Abstract: The light calcium carbonate in the form of microparticle aggregate of the present invention has a BET specific surface area not smaller than 10 m2/g and not larger than 25 m2/g, a pore volume of 0.05 cm3/g or larger for pores having a pore diameter of 0 to 1000 ? as determined by the nitrogen adsorption method, and a pore volume ratio of 25% or more for pores having a pore diameter of 250 ? or smaller based on the total pore volume as determined by the nitrogen adsorption method, and shows an oil absorption of 100 cc/100 g or more as determined by using liquid paraffin. By using this light calcium carbonate as a filler of printing paper, superior ink absorbing property and opacity (especially opacity after printing) can be imparted to the printing paper.

Abstract: Carbon dioxide containing gas is blown into a calcium hydroxide slurry having a calcium hydroxide concentration of 100 to 400 g/L obtained by wet slaking calcined lime with 4 N hydrochloric acid activity (value at 3 minutes) of 150 to 400 mL to allow them to react until the carbonation rate becomes 50 to 85%, then 1 to 20% by volume of the calcium hydroxide slurry is added, and carbon dioxide containing gas is further blown in to terminate the reaction. The calcium carbonate obtained by this method is precipitated calcium carbonate aggregates having a secondary particle diameter of 1 to 10 ?m and consisting of primary particles having a long diameter of 0.5 to 3.0 ?m, a short diameter of 0.1 to 1.0 ?m and an aspect ratio of 3 or more, has superior characteristics due to a BET specific surface area in the range of 8 to 20 m2/g and a pore volume in the range of 1.5 to 3.5 cm3/g, can be uniformly dispersed in pulp fiber, and thereby can be used to manufacture high bulk paper.

Abstract: When spherical calcium carbonate is produced by blowing a carbon dioxide gas or a carbon dioxide-containing gas into an aqueous suspension containing calcium hydroxide to react them, after start of the reaction, an aqueous solution or suspension of a water-soluble phosphoric acid compound or a water-soluble salt thereof is added to the reaction mixture when carbonation ratio reaches 2 to 10%, and the reaction is further allowed to continue at a low gas blowing rate of 1.0 NL/minute or lower (step (a)). Subsequently, an aqueous suspension containing calcium hydroxide and an aqueous solution or suspension of a water-soluble phosphoric acid compound or a water-soluble salt thereof are added to the reaction mixture, and a carbon dioxide gas or a carbon dioxide-containing gas is introduced to allow to react and thereby produce spherical calcium carbonate having a mean particle diameter of 10 ?m or larger.

Abstract: When spherical calcium carbonate is produced by blowing a carbon dioxide gas or a carbon dioxide-containing gas into an aqueous suspension containing calcium hydroxide to react them, after start of the reaction, an aqueous solution or suspension of a water-soluble phosphoric acid compound or a water-soluble salt thereof is added to the reaction mixture when carbonation ratio reaches 2 to 10%, and the reaction is further allowed to continue at a low gas blowing rate of 1.0 NL/minute or lower (step (a)). Subsequently, an aqueous suspension containing calcium hydroxide and an aqueous solution or suspension of a water-soluble phosphoric acid compound or a water-soluble salt thereof are added to the reaction mixture, and a carbon dioxide gas or a carbon dioxide-containing gas is introduced to allow to react and thereby produce spherical calcium carbonate having a mean particle diameter of 10 ?m or larger.

Abstract: When spherical calcium carbonate is produced by blowing a carbon dioxide gas or a carbon dioxide-containing gas into an aqueous suspension containing calcium hydroxide to react them, after start of the reaction, an aqueous solution or suspension of a water-soluble phosphoric acid compound or a water-soluble salt thereof is added to the reaction mixture when carbonation ratio reaches 2 to 10%, and the reaction is further allowed to continue at a low gas blowing rate of 1.0 NL/minute or lower (step (a)). Subsequently, an aqueous suspension containing calcium hydroxide and an aqueous solution or suspension of a water-soluble phosphoric acid compound or a water-soluble salt thereof are added to the reaction mixture, and a carbon dioxide gas or a carbon dioxide-containing gas is introduced to allow to react and thereby produce spherical calcium carbonate having a mean particle diameter of 10 ?m or larger.

