EP-4735688-A1 - A PAPERBOARD STRUCTURE COMPRISING A BARRIER COATING LAYER

Abstract

According to an example aspect of the present invention, there is provided a paperboard structure, comprising a paperboard substrate and a barrier coating layer on the paperboard substrate, wherein the paperboard substrate comprises folding boxboard or linerboard, wherein the barrier coating layer comprises microcrystalline cellulose and a polyester derived from succinic acid and/or adipic acid, wherein the average particle size of the microcrystalline cellulose ranges from 1 µm to less than 20 µm, wherein the barrier coating layer has been prepared by extruding a composition comprising microcrystalline cellulose and said polyester on the paperboard substrate.

Inventors

• KASTINEN, Henri
• TALJA, RIKU
• VERKASALO, LAURI
• HAKALAHTI, Minna
• HIRVONEN, KIRSI
• SAARI, TERHI
• HELANTO, Karoliina

Assignees

• Metsä Board Oyj

Dates

Publication Date

20260506

Application Date

20240627

Claims (20)

1. 1. A paperboard structure, comprising a paperboard substrate and a barrier coating layer on the paperboard substrate, wherein the paperboard substrate comprises folding boxboard or linerboard, wherein the barrier coating layer comprises microcrystalline cellulose and a polyester derived from succinic acid and/or adipic acid, wherein the average particle size of the microcrystalline cellulose ranges from 1 pm to less than 20 pm, wherein the barrier coating layer has been prepared by extruding a composition comprising microcrystalline cellulose and said polyester on the paperboard substrate.
2. 2. The paperboard structure according to claim 1, wherein the polyester comprises one or more of the following group: polybutylene succinate (PBS), polyethylene succinate (PES), polypropylene succinate (PPS), polybutylene adipate (PBA) and polybutylene succinate- co-adipate (PBSA), polybutylene adipate-co-terephthalate (PBAT), and any co-polymers and mixtures thereof.
3. 3. A paper board structure according to any of the preceding claims, wherein the polyester is selected from polybutylene succinate and polybutylene adipate or combinations thereof.
4. 4. The paperboard structure according to any of the preceding claims, wherein the barrier coating layer comprises at least 50 wt-%, for example at least 70 wt-%, of said polyester calculated from the total weight of the barrier coating layer.
5. 5. The paperboard structure according to any of the preceding claims, wherein the barrier coating layer comprises at least 10 wt-% of microcrystalline cellulose, such as at least 20 wt-%, for example at least 30 wt-%, calculated from the total weight of the barrier coating layer.
6. 6. The paperboard structure according to any of the preceding claims, wherein the thickness of the barrier coating layer is 1 to 50 pm.
7. 7. The paperboards structure according to any of the preceding claims, wherein the barrier coating layer comprises at least 10 wt-% of microcrystalline cellulose and at least 50 wt-% of polybutylene succinate, polybutylene adipate or combinations thereof calculated from the total weight of the barrier coating layer.
8. 8. The paperboards structure according to any of the preceding claims, wherein the barrier coating layer comprises at least 20 wt-% of microcrystalline cellulose and at least 70 wt-% of polybutylene succinate, polybutylene adipate or combinations thereof calculated from the total weight of the barrier coating layer.
9. 9. The paperboard structure according to any of the preceding claims, wherein the barrier coating layer consists of microcrystalline cellulose and a polyester derived from succinic acid and/or adipic acid.
10. 10. The paperboard structure according to any of the preceding claims, wherein the paper board structure comprises at least one coating layer in addition to the barrier coating layer.
11. 11. A method of coating, comprising: - melting a composition comprising microcrystalline cellulose and a polyester derived from succinic acid and/or adipic acid, and - extruding the melted composition onto a paperboard substrate to form a barrier coating layer on the paperboard substrate, wherein the paperboard substrate comprises folding boxboard or linerboard, and wherein the average particle size of the microcrystalline cellulose ranges from 1 pm to less than 20 pm.
12. 12. The method according to claim 11, wherein the polyester comprises one or more of the following group: polybutylene succinate (PBS), polyethylene succinate (PES), polypropylene succinate (PPS), polybutylene adipate (PBA) and polybutylene succinate- co-adipate (PBSA), polybutylene adipate-co-terephthalate (PBAT), and any co-polymers and mixtures thereof.
13. 13. The method according to claim 11 or 12, wherein the polyester comprises polybutylene succinate or polybutylene succinate co-adipate.
14. 14. The method according any of claims 11 to 13, wherein the polyester comprises polybutylene adipate or polybutylene adipate-co-terephthalate.
15. 15. The method according to any of claims 11 to 14, wherein the composition comprises at least 50 wt-%, for example at least 70 wt-%, of said polyester calculated from the total weight of the composition.
16. 16. The method according any of claims 11 to 15, wherein the microcrystalline cellulose has been prepared from wood, such as wood pulp.
17. 17. The method according to any of claims 11 to 16, wherein the composition comprises at least 10 wt-% of microcrystalline cellulose, such as at least 20 wt-%, for example at least 30 wt-%, calculated from the total weight of the composition.
18. 18. The method according any of claims 11 to 17, wherein during said extruding, the temperature of the melted composition is at least 150 °C, such as at least 200 °C.
19. 19. The method according to any of claims 11 to 18, wherein the thickness of the extruded barrier coating layer is in the range of 1 to 50 pm.
20. 20. The method according to any of claims 11 to 19, wherein the melt index of the barrier coating layer is below 30 g/10 min.

