Titanium dioxide powder coating modification
Surface modification of titanium dioxide powder (titanium white) is an important method to enhance its performance (such as dispersibility, weather resistance, gloss, and chemical stability). Common surface modification techniques can be broadly categorized into three types: inorganic coating, organic coating, and composite coating. The following is a detailed classification and brief introduction of these methods:
Inorganic Coating Modification
This method involves coating the surface of titanium dioxide particles with a layer of inorganic oxides or salts, forming a physical barrier to improve its chemical stability and optical properties.
1. Oxide Coating
Principle: Metal oxide hydrates (such as SiO₂, Al₂O₃, ZrO₂ etc.) are precipitated onto the surface of titanium dioxide particles, forming a uniform coating layer.
Process: Typically, a liquid phase deposition method is used, where metal salts (such as sodium silicate, aluminum sulfate) are added to the titanium dioxide slurry, and the pH is adjusted to precipitate the metal oxide hydrates onto the surface.
2. Composite Oxide Coating
Principle: Coating with two or more metal oxides (such as Al₂O₃-SiO₂, ZrO₂-SiO₂ etc.), combining the advantages of each component.
Features: Superior overall performance; for example, Al₂O₃-SiO₂ coating can simultaneously improve dispersibility and weather resistance, suitable for demanding automotive coatings and coil coatings.
3. Salt Coating
Principle: Using metal salts (such as phosphates, silicates, sulfates, etc.) to form an insoluble salt layer on the surface of titanium dioxide particles.
Organic Coating Modification
This method involves reacting organic compounds with the hydroxyl groups on the surface of titanium dioxide, forming an organic molecular layer to improve its compatibility with organic media. 1. Coupling Agent Coating
Principle: Utilizing the amphiphilic structure of coupling agents (such as silanes, titanates, and aluminates), one end binds to the hydroxyl groups on the titanium dioxide surface, while the other end reacts with the organic matrix (e.g., resin, polymer).
Functions:
Silane coupling agents: Improve the dispersibility of titanium dioxide in aqueous systems, commonly used in water-based coatings and inks.
Titanate/aluminate coupling agents: Enhance compatibility in oily systems such as plastics and rubber, reducing agglomeration during processing.
2. Surfactant Coating
Principle: Surfactants (such as fatty acids, sulfonates, and quaternary ammonium salts) adhere to the titanium dioxide surface through physical adsorption or chemical reaction, forming a charge layer or hydrophobic layer.
3. Polymer Coating
Principle: Grafting polymers (such as acrylates, epoxy resins, and siloxanes) onto the titanium dioxide surface through polymerization reactions.
Functions:
Form a thick coating layer, further protecting against chemical attack and improving weather resistance and mechanical properties.
Enhance compatibility with specific resins, suitable for high-performance composites and coatings.
4. Organosilicon Coating
Principle: Utilizing the low surface energy of polysiloxanes (silicone oil, silicone resin, etc.) to coat titanium dioxide particles.
Functions: Reduce surface tension, improve dispersibility and lubricity, commonly used in inks and cosmetics.
Composite Coating Modification
Combining the advantages of inorganic and organic coatings, a dual coating process (sequential or simultaneous) achieves complementary performance.
1. Inorganic-Organic Sequential Coating
Process: First, form a physical barrier with inorganic oxides (e.g., SiO₂), then perform organic modification with coupling agents or polymers.
Features: Balances weather resistance and compatibility, suitable for high-performance architectural coatings or automotive OEM paints. 2. Inorganic-Organic Simultaneous Coating
Process: Inorganic and organic coating agents are introduced simultaneously into the same reaction system to form a core-shell structure.
Features: The coating layer exhibits stronger adhesion and significantly improved performance, suitable for high-end applications (e.g., aerospace coatings, nanocomposites).
Other Special Coating Technologies
1. Nanoparticle Coating
Principle: Using nanoparticles (e.g., nano-SiO₂, nano-ZnO) for coating enhances UV protection and transparency, commonly used in sunscreen cosmetics and optical coatings.
2. Microencapsulation
Principle: Encapsulating titanium dioxide particles in polymeric microcapsules, releasing the titanium dioxide by controlling the capsule rupture conditions (e.g., temperature, pH), suitable for smart coatings and controlled-release systems.
The selection of different coating methods depends on the application (e.g., coatings, plastics, inks, cosmetics) and performance requirements (weather resistance, dispersibility, compatibility, etc.).