Single layer white kraftliner

Abstract

There is provided a single layer white kraftliner having a grammage from 120 to 185 g/m2 when measured according to ISO 536:2019, wherein the kraftliner: comprises bleached hardwood fibers and bleached softwood fibers in a dry weight ratio from 95:5 to 82:18; comprises a first surface that is coated with a first coating composition comprising starch and pigment; comprises a second surface that is coated with a second coating composition comprising starch and pigment; has a Bendtsen roughness of less than 300 ml/min on at least one of the surfaces when measured according to ISO 8791-2:2013; has a specific formation of less than 0.7 √g/m when measured according to SCAN-P 92:09; has a compressive strength index in the cross direction (CD) of at least 21 Nm/g when measured using a short-span compressive tester according to ISO 9895:2008; and has a geometric tensile stiffness index of at least 5.2 kNm/g when measured according to ISO 1924-3:2005. There is also provided a method of producing a single layer white kraftliner.

1 . A single layer white kraftliner having a grammage from 120 to 185 g/m 2  when measured according to ISO 536:2019, wherein the kraftliner:
 comprises bleached hardwood fibers and bleached softwood fibers in a dry weight ratio from 95:5 to 82:18;   comprises a first surface that is coated with a first coating composition comprising starch and pigment;   comprises a second surface that is coated with a second coating composition comprising starch and pigment;   has a Bendtsen roughness of less than 300 ml/min on at least one of the surfaces when measured according to ISO 8791-2:2013;   has a specific formation of less than 0.7 √g/m when measured according to SCAN-P 92:09;   has a compressive strength index in the cross direction (CD) of at least 21 Nm/g when measured using a short-span compressive tester according to ISO 9895:2008; and   has a geometric tensile stiffness index of at least 5.2 kNm/g when measured according to ISO 1924-3:2005.   
     
     
         2 . The kraftliner of  claim 1 , which has a brightness of at least 80% when measured according to ISO 2470-1:2016. 
     
     
         3 . The kraftliner of  claim 1 , wherein the coat weight of each of the first and the second coating composition is from 1 to 5 g/m 2 . 
     
     
         4 . The kraftliner of  claim 1 , wherein the grammage is from 130 to 170 g/m 2 . 
     
     
         5 . The kraftliner of  claim 1 , wherein the dry weight ratio of bleached hardwood fibers to bleached softwood fibers is from 94:6 to 88:12. 
     
     
         6 . The kraftliner of  claim 1 , wherein the dry weight ratio of starch to pigment in the coating compositions is from 30:100 to 50:100. 
     
     
         7 . The kraftliner of  claim 1 , wherein the coating compositions further comprises latex in such an amount that the dry weight ratio of latex to pigment is from 5:100 to 15:100. 
     
     
         8 . The kraftliner of  claim 1 , wherein said pigment comprises clay pigment and/or calcium carbonate pigment. 
     
     
         9 . The kraftliner of  claim 1 , wherein the Bendtsen roughness of the at least one surface is below 250 ml/s. 
     
     
         10 . The kraftliner of  claim 1 , wherein the specific formation is less than 0.60 √g/m. 
     
     
         11 . The kraftliner of  claim 1 , wherein the specific formation is less than 0.52 √g/m. 
     
     
         12 . The kraftliner of  claim 1 , wherein the compressive strength index in the CD is at least 23 Nm/g. 
     
     
         13 . The kraftliner of  claim 1 , wherein the geometric tensile stiffness index is at least 6.0 kNm/g. 
     
     
         14 . The kraftliner of  claim 1  having a density of 810-920 kg/m3 when measured according to ISO 534:2011. 
     
     
         15 . The kraftliner of  claim 1  having a thickness of 115-220 μm when measured according to ISO 534:2011. 
     
     
         16 . The kraftliner of  claim 1  having an ash content from 3.5% to 8.0% by weight when measured according to ISO 2144:2015. 
     
     
         17 . The kraftliner of  claim 16 , wherein the ash content is from 4.0% to 7.0% by weight. 
     
     
         18 . A method of producing a single layer white kraftliner comprising the steps of:
 providing a furnish comprising bleached hardwood fibers and bleached softwood fibers in a dry weight ratio from 95:5 to 82:18;   forming a web from the furnish in a wire section comprising a headbox;   pressing the web from the wire section in a pressing section;   drying the web from the pressing section in a drying section to obtain a dried web;   optionally calendering the dried web; and   applying a first aqueous coating composition comprising starch and pigment to a first surface of the web and a second aqueous coating composition comprising starch and pigment to a second surface of the web.   
     
     
         19 . The method of  claim 18 , wherein the consistency of the furnish in the headbox is from 0.65% to 0.95%. 
     
     
         20 . The method of  claim 18 , wherein calcium carbonate is added to the furnish in an amount from 30 to 80 kg per tonne of dry fiber.