Barrier film comprising microfibrillated cellulose and microfibrillated dialdehyde cellulose and a method for manufacturing the barrier film

Abstract

The present invention relates to a method for manufacturing at least one layer of a film wherein the method comprises the steps of; providing a first suspension comprising microfibrillated cellulose, providing a second suspension comprising microfibrillated dialdehyde cellulose, mixing the first suspension with the second suspension to form a mixture, applying said mixture to a substrate to form a fibrous web and drying said web to form at least one layer of said film. The present invention further relates to a film comprising said at least one layer.

Claims

1. A film comprising microfibrillated cellulose wherein the film has an oxygen transmission rate in the range of from 0.1 to 300 cc/m.sup.2/24h measured according to ASTM D-3985, at a relative humidity of 50% at 23° C. and/or at a relative humidity of 90% at 38° C., and wherein at least one layer of the film comprises a mixture of microfibrillated cellulose and microfibrillated dialdehyde cellulose.

2. The film as claimed in claim 1, wherein the film has a basis weight of less than 50 g/m.sup.2.

3. The film as claimed in claim 1, wherein said film is a multilayer film comprising more than one layer.

4. The film as claimed in claim 1, wherein said film is a multilayer film and wherein at least one layer of the film is a water vapor barrier film comprising any one of polyethylene (PE), polypropylene (PP), polyamide, polyethylene terephthalate (PET) or ethylene vinyl alcohol (EVOH).

5. The film according to claim 4, wherein the water vapor barrier film has a grammage between 10-60 g/m.sup.2.

6. The film according to claim 1, wherein said film is a multilayer film and wherein at least one layer of the film is a metallized barrier layer.

7. The film according to claim 6, wherein said metallized barrier layer is a physical vapour deposited metal or metal oxide layer, or a chemical vapour deposited metal or metal oxide layer.

8. The film according to claim 7, wherein said metal or metal oxide is selected from the group consisting of aluminium, aluminium oxides, magnesium oxides, silicium oxides, copper, magnesium and silicon.

9. The film according to claim 6, wherein said metallized barrier layer has a weight between 50-250 mg/m.sup.2.

10. A packaging material comprising a base material and at least one layer of the film as claimed in claim 1.

11. The packaging material according to claim 10, wherein the base material is paper or paperboard.

12. The packaging material according to claim 11, wherein the paper or paperboard has a grammage between 20-500 g/m.sup.2.

13. The packaging material according to claim 11, wherein the paper or paperboard has a grammage between 80-400 g/m.sup.2.

14. The film as claimed in claim 1, wherein the film has a basis weight of between 10-50 g/m.sup.2.

15. The film according to claim 4, wherein the water vapor barrier film has a grammage between 30-50 g/m.sup.2.

16. The film according to claim 6, wherein said metallized barrier layer has a weight between 75-150 mg/m.sup.2.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1: describes the particle size distribution during storage for two suspensions;

(2) FIG. 2: describes the OTR value for films at fluctuating humidity;

(3) FIG. 3: shows barrier properties in the form of OTR and WVTR respectively for free-standing films;

(4) FIG. 4: shows barrier properties in the form of OTR and WVTR respectively for PE coated films; and

(5) FIG. 5: shows barrier properties in the form of OTR and WVTR respectively of LPB structures

EXAMPLES

Example I: Stability Test

(6) The stability during storage of a suspension comprising microfibrillated dialdehyde cellulose (DA-MFC) was compared to a suspension comprising a mixture of microfibrillated cellulose and microfibrillated dialdehyde cellulose.

(7) The suspension comprising a mixture of MFC and DA-MFC comprises 40 wt-% by total dry weight of the suspension of MFC and 60 wt-% by total dry weight of the suspension of DA-MFC. The oxidation degree of the DA-MFC were 40%.

(8) Both suspension were stored for 15 days. The particle size distribution of the suspensions before storage is seen as “start material” since the particle size distribution for both suspension were the same. The particle size distribution was measured with Mastersizer 3000 (Malvern Instruments Ltd., UK).

(9) The results can be seen in FIG. 1. It is evident from FIG. 1 that the suspension comprising a mixture of DA-MFC and MFC has a much more stable particle size distribution after storage compared to the suspension only comprising DA-MFC.

Example II: OTR Values after Fluctuating Humidity

(10) The OTR value for films comprising only MFC, only DA-MFC and films comprising mixtures of MFC and DA-MFC were measured at a humidity of 90% at 38° C. at two different cycles.

(11) The films each has a grammage of about 40 g/m.sup.2 and the OTR value was measured according to standard ASTM D-3985. The oxidation degree of the DA-MFC used was 38%. The films were stored at room temperature and then the OTR value was measured at a high humidity of 90% at 38° C. and this represents the OTR value in the 1.sup.st cycle. The films were thereafter stored at room temperature again and the OTR value was once again measured at a high humidity of 90% at 38° C. and this represents the OTR value in the 2.sup.nd cycle

(12) The results can be seen in FIG. 2. It is shown in FIG. 2 that the OTR values for the films comprising a mixture of MFC and DA-MFC has a better OTR value (low value is good) in the 2.sup.nd cycle compared to the film comprising only DA-MFC and also to the film comprising only MFC.

Example III: Strain at Break for DA-MFC Films

(13) DA-MFC with an average D.O. of 30% was mixed with native MFC, with a mass ratio of 80%/20%. The solids content of the dispersion was 3 wt %. The mixture was cast coated on a plastic substrate. After drying in room temperature, the film thickness was 58 μm. Film samples were laminated to PE film with a grammage of 25 g/m.sup.2.

