Alcan International Limited

Stephen C Brown

Herbert F Askew

Natalie G Mead

Frederick H Taylor

Improved fire retardant fillers for plastics materials are described which consist of magnesium hydroxide particles of reduced average surface area. The particles are produced by contacting particles of magnesium hydroxide of a relatively high average surface area with an etching solution for a time sufficient to dissolve at least some of the particles and to leave particles of reduced average surface area.

Treatment of magnesium hydroxide and its use as plastics filler

Alumina hydrate particles have a high surface area and low dispersity and may have a low soluble soda content. They may be made by milling a liquid suspension of alumina hydrate, subjecting the milled suspension to classification into coarse and fine fractions, recycling the coarse fraction to the mill and recycling the fine fraction to the classification stage. A narrow particle size distribution is obtained.

Alumina hydrates

A method of reducing the particle size of solid particles is applicable to the production of very fine particles of a wide variety of solids, including alumina hydrate, and comprises milling a liquid suspension of solid particles in an agitated media mill, pumping the milled suspension through a particle size classification device to separate the slurry into a coarse fraction and a fine fraction, the particles of the coarse fraction having a greater median particle size than the particles of the fine fraction, recycling the coarse fraction from the particle size classification device to the input of the mill, and recycling the fine fraction by pumping it to the classification device, wherein recycling of both coarse and fine fractions are continued until solid particles of the desired reduced particle size are produced. Preferably a single classification device and a single mill can be used, and particles having a median particle size of 0.3 microns or less and a relatively narrow paricle size distribution can be produced, even using a hydrocyclone as the classification device.

Method of producing fine particles

A method of reducing the particle size of solid particles is applicable to the production of very fine particles of a wide variety of solids, including alumina hydrate, and comprises milling a liquid suspension of solid particles in an agitated media mill, pumping the milled suspension through a particle size classification device to separate the slurry into a coarse fraction and a fine fraction, the particles of the coarse fraction having a greater median particle size than the particles of the fine fraction, recycling the coarse fraction from the particle size classification device to the input of the mill, and recyling the fine fraction by pumping it to the classification device, wherein recycling of both coarse and fine fractions are continued until solid particles of the desired reduced particle size are produced. Preferably a single classification device and a single mill can be used, and particles having a median particle size of 0.3 microns or less and a relatively narrow particle size distribution can be produced, even using a hydrocyclone as the classification device.

Growing community of inventors

Middlesex, United Kingdom

Stephen C Brown