1.What is the core principle of self-cleaning coating?
Super-Hydrophilic Mechanism
The coating surface is extremely hydrophilic (water contact angle <5°). Rainwater falling on the surface quickly spreads into a water film, carrying away contaminants such as dust and oil, achieving a "rainwater self-cleaning" effect.
Applications: Outdoor environments exposed to water (such as building exteriors and photovoltaic panel backsheets) that rely on natural precipitation for cleaning.
Super-Hydrophilic Mechanism: The coating surface mimics the lotus leaf effect (water contact angle >150°, rolling angle <10°). Water rolls off the surface in a spherical manner, carrying away attached dust and liquid stains while preventing oil from adhering (due to its extremely low surface energy).
Applications: Environments requiring high oil repellency (such as kitchen equipment and machinery casings) or low precipitation areas where water residue needs to be minimized.
Photocatalytic Assisted Mechanism: The coating incorporates a photocatalyst (such as titanium dioxide TiO₂) that, under ultraviolet light, produces a strong oxidizing agent that decomposes organic contaminants (such as oil and microorganisms). This enhances hydrophilicity (photoinduced super-hydrophilicity), allowing for further cleaning with rainwater. Applicable scenarios: Outdoor environments with light (such as building decorative panels and automobile exterior panels), especially suitable for removing organic stains.
2.What are the core components and characteristics of inorganic-organic composite coatings?
Core Ingredients:
Functional Phase:
Hydrophilic: Nano-silica (SiO₂), titanium dioxide (TiO₂ (also photocatalytic), zinc oxide (ZnO), etc., using nanoparticles to create hydrophilic/photocatalytic sites.
Hydrophobic: Fluorosilicone resin, modified silicone, or micro-nano roughening of the coating surface (such as adding nano-calcium carbonate or carbon nanotubes) to enhance hydrophobicity.
Film-forming Agents: Epoxy resin, polyurethane, acrylic resin, etc., used to fix the functional particles to the galvanized coil surface, ensuring coating adhesion and corrosion resistance.
Features:
Hydrophilic: Suitable for rainy regions due to its high precipitation dependence; hydrophobic: Enhanced stain resistance, but long-term exposure may reduce effectiveness due to dust accumulation, requiring regular light washing.
3.How does photocatalytic self-cleaning coating achieve self-cleaning?
Using titanium dioxide (TiO₂) as the core functional material, self-cleaning is achieved through the following processes:
Photocatalytic degradation: TiO₂ generates hydroxyl radicals (・OH) under UV irradiation, breaking down organic pollutants (such as oil, mold, and bacteria) into CO₂ and water.
Photoinduced superhydrophilicity: After exposure to light, the TiO₂ surface becomes more hydrophilic, accelerating the removal of residual inorganic matter (such as dust) by rainwater.
Optimization Directions: TiO₂ can be modified by doping with elements such as nitrogen and carbon to enable it to utilize visible light (rather than just UV), improving performance on cloudy days or indoors. ◦ Incorporating organic resins (such as silicone) can reduce TiO₂ degradation of the coating itself (preventing coating aging).
4.What is the coating preparation process?
Pretreatment
Cleaning the galvanized coil surface: Remove oil and oxide layers (via alkaline or electrolytic cleaning). If necessary, perform a phosphating or silane treatment to enhance coating adhesion.
Coating Application
Roller Coating (mainstream): The coating slurry (functional particles + resin + solvent) is evenly applied to the galvanized coil surface using a metering roller. This method is suitable for large-scale continuous production (line speeds can reach 100-300 m/min).
Spray/Dip Coating: Suitable for small batches or special-shaped parts. While coating thickness control is somewhat limited, it can cover complex surfaces.
Film Curing
High-temperature baking (120-200°C): Crosslinks and cures the resin, stably attaching the nanoparticles to the surface and forming a dense coating (typically 5-20 μm thick; excessive thickness may affect flexibility).
UV Curing: For coatings containing photosensitive resins, UV irradiation is used for rapid curing, making it suitable for applications requiring high production efficiency.
5.What are the performance requirements and application scenarios?
Key Performance Indicators
Self-cleaning Efficiency: Passes the "Oil Residue Test" (e.g., after applying motor oil, residual residue <5% after being washed off with simulated rain).
Durability: Coating adhesion (cross-cut test ≥5B), salt spray resistance (≥1000 hours without rust), and weather resistance (QUV weathering test ≥1000 hours without chalking or flaking).
Mechanical Properties: Scratch resistance (pencil hardness ≥2H), preventing damage during processing or installation.
Typical Applications
Building exterior wall panels: Use a super-hydrophilic coating, relying on rainwater for cleaning, reducing manual maintenance.
Photovoltaic module backsheets: A photocatalytic + super-hydrophilic composite coating simultaneously degrades bird droppings and dust while ensuring light transmittance.
Home appliance panels: A super-hydrophobic coating resists fingerprints and oil stains, allowing for daily cleaning with a simple wipe.