REPULPABLE PACKAGING MATERIAL

Abstract

The invention relates to a heat-sealable packaging material comprising: a paperboard substrate comprising a first side and a second side, a first coating layer on the first side, a first barrier coating layer on the first coating layer, which first barrier coating layer comprises pigments, a second coating layer on the second side, and a second barrier coating layer on the second coating layer, which second barrier coating layer comprises pigments, wherein the coating layers and the barrier coating layers comprise a latex or a water-soluble polymer, wherein the first coating layer and the second coating layer are free of pigments, wherein the first barrier coating layer and the second barrier coating layer comprise pigments in an amount in a range from >40 wt % to <70 wt %, based on the dry solid content of the respective layer, and wherein the grammage of each of the first and second coating layer and of the first and second barrier coating layer is in a range from >1 g/m2 to <10 g/m2. The invention further relates to a method of manufacturing a respective packaging material and a packaging derived therefrom.

Claims

1. A heat-sealable packaging material comprising: a paperboard substrate (1) comprising a first side and a second side, a first coating layer (2) on the first side, a first barrier coating layer (3) on the first coating layer (2), which first barrier coating layer (3) comprises pigments, a second coating layer (4) on the second side, and a second barrier coating layer (5) on the second coating layer (4), which second barrier coating layer (5) comprises pigments, wherein the coating layers comprise a latex or a water-soluble polymer and the barrier coating layers comprise a latex, characterized in that the first coating layer (2) and the second coating layer (4) are free of pigments, wherein the first barrier coating layer (3) and the second barrier coating layer (5) comprise pigments in an amount in a range from ≥40 wt % to ≤70 wt %, based on the dry solid content of the respective layer, and wherein the grammage of each of the first and second coating layer and of the first and second barrier coating layer is in a range from ≥1 g/m.sup.2 to ≤10 g/m.sup.2.

2. The packaging material according to claim 1, wherein the packaging material has a bending resistance index, 15 degrees (determined according to ISO2493-1) in machine direction (MD) of above 12 Nm6/kg3, preferably above 13 Nm6/kg3 and/or a bending resistance index, 15 degrees (determined according to ISO2493-1) in cross direction (CD) of above 5 Nm6/kg3, preferably above 6 Nm6/kg3.

3. The packaging material according to any one of claim 1 or 2, wherein the packaging material exhibits a water absorption rate of below 15 g/m.sup.2, preferably of below 13 g/m.sup.2 and most preferably below 10 g/m.sup.2 as measured using COBB 600 in accordance with SCAN-P 12:64.

4. The packaging material according to any one of the preceding claims, wherein the first and second coating layer and the first and second barrier coating layer each have a grammage in a range from ≥5 g/m.sup.2 to ≤10 g/m.sup.2.

5. The packaging material according to any one of the preceding claims, wherein the first and second coating layer and the first and second barrier coating layer together have a coat weight in a range from ≥20 g/m.sup.2 to ≤40 g/m.sup.2, preferably in a range from ≥25 g/m.sup.2 to ≤35 g/m.sup.2.

6. The packaging material according to any one of the preceding claims, wherein the first coating layer (2) and the second coating layer (4) comprise latex in an amount in a range from ≥90 wt % to ≤100 wt %, based on the dry solid content of the layer.

7. The packaging material according to claim 6, wherein the first coating layer (2) and the second coating layer (4) comprise a co-binder in a range from ≥0 wt % to ≤5 wt %, based on the dry solid content of the layer, preferably polyvinyl alcohol (PVOH).

8. The packaging material according to any one of the preceding claims, wherein the first barrier coating layer (3) and the second barrier coating layer (5) comprise pigments in an amount in a range from ≥50 wt % to ≤70 wt %, preferably in an amount in a range from ≥55 wt % to ≤70 wt %, based on the dry solid content of the layer.

9. The packaging material according to any one of the preceding claims, wherein the pigments are selected from the group comprising clay, talc, calcium carbonate and/or nanoclay.

10. The packaging material according to any one of the preceding claims, wherein the first barrier coating layer (3) and the second barrier coating layer (5) comprise latex in an amount in a range from ≥30 wt % to ≤60 wt %, based on the dry solid content of the layer.

11. The packaging material according to any one of the preceding claims, wherein the latex in the first and second coating layer and/or the first and second barrier coating layer is selected from styrene-butadiene latex, styrene-acrylate latex, or a mixture thereof.

12. A method of manufacturing a packaging material, the method comprising the steps of: providing a paperboard substrate (1) comprising a first side and a second side, applying first coating layer (2) on the first side, applying first barrier coating layer (3) on the first coating layer (2), which first barrier coating layer (3) comprises pigments, applying a second coating layer (4) on the second side, and applying a second barrier coating layer (5) on the second coating layer (4), which second barrier coating layer (5) comprises pigments, wherein the coating layers are formed are formed by dispersion coating of a latex or a water-soluble polymer and the barrier layers are formed by dispersion coating of a latex, characterized in that the first coating layer (2) and the second coating layer (4) are free of pigments, wherein the first barrier coating layer (3) and the second barrier coating layer (5) comprise pigments in an amount in a range from ≥40 wt % to ≤70 wt %, based on the dry solid content of the respective layer, and wherein the grammage of each of the first and second coating layer and of the first and second barrier coating layer is in a range from ≥1 g/m.sup.2 to ≤10 g/m.sup.2.

