Coating kaolin powder refers to covering the surface of ultrafine kaolin flakes with organic chemical modifiers (silane, titanate, aluminate coupling agents, stearic acid, etc.) through a dedicated surface coating machine integrated into the grinding circuit. The core goal is to change kaolin’s inherent hydrophilic inorganic surface properties to lipophilic, and optimize its processing performance and functional value for different downstream industries. The detailed purposes are sorted below:
1. Improve compatibility with organic polymer substrates
Raw kaolin has abundant polar hydroxyl (-OH) groups on its surface, making it hydrophilic. It cannot blend evenly with non-polar plastics, rubber, coatings and adhesives, and severe agglomeration occurs during mixing.
After coating, the modifier molecules chemically lock onto kaolin’s hydroxyl sites, forming an outer organic molecular layer that matches the polarity of resins (PP, PE, PVC, ABS, acrylic). Kaolin distributes uniformly without hard clusters inside organic systems.
2. Boost mechanical properties of plastic and rubber products
Uncoated kaolin forms loose physical gaps at the filler-resin interface. External stress easily creates cracks along these gaps and reduces product toughness.
The coated organic layer creates strong chemical bridging between kaolin flakes and polymer chains. The stacked lamellar kaolin builds a stable internal network, significantly lifting tensile strength, flexural modulus, impact resistance, wear resistance and dimensional stability of molded plastic and rubber parts. It also lowers molding shrinkage and warpage.
3. Cut oil absorption and increase maximum filling dosage
Unmodified kaolin absorbs large volumes of resin melt, limiting filling ratios to low levels and raising raw material costs.
The smooth organic coating reduces voids between stacked kaolin flakes and greatly lowers oil absorption. Factories can raise kaolin filling proportion from 10% up to 30%–50% without sacrificing product quality, replacing expensive virgin resin and slashing production costs.
4. Optimize melt fluidity for easier plastic processing
Agglomerated bare kaolin increases melt viscosity during extrusion and injection molding, raising screw torque, power consumption and equipment wear.
Coated kaolin acts as an internal lubricant in plastic melts, reducing friction between particles and resin. It speeds up extrusion output, lowers equipment load, and eliminates molding defects such as flow lines, fish eyes and uneven discharge.
5. Eliminate moisture absorption and molding bubble defects
Exposed hydroxyl groups on raw kaolin easily absorb moisture from the air. At high molding temperatures, adsorbed water vaporizes to form internal bubbles, pinholes and surface blisters on finished plastic products.
Surface coating seals active hydroxyl groups, drastically reducing hygroscopicity of kaolin powder and improving the yield rate of injection and extrusion products.
6. Enhance barrier, heat and anti-aging performance
Lamellar kaolin naturally blocks water vapor, oxygen and UV rays, but poor interface bonding weakens this effect.
Coated kaolin tightly combines with resin to form a dense layered barrier structure. It improves heat distortion temperature, slows thermal decomposition and UV oxidation, extending the service life of outdoor plastic profiles, pipes and electrical insulating components.
7. Achieve smooth, high-gloss finished product surfaces
Uncoated kaolin agglomerates form tiny bumps on plastic, paint and masterbatch surfaces, resulting in rough matte texture and uneven gloss.
Fully dispersed coated ultrafine kaolin fills micro-pits in substrates to form flat, silky surfaces with uniform gloss, meeting requirements for high-grade plastic sheets, household appliances and decorative coatings.
8. Optimize performance in coatings, masterbatch and rubber
- Coatings: Coated kaolin improves pigment dispersion, reduces sagging, and enhances scratch resistance and weather resistance of architectural and industrial paints.
- Color masterbatch: It avoids color floating and uneven tinting, improving hiding power and color consistency of colorants.
- Rubber: Promotes uniform mixing with rubber latex, enhances tensile and wear resistance of tires, hoses and sealing strips.
9. Expand high-end application markets for kaolin
Uncoated raw kaolin is only suitable for low-end ceramics and low-grade cheap fillers. Surface coating upgrades kaolin into high-value functional filler applicable to engineering plastics, cosmetic raw materials, lithium battery separators and high-gloss paper coatings, greatly raising the market selling price and competitiveness of kaolin powder.
The fundamental purpose of coating kaolin powder is to transform its hydrophilic inorganic surface into lipophilic organic surface. It solves the core drawbacks of unmodified kaolin: poor dispersion, weak interface bonding, high oil absorption and high moisture absorption, while upgrading mechanical strength, processing fluidity and functional barrier properties. Coated kaolin becomes a high-performance filler suitable for plastics, rubber, coatings and new energy materials.
