Barrier-coated cellulose-based substrate

Abstract

The present invention relates to a barrier-coated cellulose-based substrate (25a) and to a method of manufacturing such cellulose-based substrates, by dispersion coating of a ductile base layer pre-coating (12a) and subsequent dispersion coating of a gas barrier composition (13a) and/or vapour deposition coating of a barrier deposition coating (14a). The invention further relates to laminated packaging materials (20a) comprising the barrier-coated celluose-based substrate (10), in particular intended for liquid carton food packaging, and to liquid carton packaging containers comprising the laminated packaging material.

1 . Barrier-coated cellulose-based substrate ( 10   a ;  10   b ), for use as a gas barrier sheet in a laminated packaging material for oxygen-sensitive products, comprising
 a cellulose-based substrate ( 11 ) having a density of at least 900 kg/m 3 , and a grammage from 30 to 80 g/m 2 , and   applied on a first side of the cellulose-based substrate, at least one gas barrier coating ( 13   a ,  14   a ; 14   b ) of at least one gas barrier material to a total thickness from 2 to 7000 nm, such as from 2 to 5000 nm, such as from 2 to 4000 nm, excluding any vapour deposition coating,   wherein the barrier-coated cellulose-based substrate ( 10 ) further comprises a ductile base layer pre-coating ( 12   a ; 12   b ),   which is applied by means of dispersion coating and subsequent drying, onto the surface of the first side of the cellulose-based substrate ( 11 ) and positioned beneath the at least one gas barrier coating ( 13   a ,  14   a ;  14   b ,  14 ),   the barrier-coated cellulose-based substrate thus being suitable for providing gas barrier properties in a laminated packaging material and in packages made thereof.   
     
     
         2 . Barrier-coated cellulose-based substrate ( 10   a ;  10   b ) as claimed in  claim 1 , wherein the gas barrier coating ( 13   a ) is a barrier dispersion coating, applied by means of dispersion or solution coating. 
     
     
         3 . Barrier-coated cellulose-based substrate ( 10   a ;  10   b ) as claimed in any one of  claim 1 or 2 , wherein the barrier dispersion coating ( 13   a ) comprises a polymer selected from the group consisting of vinyl alcohol polymers and copolymers, such as from the group consisting of polyvinyl alcohol, PVOH, and ethylene vinyl alcohol, EVOH, starch and starch derivatives, xylan, xylan derivative, nanofibrillar/microfibrillar cellulose, NFC/MFC, nanocrystalline cellulose, NCC, and blends of two or more thereof. 
     
     
         4 . Barrier-coated cellulose-based substrate as claimed in  any one of the preceding claims , wherein the ductile base layer pre-coating ( 12   a ;  12   b ) is made from an aqueous composition comprising a polymer binder material having inherent ductility properties selected from the group consisting of styrene-butadiene copolymer (SB) latex, styrene acrylate copolymer (SA) latex, other latexes of acrylate polymers and copolymers, such as vinyl acrylic copolymer latex and vinyl acetate acrylate copolymer latex, and of bio-based polymer materials. 
     
     
         5 . Barrier-coated cellulose-based substrate as claimed in  any one of the preceding claims , wherein the ductile base layer pre-coating ( 12   a ;  12   b ) is made from an aqueous composition comprising a bio-based polymer binder material having inherent ductility properties selected from the group comprising starch derivatives, polyisoprene, lignin-based polymers, alginates, gums, and soy-based proteins and latexes of one or more such bio-based polymer binder material. 
     
     
         6 . Barrier-coated cellulose-based substrate as claimed in any one of  claims 4-5 , wherein the ductile base layer pre-coating ( 12   a ; 12   b ) further comprises a filler material, such as an inorganic filler. 
     
     
         7 . Barrier-coated cellulose-based substrate as claimed claim  46 , wherein the ductile base layer pre-coating ( 12   a ;  12   b ) comprises from 4 to 45 wt %, such as from 4 to 35 wt %, such as from 4 to 25 wt %, such as from 4 to 20 wt %, such as from 4 to 16 wt % of the polymer binder material having inherent ductility properties, and from 55 to 96 wt %, such as from 65 to 96 wt %, such as from 75 to 96 wt %, such as from 80 to 96 wt % of a filler material, dry weight, and optionally further compounds, such as thickening agents and crosslinking compounds, at additive amounts. 
     
     
         8 . Barrier-coated cellulose-based substrate as claimed in any one of  claims 4-7 , wherein the ductile base layer pre-coating ( 12   a ; 12   b ) comprises per dry weight from 10 to 20 wt % of the polymer binder material having inherent ductility properties, from 75 to 85 wt-% of an inorganic filler, from 3 to 5 wt % of a crosslinking compound, such as starch, and from 1 to 2 wt % of a thickening agent. 
     
     
         9 . Barrier-coated cellulose-based substrate as claimed in any one of  claims 6-8 , wherein the filler material is an inorganic laminar compound, such as bentonite or kaolin. 
     
     
         10 . Barrier-coated cellulose-based substrate as claimed in any one of  claims 4-9 , wherein the ductile base layer pre-coating has a grammage from 2 to 15 g/m 2 , such as from 5 to 15 g/m 2 , such as from 8 to 15 g/m 2 , such as from 10 to 15 g/m 2 . 
     
     
         11 . Barrier-coated cellulose-based substrate ( 10   a ;  10   b ) as claimed in  any one of the preceding claims , wherein the cellulose-based substrate has a second ductile coating ( 15   a ;  15   b ) on its opposite side, such as of the same composition as the ductile base layer pre-coating ( 12   a ;  12   b ). 
     
