Application of Aluminum Silver Paste in Coatings Industry
ã€China Aluminum Industry Network】 1. Aluminum paste is used to disperse paint powders containing aluminum pigments, resulting in superior gloss, shimmer, brightness, opacity, tinting strength, flop effect, vividness, floatability, and more. For optimal performance, proper dispersion is essential. Here are some key tips to keep in mind during the process:
Tip: Aluminum flakes are delicate and can easily bend or break when subjected to high-speed stirring or intense mechanical processing. This can lead to coarse particles, dark spots, reduced hiding power, and even metal migration. Therefore, it's best to avoid high-shear dispersion methods.
Recommendation: A pre-dispersion method is advised. Begin by selecting an appropriate solvent or a blend of solvents. The ratio of aluminum slurry to solvent should be around 1:1 or 1:2. Add the solvent to the aluminum slurry and stir slowly for about 10–20 minutes until the mixture is smooth. It’s also recommended to add a wetting agent or dispersant to enhance the stability of the system.
2. Resin System: Many common coating bases, including oil-based varnishes, acrylics, alkyds, epoxies, polyurethanes, and waterborne systems, are compatible with both floating and non-leafing aluminum silver pigments. In general, most coating bases or solvents are suitable for aluminum silver pastes, as long as they don’t cause chemical damage. It's important to note that aluminum is an amphoteric metal, so the acid value of the paint should be kept below 7 to prevent unwanted reactions.
Solvent Selection: The choice of solvent depends on the paint formulation. Non-floating aluminum silver pastes work well with polar solvents like aliphatic or aromatic hydrocarbons, esters (e.g., butyl acetate), ketones (e.g., methyl ethyl ketone, methyl isobutyl ketone), and alcohols (e.g., ethanol). However, floating aluminum pastes require non-polar solvents, preferably those with high surface tension, such as petroleum ether, diphenyl, toluene, or high flash point naphtha, which help improve floatability. Water reacts with aluminum and produces hydrogen gas, leading to foaming and instability. Thus, the water content in the paint must be strictly controlled to less than 0.15%. Using a dehydrating agent like Bayer OF is recommended to remove excess moisture from the coating, solvent, or diluent. Water-based solvents are not suitable for use with any aluminum silver pigment.
Particle Size and Distribution: The size and distribution of aluminum silver pigment particles significantly affect color, opacity, flop effect, and gloss. As such, particle size distribution is a critical factor when choosing an aluminum paste. It's important to select a product with consistent and stable particle size characteristics. While particle size and distribution are important, they are not the only factors to consider. Even if two aluminum pastes have similar particle sizes, differences in surface treatment or flake shape can result in variations in color tone, hue, metallic appearance, whiteness, and flop effect. Therefore, it's crucial to evaluate the final application requirements and choose the most suitable aluminum-silver pigment accordingly.
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