Titanium dioxide coating modification
The coating modification of titanium dioxide (titanium dioxide) is an important means to improve its performance (such as dispersibility, weather resistance, glossiness, chemical stability, etc.). Common coating modification methods mainly include three categories: inorganic coating, organic coating and composite coating. The following is a specific classification and brief introduction:
Inorganic coating modification
By coating a layer of inorganic oxides or salts on the surface of titanium dioxide particles, a physical barrier is formed to improve its chemical stability and optical properties.
1. Oxide coating
Principle: Use the hydrate of metal oxides (such as SiO₂, Al₂O₃, ZrO₂, etc.) to precipitate on the surface of titanium dioxide to form a uniform coating layer.
Process: Usually through liquid phase deposition method, metal salts (such as sodium silicate, aluminum sulfate) are added to the titanium dioxide slurry, and the pH value is adjusted to precipitate and coat the metal oxide hydrate.
2. Composite oxide coating
Principle: Coating two or more metal oxides (such as Al₂O₃-SiO₂, ZrO₂-SiO₂, etc.), combining the advantages of each component.
Features: Better overall performance, for example, Al₂O₃-SiO₂ coating can simultaneously improve dispersibility and weather resistance, suitable for high-demand automotive paints and coil coatings.
3. Salt coating
Principle: Use metal salts (such as phosphates, silicates, sulfates, etc.) to form a poorly soluble salt layer on the surface of titanium dioxide.
Organic coating modification
Through the reaction of organic compounds with the hydroxyl groups on the surface of titanium dioxide, an organic molecular layer is formed to improve its compatibility with organic media.
1. Coupling agent coating
Principle: Using the amphiphilic structure of coupling agent molecules (such as silanes, titanates, aluminates), one end is combined with the hydroxyl group on the surface of titanium dioxide, and the other end reacts with the organic matrix (such as resin, polymer).
Silane coupling agent: Improves the dispersibility of titanium dioxide in water-based systems, commonly used in water-based coatings and inks.
Titanate/aluminate coupling agent: Enhances compatibility in oily systems such as plastics and rubbers, and reduces agglomeration during processing.
2. Surfactant coating
Principle: Surfactants (such as fatty acids, sulfonates, quaternary ammonium salts, etc.) attach to the surface of titanium dioxide through physical adsorption or chemical reaction to form a charge layer or hydrophobic layer.
Function:
Anionic surfactants (such as stearic acid): Improve dispersibility in oily media, commonly used in plastics and rubber.
Cationic surfactants (such as dodecyltrimethylammonium chloride): Suitable for polar systems to improve stability.
3. Polymer coating
Principle: Graft polymers (such as acrylates, epoxy resins, siloxanes, etc.) on the surface of titanium dioxide through polymerization reactions.
Function:
Form a thick coating layer to further isolate chemical erosion and improve weather resistance and mechanical properties.
Improve compatibility with specific resins, suitable for high-performance composite materials and coatings.
4. Silicone coating
Principle: Use the low surface energy characteristics of polysiloxane (silicone oil, silicone resin, etc.) to coat titanium dioxide particles.
Function: Reduce surface tension, improve dispersibility and smoothness, commonly used in inks and cosmetics.
III. Composite coating modification
Combining the advantages of inorganic and organic coatings, double coating is carried out in stages or simultaneously to achieve complementary performance.
1. Inorganic first and then organic coating
2. Inorganic-organic synchronous coating
Other special coating technologies
1. Nano coating
2. Microcapsule coating
Principle: Encapsulate titanium dioxide particles in polymer microcapsules, release titanium dioxide by controlling the capsule rupture conditions (such as temperature, pH value), suitable for smart coatings and slow-release systems.