Corrugated board comprising an adhesive comprising starch and fine micofibrillated cellulose

Abstract

The present invention relates to a corrugated board comprising an adhesive arranged to attach a fluted corrugated medium to a liner wherein the adhesive comprises starch and microfibrillated cellulose. The invention also relates to a method to produce said corrugated board.

Claims

1. A corrugated board comprising a fluted corrugated medium, a liner and an adhesive arranged to attach the fluted corrugated medium to the liner wherein the adhesive comprises starch and microfibrillated cellulose, the microfibrillated cellulose having a Schopper-Riegler (SR) value above 97.

2. The corrugated board according to claim 1 wherein the adhesive comprises starch in an amount above 50 wt % of the total solid content of the adhesive.

3. The corrugated board according to claim 1 wherein the adhesive comprises microfibrillated cellulose in an amount between 0.5-50 wt-% of the total solid content of the adhesive.

4. The corrugated board according to claim 1 wherein the starch in the adhesive is a native starch.

5. The corrugated board according to claim 1 wherein the adhesive comprises a raw starch component.

6. The corrugated board according to claim 1 wherein the adhesive comprises a starch carrier medium.

7. The corrugated board according to claim 1 wherein the liner has a grammage of below 160 g/m.sup.2.

8. The corrugated board according to claim 1 wherein the board comprises adhesive in an amount of 3-20 g/m.sup.2 (dry).

9. An adhesive for corrugated boards wherein said adhesive comprises starch and a microfibrillated cellulose wherein said microfibrillated cellulose has a Schopper-Riegler (SR) value above 97.

10. The adhesive according to claim 9 wherein the adhesive has a solid content between 10-45 wt-%.

11. The adhesive according to claim 9 wherein the adhesive comprises more than 50 wt-% starch based on total dry solid content of the adhesive.

12. The adhesive according claim 9 wherein the adhesive comprises both a raw starch component and a starch carrier medium.

13. The adhesive according to claim 9 wherein the adhesive comprises between 0.1-50 wt-% of microfibrillated cellulose based on total dry solid content of the adhesive.

14. A method for producing a corrugated board comprising the steps of; providing a corrugated medium and a liner, providing an adhesive comprising starch and microfibrillated cellulose wherein the microfibrillated cellulose has a Schopper-Riegler (SR) value above 97 and adding the adhesive between the corrugated medium and the liner so that the corrugated medium is attached to said liner.

15. The method according to claim 14 wherein the adhesive is made by swelling the starch by alkali or temperature treatment and adding the microfibrillated cellulose either before, during or after the swelling of the starch.

16. The method according to claim 14 wherein the adhesive is made by cooking the starch to form a starch carrier medium and adding the microfibrillated cellulose either before, during or after cooking of the starch.

17. The method according to claim 15 wherein temperature of the added microfibrillated cellulose is above 30 C.

Description

EXAMPLE

(1) Adhesives were prepared by mixing 5 wt % MFC of different quality with wheat starch (9.6 g), water and NaOH, followed by stirring and heating at 45 C. to form a mixture. Thereafter, more wheat starch (75.6 g) and water was added to the mixture in a second step and stirred at 35 C. for 30 minutes. If the adhesive comprises 10 wt-% of MFC, an additional 5 wt-% MFC was also added in the second step together with the additional starch and water. The amount of starch in each adhesive can be seen in Table 1 where the glue solid content is shown which represents the amount of starch and MFC in the adhesive. For the reference adhesives, 1.1 wt-% of Borax in relation to total amount of starch was added.

(2) The coarse MFC grade added has a SR value below 97. The fine MFC grade added has a SR value above 97.

(3) The adhesive characterization and application of adhesive on a corrugated board was performed at room temperature (23 C.) and at a pH of about 12. The viscosity of the adhesive was measured using a rheometer (Malvern Kinexus pro) operated with a shear rate between 0.01-1000 1/s.

(4) The adhesive prepared above was thereafter used for the production of a corrugated board comprising one liner attached to each side of a corrugated medium. The application of the adhesive was done in a SUW Gluability tester and the adhesion strength of the liner was done by PIN Adhesion test (PAT). The corrugated boards were dried at two temperatures, i.e. 110 C. and 180 C., respectively. The wash-board effect, i.e. the unevenness of the outer liner of corrugated board, was measured optically by Optitopo. Optitopo generates two images of the same exact region of a sample by illuminating in low angles from opposite directions. A height map is thereafter calculated using a photometric stereo technique. Topography variations at different wavelength classes are generated and the average wash-board is given in m.

(5) It could be seen that at higher shear rates the viscosity of the starch-MFC adhesives are similar as for the starch borax reference sample. The adhesive according to the invention, comprising MFC-starch with a MFC having a SR value above 97, shows a stronger shear thinning behavior, i.e. a higher viscosity at low shear rates, which is beneficial in adhesive setting. The wash-board effect is also improved with the addition of a MFC having a SR value above 97. Also, the PAT value is increased which means that the adhesion is very good.

(6) TABLE-US-00001 TABLE 1 4A 4B 1A 1B 2A 3A 3B (Ref) (Ref) Basic Starch Starch Starch Starch Starch Starch Starch component Additive Borax Borax MFC 5% 5% 10% 5% 5% amount/Grade MFC MFC MFC MFC MFC (wt-%) Coarse Coarse Coarse Fine Fine Glue solid 23.2 23.2 24.0 22.3 22.3 22.5 22.5 content (wt- %) pH 12 12 12 12 12 12 12 Drying 110 180 110 110 180 110 180 Temperature ( C.) Washboard 163 289 133 124 251 161 272 (um) Viscosity (1 10 10 40 40 0.8 0.8 1/s) Pa s Viscosity (100 0.4 0.4 1 1 0.4 0.4 1/s) Pa s PAT Adhesion 550 490 490 520 380 600 400 (N/m)

(7) Consequently, it is clearly shown in Table 1 that an adhesive comprising finer MFC grades makes it possible to produce a corrugated board having increased quality with good strength and reduced wash-boarding.

(8) 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.