Anhydrous kaolin clay pigment and method of preparation

Claim 1

An anhydrous white kaolin clay pigment having high light scattering when incorporated as a filler in paper, said pigment consisting of porous aggregates formed from sub-micron sized kaolin clay platelets obtained by classification of a dispersed kaolin clay to a 100% less than one micron ESD fraction, said aggregates having an average specific gravity in the range of 0.5 to 0.6 and a mean internal pore size of less than 0.55 microns; the size distribution of said aggregates being such that not more than 5% by weight thereof are greater than 10 microns ESD, at least 75% are of less than 2 microns ESD, and not more than 15% by weight are of less than 1 micron ESD; said pigment having a Valley abrasion value below 30 mg, and a GE brightness of at least 93.

Claim 5

A method for producing an anhydrous high-brightness white kaolin clay pigment having enhanced light-scattering properties when incorporated as a filler in paper; said method comprising: blunging and dispersing a crude kaolin clay, to form an aqueous dispersion of same; said crude clay including a total of not more than 0.5% by weight of glass-forming metal oxides, and not more than 1.5% by weight of iron, expressed as Fe 2 O 3 , nor more than 2% by weight of titanium, expressed as TiO 2 ; subjecting said aqueous clay dispersion to a particle size separation, and recovering from said separation a slurry of said clay, wherein 100% by weight of the particles are of less than 1 micron ESD; drying said slurry to produce a moisture-free clay; milling said clay to break up agglomerates; calcining the milled clay product by heating same to a temperature of at least 900° C., and under conditions such that substantially none of said clay is heated to a temperature in excess of 1100° C.; and cooling the product of said calcination step and milling same to provide a pigment consisting of porous high light-scattering aggregates of kaolin clay platelets, said aggregates having an average specific gravity in the range of 0.5 to 0.6 and a mean internal pore size of less than 0.55 microns; the size distribution of said aggregates being such that not more than 5% by weight thereof are greater than 10 microns ESD, at least 75% are of less than 2 microns ESD, and not more than 15% by weight are of less than 1 micron ESD; said pigment having a Valley abrasion value below 30 mg, and a GE brightness of at least 93.

Claim 6

A method for producing an anhydrous high-brightness white kaolin clay pigment having enhanced light-scattering properties when incorporated as a filler in paper; said method comprising: blunging and dispersing a crude kaolin clay, to form an aqueous dispersion of same; said crude clay including a total of not more than 0.5% by weight of glass-forming metal oxides, and not more than 1.5% by weight of iron, expressed as Fe 2 O 3 , nor more than 2% by weight of titanium, expressed as TiO 2 ; subjecting said aqueous clay dispersion to a particle size separation, and recovering from said separation a slurry of said clay, wherein 100% by weight of the particles are of less than 1 micron ESD; drying said slurry to produce a moisture-free clay; milling said clay to break up agglomerates; calcining the milled clay product by heating same to a temperature of at least 900° C., and under conditions such that substantially none of said clay is heated to a temperature in excess of 1100° C.; and cooling the product of said calcination step and milling same to provide a pigment consisting of porous high light-scattering aggregates of kaolin clay platelets, said aggregates having an average specific gravity in the range of 0.5 to 0.6 and a mean internal pore size of less than 0.55 microns; the size distribution of said aggregates being such that not more than 5% by weight thereof are greater than 10 microns ESD, at least 75% are of less than 2 microns ESD, and not more than 15% by weight are of less than 1 micron ESD; said pigment having a Valley abrasion value below 30 mg, and a GE brightness of at least 93.