US-12624501-B2 - Method for manufacturing a barrier film comprising highly refined cellulose

Abstract

The present invention relates to a method for manufacturing a barrier film comprising highly refined cellulose, said method comprising: a) providing a highly refined cellulose pulp suspension comprising highly refined cellulose pulp having a Schopper-Riegler (SR) number in the range of 40-98 as determined by standard ISO 5267-1 and a content of fibers having a length >0.2 mm of at least 7 million fibers per gram based on dry weight, at a consistency in the range of 0.1-1.5 wt %; b) forming a web of the highly refined cellulose pulp suspension and dewatering the web in a paper machine former on a wire to a consistency of at least 5 wt % to obtain a substrate web, wherein the white water removed from the pulp contains 2-25 wt %, preferably 5-20 wt % and more preferably at least 5-15 wt % of the solids of the highly refined cellulose pulp suspension provided in step a); c) optionally further dewatering and optionally drying the substrate web; d) coating the optionally further dewatered and optionally dried substrate web with a coating suspension comprising cellulose fines or microfibrillated cellulose to obtain a coated web; and e) dewatering and/or drying the coated web to obtain a barrier film comprising highly refined cellulose.

Inventors

• Isto Heiskanen
• Kaj Backfolk
• Katja Lyytikäinen
• Anders Moberg
• Jukka Kankkunen

Assignees

• STORA ENSO OYJ

Dates

Publication Date

20260512

Application Date

20220308

Priority Date

20210310

Claims (20)

1. 1 . A method for manufacturing a barrier film comprising highly refined cellulose, said method comprising: a) providing a highly refined cellulose pulp suspension comprising at least 80% by a total dry weight of highly refined cellulose from a highly refined cellulose pulp having a Schopper-Riegler (SR) number in the range of 40-98 as determined by standard ISO 5267-1 and a content of fibers having a length >0.2 mm of at least 7 million fibers per gram based on a dry weight, at a consistency in a range of 0.1-1.5 wt %; b) forming a web of the highly refined cellulose pulp suspension and dewatering the web in a paper machine former on a wire to a consistency of at least 5 wt % to obtain a substrate web, wherein a dwell time of the substrate web on the wire is below 7 seconds and a white water removed from the pulp contains 2-25 wt % of solids of the highly refined cellulose pulp suspension provided in step a); c) optionally further dewatering and optionally drying the substrate web; d) coating the substrate web with a coating suspension comprising cellulose fines or microfibrillated cellulose to obtain a coated web; and e) dewatering, drying or both, the coated web to obtain a barrier film comprising highly refined cellulose.
2. 2 . The method according to claim 1 , wherein the consistency of the highly refined cellulose pulp suspension provided in step a) is in a range of 0.1-1 wt %.
3. 3 . The method according to claim 1 , wherein step b) comprises dewatering the substrate web to a consistency of at least 7.5 wt %.
4. 4 . The method according to claim 1 , wherein a dry basis weight of the substrate web formed in step b) is in a range of 20-160 gsm.
5. 5 . The method according to claim 1 , wherein a dry density of the substrate web formed in step b) is in a range of 550-1100 kg/m 3 .
6. 6 . The method according to claim 1 , wherein the substrate web formed in step b) has a Gurley hill porosity in a range of 100-20 000 s/100 ml, as measured according to standard ISO 5636/5.
7. 7 . The method according to claim 1 , wherein the paper machine former is a single-wire type former.
8. 8 . The method according to claim 1 , wherein the paper machine former is a twin-wire type former.
9. 9 . The method according to claim 1 , wherein the wire has an air permeability above 4000 m 3 /m 2 /hour at 100 Pa.
10. 10 . The method according to claim 1 , wherein the wire moves at rate of at least 300 m/min.
11. 11 . The method according to claim 1 , wherein the dwell time of the substrate web on the wire is below 5 seconds.
12. 12 . The method according to claim 1 , wherein the dewatering is assisted by vacuum, or pressure, or both.
13. 13 . The method according to claim 1 , wherein the coating suspension comprises at least 50% cellulose fines or MFC based on a dry weight of the coating suspension.
14. 14 . The method according to claim 1 , wherein the coating suspension further comprises nanoparticles, or an anti-slip agent, or both.
15. 15 . The method according to claim 1 , wherein the coating suspension comprises cellulose fines obtained by a fractionation of a highly refined cellulose pulp.
16. 16 . The method according to claim 1 , wherein the coating suspension comprises cellulose fines obtained from the white water removed in step b).
17. 17 . The method according to claim 1 , wherein the coating suspension is applied by curtain coating.
18. 18 . The method according to claim 1 , wherein the coating suspension has a temperature in a range of 40-95° C.
19. 19 . The method according to claim 1 , wherein a dry coat weight of cellulose fines or MFC coated on the web in step d) is in the range of 0.1-10 gsm.
20. 20 . The method according to claim 1 , wherein a dry basis weight of the coated web obtained in step d) is in a range of 20-160 gsm.

