Papermaking processes using coagulants and optical brighteners

Abstract

A method of making paper or paperboard is described, which includes introducing at least one charged starch, preferably having a degree of substitution greater than 0.045, and at least one optical brightening agent to a papermaking pulp and then forming the pulp into paper or paperboard. The present invention further describes methods of improving optical brightener performance.

1 . A method of making paper or paperboard comprising introducing
 a) at least one charged starch, having a degree of substitution greater than 0.045, and   b) at least one optical brightening agent, in any order, and at the same time or at a different time, to a papermaking pulp to form a treated pulp and then forming the treated pulp into paper or paperboard.   
   
   
       2 . The method of  claim 1 , wherein said charged starch is a cationic starch. 
   
   
       3 . The method of  claim 1 , wherein said charged starch is a blend of two or more charged starches. 
   
   
       4 . The method of  claim 1 , wherein at least two charged starches are introduced. 
   
   
       5 . The method of  claim 1 , wherein said optical brightening agent is a stilbene compound or a distyrylbiphenyl compound. 
   
   
       6 . The method of  claim 1 , wherein the optical brightening agent is a dyestuff. 
   
   
       7 . The method of  claim 1 , wherein said charged starch has a degree of substitution of from about 0.01 to about 0.5. 
   
   
       8 . The method of  claim 1 , wherein said charged starch has a degree of substitution of from about 0.15 to about 0.42 
   
   
       9 . The method of  claim 1 , wherein said charged starch has a degree of substitution of from about 0.12 to about 0.3. 
   
   
       10 . The method of  claim 1 , wherein said method forms fine paper or coated or non-coated free-sheet, newsprint, specialty newsprint, supercalendared, or light weight coated grades of paper. 
   
   
       11 . The method of  claim 1 , wherein at least one charged starch and said at least one optical brightening agent are introduced at or prior to said pulp entering a blend chest. 
   
   
       12 . The method of  claim 1 , wherein said at least one charged starch and said at least one optical brightening agent are added at or prior to said pulp entering a machine chest. 
   
   
       13 . The method of  claim 1 , wherein said least one charged starch and said at least one optical brightening agent are introduced prior to a size press. 
   
   
       14 . The method of  claim 1 , wherein said charged starch is added in an amount of from about 1 to about 20 pounds per ton of dried pulp. 
   
   
       15 . The method of  claim 1 , wherein said charged starch is added in an amount of from about 0.25 to about 5 pounds per ton of dried pulp. 
   
   
       16 . A method of improving optical brightener performance comprising introducing
 a) at least one charged starch, and   b) at least one optical brightening agent, in any order, at the same time, or at a different time, to a papermaking pulp to form a treated pulp and then forming the treated pulp into paper or paperboard.   
   
   
       17 . The method of  claim 16 , wherein improving said optical brightener performance includes an increase in paper ISO brightness compared to the same method but with no charged starch being added prior to any size press. 
   
   
       18 . The method of  claim 16 , wherein said optical brightener performance includes an increase in paper fluorescence intensity as compared to the same method being practiced, but with no charged starch being added prior to any size press. 
   
   
       19 . The paper or paperboard obtained from the method of  claim 1 . 
   
   
       20 . A pulp composition comprising pulp, at least one charged starch having a degree of substitution of greater than 0.045 and at least one optical brightening agent. 
   
   
       21 . The pulp composition of  claim 20 , wherein said charged starch is a cationic starch and has a degree of substitution of greater than 0.045 to about 0.5. 
   
   
       22 . The method of  claim 16 , wherein at least one of the following properties is improved:
 (a) an increase in filler retention compared to no charged starch being present;   (b) an increase in sheet ash content in the paper compared to when no charged starch is used;   (c) an increase in drainage compared to when no charged starch is present;   (d) an increase in sizing retention compared to when no charged starch is present;   (e) a reduction in breaks compared to when no charged starch is present;   (f) a reduction in linting and/or dusting compared to when no charged starch is present.