Modification of paper coating rheology

Abstract

Thickener compositions for addition to paper coating compositions in order to obtain low high shear viscosity and good water retention. The thickener compositions comprise an associative thickener with an associative content below 10%, a molecular weight below one million and an acid content of at least 10% by weight.

1 . A thickener composition for modifying the rheology of paper coatings comprising an associative thickener characterised in that the associative content is below 10%, the molecular weight of the thickener is below about 1 million and the acid content is at least 10% by weight.  
   
   
       2 . A thickener composition as claimed in  claim 1 , wherein the associative thickener is a hydrophobic alkali-soluble emulsion.  
   
   
       3 . A thickener composition as claimed in  claim 1 , wherein the thickener has a molecular weight of from 10,000 to 700,000.  
   
   
       4 . A thickener composition as claimed in  claim 1 , wherein the acid functionality is provided by an acid selected from methacrylic acid, acrylic acid and mixtures thereof.  
   
   
       5 . A thickener composition as claimed in  claim 1 , wherein the thickener is branched or cross linked.  
   
   
       6 . A thickener composition as claimed in  claim 1 , wherein the associative content is below 5.0%.  
   
   
       7 . A paper coating composition which includes a thickener composition as claimed in  claim 1 .  
   
   
       8 . A paper coating composition as claimed in  claim 7 , wherein the pH is from 8 to 10.  
   
   
       9 . A paper coating composition as claimed in  claim 7 , for roll and blade coating, wherein the amount of thickener composition present is chosen to achieve a Brookfield viscosity (100 rpm) of the order of 1000 to 1400 mPas.  
   
   
       10 . A paper coating composition as claimed in  claim 7 , for coating by film press, wherein the amount of thickener composition present is chosen to achieve a Brookfield viscosity (100 rpm) of the order of 700 to 1000 mPas.  
   
   
       11 . A paper coating composition as claimed in  claim 7 , for coating by jet applicator wherein the amount of thickener composition present is chosen to achieve a Brookfield viscosity (100 rpm) of the order of 2000 to 2500 mPas.  
   
   
       12 . A paper coating composition as claimed in  claim 7 , wherein the thickener composition is the sole thickener ingredient.  
   
   
       13 . A method of modifying the rheology of a paper coating composition comprising adding a thickener composition as claimed in  claim 1  to the paper coating composition.  
   
   
       14 . A method as claimed in  claim 13 , wherein the pH is adjusted to between 8 and 10.  
   
   
       15 . A method as claimed in  claim 13 , wherein the thickener composition is added to the paper coating composition in an amount to achieve a Brookfield viscosity (100 rpm) of the order of 1000 to 1400 mPas.  
   
   
       16 . A method as claimed in  claim 13 , wherein the thickener composition is added to the paper coating composition in an amount to achieve a Brookfield viscosity (100 rpm) of the order of 700 to 1000 mPas.  
   
   
       17 . A method as claimed in  claim 13 , wherein the thickener composition is added to the paper coating composition in an amount to achieve a Brookfield viscosity (100 rpm) of the order of 2000 to 2500 mPas.  
   
   
       18 . A method of modifying the rheology of a paper coating composition comprising adding a thickener composition as claimed in  claim 1  to the paper coating composition, wherein the thickener composition of  claim 1  is the sole thickener ingredient.  
   
   
       19 . A method of coating a sheet of paper comprising applying to the surface of the sheet a coating composition as defined by  claim 7 .  
   
   
       20 . A coated sheet of paper obtainable by the method of  claim 19.