EP-4735684-A1 - A METHOD FOR PRODUCING A MICROFIBRILLATED CELLULOSE WEB

Abstract

The present invention relates to a method for producing a microfibrillated cellulose (MFC) web. The method comprises providing an MFC suspension (2) comprising water as suspension medium. A wet MFC web (4) is formed of the MFC suspension by casting on a non-porous support (5). The wet MFC web (4) positioned on the non- porous support (5) is subjected to water removal by means of press dewatering and/or non-contact drying to form a dry MFC web (8). The water removal further comprises at least one induction heating step, wherein each induction heating step comprises heating said wet MFC web (4) by means of an induction heated device (10). The dry MFC web (8) is separated from the non-porous support (5).

Inventors

• NYLÉN, Otto
• KARPPINEN, Anni
• BACKFOLK, KAJ

Assignees

• Stora Enso Oyj

Dates

Publication Date

20260506

Application Date

20240611

Claims (20)

1. 1 . A method for producing a microfibrillated cellulose (MFC) web, wherein the method comprises the steps of: providing an MFC suspension (2) comprising between 50 weight-% to 100 weight-% MFC based on total dry weight and a suspension medium, wherein the suspension medium comprises water, wherein said MFC suspension (2) has a dry content of 1-30 weight-%; forming a wet MFC web (4) of said MFC suspension (2) by casting on a non- porous casting support (5); subjecting said wet MFC web (4) positioned on said non-porous casting support (5) to water removal to form a dry MFC web (8), wherein the water removal comprises press dewatering of said wet MFC web (4) and/or noncontact drying of said wet MFC web (4), wherein the water removal further comprises at least one induction heating step, wherein each induction heating step comprises heating said wet MFC web (4) by means of an induction heated device (10, 10a, 10b), and separating said dry MFC web (8) from said non-porous casting support (5).
2. 2. The method according to claim 1 , wherein at least one induction heating step of said at least one induction heating step comprises heating said wet MFC web (4) by means of at least a part (10a) of said non-porous casting support (5) being induction heated.
3. 3. The method according to claim 1 or 2, wherein at least one induction heating step of said at least one induction heating step comprises heating said wet MFC web (4) by means of an induction heated roll (10b) which is provided in indirect or direct contact with said wet MFC web (4) on the side opposite the non-porous casting support (5) during heating of said wet MFC web (4) by means of the induction heated roll (10b).
4. 4. The method according to any one of the preceding claims, wherein at least one induction heating step of said at least one induction heating step comprises heating said wet MFC web (4) by means of at least a part of said non-porous casting support (5) being induction heated and heating said wet MFC web (4) by means of an induction heated roll (10b) which is provided in indirect or direct contact with said wet MFC web (4) on the side opposite the non-porous casting support (5) during heating of said wet MFC web (4) by means of the induction heated roll (10b).
5. 5. The method according to any one of the preceding claims, wherein at least one induction heating step of said at least one induction heating step is performed during at least a part of said press dewatering of said wet MFC web (4) and/or at least one induction heating step of said at least one induction heating step is performed during at least a part of said non-contact drying of said wet MFC web (4).
6. 6. The method according to any one of the preceding claims, wherein said water removal comprises said press dewatering, wherein at least one induction heating step of said at least one induction heating step is performed during at least a part of said press dewatering of said wet MFC web (4) and comprises heating said wet MFC web (4) by means of a part (10a) of said non-porous casting support (5) being induction heated.
7. 7. The method according to any one of the preceding claims, wherein said water removal comprises said press dewatering, wherein at least one induction heating step of said at least one induction heating step is performed during at least a part of said press dewatering of said wet MFC web (4) and comprises heating said wet MFC web (4) by means of an induction heated roll (10b) which is provided in indirect or direct contact with said wet MFC web (4) on the side opposite the non-porous casting support (5) during heating of said wet MFC web (4) by means of the induction heated roll (10b).
8. 8. The method according to any one of the preceding claims, wherein said water removal comprises said press dewatering, wherein at least one induction heating step of said at least one induction heating step is performed during at least a part of said press dewatering of said wet MFC web (4) and comprises heating said wet MFC web (4) by means of a part (10a) of said non-porous casting support (5) being induction heated and by means of an induction heated roll (10b) which is provided in direct or indirect contact with said wet MFC web (4) on the side opposite the non-porous casting support (5) during heating of said wet MFC web (4) by means of the induction heated roll (10b).
