Method for the production of a film comprising microfibrillated cellulose, a film and a paper or paperboard product
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 between 70 weight-% to 100 weight-% of microfibrillated cellulose based on total dry weight, forming a fibrous web of said suspension, drying the web in a drying equipment wherein the web is at least partly dried at a drying rate above 75 kg(H 2 O)/m 2 /h by use of hot air whereby a film is formed. The invention also relates to a film produce according to the method and a paper or paperboard substrate comprising said film.
1. A method for the production of a film comprising microfibrillated cellulose, wherein the method comprises the steps of:
providing a suspension comprising between 70 weight-% to 100 weight-% of microfibrillated cellulose based on total dry weight,
forming a fibrous web of said suspension,
drying the web in a drying equipment wherein the web is at least partly dried at a drying rate above 75 kg(H 2 O)/m 2 /h by use of hot air whereby a film is formed.
2. The method as claimed in claim 1 , wherein the air has a temperature of 100-350° C. and is applied at a velocity of 20-100 m/s.
3. The method according of claim 1 wherein the web is applied to a support and thereafter conducted through the drying equipment on said support.
4. The method according to claim 3 wherein the support is a metal belt.
5. The method according to claim 3 wherein the support is heated to a temperature between 60-150° C. before the web is applied to the support.
6. The method according to claim 1 wherein the fibrous web is formed by adding the suspension onto a substrate.
7. The method according to claim 6 wherein the fibrous web is formed by casting the suspension onto the substrate.
8. The method according to claim 6 wherein the substrate is a paper or paperboard substrate.
9. The method according to claim 6 wherein the substrate is a polymer or metal substrate.
10. The method according to claim 1 wherein the fibrous web is formed by subjecting the suspension onto a wire.
11. The method according to claim 1 wherein pressure is applied to the fibrous web prior and/or during the drying of the web in the drying equipment.
12. The method according to claim 1 wherein the fibrous web has a dry content of 10-40 weight-% before being dried in the drying equipment.
13. The method according to claim 1 wherein the microfibrillated cellulose of the suspension has a Shopper-Riegler (SR) value above 90.
14. The method according to claim 1 wherein the film has an Oxygen Transmission Rate (OTR) value (23° C., 50% RH) below 400 cc/m 2 /24 h according to ASTM D-3985 after drying.
15. The method according to claim 1 wherein the drying equipment is an impingement drying equipment.