(14) The strain at break was measured by means of a standard tensile test (ISO 1924-2 with a span length of 20 mm), wherein the film to be tested was stretched with test speed of 2 mm/minute until a point where it ruptured. The strain at break then corresponds to the percent elongation when rupturing, i.e. to what extent in % the film deforms without breaking upon being subjected to stretching.

(15) The results are seen in Table 1 below and shows that application of a PE layer onto a film comprising DA-MFC leads to improved strain at break.

(16) TABLE-US-00001 TABLE 1 Material tested Strain at break (%) DA-MFC film 1.0 DA-MFC film + PE layer 1.2

Example IV: Barrier Properties of DA-MFC Films and Laminates

(17) DA-MFC with an average D.O. of 30% was mixed with native MFC, with a mass ratio of 80%/20%. The solids content of the dispersion was 3 wt %. The mixture was cast coated on a plastic substrate. After drying in room temperature, the film thickness was 58 μm. This film is referred to as “DA-MFC film”. Films were also made with 100% native MFC as a comparison, referred to as “MFC film”. The adhesion of the native MFC film to the substrate was too low for successful casting. To solve this problem, 15 wt % of sorbitol was added to the films. The addition of sorbitol is noted with (s) in Table 2 and the figures.

(18) Film samples were laminated to PE film with a grammage of 25 g/m.sup.2, and other film samples were laminated to board with a grammage of 239 g/m.sup.2 and PE to form an LPB structure. Said LPB structure was: (15+board+15+film+50) where the numbers are the grammage of the PE layers in g/m.sup.2. The results were compared to a commercial board grade with a grammage of 265 g/m.sup.2, with PE layers on both sides. The grammage of the PE layers was 14 g/m.sup.2 on the top side and 24 g/m.sup.2 on the bottom side.

(19) The OTR was measured according to ASTM F-1927, at the following climates: 23° C., 50% RH; 23° C., 80% RH; and 38° C., 90% RH. The WVTR was measured according to ASTM F-1249, at the following climates: 23° C., 50% RH; 23° C., 80% RH; and 38° C., 90% RH. For the two higher climates, the laminates were stored in the measuring climate for 2 weeks before measurement, to ensure that moisture equilibrium was attained in the sample during the measurement. This was not needed for the films without PE.

(20) The results are seen in Table 2 and in FIGS. 3-5. Herein can be seen that the DA-MFC film has a lower OTR at high humidity (i.e. 80% and 90% RH respectively) compared to native MFC film.

(21) TABLE-US-00002 TABLE 2 Barrier properties of DA-MFC films and laminates (— = not measured). OTR OTR OTR WVTR WVTR WVTR 23/50 23/80 38/90 23/50 23/80 38/90 MFC film 1.3 43 112 9.8 351 >2000 DA-MFC film 2.4 3.6 82 67 214 900 MFC film (s) + 0.3 146 720 2.4 2.3 14 PE DA-MFC 1.0 8.3 128 1.3 1.8 8.6 film + PE PE + board + >1000 >1000 — 1.9 7.2 23 PE LPB with MFC 0.8 69 447 1 1.4 9.5 film (s) LPB with DA- 0.24 8.2 134 0.77 1.4 4.6 MFC film

(22) The results of Example IV shows that DA-MFC film had a better oxygen barrier than native MFC film, especially at 23 C, 80% RH (FIG. 1; Table 2). Further, DA-MFC film had a slight water vapor barrier, even at high relative humidity where native MFC failed to give a water vapor barrier. WVTR of native MFC film was overrange at 38° C., 90% RH. At low relative humidity the native MFC had a better water vapor barrier (FIG. 3; Table 2).

(23) Insertion of DA-MFC film instead of native MFC film with sorbitol in a packaging material gave better oxygen barrier function at high relative humidity (FIG. 4-5). The level of WVTR in the structure was largely controlled by the amount of PE in the structure, but the LPB with DA-MFC film was better than the one with MFC film at 38° C., 90% RH (Table 2).

(24) It is thus possible to tailor-make packaging materials including DA-MFC films, according to the need of barrier properties

Example V: OTR of Metallized DA-MFC Films and Laminates

(25) DA-MFC with an average D.O. of 30% was mixed with native MFC, with a mass ratio of 80%/20%. The solids content of the dispersion was 3 wt %. The mixture was cast coated on a plastic substrate. After drying in room temperature, the film thickness was 58 μm. This film is referred to as “DA-MFC film”. Films were also made with 100% native MFC as a comparison, referred to as “MFC film”. The adhesion of the native MFC film to the substrate was too low for successful casting. To solve this problem, 15 wt % of sorbitol was added to the films. The addition of sorbitol is noted with “(s)” in Table 3.

(26) The films were metallized with Physical Vapour Deposition technology, performed in a vacuum chamber. Aluminum was vaporized by heat, and when it had reached the film it condensated on top of it. The thickness of the Al layer was about 30-40 nm (100 mg/m2).

(27) TABLE-US-00003 TABLE 3 OTR 23/80 OTR 38/90 Metallized MFC film (s) 74 316 Metallized DA-MFC film 6.1 48 LPB with metallized MFC film (s) 13.5 343 LPB with metallized DA-MFC film 4.0 141

(28) As can be seen from Table 3, the metallized DA-MFC film proves to be a very efficient oxygen barrier compared to the metallized MFC film both at 23/80 (i.e. 23° C. and 80% RH) and 38/90. Also the laminate comprising LPB with metallized DA-MFC film has a significantly lower OTR compared to the LPB with metallized MFC film.

(29) In view of the above detailed description of the present invention, other modifications and variations will become apparent to those skilled in the art. However, it should be apparent that such other modifications and variations may be effected without departing from the spirit and scope of the invention.