Process for Producing Optically Brightened Paper

Abstract

The instant invention relates to a process for the production of optically brightened paper by treating the pulp suspension with an optically brightened filler composition comprising optically brightened plastic fibres, preferably polyester fibres, which leads to a surprising high lightfastness of the resulting paper.

1 . A process for optical brightening of paper comprising the step of adding an optically brightened filler composition comprising at least one optically brightened plastic fiber to a pulp suspension. 
   
   
       2 . A process according to  claim 1 , wherein the at least one optically brightened plastic fiber comprises a polymer selected from the group consisting of: polyester, polyethylene, polypropylene and polyamide. 
   
   
       3 . A process according to  claim 1  wherein the at least one optically brightened plastic fiber comprises polyester. 
   
   
       4 . A process according to  claim 1 , wherein the at least one optically brightened plastic fiber has a fineness between 1 and 10 dtex and is cut to a length of between 0.1 and 1 mm. 
   
   
       5 . A process according to  claim 1 , wherein the at least one optically brightened plastic fiber has a fineness between 1 and 2 dtex and is cut to a length of between 0.2 and 0.6 mm. 
   
   
       6 . A process according to  claim 1 , wherein the at least one optically brightened plastic fiber is optically brightened with at least one compound of formulae (1) to (4) 
     
       
         
         
             
             
         
       
       where in formula (1) 
       R 1  to R 8  independently of one another are hydrogen, C 1 -C 20 -alkyl or groups of the formula —COOR 9 , 
       R 9  is hydrogen, C 1 -C 20 -alkyl or phenyl, 
       or 
       R 1  to R 8  are a group of the formula —SO 2 R 10 , where
 R 10  is hydrogen, C 1 -C 10 -alkyl or C 1 -C 10 -hydroxyalkyl, 
 
       and 
       A is stilbene, naphthalene, phenylene, thiophenylene or biphenylene, or a mixture thereof. 
     
   
   
       7 . A process according to  claim 6 , wherein the at least one optically brightened fiber is optically brightened with at least one compound of formula (1) wherein
 R 1  to R 8  independently of one another are hydrogen or C 1 -C 4 -alkyl, and   A is stilbene, naphthalene, phenylene, thiophenylene or biphenylene.   
   
   
       8 . A process according to  claim 7 , wherein
 R 1  to R 8  independently of one another are hydrogen or methyl, and   A is stilbene.   
   
   
       9 . A process according to  claim 1 ,
 wherein the at least one optically brightened plastic fiber contains between 10 and 500 ppm optical brightener.   
   
   
       10 . A process according to  claim 1 , wherein the at least one optically brightened plastic fiber contains between 20 and 250 ppm optical brightener. 
   
   
       11 . A process according to  claim 1 , wherein 2 to 60% by weight, based on the weight of the dry pulp, of the optically brightened filler composition is added to the pulp suspension. 
   
   
       12 . A process according to  claim 1 , wherein 10 to 40% by weight, based on the weight of the dry pulp, of the optically brightened filler composition is added to the pulp suspension. 
   
   
       13 . A process according to  claim 1 , wherein the optically brightened filler composition is added to the pulp suspension in the form of an aqueous dispersion. 
   
   
       14 . An optically brightened paper produced by a process according to  claim 1 .