Water-Washed Kaolin (Surface Treated)
Key Features
- Soft platelet morphology — gentle on processing equipment
- Surface-treated for improved compatibility with polar and non-polar resins
- Mild flatting agent to reduce surface gloss in gelcoat and topcoat
- Excellent electrical insulation properties for PCB and laminate applications
- Good barrier properties against moisture and chemical permeation
Water-washed kaolin is a refined aluminum silicate clay mineral (Al₂Si₂O₅(OH)₄) produced by hydraulic processing of primary kaolin ore to remove impurities, coarse particles, and iron-containing minerals, resulting in a bright white, fine-particle-size product. This surface-treated grade incorporates a compatible coupling agent to improve adhesion to polymer matrices and reduce moisture sensitivity.
Kaolin's hexagonal plate-like crystal structure provides gentle reinforcing and barrier properties in filled polymer systems. At typical loadings of 20–50 phr in UPR and epoxy systems, water-washed kaolin improves flexural modulus, reduces permeability to gases and liquids, and improves dimensional stability compared to unfilled resin. The soft, smooth particle surface is gentle on processing equipment and does not cause the abrasive wear associated with harder fillers such as wollastonite or quartz.
In gelcoat and topcoat formulations, surface-treated kaolin improves brushing and spraying characteristics, contributes to a smooth surface texture, and acts as a mild flatting agent to control surface gloss. The silane surface treatment on this grade improves compatibility with both polar (water) and non-polar (solvent-borne) resin systems, making it a versatile multi-matrix filler. Excellent electrical insulation properties make it suitable for laminating systems used in PCB and electrical insulation panels.
Specifications
| Parameter | Value |
|---|---|
| Appearance | White fine powder |
| Top cut (d98) | ≤ 15 µm |
| SiO₂ content | 44–46% |
| Brightness (GE) | ≥ 88% |
| BET surface area | 12–18 m²/g |
| Al₂O₃ content | 37–39% |
| Surface treatment | Silane coupling agent (0.5–1.0%) |
| Bulk density (tapped) | 0.4–0.7 g/cm³ |
| Loss on ignition (1000°C) | 13–14% |
| Median particle size (d50) | 2–4 µm |
Applications
FAQ
Water-washed kaolin retains its layered hydroxyl structure and soft, lubricating surface character (Mohs hardness ~2). This means it does not scratch processing equipment or mold surfaces and creates a smoother surface texture in cured composites. Calcined kaolin (Mohs ~6) is harder and provides better abrasion resistance in the cured part but can cause more wear on equipment during processing.
Direct Contact
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