Airfloat clay

Airfloat clay, the type most used in rubber compounds, is dry-ground hydrous kaolin that has been air-separated to reduce impurities and control particle-size distribution. However, some water-washed clay (slurried in water and centrifuged or hydrocycloned to remove impurities) is used, because it contains a lower level of impurities and gives compounds that are more colorable. The water-washed clay also causes less die wear during extrusion. 

Ultrafine airfloated clay is used to a limited extent as a pulp mill piteh control agent. The clay has a very high surface area that adsorbs piteh in a manner similar to talc. 

The United States is the leading supplier of kaolin cl, with about 40% of world production. Second largest is the United Kingdom with about 12%. US annual production capacity of 10 million metric tons is comprised of 40% water-washed, 15% airfloated, 13% calcined, and 10% delaminated clay. The major worldwide use for kaolin is in paper. In the US 40% of kaolin consumption is for coating and filling paper. Much lower but still substantial... 

Paper fillers - High-brightness, low-abrasion airfloated, water-washed and delaminated kaolins are used as pulp extenders in acid-sized paper, where they improve opacity, smoothness and ink receptivity. Partially calcined clay is used as a Ti02 extender. 

Ceramics - Whitewares use a combination of china clay (usually airfloat) and ball clay selected for consistent chemical composition so that firing and vitrifying characteristics of the body are controlled and color and translucency of the fired ware are satisfactory. The ratios used are chosen to optimize green strength, plasticity, and casting behavior. 

Rubber - About 80% of the kaolin for rubber is airfloated hard clay. Water-washed and delaminated clays are used for further improved color, physical propeties, and abrasion resistance. Calcined and smface-treated clays are used for improved electrical properties and ease of extrusion. 

Adhesives and sealants - Kaolin is used to control flow, penetration, and specific adhesion on application, and adhesive strength, tear strength, tensile strength, and elongation after cure. For aqueous systems the choice of airfloated vs. water-washed clay is dictated by cost, color, abrasion, and rheological properties pre-cure and reinforcing properties post-cure. Stearate-coated clays are used for improved compatibility in nonaqueous systems. 

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