Process for preparing high strength paper

Abstract

The present invention provides a process for the preparation of an aqueous composition comprising polysilicate coated mineral particles, wherein the process comprises subjecting an aqueous composition comprising gelled polysilicate and a mineral to shear of at least 5000 rpm for at least 30 seconds. The present invention also provides polysilicate coated mineral particles obtainable by this process as well as paper filled with these particles.

1 . A process for the preparation of an aqueous composition comprising polysilicate coated mineral particles, wherein the process comprises subjecting an aqueous composition comprising gelled polysilicate and a mineral to shear of at least 5,000 rpm for at least 30 seconds. 
     
     
         2 . The process of  claim 1  wherein the aqueous composition comprising gelled polysilicate and a mineral is obtainable by polymerization of a silicate in the presence of a mineral. 
     
     
         3 . The process of  claim 2 , wherein the polymerization of the silicate is initiated by adjusting the pH to a pH of below 10 by addition of an acid. 
     
     
         4 . The process of  claim 2 , wherein the polymerization of the silicate is performed at a temperature of below 50° C. 
     
     
         5 . The process of  claim 2 , wherein the polymerization of the silicate is substantially complete within 12 hours. 
     
     
         6 . The process of  claim 2 , wherein the amount of mineral is in the range of 5 to 20% by weight based on the weight of the aqueous composition comprising gelled polysilisate and mineral. 
     
     
         7 . The process of  claim 2 , wherein the amount of silicate is in the range of 0.01 to 10% by weight based on the weight of the aqueous composition comprising gelled polysilisate and mineral. 
     
     
         8 . The process of  claim 2 , wherein the amount of gelled polysilicate and mineral is in the range of 1 to 30% by dry weight based on the weight of the aqueous composition comprising the gelled polysilicate and mineral. 
     
     
         9 . An aqueous composition comprising polysilicate coated mineral particles, which is obtained by the process of  claim 1 . 
     
     
         10 . The aqueous composition of  claim 9 , which is characterized by a viscosity of at least 500 mPas (when measured at a concentration of 12% by dry weight polysilicate coated mineral particles based on the weight of the composition, using a Brookfield viscometer at 25° C. and 100 rpm, spindle 4, and the result is taken 30 seconds after the start of the test). 
     
     
         11 . The aqueous composition of  claim 9 , wherein the amount of mineral is between 40 and 99% by weight based on the weight of the polysilicate coated mineral particle. 
     
     
         12 . The aqueous composition of  claim 9 , wherein the amount of polysilicate is between 1 and 60% by weight based on the weight of the mineral. 
     
     
         13 . The aqueous composition of  claim 9 , wherein the size of the polysilicate coated mineral particles is between 1 and 1000 μm. 
     
     
         14 . The aqueous composition of  claim 9 , wherein the amount of polysilicate coated mineral particles is between 1 and 30% by weight based on the weight of the aqueous composition. 
     
     
         15 . Polysilicate coated mineral particles obtained from the aqueous composition of  claim 9  by removal of water. 
     
     
         16 . Paper or paper board filled with the polysilicate coated mineral particles of  claim 15 . 
     
     
         17 . A process for the preparation of the paper or paper board filled with polysilicated coated mineral particles, which comprises the step of adding the polysilicate coated mineral particles of  claim 15  to a cellulosic suspension prior to drainage of the cellulosic suspension on a wire, where a web is formed, which is subsequently dried. 
     
     
         18 . A method for improving the tensile strength and internal bond strength of filled paper or paper board with respect to the basis weight of the filled paper or paper board, which method comprises adding the polysilicate coated mineral particles of  claim 15  to a cellulosic suspension prior to drainage of the cellulosic suspension on a wire, where a web is formed, which is subsequently dried. 
     
     
         19 . (canceled) 
     
     
         20 . A process for the preparation of the paper or paper board filled with polysilicated coated mineral particles, which comprises the step of adding the aqueous composition comprising the polysilicate coated mineral particles according to  claim 9  to a cellulosic suspension prior to drainage of the cellulosic suspension on a wire, where a web is formed, which is subsequently dried. 
     
     
         21 . A method for improving the tensile strength and internal bond strength of filled paper or paper board with respect to the basis weight of the filled paper or paper board, which method comprises adding the aqueous composition comprising the polysilicate coated mineral particles of  claim 9  to a cellulosic suspension prior to drainage of the cellulosic suspension on a wire, where a web is formed, which is subsequently dried.