     
         12 . Barrier-coated cellulose-based substrate ( 10   a ;  10   b ) as claimed in any one of  claims 6-11 , having an ash content from 15 to 25 wt %, such as from 15 to 23 wt %, as determined by ISO1762:2019. 
     
     
         13 . Barrier-coated cellulose-based substrate as claimed in  any one of the preceding claims , wherein the cellulose-based substrate including the ductile base layer pre-coating ( 12   a ; 12   b ), is calendered to an air permeance value lower than 100 nm/(Pa·s) which is the lower limit of applicability of the test method ISO 5636-5:2013, and further lower than 1 nm, such as from 40 to 900 pm/(Pa·s), such as from 40 to 800 pm/(Pa·s), such as from 100 to 700 pm/(Pa·s), such as from 200 to 500 pm/(Pa·s), as determined by SCAN-P 26:78. 
     
     
         14 . Barrier-coated cellulose-based substrate ( 10   a ;  10   b ) as claimed in  any one of the preceding claims , wherein the cellulose-based substrate including the ductile base layer pre-coating ( 12   a ;  12   b ) and the at least one gas barrier coating ( 13   a ,  14   a ; 14   b ), has a PPS surface roughness lower than 3.0 μm, such as lower than 2.8 μm, such as lower than 2.5 μm, such as lower than 2.2 μm, such as lower than 2.0 μm, such as 1.8 μm or below, as measured according to TAPPI 555 om-15, being the same as ISO 8791-4. 
     
     
         15 . Barrier-coated cellulose-based substrate as claimed in  any one of the preceding claims , wherein the cellulose-based substrate comprises at least 50 wt %, such as from 60 to 100 wt %, such as from 70 to 100 wt % softwood cellulose, such as Kraft softwood cellulose. 
     
     
         16 . Method of manufacturing a barrier-coated cellulose-based substrate ( 10 ;  25   a ;  25   b ;  43 ;  44   b ) as claimed in any one of  claims 1-15 , which comprises
 a) a first step of providing a cellulose-based substrate, having a first side and a second side, as a moving web ( 31   a ) in a roll-to-roll system,   b) a second step of applying ( 32   a ) a first aqueous dispersion of a ductile base layer pre-coating composition, onto the first side of the moving cellulose-based substrate ( 31   a ), optionally applying a second aqueous dispersion of a ductile coating composition onto the other side of the moving substrate, and drying ( 33   a ) the applied ductile base layer pre-coating, and the optional second ductile coating composition, by forced evaporation,   c) a third step of calendering the pre-coated and dried cellulose-based substrate from step b) to obtain a density of at least 900 kg/m 3 , such as at least 1000 kg/m 3 , and   d) a fourth step of applying a gas barrier coating by means of dispersion coating ( 32   a ′) a second aqueous dispersion or solution of a barrier composition, onto the first side of the moving cellulose-based substrate ( 31   a ′) and the ductile base layer pre-coating ( 12   a ; 12   b ), and subsequently drying ( 33   a ′) the applied barrier dispersion coating by forced evaporation, to a total gas barrier coating thickness from 2 to 7000 nm, such as from 2 to 5000 nm.   
     
     
         17 . Method as claimed in  claim 16 , wherein the first aqueous dispersion of the ductile base layer pre-coating composition ( 12   a ; 12   b ) is applied in the form of an aqueous composition comprising a polymer binder material having inherent ductility properties selected from the group consisting of styrene-butadiene copolymer (SB) latex, styrene acrylate copolymer (SA) latex, other latexes of acrylate polymers and copolymers, such as vinyl acrylic copolymer latex and vinyl acetate acrylate copolymer latex, and of bio-based polymer materials. 
     
     
         18 . Method as claimed in any one of  claims 16 and 17 , wherein the first aqueous dispersion of the ductile base layer pre-coating composition ( 12   a ; 12   b ) further comprises a filler material. 
     
     
         19 . Method as claimed in any one of  claims 16-18 , wherein the pre-coated and dried cellulose-based substrate from step b) is calendered in the third step c) to obtain an air permeance value lower than 100 nm/(Pa·s), which is the lower limit of applicability of the test method ISO 5636-5:2013, and further lower than 1 nm, such as from 40 to 900 pm/(Pa·s), such as from 40 to 800 pm/(Pa·s), such as from 100 to 700 pm/(Pa·s), such as from 200 to 500 pm/(Pa·s), as determined by SCAN-P 26:78. 
     
     
         20 . Method as claimed in any one of  claims 16-19 , wherein in the third step c) the pre-coated and dried cellulose-based substrate from step b) is calendered to obtain a PPS surface roughness lower than 3.0 μm, such as lower than 2.8 μm, such as lower than 2.5 μm, such as lower than 2.2 μm, such as lower than 2.0 μm, such as 1.8 μm or below, as measured according to TAPPI 555 om-15, being the same as ISO 8791-4. 
     
     
         21 . Method as claimed in any one of  claims 16-20 , wherein the ductile base layer pre-coating ( 12   a ;  12   b ) is applied as an aqueous latex composition having a solids content from 48 to 51 wt %, and a Brookfield viscosity from 100 to 1000 mPa·s, a pH from 5.5 to 8. 
     
     
         22 . Method as claimed in any one of  claims 16-21 , wherein the pre-coated and dried cellulose-based substrate from step b) is super-calendered in step c). 
     
     
         23 . Method as claimed in  claim 22 , wherein super-calendering is performed by from 3 to 8 roller nips, such as from 4 to 8 roller nips, at a nominal nip pressure of at least 100 kN, such as at least 200 kN, such as 300 kN or above and at a thermo-roller surface temperature from 100 to 300° C., such as from 100 to 240° C.