White corundum (white fused alumina) is a very important functional filler in super wear-resistant polyurethane coatings due to its extremely high hardness, excellent wear resistance, chemical inertness and high temperature resistance. The main purpose of its addition is to significantly improve the wear resistance of the coating.
The following are the key points of the application of white corundum in super wear-resistant polyurethane coatings:
Core purpose: Improve wear resistance
Mechanism: The Mohs hardness of white corundum is as high as 9 (second only to diamond and silicon carbide), which is much higher than most friction materials (such as gravel, metal, rubber, plastic, etc.). When the coating surface is subjected to friction or impact, these hard particles act as “armor”, bearing and dispersing external forces, effectively protecting the relatively soft polyurethane resin matrix from rapid wear or scratches.
Effect: Significantly improve the wear resistance of the coating (such as Taber wear test, falling sand wear test, etc. The results will be greatly improved), and extend the service life of the coating.
Other performance improvements:
Improve hardness: The addition of white corundum will increase the surface hardness and overall rigidity of the coating, making it more resistant to pressure and scratches.
Increase scratch resistance: Hard particles can effectively resist scratches from sharp objects.
Improve high temperature resistance: White corundum itself has an extremely high melting point (>2000°C), which can improve the stability and resistance to thermal softening of the coating in high temperature environments.
Certain anti-slip properties: The appropriate particle size and addition amount can increase the roughness of the coating surface at the micro level, providing a certain anti-slip effect (but pay attention to the particle size selection, too coarse may affect the appearance and cleaning).
Chemical stability: White corundum has excellent tolerance to most acids, alkalis and solvents, which helps to improve the overall chemical corrosion resistance of the coating.
Key factors for application:
Particle size selection:
Coarse particle size (such as 80 mesh-320 mesh): Mainly provides macro wear resistance and anti-slip properties, often used in extreme wear-resistant occasions such as heavy industrial floors, mining equipment, conveyor belts, etc. The coating surface will have obvious granularity and texture.
Fine particle size (such as 400 mesh-3000 mesh): Provides a more delicate surface and micro wear resistance. It is suitable for occasions that require high wear resistance but also require good surface smoothness and appearance, such as electronics factories, pharmaceutical factories, high-end garage floors, high-end wood paint topcoats, etc. Ultrafine powder (micron level) is used in places that pursue extreme surface smoothness but still require high wear resistance.
Mixed particle size: Sometimes different particle sizes are used to achieve a balance between performance and appearance.
Addition amount:
The addition amount directly affects the degree of wear resistance improvement. It usually accounts for 5% – 40% of the solid content in the formula, depending on:
The required wear resistance level (the higher the wear resistance requirement, the greater the addition amount).
Particle size (usually the addition amount of coarse particles can be higher).
Requirements for other properties of the coating (such as flexibility, gloss, leveling, cost).
The carrying capacity of the resin system for fillers.
Too high an addition amount may lead to a sharp increase in viscosity, poor leveling, decreased flexibility, easy cracking, increased cost and other problems, and the best balance needs to be found.
Dispersibility:
It is crucial! White corundum must be fully and evenly dispersed in the polyurethane resin matrix. Agglomerated particles will become weak points, reduce wear resistance, and may affect the appearance and mechanical properties of the coating.
It is necessary to select suitable high-shear dispersion equipment (such as high-speed disperser, sand mill, three-roller mill).
It is usually necessary to add efficient dispersants to help wet the white corundum particles, prevent agglomeration, and ensure stable dispersion.
Surface treatment:
In order to improve the compatibility of white corundum particles with organic polyurethane resin, enhance interfacial bonding, further improve dispersion stability and final wear resistance, white corundum is often surface treated.
Commonly used treatment agents include silane coupling agents (such as KH-550, KH-560) or titanate coupling agents. These coupling agents can form an organic film on the surface of white corundum, chemically bonded or physically entangled with the resin.
Matching with resin:
Select a polyurethane resin (usually a solvent-free or high-solid system) with good toughness, adhesion and filler-bearing capacity as the base material. The resin needs to be able to “wrap” and “bond” the hard particles firmly.
Ensure that the addition of white corundum does not excessively damage the inherent excellent properties of the resin (such as flexibility and impact resistance).
Typical application areas:
Ultra-high performance industrial flooring: factory workshops, warehouses, logistics centers, parking lots (especially heavy-load areas), maintenance workshops, etc.
Wear-resistant topcoat: For concrete, metal, and wood surfaces that require additional wear protection.
Sports venues: Such as tennis courts, basketball courts, and running tracks (surface layers or anti-slip layers).
Conveyor belts and roller lagging: Conveying systems that require extremely high wear resistance.
Mining equipment protection: Mine cars, chutes, vibrating screens, etc.
High-end wood paint: Such as high-end furniture, countertops, and musical instrument surfaces, providing scratch-resistant protection.
Summary:
White corundum is the core contributor to giving polyurethane coatings super wear resistance. By carefully selecting the particle size, controlling the addition amount, ensuring good dispersion (with dispersants and appropriate equipment), performing effective surface treatment, and combining it with a polyurethane resin system with matching performance, it is possible to produce ultra-wear-resistant protective coatings that meet the needs of various harsh working conditions. Its application significantly improves the service life and reliability of polyurethane coatings in heavy friction and high wear environments.