Method of producing a pigment containing, cationic, high solids aqueous dispersion, aqueous dispersion containing pigments, and use thereof

Abstract

A method of producing an aqueous dispersion of a pigment, and the aqueous dispersion of the pigment and the uses of the aqueous dispersion of the pigment. In the present method, an inorganic pigment is dispersed in water, in the presence of a dispersing agent. According to the present invention, the inorganic pigment comprises cationic calcium carbonate, especially precipitated calcium carbonate, which is dispersed using a cationic biopolymer, such as starch, in order to prepare an aqueous dispersion, the solids content of which is approximately 30-75% by weight. The dispersion generated can be used, among others, as pigment or filler for ink-jet paper.

What is claimed is: 
     
         1 . A method of producing an aqueous dispersion of a pigment, wherein the inorganic pigment is dispersed into water in the presence of a dispersing agent, characterised in that the inorganic pigment comprises cationic calcium carbonate, which is dispersed using a cationic biopolymer in order to produce a stable dispersion which has a solids content of approximately 30-75% by weight. 
     
     
         2 . The method according to  claim 1 , wherein the dispersion obtained remains stable for a period of at least 2 weeks, more preferably for at least 4 weeks, most preferably for more than 6 weeks. 
     
     
         3 . The method according to  claim 1 , wherein dispersing the mixture, which comprises a dry pigment or an aqueous slurry or aqueous paste of the pigment, a dispersing agent and possibly water, by directing shear forces at the mixture. 
     
     
         4 . The method according to  claim 1 , wherein the solids content of the dispersion is 50-60% by weight, preferably approximately 57% by weight. 
     
     
         5 . The method according to  claim 1 , wherein the pigment to be dispersed is in the form of a dry pigment, an aqueous slurry of the pigment or an aqueous paste of the pigment. 
     
     
         6 . The method according to  claim 1 , wherein introducing into the dispersion of a pigment, charge state of which is not rendered anionic during the time between the production and the dispersion of the pigment. 
     
     
         7 . The method according to  claim 1 , wherein the surface area of the calcium carbonate pigment is approximately 5-100 m 2 /g, in particular approximately 10-50 m 2 /g. 
     
     
         8 . The method according to  claim 1 , wherein the pigment comprises calcium carbonate and another, in particular a light-scattering pigment, such as titanium dioxide, kaolin, gypsum, silicate-based material, talc or a different calcium carbonate. 
     
     
         9 . The method according to  claim 1 , wherein the pigment consists of calcium carbonate. 
     
     
         10 . The method according to  claim 1 , wherein the pigment consists of a porous calcium carbonate material, in particular it consists of a calcium carbonate material, the particles of which are formed of calcium carbonate agglomerates. 
     
     
         11 . The method according to  claim 1 , wherein the pigment comprises or consists of precipitated calcium carbonate. 
     
     
         12 . The method according to  claim 1 , wherein the cationic biopolymer is a cationic, modified, substituted starch or a cationic sorbitol or maltodextrin. 
     
     
         13 . The method according to  claim 1 , wherein the modified, substituted starch comprises cationic, nitrogenous substituents, such as amine or amide groups. 
     
     
         14 . The method according to  claim 1 , wherein the nitrogen content of the modified starch is approximately 0.1-2% of its dry weight. 
     
     
         15 . The method according to  claim 1 , wherein the degree of substitution of the modified starch is 0.1-0.2, preferably approximately 0.16. 
     
     
         16 . The method according to  claim 1 , wherein the pigment is precipitated calcium carbonate that has been dried after the process of the production of the precipitated calcium carbonate. 
     
     
         17 . The method according to  claim 1 , wherein the pigment is an aqueous slurry or aqueous paste of calcium carbonate, obtained by filtering the dilute aqueous slurry of precipitated calcium carbonate, which slurry is generated during process of the production of pigment, is precipitated calcium carbonate. 
     
     
         18 . The method according to  claim 1 , wherein the aqueous dispersion is prepared without adding a polyelectrolyte, such as polyacrylate, before dispersion, during dispersion or after it. 
     
     
         19 . The method according to  claim 1 , wherein a dispersion is prepared, the aqueous phase of which is essentially polyacrylate-free, especially its polyacrylate content is lower than 0.1%, most suitably lower than 0.01%, especially lower than 0.001%, of the dry matter content of the dispersion. 
     
     
         20 . The method according to  claim 1 , wherein the aqueous dispersion comprises a cationic starch derivative approximately 0.1-2.0% by weight, especially approximately 0.5-0.99% by weight, of the dry weight of the dispersion. 
     
     
         21 . The method according to  claim 1 , wherein
 the pigment content of the aqueous dispersion is approximately 30-75% by weight, preferably 50-60% by weight, most preferably approximately 57% by weight, and   the dispersing agent content of the aqueous dispersion is 0.2-5.0% by weight, preferably 0.5-3.0% by weight, most preferably 0.7-1.5% by weight, in particular approximately 0.7% by weight.   
     
