Method for the production of a film comprising microfibrillated cellulose and a film comprising microfibrillated cellulose
The present invention relates to a method for the production of a film comprising microfibrillated cellulose, wherein the method comprises the steps of; providing a suspension comprising microfibrillated cellulose, applying the suspension on a substrate to form a fibrous web, wherein the web has a first and a second side, conducting the web to a contact drying equipment wherein the first side of said web is in direct contact with of the contact drying equipment at a temperature above 100° C. whereby the web is at least partly dried forming a film. The invention also relates to a film produced according to the method.
1. A method for the production of a film comprising microfibrillated cellulose, wherein the method comprises the steps of:
providing a suspension comprising microfibrillated cellulose wherein the suspension comprises between 70 weight-% to 100 weight-% of microfibrillated cellulose based on the total dry weight of the film,
applying the suspension on a porous wire to form a fibrous web, wherein the fibrous web has a first and a second side, and,
conducting the fibrous web to a contact drying equipment having a heated surface wherein only the first side of said fibrous web is in direct contact with the heated surface of the contact drying equipment at a temperature above 100° C. and the second side of the fibrous web is not in direct contact with the heated surface of the contact drying equipment whereby the fibrous web is at least partly dried forming a film with a second side of the film is coarser compared to a first side of the film,
wherein the film has a grammage below 40 gsm and a density above 700 kg/cm 3 .
2. The method according to claim 1 wherein the contact drying equipment used is a Yankee drying cylinder, a metal belt dryer equipment or a Condebelt drying equipment.
3. The method according to claim 1 wherein the suspension also comprises a wet strength additive.
4. The method according to claim 1 wherein the suspension also comprises a crosslinking agent.
5. The method according to claim 1 wherein the method further comprises the step of applying a surface size, a foam coating and/or a dispersion coating comprising a polymer to the second side of the film that has not been in direct contact with the contact drying equipment.
6. The method according to claim 1 wherein the method further comprises the step of applying a polymer layer to the second side of the film that has not been in direct contact with the contact drying equipment, either through lamination of a polymer film or by extrusion coating of a polymer.
7. The method according claim 1 wherein the method further comprises the step of applying water and/or a chemical solution to the first side of the fibrous web prior to conducting the web to the contact drying equipment.
8. The process according to claim 1 , wherein the film has a grammage below 30 gsm.
9. The process according to claim 1 , wherein the film has an Oxygen Transmission Rate (OTR) value (23° C., 50% RH) below 100 cc/m 2 *day*atm according to ASTM D-3985.