Process for controlling the brightness of paper products

Abstract

A process for shading white paper characterized in that a mixture comprising at least one direct dye or pigment and at least one optical brightener is used, is claimed as well as the mixture and the paper dyed with this method.

1 . A process for shading white paper by using a mixture comprising at least one direct dye or pigment and at least one optical brightener characterised in that the mixture consists of one or more direct dyes and one or more optical brighteners in a ratio of 25/75 to 90/10 percent by weight, preferably 50/50 percent by weight.  
     
     
         2 . A process according to  claim 1  characterized in that C.I. Direct Violet 51, C.I. Direct Blue 267, C.I. Direct Violet 35 and/or C.I. Direct Red 253 are used.  
     
     
         3 . A process according to  claim 1  characterized in that C.I. Pigment Violet 23, C.I. Pigment Violet 3 and/or C.I. Pigment Blue 15 are used.  
     
     
         4 . Mixture for adding fluorescence to shading dyes for paper comprising one or more direct dyes and one or more optical brighteners in a ratio of 25/75 to 90/10 percent per weight.  
     
     
         5 . Mixture for adding fluorescence to shading dyes for paper comprising one or more pigments and one or more optical brighteners in a ratio of 25/75 to 90/10 percent per weight.  
     
     
         6 . A process according to any one of  claims 1  to  3  or a composition according to  claim 4  or  5 , characterized in that the optical brightener are Wet-end OBA's, Size-press OBA's and/or Coating OBA's.  
     
     
         7 . A process according to  claim 6 , characterized in that the optical brightener C.I. Fluorescent Brightener 220, C.I. Fluorescent Brightener 28 and/or C.I. Fluorescent Brightener 264.  
     
     
         10 . Paper obtained by the process of  claim 1  or  2  or  3  or  6  or  7 .