PAPER OR PAPERBOARD COATED WITH A FOAM COATING LAYER COMPRISING NANOCELLULOSE

Abstract

The present invention relates to coated paper or paperboard comprising: a paper or paperboard substrate, and a solid closed cell foam coating layer disposed on a surface of said a paper or paperboard substrate, wherein said solid closed cell foam coating layer comprises a nanocellulose, and a foaming agent. The invention further relates to a food container, preferably a cup, comprising such coated paper or paperboard.

Claims

1. A coated paper or paperboard comprising: a paper or paperboard substrate, and a solid closed cell foam coating layer disposed on a surface of said paper or paperboard substrate, wherein said solid closed cell foam coating layer comprises a nanocellulose, and a foaming agent.

2. The coated paper or paperboard according to claim 1, wherein the nanocellulose is unmodified nanocellulose or modified nanocellulose, or a mixture thereof.

3. The coated paper or paperboard according to claim 1, wherein the closed cell foam of the coating layer comprises in a range of 50-99.5 wt % of nanocellulose, based on a total dry weight of the closed cell foam.

4. The coated paper or paperboard according to claim 1, wherein the foaming agent is a polymeric foaming agent.

5. The coated paper or paperboard according to claim 1, wherein the foaming agent is selected from a group consisting of: polysaccharide ethers, starch, hemicellulose, polyvinyl alcohol, and mixtures thereof.

6. The coated paper or paperboard according to claim 1, wherein the foaming agent is selected from a group consisting of: methyl cellulose (MC), ethyl cellulose (EC), hydroxyethyl cellulose (HEC), hydroxypropyl cellulose (HPC), methylethyl cellulose (MEC), hydroxyethylmethyl cellulose (HEMC), hydroxypropylmethyl cellulose (HPMC), ethylhydroxyethyl cellulose, carboxymethylhydroxyethyl cellulose, and mixtures thereof.

7. The coated paper or paperboard according to claim 1, wherein the foaming agent is methyl cellulose.

8. The coated paper or paperboard according to claim 7, wherein the methyl cellulose has an average degree of substitution in a range of 1.0-2.5.

9. The coated paper or paperboard according to claim 1, wherein the foaming agent has a viscosity in aqueous solution at 2 wt % concentration between 10 and 10,000 cPs.

10. The coated paper or paperboard according to claim 1, wherein the closed cell foam of the coating layer comprises in a range of 0.1-10 wt % of foaming agent, based on a total dry weight of the closed cell foam.

11. The coated paper or paperboard according to claim 1, wherein the closed cell foam of the coating layer further comprises a polymeric dispersing agent, a rheology modifying agent, or a combination thereof.

12. The coated paper or paperboard according to claim 11, wherein said polymeric dispersing agent, said rheology modifying agent, or said combination thereof is a carboxymethyl cellulose (CMC).

13. The coated paper or paperboard according to claim 11, wherein the closed cell foam of the coating layer comprises in a range of 0.1-20 wt % of the polymeric dispersing agent, the, or the combination thereof, based on a total dry weight of the closed cell foam.

14. The coated paper or paperboard according to claim 1, wherein an average diameter of the closed cells in the closed cell foam coating layer is in a range of 5-300 μm.

15. The coated paper or paperboard according to claim 1, further comprising a particulate material dispersed in the closed cell foam coating layer.

16. The coated paper or paperboard according to claim 15, wherein the particulate material is cork particles.

17. The coated paper or paperboard according to claim 15, wherein the particulate material has an average particle diameter in a range of 0.1-1000 μm.

18. The coated paper or paperboard according to claim 15, wherein the closed cell foam of the closed cell foam coating layer comprises in a range of 1-50 wt % of the particulate material, based on a total dry weight of the closed cell foam.

19. The coated paper or paperboard according to claim 1, wherein a basis weight of the closed cell foam coating layer is in a range of 10-50 gsm.

20. The coated paper or paperboard according to claim 1, wherein a basis weight of the paper or paperboard substrate is in a range of 60-500 gsm.

21. The coated paper or paperboard according to claim 1, wherein the coated paper or paperboard has a thermal conductivity below 0.1 W/mK.

22. A carton blank comprising a coated paper or paperboard according to claim 1.

23. A food container comprising a coated paper or paperboard according to claim 1.

24. A method of manufacturing a coated paper or paperboard, comprising the steps: a) preparing an aqueous mixture of a nanocellulose, and a foaming agent, b) foaming said mixture to obtain a foam, c) coating a surface of a paper or paperboard substrate with the foam and drying the coated substrate to obtain a solid closed cell foam coated paper or paperboard.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0119] FIG. 1 is a diagram comparing the thermal resistance of baseboard 1, baseboard 2, baseboard 1 with foam coating, and baseboard 2 with foam coating with cork dust.

[0120] FIG. 2 is a 500× scanning electron microscope (SEM) image of a cross-cut of a foam coating with cork dust.