13. A packaging comprising or being made from the packaging material according to any one of claims 1 to 11.

14. The packaging according to claim 13, wherein the reject received from the repulping of the packaging material (determined according to PTS test method RH021/97) is less than 12 wt % preferably less than 10 wt %, more preferably less than 7 wt %, based on a dry weight of the packaging material of 100 weight %.

15. The packaging according to claim 13 or 14, wherein the packaging is a cup.

Description

[0057] Further features of the present invention will become apparent from the example and FIGURE, wherein:

[0058] FIG. 1 is a schematic drawing of a packaging material according to an embodiment of the invention.

[0059] The packaging material shown in FIG. 1 comprises a paperboard substrate 1, comprising three plies, a middle ply 1a, a top ply 1b, and a back ply 1c. The middle layer 1a contains CTMP and sulphate pulp. The top ply 1b and the back ply 1c comprise sulphate pulp. The paperboard substrate comprises a first side and a second side, wherein the top ply 1b is arranged on first side and the back ply 1c on the second side. The first side refers to the print side of a packaging such as a container made from the heat-sealable packaging material, while the second side refers to the inside of such a container. On the first side the packaging material, the top ply 1b is coated with a first coating layer 2. On the second side the back ply 1c is coated with a second coating layer 4. The first coating layer 2 and the second coating layer 4 are free of pigments. A first barrier coating layer 3 is arranged on the first coating layer 2. The first barrier coating layer 3 forms the printing surface of the packaging material. The packaging material may be printed directly on the barrier coating layer 3. A second barrier coating layer 5 is arranged on the second coating layer 4. The second barrier coating layer 5 will be in contact with the content of a container produced from the packaging material. While the first coating layer 2 and the second coating layer 4 are free of pigments, the first barrier coating layer 3 and the second barrier coating layer 5 comprise pigments in an amount in a range from ≥40 wt % to ≤70 wt %, based on the dry solid content. The first and second coating layers 2 and 4 and the first and second barrier coating layers 3 and 5 comprise a latex, preferably selected from styrene-butadiene latex, styrene-acrylate latex, or a mixture thereof. The coating layers 2 and 4 and barrier coating layers 3 and 5 are applied by dispersion coating onto the paperboard substrate. The grammage of each of the first and second coating layers and of the first and second barrier coating layers is in a range from ≥1 g/m.sup.2 to ≤10 g/m.sup.2. The material as shown in FIG. 1 is particularly suitable for the manufacture of heat-sealed product packages for liquids such as disposable cups.

Example 1

[0060] In order to evaluate the packaging material of the invention, a test series was performed in which the barrier properties and the stiffness of packaging material manufactured in accordance with the invention was evaluated in a laboratory trial using a rod coater.

[0061] Coating compositions (Dispersion 1, dispersion 2 and Ref 1) were prepared according to the table 1. All percentages calculated as dry solid content (wt %).

TABLE-US-00001 TABLE 1 Dispersion 1 Dispersion 2 Raw material [wt %] [wt %] Styrene acrylate latex 100 40.6 Clay pigment 58.1 Dispersion agent 0.1 NaOH 0.1 PVOH 0.3 Crosslinker 0.3 Defoamer 0.4 Thickener 0.1

[0062] The coating compositions were coated by use of a rod coater on paperboard Cupforma Natura, of different grammages from 184 to 295 gsm, which is a three-layer paperboard with two outer layers made of bleached kraft pulps and a middle layer comprising bleached kraft pulp and CTMP. The dispersion 1 were coated on both sides of the paperboard to form first, innermost coatings, at an amount of 10 gsm on each side, whereupon the dispersion 2 were coated on both sides of the paperboard onto said first inner coatings at an amount of 5 gsm on each side. The thereof prepared packaging material samples (sample 1-4) had thus the following structure:

[0063] dispersion 2/dispersion 1/Cupforma Natura/dispersion 1/dispersion 2

[0064] As a reference, coating compositions (Ref 1 and Ref 2) were prepared in accordance with table 2. A reference sample (Ref Board) was prepared by coating Cupforma Natura 195 g/m.sup.2 with said reference coating compositions to form the following structure:

[0065] Ref 2, 5 gsm/Ref 1, 10 gsm/Cupforma Natura/Ref 1, 10 gsm/Dispersion 2, 5 gsm

TABLE-US-00002 TABLE 2 Raw material [pph] Ref 1% Ref 2% SA latex 1 35.6 SA latex 2 35.6 40.7 Rheology modifier 0.3 Calcium Carbonate 28.4 46.5 NaOH 0.1 0.1 Clay pigment 11.6 Disp. Agent 0.1 PVA 0.3 Crosslinker 0.3 Defoamer 0.4

[0066] The properties of the packaging materials of the invention and the reference board are summarized in table 3.

[0067] As can be seen in table 3, the packaging materials made in accordance with the invention shows a low water absorption and a high stiffness. The reject level (PTS) for Sample 1-4 was between 10-11%.

TABLE-US-00003 TABLE 3 Sample Sample Sample Sample Ref 1 2 3 4 Board Grammage [g/m.sup.2] 226 244 290 320 240 Bending resistance 165 196 330 466 158 15°, MD Bending resistance 14.3 13.5 13.5 14.2 11.4 index 15° MD Bending resistance 71 76 149 236 65 15°, CD Bending resistance 6.2 5.2 6.1 7.2 4.7 index 15° CD Cobb600 RS [g/m2] 1.9 8 11 4.5 20