In-Situ Precipitated Calcium Carbonate Paper Filler Material: A Review

Abstract

Since the invention of the paper by in 105 CE to Chai Lun many improvements have been made to the paper product we know today. Today a paper machines can be over 600 m long and 11.5 m wide, running at speeds of over 2000 m/min, and producing up to 4,500 metric tons per hour. Paper as we know it today, can be characterized as an orthotropic thin plate with a thickness of over 500 μm and a basis weight of over 500 g/m² requiring additives to achieve the needed paper properties. Calcium carbonate based filler additive materials have approximately 70% market share in North America, and can be added to a maximum of 20 to 25% based on fiber material. In the 1970s a shift from acid to neutral papermaking started which made it possible to use precipitated calcium carbonate in the paper manufacturing process. New printing technologies required paper with superior properties. This led to an increase in filler content and specially designed filler particles. The in-situ precipitation and filler manufacturing processes are known today, can be divided into (i) mechanical method which uses high shear and centrifugal forces to load the fiber pores with the filler particle, (ii) a chemical method which is the common method in producing precipitated calcium carbonate in a solution since the 1980’s for papermaking applications, and (iii) a combination of the mechanical and chemical method which precipitates the calcium carbonate particles on and into the fiber material present in the solution. All research on various in situ precipitation processes, including patented technologies, since the 1970’s showed that the achieved handsheet properties have higher brightness and opacity values as well as a coarser surface structure, lower smoothness and gloss. In-Situ processes showed improvements for the paper manufacturing process in regards to physical and mechanical handsheet paper properties. However, no commercial applications of this process have been found at present time. However, mixing the filler particles with the pulp suspension and storing this suspension in the headbox feed chest, for a specific time, applies indirectly in-situ principles in today’s paper making process operations.