Method to produce a paperboard, a paperboard and a corrugated board

Abstract

A method for producing a paperboard comprising the steps of; providing a furnish comprising cellulosic fibers, applying the furnish on at least one wire to form a web, dewatering the web on said at least one wire by subjecting the web to a pressure above 150 kPa without the use of a press roll nip and thereafter pressing the dewatered web to form a paperboard. Also a paperboard and a corrugated board produced by such a process.

1 . A paperboard comprising:
 a top part, a bottom part, and a middle part,   wherein the top and bottom parts of the paperboard have a first density and the middle part of the paperboard has a second density, and   wherein the second density is higher than the first density.   
     
     
         2 . The paperboard according to  claim 1  wherein the second density is at least 10% higher than the first density. 
     
     
         3 . The paperboard according to  claim 1  wherein the paperboard has a density above 680 kg/m 3 . 
     
     
         4 . The paperboard according to  claim 1  wherein the paperboard has a geometrical SCT value above 32 Nm/g. 
     
     
         5 . The paperboard according to  claim 1  wherein the paperboard comprises more than 50% by weight of NSSC pulp based on the total fiber amount. 
     
     
         6 . The paperboard according to  claim 1  wherein the paperboard comprises 0.1-10% by weight of microfibrillated cellulose based on the total fiber amount. 
     
     
         7 . The paperboard according to  claim 1  wherein the paperboard is a liner. 
     
     
         8 . The paperboard according to  claim 1  wherein the paperboard is a corrugated medium. 
     
     
         9 . The paperboard according to  claim 8  wherein the corrugated medium has a grammage between 80-220 g/m 2 . 
     
     
         10 . A corrugated board comprising:
 a corrugated medium and at least one liner,   wherein the corrugated medium, or the liner, or both comprise
 a top part, a bottom part, and a middle part, 
 wherein the top and bottom parts have a first density and the middle part has a second density, and 
 wherein the second density is higher than the first density. 
   
     
     
         11 . The corrugated board according to  claim 10  wherein the second density is at least 10% higher than the first density. 
     
     
         12 . The corrugated board according to  claim 10  wherein the paperboard has a density above 680 kg/m 3 . 
     
     
         13 . The corrugated board according to  claim 10  wherein the paperboard has a geometrical SCT value above 32 Nm/g. 
     
     
         14 . The corrugated board according to  claim 10  wherein the paperboard comprises more than 50% by weight of NSSC pulp based on the total fiber amount. 
     
     
         15 . The corrugated board according to  claim 10  wherein the top part constitutes between 20-25% of a total thickness of the corrugated board, wherein the bottom part constitutes between 20-25% of the total thickness of the corrugated board, and wherein the middle part constitutes between 50-60% of the total thickness of the corrugated board. 
     
     
         16 . The corrugated board according to  claim 10  wherein the paperboard comprises 0.1-10% by weight of microfibrillated cellulose based on the total fiber amount.