Shiraishi Kogyo Kaisha, Ltd.

Kao Soap Company, Ltd.

Hiroji Shibazaki

Setsuji Edagawa

Hisashi Hasegawa

Satoshi Kondo

Noboru Moriyama

Takashi Takeuchi

Yoshinaga Okamoto

Yukihiro Fukuyama

Kazuo Ohnawa

The invention provides calcium carbonate particles comprising a core and projections formed thereon, and process for preparing same. The calcium carbonates of this invention are useful as fillers and pigments for rubbers, plastics, papers, etc. because of their peculiar configuration and unique properties.

Calcium carbonate particles and processes for preparing same

The filled paper is filled with at least one of (i) a calcium carbonate in the form of particles comprising a core about 0.5 to about 6.5 .mu.m in average diameter and about 100 to about 4000 projections formed on the surface of the core and having a length (L) of about 0.25 to about 2.00 .mu.m, a diameter (D) of about 0.08 to about 0.20 .mu.m and an aspect ratio (L/D) of about 3 to about 10, the calcium carbonate having a void volume of about 1.0 to about 1.8 ml/g and an oil absorption of about 45 to about 60 ml/100 g, and (ii) a calcium carbonate in the form of particles comprising a core about 0.2 to about 2.0 .mu.m in average diameter and about 100 to about 4000 projections formed on the surface of the core and having a length (L) of about 0.15 to about 4.00 .mu.m, a diameter (D) of about 0.05 to about 0.20 .mu.m and an aspect ratio (L/D) of about 3 to about 20, the calcium carbonate having a void volume of about 1.8 to about 3.3 ml/g and an oil absorption of about 50 to about 100 ml/100 g. The paper has increased stiffness and enhanced opacity with reduced weight.

Filled paper

A method for improving calcium carbonate by causing calcium carbonate particles to undergo contact reaction with an acid gas capable of reacting with calcium carbonate for finely uniformizing the calcium carbonate particle size and, at the same time, coating the surface of the calcium carbonate particles with the calcium salt of the acid of the acid gas.

Method for improving calcium carbonate

Calcium carbonate is dispersed by a dispersant comprising a salt of an acrylic acid/maleic acid copolymer.

Dispersant for calcium carbonate

Surface-treated calcium carbonate powders of this invention are easy to handle and highly dispersible in water, give slurries of high concentration and are useful as pigments and various other applications.

Calcium carbonate powders

Precipitated calcium carbonate of uniform particle size is produced by contacting a suspension of calcium hydroxide with a carbon dioxide-containing gas in three steps. The particle size of precipitated calcium carbonate can be optionally selected by suitably adjusting reaction conditions.

Process for preparing precipitated calcium carbonate

Cubic calcium carbonate crystals of uniform size are prepared by contacting with CO.sub.2 a starting aqueous suspension containing Ca(OH).sub.2 and cubic CaCO.sub.3 crystals less than 0.1.mu.m in size, adding Ca(OH).sub.2 to the suspension resulting from the first step and contacting the resultant mixture with CO.sub.2.

Growing community of inventors

Takarazuka, Japan

Hiroji Shibazaki