Multilayer film comprising highly refined cellulose fibers
The present invention relates to a method for manufacturing a multilayer film comprising highly refined cellulose fibers, the method comprising the steps of: a) forming a first wet web by applying a first pulp suspension comprising highly refined cellulose fibers on a first wire; b) partially dewatering the first wet web to obtain a first partially dewatered web; c) forming a second wet web by applying a second pulp suspension comprising highly refined cellulose fibers on a second wire; d) partially dewatering the second wet web to obtain a second partially dewatered web; e) applying a binder between the first and second partially dewatered web and joining the first and second partially dewatered web to obtain a multilayer web; and f) further dewatering, and optionally drying, the multilayer web to obtain a multilayer film comprising highly refined cellulose fibers.
1. A method for manufacturing a multilayer film comprising highly refined cellulose fibers, the method comprising the steps of:
a) forming a first wet web by applying a first pulp suspension comprising highly refined cellulose fibers having a Schopper-Riegler (SR) value of 65 or higher, as determined by standard ISO 5267-1, on a first wire;
b) partially dewatering the first wet web to obtain a first partially dewatered web;
c) forming a second wet web by applying a second pulp suspension comprising highly refined cellulose fibers having a Schopper-Riegler (SR) value of 65 or higher, as determined by standard ISO 5267-1, on a second wire;
d) partially dewatering the second wet web to obtain a second partially dewatered web;
e) applying a binder between the first partially dewatered web and the second partially dewatered web by spray coating, curtain coating, or foam coating and joining the first partially dewatered web and the second partially dewatered web to obtain a multilayer web; and
f) further dewatering the multilayer web to obtain a multilayer film comprising highly refined cellulose fibers,
wherein a dry solids content of the first pulp suspension, the second pulp suspension, or both is in a range of 0.1-0.7 wt %.
2. The method according to claim 1 , wherein the first pulp suspension, the second pulp suspension, or both comprises at least 50 wt % highly refined cellulose fibers, based on a total dry weight of the pulp suspension.
3. The method according to claim 1 , wherein the first pulp suspension, the second pulp suspension, or both is formed from a cellulose furnish having a Schopper-Riegler (SR) value in a range of 65-99, as determined by standard ISO 5267-1.
4. The method according to claim 1 , wherein the highly refined cellulose fibers comprise microfibrillated cellulose (MFC).
5. The method according to claim 4 , wherein the first pulp suspension, the second pulp suspension, or both comprises 50-99 wt % MFC, based on a total dry weight of said pulp suspension.
6. The method according to claim 1 , wherein the first pulp suspension, the second pulp suspension, or both comprise less than 50 wt % of unrefined or slightly refined cellulose fibers having a Schopper-Riegler (SR) value below 30 as determined by standard ISO 5267-1, based on a total dry weight of the pulp suspension.
7. The method according to claim 1 , wherein the first pulp suspension and the second pulp suspension have the same composition.
8. The method according to claim 1 , wherein a basis weight of the first wet web, the second wet web, or both based on a total dry weight of said wet web is less than 50 g/m 2 .
9. The method according to claim 1 , wherein the binder is a polymeric binder.
10. The method according to claim 1 , wherein the binder is selected from a group consisting of: nanocellulose, lignin, and derivatives thereof.
11. The method according to claim 1 , wherein the binder is applied at a basis weight in a range of 0.1-20 g/m 2 .
12. The method according to claim 1 , wherein a dry solids content of the first partially dewatered web and the second partially dewatered web prior to the joining step is in a range of 1.5-8 wt %.
13. The method according to claim 1 , wherein a basis weight of the multilayer web based on a total dry weight of the multilayer web is in a range of 10-100 g/m 2 .
14. The method according to claim 1 , wherein the multilayer film is transparent or translucent to visible light.
15. The method according to claim 1 , wherein a KIT value of the multilayer film is at least 6, as measured according to standard ISO 16532-2.
16. The method according to claim 1 , wherein the multilayer film comprises less than 10 pinholes/m 2 , as measured according to standard EN13676:2001.
17. The method according to claim 1 , wherein the multilayer film has a Gurley Hill value of at least 10 000 s/100 ml, as measured according to standard ISO 5636/6.
18. A multilayer film with highly refined cellulose fibers, said film comprising:
a first layer comprising highly refined cellulose fibers having a Schopper-Riegler (SR) value of 65 or higher, as determined by standard ISO 5267-1, and
a second layer comprising highly refined cellulose fibers having a Schopper-Riegler (SR) value of 65 or higher, as determined by standard ISO 5267-1,
wherein said first and second layers are joined by a binder applied by spray coating, curtain coating, or foam coating between said first and second layer,
wherein the first layer, the second layer or both are formed from a suspension with a dry solids content in a range of 0.1-0.7 wt % such that multilayer film comprises less than 10 pinholes/m 2 , as measured according to standard EN13676:2001.
19. The multilayer film according to claim 18 , wherein the binder is a polymeric binder.
20. The multilayer film according to claim 18 , wherein the binder is selected from a group consisting of: nanocellulose, lignin, and derivatives thereof.
21. The multilayer film according to claim 18 , wherein the binder is applied at a basis weight of less than 20 g/m 2 .