9. 9. The method according to any one of the preceding claims, wherein said water removal comprises said non-contact drying, wherein at least one induction heating step of said at least one induction heating step is performed during at least a part of said non-contact drying of said wet MFC web (4) and comprises heating said wet MFC web (4) by means of a part (10a) of said non-porous casting support (5) being induction heated.
10. 10. The method according to any one of the preceding claims, wherein said water removal comprises said non-contact drying, wherein at least one induction heating step of said at least one induction heating step is performed during at least a part of said non-contact drying of said wet MFC web (4) and comprises heating said wet MFC web (4) by means of an induction heated roll (10) which is provided in direct contact with said wet MFC web (4) on the side opposite the non-porous casting support (5) during heating of said wet MFC web (4) by means of the induction heated roll (10b).
11. 11 . The method according to any one of the preceding claims, wherein said water removal comprises said non-contact drying, wherein at least one induction heating step of said at least one induction heating step is performed during at least a part of said non-contact drying of said wet MFC web (4) and comprises heating said wet MFC web (4) by means of a part of said non- porous casting support (5) being induction heated and by means of an induction heated roll (10b) which is provided in direct contact with said wet MFC web (4) on the side opposite the non-porous casting support (5) during heating of said wet MFC web (4) by means of the induction heated roll (10b).
12. 12. The method according to any one of the preceding claims, wherein said water removal comprises said press dewatering, wherein at least one induction heating step of said at least one induction heating step is performed after said press dewatering.
13. 13. The method according to claim 12, wherein said at least one induction heating step performed after said press dewatering comprises heating said wet MFC web (4) by means of a part of said non-porous casting support (5) being induction heated and/or by means of an induction heated roll (10b) which is provided in direct contact with said wet MFC web (4) on the side opposite the non-porous casting support (5) during heating of said wet MFC web (4) by means of the induction heated roll (10b).
14. 14. The method according to any one of the preceding claims, wherein said water removal comprises said non-contact drying, wherein at least one induction heating step of said at least one induction heating step is performed before said non-contact drying and/or wherein at least one induction heating step of said at least one induction heating step is performed after said non-contact drying.
15. 15. The method according to claim 14, wherein each of said at least one induction heating step performed before said non-contact drying and said at least one induction heating step performed after said non-contact drying comprises heating said wet MFC web (4) by means of a part of said non- porous casting support (5) being induction heated and/or by means of an induction heated roll (10b) which is provided in direct contact with said wet MFC web (4) on the side opposite the non-porous casting support (5) during heating of said wet MFC web (4) by means of the induction heated roll (10b).
16. 16. The method according to any one of the preceding claims, wherein said non- porous casting support (5) is a metal belt.
17. 17. The method according to any one of the preceding claims, wherein said press dewatering comprises at least one press dewatering step, wherein each press dewatering step comprises applying a press fabric (12) into direct or indirect contact with said wet MFC web (4) positioned on said non-porous casting support (5) and conducting said wet MFC web (4), arranged between said press fabric (12) and said non-porous casting support (5), through a pressing device (6) to remove water from said wet MFC web (4) by transferring water from said wet MFC web (4) into the press fabric (12).
18. 18. The method according to any one of the preceding claims, wherein said noncontact drying comprises at least one non-contact drying step, wherein each non-contact drying step comprises hot gas impingement drying, microwave drying, ultraviolet drying, electron beam drying, infrared drying, near infrared drying or a combination thereof.
19. 19. The method according to any one of the preceding claims, wherein said formed wet MFC web (4) comprises a single web layer or two or more web layers formed on top of each other.
20. 20. The method according to any one of the preceding claims, wherein said MFC web is an MFC film.

