Precisely sized precipitated calcium carbonate (PCC) crystals of preselected crystal habit, manufactured using pressure carbonation

Abstract

Precipitated calcium carbonate crystals of selected crystal habit. A pressure carbonation process is used to manufacture precipitated calcium carbonate. A slurry of calcium hydroxide is agitated in a pressurized reactor, and carbon dioxide is provided to a reactor to produce calcium ions and carbonate ions that react under pressure to produce precipitated calcium carbonate at a high reaction rate. Control of process conditions such as pressure, temperature, and hydroxide slurry concentration, enables production of (1) a desired crystal habit (including sclenohedral, rhombohedral, stacked rombohedral, or aragonite calcium carbonate crystal structures), (2) a desired crystal size, or (3) a desired crystal aspect ratio. The precipitated calcium carbonate produced by the process is useful as either a paper filler or as an ingredient in paper coatings, and provides a paper product with improved properties.

1 . A precipitated calcium carbonate having sclenohedral crystal structure, said sclenohedral crystal structure, said rhomboheral crystal structure precipitated at a pressure greater than atmospheric pressure, and comprising a surface area of approximately 28,200 cm 2 /gram (measured by Blaine method), and a GE brightness of at least 96.7.  
     
     
         2 . A precipitated calcium carbonate having rhombohedral crystal structure, said rhombohedral crystal structure precipitated at a pressure greater than atmospheric pressure, and having an aspect ratio of approximately 1:1, said rhombohedral crystal structure comprising a surface area of approximately 40,000 cm 2 /gram (measured by Blaine method), and a GE brightness of at least 92.1.  
     
     
         3 . A precipitated calcium carbonate having rhombohedral crystal structure, said rhombohedral crystal structure precipitated at a pressure greater than atmospheric pressure, and having an aspect ratio of approximately 1:1.5, said rhombohedral crystal structure comprising a surface area of approximately 21,500 cm 2 /gram (measured by Blaine method), and a GE brightness of at least 98.6.  
     
     
         4 . A precipitated calcium carbonate having rhombohedral crystal structure, said rhombohedral crystal structure precipitated at a pressure greater than atmospheric pressure, and having an aspect ratio from approximately 1:1 to approximately 1:1.5, said rhombohedral crystal structure comprising a surface area of approximately from approximately 40,000 cm 2 /gram to approximately 21,500 cm 2 /gram (measured by Blaine method), and a GE brightness of at least 92.1.  
     
     
         5 . A precipitated calcium carbonate produced having stacked rhombohedral crystal structure, said stacked rhombohedral crystal structure precipitated at a pressure greater than atmospheric pressure, and comprising a surface area of approximately 16,400 cm 2 /gram (measured by Blaine method), and a GE brightness of at least 87.3.  
     
     
         6 . A precipitated calcium carbonate having an aragonite crystal structure, said aragonite crystal structure precipitated at a pressure greater than atmospheric pressure, and comprising a surface area of approximately 23,500 cm 2 /gram (measured by Blaine method), and a GE brightness of at least 95.0.