Method for manufacturing a barrier film, and a barrier film

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.