Description

This application is a U.S. National Phase under 35 U.S.C. § 371 of International Application No. PCT/IB2022/052037, filed Mar. 8, 2022, which claims priority under 35 U.S.C. §§ 119 and 365 to Swedish Application No. 2150272-9 filed Mar. 10, 2021. TECHNICAL FIELD The present disclosure relates to barrier films, e.g. gas, aroma, and/or moisture barrier films useful in paper and paperboard based packaging materials. More specifically, the present disclosure relates to methods for manufacturing barrier films comprising highly refined cellulose fibers. BACKGROUND Effective gas, aroma, and/or moisture barriers are required in packaging industry for shielding sensitive products. Particularly, oxygen-sensitive products require an oxygen barrier to extend their shelf-life. Oxygen-sensitive products include many food products, but also pharmaceutical products and electronic industry products. Known packaging materials with oxygen barrier properties may be comprised of one or several polymer films or of a fibrous paper or board coated with one or several layers of an oxygen barrier polymer, usually as part of a multilayer coating structure. Another important property for packaging for food products is resistance to grease and oil. More recently, films produced from highly refined cellulose and microfibrillated cellulose (MFC) have been developed, in which defibrillated cellulosic fibrils have been suspended e.g. in water, re-organized and rebonded together to form a continuous film. Such films have been found to provide good gas barrier properties as well as good resistance to grease and oil. The films can be made by applying a highly refined cellulose suspension on a porous substrate forming a web followed by dewatering of the web by draining water through the substrate for forming the film. Formation of the web can be accomplished e.g. by use of a paper- or paperboard machine type of process. The porous substrate may for example be a membrane or wire fabric or it can be a paper or paperboard substrate. Manufacturing of films and barrier substrates from highly refined cellulose or MFC suspensions on a paper machine is difficult because of the high water retention and/or high drainage resistance of the suspensions and the formed webs. Rapid or forced dewatering, e.g. assisted by pressure or suction tends to lead to high loss of fines from the web, or uneven vertical distribution of fines in the web, and formation of pinholes, resulting in a film with poor barrier properties. On the other hand, reducing the dewatering speed to prevent these problems will require an excessively long dewatering section. A problem with webs and films formed from highly refined cellulose or MFC suspensions is that they will typically exhibit poor tensile and tearing strength. From a technical and economical point of view, it would be preferable to find a solution that enables fast dewatering, and at the same time improves the film barrier and tear strength properties. DESCRIPTION OF THE INVENTION It is an object of the present disclosure to provide a method for manufacturing a barrier film comprising highly refined cellulose fibers, which alleviates at least some of the above mentioned problems associated with prior art methods. It is a further object of the present disclosure to provide an improved method for manufacturing a barrier film comprising highly refined cellulose fibers in a paper- or paperboard machine type of process. It is a further object of the present disclosure to provide a barrier film useful as a gas barrier in a paper or paperboard based packaging material which is based on renewable raw materials. It is a further object of the present disclosure to provide a barrier film useful as a gas barrier in a paper or paperboard based packaging material with high repulpability, providing for high recyclability of packaging products comprising the barrier film. The above-mentioned objects, as well as other objects as will be realized by the skilled person in the light of the present disclosure, are achieved by the various aspects of the present disclosure. According to a first aspect illustrated herein, there is provided a method for manufacturing a barrier film comprising highly refined cellulose, said method comprising: a) providing a highly refined cellulose pulp suspension comprising highly refined cellulose pulp having a Schopper-Riegler (SR) number in the range of 40-98 as determined by standard ISO 5267-1 and a content of fibers having a length >0.2 mm of at least 7 million fibers per gram based on dry weight, at a consistency in the range of 0.1-1.5 wt %;b) forming a web of the highly refined cellulose pulp suspension and dewatering the web in a paper machine former on a wire to a consistency of at least 5 wt % to obtain a substrate web, wherein the white water removed from the pulp contains 2-25 wt %, preferably 5-20 wt % and more preferably at least 5-15 wt % of the solids of the highly refined cellulose pulp suspensio