Barrier-coated cellulose-based substrate for laminated packaging material

Abstract

The present invention relates to a barrier-coated cellulose-based substrate and to a method of manufacturing such cellulose-based substrates, by dispersion coating of a ductile base layer pre-coating and subsequent dispersion coating of a gas barrier composition and/or vapour deposition coating of a barrier deposition coating.

1 . Barrier-coated cellulose-based substrate, for use as a gas barrier sheet in a laminated packaging material for oxygen-sensitive products, comprising
 a cellulose-based substrate 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 of at least one gas barrier material to a total thickness from 2 to 7000 nm, the gas barrier material excluding nanocrystalline cellulose, NCC,   wherein the barrier-coated cellulose-based substrate further comprises a ductile base layer pre-coating,   which is applied by dispersion coating and subsequent drying, onto the surface of the first side of the cellulose-based substrate and positioned beneath the at least one gas barrier coating,   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 as claimed in  claim 1 , wherein the gas barrier coating is a barrier dispersion coating, applied by dispersion or solution coating, and/or a barrier deposition coating, applied by a vapour deposition method. 
     
     
         3 . Barrier-coated cellulose-based substrate as claimed in  claim 1 , wherein the barrier dispersion coating 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, and blends of two or more thereof. 
     
     
         4 . Barrier-coated cellulose-based substrate as claimed in  claim 1 , wherein the barrier deposition coating is a vapour deposition coating of a material selected from metals, metal oxides, inorganic oxides and carbon coatings. 
     
     
         5 . Barrier-coated cellulose-based substrate as claimed in  claim 1 , wherein the barrier deposition coating is an aluminium metallisation coating, which is applied to an optical density OD of from 1.8 to 2.5. 
     
     
         6 . Barrier-coated cellulose-based substrate as claimed in  claim 1 , wherein the at least one gas barrier coating comprises a barrier dispersion coating, first applied by means dispersion or solution coating onto the ductile base layer pre-coating, and a barrier deposition coating, subsequently applied by a vapour deposition method, onto the barrier dispersion coating. 
     
     
         7 . Barrier-coated cellulose-based substrate as claimed in  claim 1 , wherein the ductile base layer pre-coating is made from an aqueous composition comprising a polymer binder material having inherent ductility properties selected from the group consisting of styrene-butadiene copolymer latex, styrene acrylate copolymer latex, other latexes of acrylate polymers and copolymers, and of bio-based polymer materials. 
     
     
         8 . Barrier-coated cellulose-based substrate as claimed in  claim 1 , wherein the ductile base layer pre-coating 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. 
     
     
         9 . Barrier-coated cellulose-based substrate as claimed in  claim 7 , wherein the ductile base layer pre-coating further comprises a filler material. 
     
     
         10 . Barrier-coated cellulose-based substrate as claimed in  claim 7 , wherein the ductile base layer pre-coating comprises from 4 to 45 wt % of the polymer binder material having inherent ductility properties, and from 55 to 96 wt % of a filler material, dry weight, and optionally further compounds, such as thickening agents and crosslinking compounds, at additive amounts. 
     
     
         11 . Barrier-coated cellulose-based substrate as claimed in  claim 7 , wherein the ductile base layer pre-coating 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, and from 1 to 2 wt % of a thickening agent. 
     
     
         12 . Barrier-coated cellulose-based substrate as claimed in  claim 9 , wherein the filler material is an inorganic laminar compound. 
     
     
         13 . Barrier-coated cellulose-based substrate as claimed in  claim 7 , wherein the ductile base layer pre-coating has a grammage from 2 to 15 g/m 2 . 
     
     
         14 . Barrier-coated cellulose-based substrate as claimed in  claim 1 , wherein the cellulose-based substrate has a second ductile coating on its opposite side. 
     
     
         15 . Barrier-coated cellulose-based substrate as claimed in  claim 9 , having an ash content from 15 to 25 wt % as determined by ISO1762:2019. 
     
     
         16 . Barrier-coated cellulose-based substrate as claimed in  claim 1 , wherein the cellulose-based substrate including the ductile base layer pre-coating, 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 as determined by SCAN-P 26:78. 
     
     
         17 . Barrier-coated cellulose-based substrate as claimed in  claim 1 , wherein the cellulose-based substrate including the ductile base layer pre-coating and the at least one gas barrier coating, has a PPS surface roughness lower than 3.0 μm as measured according to TAPPI 555 om-15, being the same as ISO 8791-4. 
     
     
         18 . Barrier-coated cellulose-based substrate as claimed in  claim 1 , wherein the cellulose-based substrate comprises at least 50 wt % softwood cellulose. 
     
     
         19 . Method of manufacturing a barrier-coated cellulose-based substrate as claimed in  claim 1 , which comprises
 a) a first step of providing a cellulose-based substrate, having a first side and a second side, as a moving web in a roll-to-roll system,   b) a second step of applying a first aqueous dispersion of a ductile base layer pre-coating composition, onto the first side of the moving cellulose-based substrate, optionally applying a second aqueous dispersion of a ductile coating composition onto the other side of the moving substrate, and drying 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 , and   d) a fourth step of applying a gas barrier coating by means of dispersion coating a second aqueous dispersion or solution of a barrier composition, excluding nanocrystalline cellulose, NCC, onto the first side of the moving cellulose-based substrate and the ductile base layer pre-coating, and subsequently drying the applied barrier dispersion coating by forced evaporation, and/or by means of vapour depositing a barrier deposition coating onto the first side of the moving cellulose-based substrate with the ductile base layer pre-coating, to a total gas barrier coating thickness from 2 to 7000 nm.   
     
     
         20 . Method as claimed in  claim 19 , wherein the first aqueous dispersion of the ductile base layer pre-coating composition 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 latex, styrene acrylate copolymer latex, other latexes of acrylate polymers and copolymers, and of bio-based polymer materials. 
     
     
         21 . Method as claimed in  claim 19 , wherein the first aqueous dispersion of the ductile base layer pre-coating composition further comprises a filler material. 
     
     
         22 . Method as claimed in  claim 19 , 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 as determined by SCAN-P 26:78. 
     
     
         23 . Method as claimed in  claim 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 as measured according to TAPPI 555 om-15, being the same as ISO 8791-4. 
     
     
         24 . Method as claimed in  claim 19 , wherein the ductile base layer pre-coating 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, and a pH from 5.5 to 8. 
     
     
         25 . Method as claimed in  claim 19 , wherein the pre-coated and dried cellulose-based substrate from step b) is super-calendered in step c). 
     
     
         26 . Method as claimed in  claim 25 , wherein super-calendering is performed by from 3 to 8 roller nips at a nominal nip pressure of at least 100 KN and at a thermo-roller surface temperature from 100 to 300° C.