Description

A PAPERBOARD STRUCTURE COMPRISING A BARRIER COATING LAYER FIELD [0001] The present disclosure belongs to the field of paperboard products. More specifically, it belongs to the field of barrier coated paperboard structures formed by extrusion coating. BACKGROUND [0002] Extrusion coating is a process where a thin layer of coating composition is extruded on to a substrate, such as paper, paperboard, metal or plastic. Typically, the extrusion coating composition is based on polymers, such as low-density polyethylene (LDPE). It would however be important to replace plastic components with bio-based solutions. [0003] Cellulose-based components could serve as potential coating components. One issue with cellulose-based components is that they cannot be readily mixed with typical coating polymers because the surface chemistries of the two components are not compatible. Therefore, cellulose-based materials do not mix/disperse well in polymer matrixes. In addition, cellulose based materials in some cases have poor adhesion to surface of a polymer. Typically, these issues are alleviated by using additives or by treating the surface of the cellulose based components. [0004] Extrusion coating sets requirements on the used composition that make only certain polymers or compositions suitable for extrusion. At high extrusion coating speed, even a minor disturbance on the melt web causes major quality problems that can very rapidly lead to large quantities of waste. Neck-in is another common issue in extrusion coating. Therefore, polymers are required with high and consistent quality to avoid waste due to polymer edge instability and web breaks. Compositions used for extrusion coating must further adhere to the surface to be coated. Further, the composition must be heat- resistant because extrusion requires use of high temperatures. Such requirements are not present for example in spray coating. SUMMARY OF THE INVENTION [0005] The invention is defined by the features of the independent claims. Some specific embodiments are defined in the dependent claims. [0006] According to the first aspect of the present invention, there is provided a paperboard structure, comprising a paperboard substrate and a barrier coating layer on the paperboard substrate. The paperboard substrate comprises folding boxboard or linerboard. The barrier coating layer comprises microcrystalline cellulose and a polyester derived from succinic acid and/or adipic acid, and the average particle size of the microcrystalline cellulose ranges from 1 pm to less than 20 pm. The barrier coating layer has been prepared by extruding a composition comprising microcrystalline cellulose and said polyester on the paperboard substrate. [0007] According to the second aspect of the present invention, there is provided a method of coating. The method comprises melting a composition comprising microcrystalline cellulose and a polyester derived from succinic acid and/or adipic acid, and extruding the melted composition onto a paperboard substrate to form a barrier coating layer on the paperboard substrate. The paperboard substrate comprises folding boxboard or linerboard, and the average particle size of the microcrystalline cellulose ranges from 1 pm to less than 20 pm. [0008] According to the third aspect of the present invention, there is provided use of a polyester derived from succinic acid and/or adipic acid in an extrusion coated layer on a folding boxboard substrate or a linerboard substrate. [0009] According to the fourth aspect of the present invention, there is provided use of a polyester derived from succinic acid and/or adipic acid in an extrusion coated layer on a linerboard substrate. [0010] Various embodiments of the first aspect or the second aspect or the third aspect or the fourth aspect may comprise one or more features from the following bulleted list: • The polyester is selected from the following group: polybutylene succinate (PBS), polyethylene succinate (PES), polypropylene succinate (PPS), polybutylene adipate (PBA), polybutylene succinate-co-adipate (PBSA), polybutylene adipate-co- terephthalate (PBAT), and any co-polymers and mixtures thereof. • The polyester is selected from polybutylene succinate and polybutylene adipate or combinations thereof • The polyester comprises polybutylene succinate and/or polybutylene succinate coadipate. • The polyester comprises polybutylene adipate and/or polybutylene adipate-co- terephthalate. • The composition comprises at least 50 wt-%, for example at least 70 wt-%, of said polyester, calculated from the total weight of the composition. • The average particle size of the microcrystalline cellulose is in the range 1 pm to less than 20 pm. • The microcrystalline cellulose has been prepared from wood, such as wood pulp. • The composition comprises a homogeneous dispersion of microcrystalline cellulose particles in a polyester matrix or a polyester medium. • The barrier coating layer comprises at least 10 wt-%