Production of paper- or linerboard

Abstract

There is provided a method of producing a paper- or linerboard having a grammage measured according to ISO 536:2019 of 170-310 g/m2 and comprising a print layer, a middle layer and a back layer, wherein the middle layer is formed from a middle layer furnish comprising at least 25% by dry weight CTMP and the back layer is formed from a back layer furnish comprising an unbleached pulp, such as an unbleached kraft pulp, said method comprising the step of subjecting a multi-layered web at a speed of at least 600 m/min to pressing in a press section comprising a first and a second double-felted shoe press nip arranged in series, wherein the total press impulse of the double-felted shoe press nips is at least 95 kPa*s, preferably at least 100 kPa*s.

1 . A method of producing a paper- or linerboard having a grammage measured according to ISO 536:2019 of 170-310 g/m 2  and comprising a print layer, a middle layer and a back layer, wherein the middle layer is formed from a middle layer furnish comprising at least 25% by dry weight CTMP and the back layer is formed from a back layer furnish comprising an unbleached pulp, such as an unbleached kraft pulp, said method comprising the step of subjecting a multi-layered web at a speed of at least 600 m/min to pressing in a press section comprising a first and a second double-felted shoe press nip arranged in series, wherein the total press impulse of the double-felted shoe press nips is at least 95 kPa*s. 
     
     
         2 . The method of  claim 1 , wherein the speed is at least 650 m/min. 
     
     
         3 . The method of  claim 1 , wherein the line load of the second double-felted shoe press nip is higher than the line load of the first double-felted shoe press nip. 
     
     
         4 . The method of  claim 1 , wherein the head box consistency of the middle layer furnish is 0.15%-0.42%. 
     
     
         5 . The method of  claim 1 , wherein the head box consistency of the print layer furnish is 0.12%-0.25%. 
     
     
         6 . The method of  claim 1 , wherein the head box consistency of the back layer furnish is 0.12%-0.25%. 
     
     
         7 . The method of  claim 1 , wherein the middle layer furnish comprises at least 30% by dry weight CTMP. 
     
     
         8 . The method of  claim 1 , wherein the middle layer furnish further comprises at least 20% by dry weight broke pulp, by dry weight broke pulp. 
     
     
         9 . The method of  claim 8 , wherein CTMP and broke pulp together constitute at least 65% by dry weight of the middle layer furnish by dry weight of the middle layer furnish. 
     
     
         10 . The method of  claim 1 , wherein the middle layer furnish further comprises kraft pulp. 
     
     
         11 . The method of  claim 1 , wherein the print layer furnish comprises a mixture of hardwood kraft pulp and softwood kraft pulp. 
     
     
         12 . The method of  claim 11 , wherein hardwood kraft pulp and softwood kraft pulp together constitute at least 80% by dry weight of the print layer furnish. 
     
     
         13 . The method of  claim 1 , wherein the back layer furnish further comprises broke pulp. 
     
     
         14 . The method of  claim 13 , wherein unbleached kraft pulp and broke pulp together constitute at least 80% by dry weight of the back layer furnish. 
     
     
         15 . The method of  claim 1 , wherein the forming of the middle layer comprises use of a breast roll shaker. 
     
     
         16 . The method of  claim 1 , wherein the press section comprises a further nip arranged downstream the double-felted shoe press nips. 
     
     
         17 . The method of  claim 16 , wherein the further nip is a hard nip or a single-felted shoe press nip.