Fully bleached sulfite chemical pulp, a process for the production thereof and products derived therefrom

Abstract

A process for preparing a bleached sulfite chemical pulp includes delignification of chips of a lignocellulosic material in a sulfite pulping process until the defibration point of the material is reached, and bleaching of the fibrous material thus obtained by a chlorine-free bleaching sequence which includes at least one first bleaching step with a chlorine-free oxidant in the presence of a base. The chemical pulp prepared according to this process and paper or nonwoven made from such pulp have a high degree of brightness (at least 83% ISO) and high strength.

1 . A process for preparing bleached sulfite chemical pulp, comprising the following steps: 
 delignifying chips of a lignocellulosic material in a sulfite pulping process until a defibration point of said lignocellulosic material is reached, and a fibrous material is obtained; and    bleaching the fibrous material with a bleaching sequence which is performed exclusively with chlorine-free reagents and comprises at least a first bleaching step with a chlorine-free oxidant in the presence of a base.    
     
     
         2 . The process according to  claim 1 , wherein the fibrous material has a kappa value ranging between 50 and 75.  
     
     
         3 . The process according to  claim 1 , wherein the sulfite pulping is conducted under acidic conditions.  
     
     
         4 . The process according to  claim 1 , wherein the sulfite pulping is conducted in the presence of magnesium in an acidic environment.  
     
     
         5 . The process according to  claim 1 , wherein the sulfite pulping is conducted with an aqueous solution containing magnesium bisulfite, optionally an excess of SO 2 , at a temperature of 130° to 165° C. and at a pH of 1.5 to 4.  
     
     
         6 . The process according to  claim 1 , wherein the oxidant is hydrogen peroxide.  
     
     
         7 . The process according to  claim 1 , wherein the reaction sequence for chlorine-free bleaching of pulp comprises at least one additional bleaching step with a chlorine-free oxidant in the presence of a base.  
     
     
         8 . The process according to  claim 7 , wherein the oxidant used in the additional bleaching step is hydrogen peroxide or peractic acid.  
     
     
         9 . The process according to  claim 1 , wherein prior to treatment with an oxidant, treatment with a metal ion complexing agent is conducted.  
     
     
         10 . The process according to  claim 1 , wherein the reaction sequence for chlorine-free bleaching of pulp comprises a final bleaching step with a reducing bleaching agent.  
     
     
         11 . The process according to  claim 10 , wherein the reducing bleaching agent is selected from the group consisting of a water-soluble dithionite salt, hydroxylamine, thio urea, thioglycolic acid, borohydride hydride, and formamidinosulfinic acid.  
     
     
         12 . A chemical pulp, obtainable by a sulfite pulping process and subsequent chlorine-free bleaching, wherein said chemical pulp has a degree of brightness of at least 83% ISO and a test sheet produced from said chemical pulp without beating has a strength, expressed as breaking length (measured according to Zellcheming V/12/57), of at least 6 km.  
     
     
         13 . The chemical pulp according to  claim 12 , wherein said chemical pulp has a kappa number of between 10 and 30.  
     
     
         14 . The chemical pulp according to  claim 12 , wherein said chemical pulp is subjected to a beating step following bleaching.  
     
     
         15 . A paper or nonwoven prepared from a chemical pulp according to  claim 12 .  
     
     
         16 . A paper according to  claim 15  which is tissue paper.  
     
     
         17 . A product prepared from nonwoven or paper according to  claim 15 .  
     
     
         18 . The process according to  claim 6 , wherein the reaction sequence for chlorine-free bleaching of pulp comprises at least one additional bleaching step with a chlorine-free oxidant in the presence of a base.  
     
     
         19 . The process according to  claim 18 , wherein the oxidant used in the additional bleaching step is hydrogen peroxide or peractic acid.  
     
     
         20 . The process according to  claim 6 , wherein prior to treatment with an oxidant, treatment with a metal ion complexing agent is conducted.  
     
     
         21 . The process according to  claim 6 , wherein the reaction sequence for chlorine-free bleaching of pulp comprises a final bleaching step with a reducing bleaching agent.  
     
     
         22 . The process according to  claim 10 , wherein the reducing bleaching agent is selected from the group consisting of a water-soluble dithionite salt, hydroxylamine, thio urea, thioglycolic acid, borohydride hydride, and formamidinosulfinic acid.