Method for manufacturing a barrier film, and a barrier film
The present invention relates to a process for manufacturing a barrier film, wherein the method comprises: —providing an aqueous suspension comprising at least 70 weight-% highly refined cellulose pulp having an SR value of 70-95 and having a content of fibers having a length>0.2 mm of at least 10 million fibers per gram based on dry weight: —forming a wet web; —dewatering and/or drying to form a substrate; —calendering said substrate in at least a first calender nip and a second calender nip; —providing said substrate with at least one first layer of a barrier chemical to form a coated substrate, wherein each first layer has a coat weight of 0.5-5 gsm, and wherein a total coat weight on of the first layers is ≤8 gsm, and—drying to form said barrier film having a thickness of <50 μm. The invention relates also to a barrier film, a barrier film laminate with a polymer layer and a packaging material comprising the barrier film.
1 . A method for manufacturing a barrier film, comprising the steps of:
providing an aqueous suspension comprising at least 70 weight-% highly refined cellulose pulp based on a total dry weight of the aqueous suspension, wherein said highly refined cellulose pulp has a Schopper-Riegler value of 70-95° SR, and wherein said highly refined cellulose pulp has a content of fibers having a length>0.2 mm of at least 12 million fibers per gram based on a dry weight;
forming a wet web from said aqueous suspension;
dewatering, or drying, or dewatering and drying said wet web to form a substrate having a first side and an opposite second side;
calendering said substrate in at least a first calender nip in a first calendering step and a second calender nip in a second calendering step, wherein said substrate has a moisture content of 1-25 weight-% when entering said first calender nip;
providing said substrate with at least one layer of:
a) a water-based solution or dispersion comprising a polymer selected from a group consisting of: a polyvinyl alcohol, a modified polyvinyl alcohol, a polysaccharide, a modified polysaccharide, and combinations thereof,
on said first side in a coating step to form a coated substrate, wherein each layer on said first side has a coat weight of 0.5-3 gsm, calculated as a dry weight, and wherein a total coat weight on the first side is equal to or less than 6 gsm calculated as a dry weight, and
drying said coated substrate after said calendering and said coating step so as to form said barrier film, wherein said barrier film has a thickness of less than 50 μm.
2 . The method according to claim 1 , wherein said calendering is performed before said coating step.
3 . The method according to claim 1 , wherein said coating step is performed before said calendering.
4 . The method according to claim 1 , wherein said first calender nip and said second calender nip are respectively constituted by a calender nip selected from a group consisting of: a soft calender nip, a hard calender nip, a super calender nip, a belt calender nip, and a nip in a multi-nip calender.
5 . The method according to claim 2 , further comprising an additional calendering step after said coating step, wherein said additional calendering step comprises calendering said coated substrate in at least one further calender nip selected from a group consisting of: a soft calender nip, a hard calender nip, a super calender nip, and a belt calender nip.
6 . The method according to claim 1 , wherein a Gurley Hill porosity value of the substrate obtained in said step of dewatering, or drying, or dewatering and drying said wet web is at least 25000 s/100 ml.
7 . The method according to claim 1 , wherein said substrate is provided with at least one layer of a water-based solution or dispersion comprising polyvinyl alcohol in the coating step.
8 . The method according to claim 1 , wherein said method further comprises providing said substrate with at least one layer of said water-based solution or dispersion on said second side in a second coating step, wherein each layer on said second side has a coat weight of 0.5-5 gsm, calculated as a dry weight, wherein the total coat weight of said at least one layer on said first side is equal to or less than 5 gsm calculated based on dry weight, and wherein a total coat weight of said at least one layer on said second side is equal to or less than 5 gsm calculated as a dry weight, and wherein said drying of said coated substrate is performed after said second coating step.
9 . The method according to claim 8 , wherein said substrate is provided with at least one layer on said section side of a water-based solution or dispersion comprising polyvinyl alcohol in the second coating step.
10 . The method according to claim 8 , wherein said coating step and said second coating step are performed simultaneously.
11 . The method according to claim 1 , wherein said substrate obtained in said step of dewatering, or drying, or dewatering and drying said wet web has a density of 600-950 kg/m 3 .
12 . The method according to claim 1 , wherein a basis weight of said substrate obtained in the step of dewatering, or drying, or dewatering and drying is less than 90 g/m 2 .
13 . The method according to claim 1 , further comprising a step of pre-moisturizing said substrate prior to said calendaring.
14 . The method according to claim 1 , wherein said calendering comprises using a line load of up to 500 kN/m.
15 . The method according to claim 1 , wherein said calendering comprises using a temperature of 50-250° C.
16 . The method according to claim 1 , wherein said highly refined cellulose pulp has a length weighted mean fibril area of fibers having a length>0.2 mm of at least 15%.
17 . The method according to claim 1 , wherein the wet web is a single or multilayer web made with one or several headboxes.
18 . The method of claim 1 further comprising:
applying a vacuum coating layer having a thickness in a range of 0.1-500 nm on at least said first side of said barrier film to form a barrier film laminate.
19 . The method of claim 18 further comprising:
laminating said barrier film laminate with a paper or paperboard base material to produce a paper or paperboard based packaging material laminate.
20 . A barrier film comprising a coated substrate,
wherein said substrate comprises at least 70 weight-% highly refined cellulose pulp, wherein said highly refined cellulose pulp has a Schopper-Riegler value of 70-95° SR, and wherein said highly refined cellulose pulp has a content of fibers having a length>0.2 mm of at least 12 million fibers per gram based on a dry weight;
wherein said substrate has a first side and a second, opposite side;
wherein said substrate is provided with at least one layer comprising:
b) a polymer selected from a group consisting of: a polyvinyl alcohol, a modified polyvinyl alcohol, a polysaccharide, a modified polysaccharide, and combinations thereof,
on said first side, wherein each layer has a coat weight of 0.5-3 gsm, calculated as a dry weight, and wherein a total coat weight on the first side is equal to or less than 6 gsm calculated as a dry weight;
wherein the barrier film has a thickness of less than 50 μm,
wherein a tensile strength index of the barrier film in the machine direction is >60 Nm/g and a tensile strength index of the barrier film in the cross-machine direction is >30 Nm/g, and
wherein a tensile stiffness index of the barrier film in the machine direction is >9 kNm/g and a tensile stiffness index of the barrier film in the cross-machine direction is >3.5 kNm/g.
21 . The barrier film of claim 20 , further comprising:
a vacuum coating layer having a thickness in a range of 0.1-500 nm.
22 . The barrier film according to claim 21 , wherein the barrier film has a water vapor transmission rate of less than 20 g/m 2 /day.