the aluminum from undergoing acidic corrosion and turning black or producing gas.
Avoid Overmixing: Just ensure uniform dispersion; prolonged mixing will increase the risk of aluminum damage.
Conclusion
Adhering to the above gentle and low-shear dispersion process is the foundation for ensuring that the aluminum silver paste can achieve its optimal metallic effect and maintain stable color.
