Process for the preparation of a pigment-fibre composite

Abstract

The invention relates to a process for the preparation of a pigment-cellulosic fibre composite, wherein the pigment comprises an inorganic pigment which comprises local cationic charges, said process comprises contacting an aqueous cellulosic fibre suspension and inorganic pigment particles such that crystals of said pigment are attached to the surface of the fibre, said crystals having a size of at most 5 μm. The produced composite product can be used as a filler pigment or coating pigment in the production of paper.

1 . A process for the preparation of a pigment-cellulosic fibre composite, wherein the pigment comprises an inorganic pigment which comprises local cationic charges, said process comprises contacting an aqueous cellulosic fibre suspension and inorganic pigment particles such that crystals of said pigment are attached to the surface of the fibre, said crystals having a size of at most 5 μm. 
     
     
         2 . The process according to  claim 1 , wherein the inorganic pigment particles comprise gypsum, calcium carbonate, kaolin, titanium dioxide, talc, silica or silicate, preferably gypsum, calcium carbonate or kaolin. 
     
     
         3 . The process according to  claim 2  wherein the inorganic pigment particles additionally comprise calcium sulphate hemihydrate or calcium sulphate anhydrite which are converted to gypsum crystals which are attached to the surface of the fibre, said crystals having a size of at most 5 μm. 
     
     
         4 . The process according to  claim 1 , wherein the net charge of the inorganic pigment is anionic. 
     
     
         5 . The process according to  claim 1 , wherein the net charge of the cellulosic fibre is anionic. 
     
     
         6 . The process according to  claim 1 , wherein the pigment crystals attached to the surface of the cellulosic fibre have a size between 0.1 and 5.0 μm. 
     
     
         7 . The process according to  claim 1 , wherein the pigment particles are provided in the form of a powder or as a slurry. 
     
     
         8 . The process according to  claim 1 , wherein the aqueous cellulosic fibre suspension and the inorganic pigment particles are contacted under high shear forces. 
     
     
         9 . The process according to  claim 1 , wherein the weight ratio of pigment to cellulosic fibre on dry basis in the produced composite is in the range from 70:30 to 10:90, preferably from 50:50 to 10:90, more preferably from 40:60 to 20:80, and most preferably from 40:60 to 30:70. 
     
     
         10 . The process according to  claim 1 , wherein the cellulosic fibre content on dry basis in the contacting stage is from 0.1 to 15% by weight, preferably from 0.2 to 10% by weight, more preferably from 0.3 to 8% by weight. 
     
     
         11 . The process according to  claim 1 , wherein the content of pigment on dry basis in the contacting stage is from 0.3 to 20% by weight, preferably from 0.5 to 20% by weight, more preferably from 1 to 15% by weight, and most preferably from 2 to 10% by weight. 
     
     
         12 . The process according to  claim 1 , wherein the weight ratio of pigment to cellulosic fibre on dry basis in the contacting stage is from 95:5 to 20:80, preferably from 90:10 to 30:70. 
     
     
         13 . The process according to  claim 1 , wherein the weigh ratio of pigment to water in the contacting stage is in the range from 0.005 to 0.6:1, preferably from 0.01 to 0.6:1, more preferably from 0.05 to 0.5:1. 
     
     
         14 . The process according to  claim 1 , wherein the cellulosic fibre comprises a chemical pulp fibre, such as a kraft pulp fibre, or a mechanical pulp fibre including chemi-mechanical pulp fibre, or a deinked pulp fibre. 
     
     
         15 . The process according to  claim 14 , wherein the cellulosic fibre is refined cellulosic fibre, preferably having a length of at most 5 mm. 
     
     
         16 . The process according to  claim 1 , wherein the pigment-cellulosic fibre composite is prepared in a pulp production unit. 
     
     
         17 . Use of a pigment-cellulosic fibre composite produced according to  claim 1  as a filler pigment or coating pigment in the production of paper. 
     
     
         18 . The use according to  claim 17 , wherein the pigment-cellulosic fibre composite is added into the long circulation of the paper machine. 
     
     
         19 . A paper product comprising a pigment-cellulosic fibre composite produced according to  claim 1  as a filler pigment or coating pigment. 
     
     
         20 . The paper product according to  claim 19 , wherein the amount of the pigment-cellulosic fibre composite is from 10 to 80%, preferably from 20 to 60% by weight on dry basis.