Composition and process for whitening paper

Abstract

The invention relates to a composition suitable for surface treatment of paper, wherein the composition contains a specified fluorescent whitening agent with a combination of specific terminal groups, a salt of a bivalent cation, and a carrier. The composition is used for whitening paper, in particular in the size press.

1 . A composition suitable for surface treatment of paper, wherein the composition comprises
 (a) at least one fluorescent whitening agent of the formula (I)   
       
         
           
           
               
               
           
         
       
       wherein n and m are, independently of each other, an integer of 1, 2, or 3;
 R 1 , R 2 , R 3  and R 4  represent, independently of each other, hydrogen, C 1 -C 4  alkyl, C 2 -C 4  alkoxyalkyl, C 2 -C 4  cyanoalkyl, or C 2 -C 4  hydroxyalkyl; or R 1  and R 2  or R 3  and R 4  independently of each other together with N atom form morpholine, piperidine or pyrrolidine ring; 
 wherein at least one of R 1 , R 2 , R 3  and R 4  contains at least 3 carbon atoms; 
 M represents hydrogen, or one equivalent of a cation, in particular Li, Na, K, Ca, Mg, ammonium, or ammonium which is mono-, di-, tri- or tetra-substituted by C 1 -C 4  alkyl or C 2 -C 4  hydroxyalkyl; 
 (b) at least one salt of a bivalent cation; 
 (c) at least one carrier; and 
 (d) water. 
 
     
     
         2 . The composition of  claim 1 , wherein n and m each are 2, and the —SO 3 M groups are in 2,5-position. 
     
     
         3 . The composition of  claim 1  wherein R 1 , R 2 , R 3  and R 4  are, independently of each other, propyl, cyanoethyl, or hydroxypropyl. 
     
     
         4 . The composition of  claim 1 , wherein n and m are 2, and R 1 , R 2 , R 3  and R 4  are propyl. 
     
     
         5 . The composition of  claim 1 , wherein n and m are 2, and R 1 , R 2 , R 3  and R 4  are hydroxypropyl, in particular hydroxyisopropyl. 
     
     
         6 . The composition of  claim 1 , wherein n and m are 2, R 1  and R 3  are hydroxypropyl, in particular hydroxyisopropyl, and R 2  and R 4  are cyanoethyl. 
     
     
         7 . The composition of  claim 1 , wherein M is Na or K. 
     
     
         8 . The composition of  claim 1 , wherein the salt of component (b) is calcium chloride. 
     
     
         9 . The composition of  claim 1 , wherein the carrier of component (c) is selected from carboxymethylcellulose, polyvinyl alcohol, starch, and mixtures thereof. 
     
     
         10 . The composition of  claim 9 , wherein the carrier is starch. 
     
     
         11 . The composition of  claim 1 , wherein the composition contains component (a) in an amount of 0.02 to 3 weight-%, component (b) in an amount of 0.2 to 8 weight-%, and component (c) in an amount of 3 to 20 weight-%, each based on 100 weight-% of the composition. 
     
     
         12 . The composition of  claim 1 , wherein the composition is a size press liquor which optionally contains a sizing agent. 
     
     
         13 . A process for whitening paper comprising contacting a cellulose sheet with the composition of  claim 1 . 
     
     
         14 . The process of  claim 13 , wherein the contacting is conducted in a size press. 
     
     
         15 . A paper obtainable by the process according to  claim 13 .