Process for Grinding Minerals in Aqueous Dispersion Using a Dispersing Agent Comprising Homopolymers and/or Copolymers of (Meth)Acrylic Acid

Abstract

The process of the present invention produces an aqueous dispersion of mineral materials, suitable for use in pigments and other coatings, by introducing a fully neutralized dispersing agent to an aqueous dispersion of coarse mineral materials, grinding the aqueous dispersion and, during grinding, adding a partially neutralized dispersing agent to the aqueous dispersion. The process of the present invention produces aqueous dispersions of very fine particles, having a solids content of at least 75% by weight, based on the total weight of the aqueous dispersion, and wherein 95% or more of the particles are below 2 microns.

What is claimed is: 
     
         1 . A dispersion of particulate mineral solids in a medium containing water and at least one dispersing agent, wherein the dispersing agent comprises a water soluble, phosphonate terminated polymer of acrylic acid with a weight average weight of from 2,000 to 10,000 and wherein 95% or more of the particulate mineral solids has a particle size of less than 2 micrometers and said dispersion has a solids content of at least 75% by weight, based on the total weight of the dispersion. 
     
     
         2 . The dispersion of  claim 1 , wherein said mineral comprises at least one mineral selected from the group consisting of: calcium carbonate, aluminum silicate, kaolin, talc, and titanium oxides. 
     
     
         3 . A dispersion of particulate mineral solids in a medium containing water and at least one dispersing agent, wherein the dispersing agent comprises a water soluble, phosphonate terminated polymer of acrylic acid and has the formula: 
       
         
           
           
               
               
           
         
       
       wherein A is a polymer derived from units comprising ethylenically unsaturated monomers; B is a hydrogen, phenyl, C 1 -C 6  alkyl, or is a polymer consisting of ethylenically unsaturated monomers; X is hydrogen, an alkali metal, an alkaline earth metal, ammonium or an amine residue, wherein the ethylenically unsaturated monomers are selected from the group consisting of: acrylic acid, methacrylic acid, maleic acid, maleic anhydride, a sulfonic unsaturated monomer and an unsaturated polymerizable monomer having a COOH group, and 
       wherein the at least one dispersing agent comprises:
 (a) from 55% to 80% by weight acrylic acid, 
 (b) from 20% to 45% by weight methacrylic acid, and 
 (c) from 0% to 10% by weight of at least one monomer selected from the group consisting of: maleic acid, maleic anhydride, a sulfonic unsaturated monomer and an unsaturated polymerizable monomer having a COOH group, 
 
       wherein the weight percents are based on the total weight of the dispersing agent and the total of the percentages of components (a), (b) and (c) does not exceed 100. 
     
     
         4 . The dispersion of  claim 3 , wherein said mineral comprises at least one mineral selected from the group consisting of: calcium carbonate, aluminum silicate, kaolin, talc, and titanium oxides. 
     
     
         5 . The dispersion of  claim 3 , wherein the at least one dispersing agent comprises:
 (a) from 55% to 75% by weight acrylic acid,   (b) from 25% to 45% by weight methacrylic acid, and   (c) from 0% to 10% by weight of at least one monomer selected from the group consisting of: maleic acid, maleic anhydride, a sulfonic unsaturated monomer and an unsaturated polymerizable monomer having a COOH group.   
     
     
         6 . A process for producing a dispersion of mineral materials suitable for use as pigments, comprising the steps of:
 (A) preparing a mixture comprising water and a mineral to be ground, comprising particles and said mixture having at least 75% solids content by weight, based on the total weight of the mixture;   (B) grinding the mixture in the presence of at least one dispersing agent; and   (C) continuing grinding said dispersion until 95% or more of the mineral particles have a minimum dimension below 2 microns,   
       wherein the at least one dispersing agent is selected from one or more water soluble, phosphorus-containing polymers having the formula: 
       
         
           
           
               
               
           
         
       
       wherein A is a polymer derived from units comprising ethylenically unsaturated monomers; B is a hydrogen, phenyl, C 1 -C 6  alkyl, or is a polymer consisting of ethylenically unsaturated monomers; X is hydrogen, an alkali metal, an alkaline earth metal, ammonium or an amine residue, wherein the ethylenically unsaturated monomers are selected from the group consisting of: acrylic acid, methacrylic acid, maleic acid, maleic anhydride, a sulfonic unsaturated monomer and an unsaturated polymerizable monomer having a COOH group. 
     
     
         7 . The process of  claim 6 , wherein said mineral comprises at least one mineral selected from the group consisting of: calcium carbonate, aluminum silicate, kaolin, talc, and titanium oxides. 
     
     
         8 . The process of  claim 6 , wherein the at least one dispersing agent comprises:
 (a) from 55% to 80% by weight acrylic acid,   (b) from 20% to 45% by weight methacrylic acid, and   (c) from 0% to 10% by weight of at least one monomer selected from the group consisting of: maleic acid, maleic anhydride, a sulfonic unsaturated monomer and an unsaturated polymerizable monomer having a COOH group,   
       wherein the weight percents are based on the total weight of the dispersing agent and the total of the percentages of components (a), (b) and (c) does not exceed 100.