Overview of Metal Dyes
Metal dye is a pigment made from ground particles or flakes of metal or alloys. It has a metallic luster. Metal dyes are widely used in the paint industry as decorative coatings. The global annual production reaches 70kt, extensively used in the paint industry. The main varieties of metal dyes are aluminum powder, copper powder, zinc powder, and stainless steel powder. Among them, aluminum powder is used in large quantities, copper powder is used less than aluminum powder, and its light reflection intensity is slightly inferior to that of aluminum powder. Aluminum powder, zinc powder, and stainless steel powder all have anti-corrosive properties, and aluminum powder has good decorative qualities. Let's learn about the overview of metal dyes!
Copper Powder
Metal dye is a glossy powder made from metallic copper or its alloys with zinc, tin, etc., ranging from gold to bronze colors. The coarse powder of the aforementioned metals is mixed with stearic acid or its esters, ground into bright micro-powder using a ball mill, and processed to produce gloss. Copper-zinc alloy powder can be made into red or green gold; copper-tin alloy powder can change from bronze to golden yellow. It is used in educational supplies, inks, paints, etc.
Zinc Powder
Metal dye is a pigment made from metallic zinc, appearing as blue-gray spherical particles. Zinc can be electroplated on iron surfaces to provide protection. After 1840, zinc powder began to be used in paints, leading to the development of zinc-rich primers with high anti-corrosive properties. The volume concentration of pigments in zinc-rich primers can reach 30% to 45%. Metallic zinc is heated and melted in a closed state, evaporating into zinc vapor, which rapidly condenses into spherical zinc particles.
The faster the condensation speed, the finer the particle size. The condensed zinc powder accumulates at the bottom of the equipment, and after collection, it is screened or air-classified to obtain products with uniform particle size. The oxygen content in the condenser needs to be strictly controlled to ensure product purity, keeping the zinc oxide content below 6%.
II. Introduction to Aluminum Pigments
Metal dye is a silver-white powder with metallic luster made from metallic aluminum. Under cooling conditions, aluminum powder is ground to about 40m in petroleum solvent, filtered, and mixed with an appropriate amount of wetting agent and solvent, adjusted to standard content (65), resulting in aluminum powder slurry. After grinding, filtering the solvent, and vacuum drying, dry aluminum powder can be prepared.
Dry powder can be floating or non-floating, mainly used in paint production, oil storage tanks, bridges, and also in paper, rubber, and inks. Aluminum powder can reflect sunlight, ultraviolet, and infrared rays, reducing the photodegradation of polymer compounds and extending their lifespan. Due to its low water vapor permeability, aluminum powder has good rust resistance.
III. Overview of Vacuum Metallized Pigments
Vacuum metallized pigments (VMPs) are produced using vacuum metallization technology, which differs significantly from traditional metal pigments in operational requirements, physical properties, and results, offering good development potential in applications.
Traditional Powder Pigments
The gloss of metal pigments in coatings relies on an important physical phenomenon—floating. Adding fatty acids during pigment grinding allows the surface tension of the pigment to suspend on the coating surface, giving the film a high-gloss metallic feel. The brightness of floating-type coating systems is easily affected by poor surface properties; the coating surface is sensitive to damage, and metal flakes exposed on the surface are easily oxidized and deteriorated by air, moisture, and grease. Additionally, metal flakes on the coating surface are prone to flaking due to external factors, resulting in poor inter-coating adhesion. On the other hand, non-floating coatings generally lack high-gloss reflection effects but excel in adhesion and tinting between coatings compared to floating types. In the automotive coating field, non-floating systems have become predominant.
The new generation of vacuum metallized pigments (VMPs) aims to achieve the gloss of floating-type pigments while addressing their poor inter-coating adhesion issues. In fact, the metallic luster, smoothness, and hiding power are superior to traditional metal pigments, producing a chrome-like metallic effect.
VMP Manufacturing Process
Metal is deposited on a continuous film of pre-coated release agent, and the film is separated using a solvent release method, then classified to the desired size and specifications. This process can produce metal pigments with smooth surfaces, particularly thin, small particles, and high brightness.
VMP Formulation Design
The brightness of VMP coatings depends on whether the aluminum flakes can be arranged flatly, simulating the smooth effect of aluminum plating. The required metal content for VMP coatings is relatively lower than that of traditional pigment coatings. Generally, the metallic brightness of the coating increases with the amount of pigment until it reaches a peak, where aluminum flakes form a flat and uniform single-layer arrangement in the coating.
After that, if the amount of VMP used increases, the submerged portion of the aluminum flakes will thicken, scattering the light, and the final brightness will decrease. Therefore, the key to preparing VMP coatings is to ensure that aluminum flakes are arranged in a single layer within the coating.
The above is an overview of metal dyes. If you would like to know more, feel free to contact us!
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