     
         22 . The method according to  claim 1 , wherein the dry pigment or the aqueous slurry or aqueous paste of the pigment, the dispersion agent and, if needed, water, is directed into the dispersion unit, which is typically a disintegration device operating according to the impact-repulsion mill principle. 
     
     
         23 . The method according to  claim 1 , wherein an aqueous dispersion is prepared, the Z-potential of which is at least +1 mV, at a pH value of 9.5 and a dry matter content of 20%. 
     
     
         24 . An aqueous dispersion which comprises an inorganic pigment and a dispersion agent, wherein the inorganic pigment comprises cationic calcium carbonate, that the dispersion agent comprises a cationic biopolymer and that the solids content of the aqueous dispersion is approximately 30-75% by weight, preferably 50-60% by weight, most preferably approximately 57% by weight. 
     
     
         25 . The aqueous dispersion according to  claim 24 , wherein the dispersion is stable, especially the dispersion remains stable for a period of at least 2 weeks, preferably a period of at least 4 weeks, most preferably a period of over 6 weeks. 
     
     
         26 . The aqueous dispersion according to  claim 24 , wherein the mixture which comprises a dry pigment or an aqueous slurry or an aqueous paste of the pigment, a dispersing agent and possibly water, is dispersed by directing shear forces at the mixture. 
     
     
         27 . The aqueous dispersion according to  claim 24 , wherein the particle size of the dispersed particle is in the nano-range, typically 20-400 nm, more preferably over 20 and less than 250 nm, especially 40-200 nm, in particular 40-100 nm. 
     
     
         28 . The aqueous dispersion according to  claim 24 , wherein the aqueous phase of the dispersion is essentially polyacrylate-free, especially its polyacrylate content is lower than 0.1%, most suitably lower than 0.01%, preferably lower than 0.001%, of the dry matter content of the dispersion. 
     
     
         29 . The aqueous dispersion according to  claim 24 , wherein the Z-potential of the dispersion is at least +1 mV, at a pH value of 9.5 and a dry matter content of 20%. 
     
     
         30 . The aqueous dispersion according to  claim 24 , wherein the surface area of the calcium carbonate pigment is approximately 5-100 m 2 /g, especially approximately 10-50 m 2 /g. 
     
     
         31 . The aqueous dispersion according to  claim 24 , wherein the pigment comprises calcium carbonate and another, especially a light-scattering pigment, such as titanium dioxide, kaolin, gypsum, silicate-based material, talc or a different calcium carbonate. 
     
     
         32 . The aqueous dispersion according to  claim 24 , wherein the pigment consists of calcium carbonate. 
     
     
         33 . The aqueous dispersion according to  claim 24 , wherein the pigment consists of porous calcium carbonate material, especially it consists of a calcium carbonate material, the particles of which are formed of calcium carbonate agglomerates. 
     
     
         34 . The aqueous dispersion according to  claim 24 , wherein the pigment comprises or consists of precipitated calcium carbonate. 
     
     
         35 . The aqueous dispersion according to  claim 24 , wherein the modified, substituted starch comprises cationic, nitrogen-containing substituents such as amine or amide groups. 
     
     
         36 . The aqueous dispersion according to  claim 24 , wherein the nitrogen content of the modified starch is approximately 0.1-2% of its dry weight. 
     
     
         37 . The aqueous dispersion according to  claim 24 , wherein the degree of substitution of the modified starch is 0.1-0.2, preferably approximately 0.16. 
     
     
         38 . The aqueous dispersion according to  claim 24 , wherein the pigment is precipitated calcium carbonate, which has been dried after the process of the production of the precipitated calcium carbonate. 
     
     
         39 . A dispersion according to  claim 24 , wherein
 the pigment content of the aqueous dispersion is approximately 30-60% by weight, preferably 50-60% by weight, most preferably approximately 57% by weight, and   the dispersing agent content of the aqueous dispersion is 0.2-5.0% by weight, preferably 0.5-3.0% by weight, most preferably 0.7-1.5% by weight, in particular approximately 0.7% by weight,   calculated from the dry weight.   
     
     
         40 . A use of a dispersion according to  claim 24  as a paper or cardboard filler, in which case the dispersion is, if needed, diluted with water and directed into the headbox of the paper or cardboard machine. 
     
     
         41 . A use of a dispersion according to  claim 24  as a paper or cardboard filler, without the use of a separate retention agent. 
     
     
         42 . A use of a dispersion according to  claim 24  for surface-sizing of paper or cardboard, in which case the dispersion is mixed into a cationic starch that is suitable for conventional surface-sizing, and the mixture is applied to the dried web. 
     
     
         43 . A use of a dispersion according to  claim 24  for the coating of paper or cardboard, in which case the dispersion is mixed into a coating paste, which is then applied to the dried web. 
     
     
         44 . A use of a dispersion according to  claim 24  as a pigment or filler for ink-jet paper.