Abstract: The light calcium carbonate in the form of microparticle aggregate of the present invention has a BET specific surface area not smaller than 10 m2/g and not larger than 25 m2/g, a pore volume of 0.05 cm3/g or larger for pores having a pore diameter of 0 to 1000 ? as determined by the nitrogen adsorption method, and a pore volume ratio of 25% or more for pores having a pore diameter of 250 ? or smaller based on the total pore volume as determined by the nitrogen adsorption method, and shows an oil absorption of 100 cc/100 g or more as determined by using liquid paraffin. By using this light calcium carbonate as a filler of printing paper, superior ink absorbing property and opacity (especially opacity after printing) can be imparted to the printing paper.

Abstract: A cyclone type cylindrical body 10 having a part whose diameter decreases in the direction toward a lower opening from an upper opening is used, and liquid is made fall in the inside of the cylindrical body 10 while swirling and thereby accelerated to form a vortex flow. Fine particles are charged into the center of the vortex flow so as to be wrapped by the vortex flow, and thereby the both are mixed. By this characteristic, the fine particles do not contact with an inner wall of the cylindrical body, and therefore clogging does not occur in the cylindrical body. Moreover, the pressure around the center of the vortex flow becomes negative, and the fine particles are aspirated. Therefore, dust is hardly generated. Thus, a mixing apparatus of a small size that can slurry fine particles without much maintenance cost can be provided.

Abstract: A cyclone type cylindrical body 10 having a part whose diameter decreases in the direction toward a lower opening from an upper opening is used, and liquid is made fall in the inside of the cylindrical body 10 while swirling and thereby accelerated to form a vortex flow. Fine particles are charged into the center of the vortex flow so as to be wrapped by the vortex flow, and thereby the both are mixed. By this characteristic, the fine particles do not contact with an inner wall of the cylindrical body, and therefore clogging does not occur in the cylindrical body. Moreover, the pressure around the center of the vortex flow becomes negative, and the fine particles are aspirated. Therefore, dust is hardly generated. Thus, a mixing apparatus of a small size that can slurry fine particles without much maintenance cost can be provided.

Abstract: When spherical calcium carbonate is produced by blowing a carbon dioxide gas or a carbon dioxide-containing gas into an aqueous suspension containing calcium hydroxide to react them, after start of the reaction, an aqueous solution or suspension of a water-soluble phosphoric acid compound or a water-soluble salt thereof is added to the reaction mixture when carbonation ratio reaches 2 to 10%, and the reaction is further allowed to continue at a low gas blowing rate of 1.0 NL/minute or lower (step (a)). Subsequently, an aqueous suspension containing calcium hydroxide and an aqueous solution or suspension of a water-soluble phosphoric acid compound or a water-soluble salt thereof are added to the reaction mixture, and a carbon dioxide gas or a carbon dioxide-containing gas is introduced to allow to react and thereby produce spherical calcium carbonate having a mean particle diameter of 10 ?m or larger.

Abstract: Proposed is a method for the preparation of an aqueous slurry of calcium carbonate particles suitable as a base pigment in the preparation of a paper coating composition having excellent water retentivity and high solid concentration with good flowability, which contains precipitated and ground calcium carbonate particles in combination in a specified weight proportion and characterized by several parameters. The aqueous slurry is prepared in a process comprising the steps of: (a) subjecting an aqueous slurry or wet cake containing a specified amount of specific precipitated calcium carbonate particles to a primary dispersing treatment using a mixer to a specified extent; (b) admixing the aqueous slurry with a specified amount of specific ground calcium carbonate particles; (c) subjecting the aqueous slurry to a secondary dispersing treatment using a mixer to a specified extent; and (d) subjecting the aqueous slurry to a tertiary dispersing treatment using a sand grinder to a specified extent.

Abstract: A calcium-magnesium carbonate composite consisting of particles of calcium carbonate and magnesium carbonate hydroxide and having excellent properties, for example, as a pigment for paper coating is proposed, which is a uniform blend of:(A) particles of calcium carbonate having a crystalline structure of aragonite with a columnar particle configuration having a length in the range from 0.5 to 3 .mu.m and a diameter in the range from 0.1 to 0.3 pm with an aspect ratio in the range from 5 to 15; and(B) particles of magnesium carbonate hydroxide having a plate-like particle configuration with a particle diameter in the range from 2 to 7 .mu.m and a thickness in the range from 0.05 to 0.5 .mu.m,the blend having an overall specific surface area in the range from 15 to 30 m.sup.2 /g and the weight proportion of the particles of calcium carbonate to the particles of magnesium carbonate hydroxide being in the range from 95:5 to 50:50 calculated as the respective hydroxides.