Paper Dyeing Process

Abstract

This specification discloses an improved paper dyeing process in which paper pulp stock is prepared and subjected to a hot dispersion process, adding a sulphur dye after the hot dispersion process, and acidifying the dyed pulp stock to fix the dye. The dye can be added at any suitable time immediately following hot dispersion, and may be added just prior to or during the treatment of the pulp by disperser plates or the like.

1 . A process for dyeing paper materials, comprising preparing pulp stock suitable for a paper making process, subjecting the pulp stock to a hot dispersion process, characterised by the steps of adding a sulphur dye to the pulp stock after the hot dispersion process of the pulp stock making process, and acidifying the dyed pulp stock to fix the dye. 
   
   
       2 . The process of  claim 1 , wherein the dye is added to the pulp stock just prior to or during treatment of the pulp stock by disperser plates or the like, following hot dispersion. 
   
   
       3 . The process of  claim 1 , wherein the pulp stock is de-watered prior to hot dispersion. 
   
   
       4 . The process of  claim 1 , wherein the hot dispersed pulp stock is diluted to about 5% to 6% stock concentrate and the sulphur dye is added at an addition rate of about 20% to 30%, following which the pulp stock is stored in a stock chest for paper making where it is acidified to fix the dye. 
   
   
       5 . The process of  claim 4 , wherein acidification increases the pH of the pulp stock to about 5.5 to 6.0. 
   
   
       6 . The process of  claim 5 , wherein the dyed pulp stock is acidified by means of a suitable mineral acid, such as dilute sulphuric acid. 
   
   
       7 . The process of  claim 4 , further comprising the step of extracting hydrogen sulphide gas from the stock chest for treatment. 
   
   
       8 . The process of  claim 7 , wherin the hydrogen sulphide gas is treated by passing the gas through another stock chest prior to acidification to adsorb a substantial portion of the gas. 
   
   
       9 . The process of  claim 1 , wherein the pulp stock is fractionated to produce long fibre stock for the top ply of a two-ply paper material, and a short fibre stock for the back ply of the two-ply paper material, and only the long fibre stock is subjected to the dyeing process. 
   
   
       10 . A process for dyeing paper material as described in the Example. 
   
   
       11 . Dyed paper products produced by the process as claimed in  claim 1 .