Kaolin clay

What is kaolin clay or china clay?
Kaolin clay is a dominant paper filler material which is derived from koalinite. It is also known as china clay, since the mineral primarily found in kao-ling, china. Another name of kaolin clay is white clay or light clay or heavy clay. The chemical formula of kaolin clay is hydrated aluminum silicate (Al₂O₃.2SiO₂.2H₂O). Hydrated aluminum silicate is also known as hydrous kaolin clay.

Hydrous kaolin clay is popular paper filler due to its low price, low abrasiveness, good availability and relatively white in color. Before 1990s it is most uses paper filler in Europe and the United States. The sources of kaolin clay are china, USA, Canada, Australia, UK, Brazil, Ukraine, Germany, Iran, Bulgaria, France, Korea, India and the Czech republic.

Calcined kaolin clay
Calcined kaolin clay is an anhydrous form of china clay and the chemical formulae is Al₂O₃.2SiO₂. It is produced by calcinations process heating hydrous kaolin clay at 1000°C. At the end of this process brightness and the light scattering coefficient is increased. Hence improve opacity. The opacity of calcined kaolin is better than GCC or PCC and less than titanium dioxide.

Uses benefits of kaolin clay
Kaolin clay provides smooth surface of the paper, improves opacity, gloss and printability. The particles of china clay provide the paper high density, as a result reduces the coating penetration into the paper. The light scattering coefficient is increased hence increase the opacity and brightness. Less wire abrasion therefore extends life time of the wire cloth in paper machine compare with the GCC and PCC. Improve dewatering.
Kaolin clay decreases the strength of paper and creates little foam.