Description

A METHOD FOR PRODUCING A MICROFIBRILLATED CELLULOSE WEB Technical field The present disclosure relates to a method for producing a microfibrillated cellulose (MFC) web, such as an MFC film, involving web formation by casting on a non- porous support. Oxygen, grease, water vapor and/or aroma barrier properties are required in many uses of paper and paperboard packaging. However, paper and paperboard substrates do not have these properties inherently. Most commonly barrier characteristics of paper and paperboard substrates are created by adding one or more barrier coatings and/or laminated barrier layers which are based on plastics or other non-renewable materials. The disadvantage with these coatings and barrier layers is their non-renewable raw material basis that can increase the carbon dioxide footprint of the material as well as make the otherwise biodegradable paper or paperboard non-biodegradable and in some cases non-recyclable. More recently, microfibrillated cellulose (MFC) webs have been developed, in which cellulosic fibrils, provided by fibrillation of cellulose fibers, have been suspended, e.g., in water and thereafter re-organized and re-bonded together to form a web. For example, MFC webs in the form of MFC films, which are dense films with barrier properties, such as oxygen, aroma and grease barrier properties, have been developed. MFC webs, such as MFC films, are recyclable and biodegradable as well as based on renewable raw material. One approach to produce MFC webs, such as MFC films, is to use a wet laid technique, i.e., to apply a dilute MFC suspension comprising MFC and water as suspension medium on a dewatering wire or membrane in a forming section and dewater it by vacuum, gravitation, capillary dewatering, press dewatering or a combination of these on the wire or membrane followed by drying or liquid evaporation. When this approach is utilized, most of the water of the wet MFC web is removed through the wire or membrane in the forming section. Another approach to produce MFC webs, such as MFC films, is to use a casting method in which a wet MFC web is formed by casting of an MFC suspension comprising MFC and water as suspension medium on a non-porous support, such as a plastic or metal support, and thereafter dewatering and/or drying to remove water from the wet MFC web. This type of casting method has been shown to produce MFC films with very smooth surfaces with good barrier properties, such as oxygen barrier properties and/or water vapor barrier properties. However, when the wet MFC web is positioned on the non-porous support, removal of water from the wet MFC web needs to be substantially performed through the surface of the wet MFC web opposite the non-porous support. Thus, removal of water from the wet MFC web is more complex when the method involving casting on a non-porous support is utilized compared to when the wet laid technique with a dewatering wire or membrane is utilized. In particular, a significantly higher amount of water needs to be removed in the dewatering section (such as by press dewatering) and/or the drying section (such as by evaporation) when casting on a non-porous support is utilized compared to when the wet laid technique is utilized. In order to improve the efficiency of the water removal, when casting on a non-porous support is utilized, it is known to heat the wet MFC web by heating the non-porous support by steam. However, steam heating of the non-porous support is associated with limited heat transfer and, thus, energy waste. Also, steam heating of the non-porous support may be associated with challenges in connection with cross machine direction and/or machine direction moisture profile control. In addition, direct steam heating of the non-porous substrate is sensitive for steam leakages and consequent fluctuation of temperature. Steam heating of the non-porous substrate also creates condensate on the surface of the non-porous substrate, at the opposite side of the product, and condensate layer impairs heat transfer efficiency from steam to the substrate. Due to condensate generation, steam heating is not a practical solution in process configurations where the non-porous substrate is carrying the product on the bottom surface facing downwards and being heated from the top surface facing upwards. Thus, there is still room for improvements of methods for producing an MFC web involving formation by casting on a non-porous support. Description of the invention It is an object of the present invention to provide a method for producing an MFC web involving formation by casting on a non-porous support, which method eliminates or alleviates at least some of the disadvantages of the prior art methods. The above-mentioned object, 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. The invention is defined by the appended independent clai