Method for improving rheological properties of an aqueous pigment slurry and a dispersion agent

Abstract

The invention relates to a method for improving rheological properties of an aqueous pigment slurry. In the method dispersion agent is added to an aqueous phase of a slurry comprising pigment particles or to the aqueous phase into which the pigment particles are to be added. The dispersion agent comprises styrene acrylate copolymer. The invention also relates to a dispersion agent for a pigment slurry comprising a first component comprising styrene acrylate copolymer and a second component comprising a conventional dispersion agent, such as a straight-chain polyacrylate.

The invention claimed is: 
     
       1. A method for improving the rheological high shear properties of an aqueous pigment slurry comprising calcium carbonate, kaolin, calcinated kaolin, talc, titanium dioxide, gypsum, chalk, satine white, barium sulphate, sodium aluminium silicate, aluminium hydroxide or any of their mixture, the aqueous pigment slurry having a solids content of about 68%, the method comprising adding a dispersion agent to an aqueous phase of a slurry comprising pigment particles or to the aqueous phase into which the pigment particles are to be added, the dispersion agent comprising styrene acrylate copolymer, wherein the styrene acrylate copolymer comprises starch, wherein the dispersion agent improves the rheological properties of the slurry, and wherein the dispersion agent decreases the high shear viscosity of the slurry, and further comprising adding also a conventional dispersion agent comprising straight-chain polyacrylate to the aqueous phase. 
     
     
       2. The method according to  claim 1 , comprising adding at least 0.1 parts dispersion agent comprising styrene acrylate copolymer per 100 parts pigment in the slurry. 
     
     
       3. The method according to  claim 1 , wherein the dispersion agent comprising the styrene acrylate copolymer is used in the form of an aqueous polymer dispersion having a solids content of 10-50%. 
     
     
       4. The method according to  claim 1 , wherein the proportion first component: second component of the dispersion agent:the conventional dispersion agent is in the range of 50:50-99:1. 
     
     
       5. A dispersion agent for a pigment slurry, where the pigment slurry comprises calcium carbonate, kaolin, calcinated kaolin, talc, titanium dioxide, gypsum, chalk, satine white, barium sulphate, sodium aluminium silicate, aluminium hydroxide or any of their mixture, comprising a first component comprising styrene acrylate copolymer wherein the styrene acrylate copolymer decreases the high shear viscosity of the slurry, wherein the styrene acrylate copolymer comprises starch, the aqueous pigment slurry having a solids content of about 68%, a second component comprising a conventional dispersion agent comprising straight-chain polyacrylate. 
     
     
       6. The dispersion agent according to  claim 5 , wherein the proportion of first component:second component is in the range of 50:50-99:1. 
     
     
       7. The dispersion agent according to  claim 5 , wherein the mean particle size of the styrene acrylate copolymer is 20-300 nm.