EXAMPLES

[0121]

TABLE-US-00001 TABLE 1 Materials: Solids content Material Description Producer (wt %) Baseboard 1 Paperboard, grammage = 249 gsm, 100 thickness = 309 μm Baseboard 2 Paperboard, grammage = 214 gsm, 100 thickness = 330 μm HefCel High solids content nanocellulose VTT 19.8 prepared from softwood pulp by high consistency enzyme assisted cellulose fibrillation as described in WO 2015/092146 A1. Carboxymethyl Finnfix 30 000, dispersing agent CPKelco 0.8/2.1 cellulose (CMC) and rheology modifier Methyl cellulose, M0512, foaming polymer and Sigma 0.84 high molecular rheology modifier, viscosity 4000 weight.sup.1 cPs at 2% (MeC hiMw) Methyl cellulose, M6385, foaming polymer, Sigma 2.9 low molecular viscosity 25 cPs at 2% weight.sup.1 (MeC loMw) Ground cork Particles and fibrillary structures; VTT 5.0 dust mostly < 10 μm. .sup.1Cellulose, with methoxy substitution between 27.5-31.5% (weight). Degree of substitution (DS, average number of substituent groups attached to the ring hydroxyls) is 1.5-1.9.

Example 1—Preparation of Foam Coated Paperboard

[0122] Dispersion of Polymers:

[0123] Polymer dispersions were prepared according to instructions from manufacturers.

[0124] Mixing of HefCel and Polymers:

[0125] HefCel and CMC were premixed using a Dispermat high shear mixer at low to medium speed. Methyl cellulose dispersion was added and foaming was performed using the Dispermat high shear mixer at high speed (6000 rpm) for 5 minutes.

[0126] Addition of Cork Dispersion:

[0127] Where ground cork dust was used it was added to mixture before the premixing with the Dispermat mixer.

[0128] Coating:

[0129] Foam coatings were prepared by distributing the foam on baseboard with an Erichsen lab coater applicator. The foam coating (Sample 1) was coated on baseboard 1, and the foam coating with cork dust (Sample 2) was coated on baseboard 2. The coated samples were dried in an oven for 10 minutes at 105° C. Before testing, the samples were equilibrated in a room with standard conditions (23° C. and 50% relative humidity).

[0130] Details of the coating formulation and of the coat weight, thickness and bulk of the dried foam coatings are provided in Table 2.

TABLE-US-00002 TABLE 2 Coating formulation Coat Coating Coating Coating Formulation SC, weight, thickness, bulk, Sample (pph) % g/m.sup.2 μm cm.sup.3/g Baseboard 1 — — — — — (Reference 1) Baseboard 2 — — — — — (Reference 2) Baseboard 1 + HefCel/CMC/MeC 8.4 15 93 6.2 Foam hiMw (Sample 1) 100/2.5/3.4 Baseboard 2 + HefCel/CMC/MeC 9.4 35.7 93 2.6 Foam with cork loMw/ground cork (Sample 2) 100/3.2/6.3/30

[0131] Analysis:

[0132] Stable foam structures were obtained. The cork dust was well incorporated and the coatings with cork dust had a good touch and feel.

[0133] The thermal resistance of baseboard 1 (reference 1), baseboard 2 (reference 2), baseboard 1 with foam coating (Sample 1), and baseboard 2 with foam coating with cork dust (Sample 2), was screened using a preheated plate. A temperature sensor was used to follow the temperature increase through the sample. The results are presented in Table 3 and FIG. 1. The results show a significant increase in thermal resistance with the foam coating, and a further significant increase in thermal resistance with the foam coating with cork dust.

TABLE-US-00003 TABLE 3 Thermal resistance Temperature (° C.) Baseboard 1 + Baseboard 2 + Baseboard 1 Baseboard 2 Foam Foam with cork Time (s) (Reference 1) (Reference 2) (Sample 1) (Sample 2) 10 86.0 82.4 79.7 66.5 15 89.0 84.2 85.7 71.5 20 90.0 84.9 87.0 76.9 25 91.0 86.1 87.2 78.1 30 91.0 87.2 87.2 79.4 60 92.0 89.4 86.9 81.5

[0134] The thermal conductivity of baseboard 2 (reference 2) and baseboard 2 coated with foam with cork (Sample 2) were measured using the Transient Plane Source (TPS) method with a Hot Disk Thermal Constants Analyser (Hot Disk Ltd.). The thermal conductivity of the baseboard 2 (reference 2) was 0.12 W/mK and the thermal conductivity of the baseboard 2 coated with foam with cork (Sample 2) was 0.06 W/mK. Thus, with only a relatively thin coating layer (compared to the thickness of the baseboard), the thermal conductivity of the material can be reduced by about 50%.

[0135] The porous structure of the foam coating was shown by scanning electron microscope (SEM). FIG. 2 is a 500× image of a cross-cut of a foam coating with cork dust. For the SEM imaging, a strip of the coated board was immersed into liquid nitrogen and bent broken. The sample was attached to an Al-stub with double-sided carbon tape. The sample was sputter coated with ˜4 nm of Au—Pd and imaged in secondary electron mode in SEM (Zeiss Merlin). The acceleration voltage was 2 kV and beam current 60 pA.