HEAT-SEALABLE PAPERBOARD

Abstract

The invention relates to a heat-sealable paperboard comprising a paperboard substrate (1) comprising a first side and a second side, a first dispersion coating layer (2) on the first side of the paperboard substrate (1), and a second dispersion coating layer (3) on the first dispersion coating layer (2), wherein the first dispersion coating layer (2) comprises a latex and pigment and the second dispersion coating layer (3) comprises a polyolefin.

Claims

1. A heat-sealable paperboard comprising: a paperboard substrate comprising a first side and a second side, a first dispersion coating layer on the first side of the paperboard substrate, and a second dispersion coating layer on the first dispersion coating layer, wherein the first dispersion coating layer comprises a latex and pigment, and wherein the second dispersion coating layer comprises a polyolefin.

2. The paperboard according to claim 1, wherein the latex is selected from a group consisting of styrene-acrylate latex, styrene-butadiene latex, and a mixture thereof.

3. The paperboard according to claim 1, wherein the first dispersion coating layer comprises the latex in an amount in a range from ≥30 wt % to ≤70 wt %, based on dry solid content of the layer.

4. The paperboard according to claim 1, wherein the first dispersion coating layer comprises pigment in an amount in a range from ≥30 wt % to ≤70 wt % based on a dry solid content of the layer.

5. The paperboard according to claim 1, wherein the pigment is selected a group consisting of clay, talc, and combinations thereof.

6. The paperboard according to claim 1, wherein the second dispersion coating layer comprises a polyolefin selected from a group consisting of polyethylene (PE), polypropylene (PP), copolymers of polyethylene and polypropylene, and combinations thereof.

7. The paperboard according to claim 1, wherein the second dispersion coating layer comprises the polyolefin in an amount in a range from ≥90 wt % to ≤100 wt %, based on a dry solid content of the layer.

8. The paperboard according to claim 1, wherein the second dispersion coating layer comprises a co-binder in a range from ≥0 wt % to ≤5 wt %, based on a dry solid content of the layer.

9. The paperboard according to claim 1, wherein the paperboard substrate further comprises, on the second side, a third dispersion coating layer, wherein the third dispersion coating layer comprises polyolefin in an amount in a range from ≥50 wt % to ≤100 wt %, based on the a dry solid content of the layer.

10. The paperboard according to claim 11, wherein the third dispersion coating layer further comprises a latex and pigments, together being present in a range from ≥0 wt % to ≤50 wt %, based on the dry solid content of the layer.

11. The paperboard according to claim 1, wherein the paperboard substrate further comprises, on the second side, a third dispersion coating layer, wherein the third dispersion coating layer comprises polyolefin in an amount in a range from ≥90 wt % to ≤100 wt %, based on dry solid content of the layer.

12. The paperboard according to claim 1, wherein the paperboard substrate further comprises, on the second side, a third dispersion coating layer and a fourth dispersion coating layer on the third dispersion coating layer, wherein the third dispersion coating layer comprises a latex and pigment, and wherein the fourth dispersion coating layer comprises a polyolefin.

13. The paperboard according to claim 1, wherein the paperboard has a stretch at break (CD, determined by tensile strength according to ISO 1924-2) of ≥5%, or a water absorption rate (COBB 600, determined according to SCAN-test P 12:64) of ≤10 g/m.sup.2 or, both.

14. A method of manufacturing a heat-sealable paperboard, the method comprising the steps of: providing a paperboard substrate comprising a first side and a second side, applying a first dispersion coating layer on the first side of the paperboard substrate, and, applying a second dispersion coating layer on the first dispersion coating layer wherein the first dispersion coating layer comprises a latex and pigment, and wherein the second dispersion coating layer comprises a polyolefin.

15. A packaging comprising the heat-sealable paperboard according to claim 1.

16. The paperboard according to claim 8, wherein the co-binder comprises a latex.

17. The method of claim 14 further comprising the step of: applying a third dispersion coating layer on the second side of the paperboard substrate.

Description

[0060] Further features of the present invention will become apparent from the example and figure, wherein:

[0061] FIG. 1 is a schematic drawing of a heat-sealable paperboard according to an embodiment of the invention.

[0062] FIG. 2 is a schematic drawing of a heat-sealable paperboard according to another embodiment of the invention.

[0063] The heat-sealable paperboard as 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 the second side and the back ply 1c on the first side. The first side refers to the inside of a packaging such as a container made from the heat-sealable paperboard, while the second side refers to the print side of such a packaging.

[0064] On the first side of the heat-sealable paperboard, on the back ply 1c, the paperboard substrate 1 comprises a first dispersion coating layer 2, forming a first inside layer. The first dispersion coating layer 2 comprises a latex and pigment. The latex preferably is selected from styrene-butadiene latex, styrene-acrylate latex, or a mixture thereof. The pigment preferably is selected from clay or talc. A second dispersion coating layer 3 comprising a polyolefin is coated on the first dispersion coating layer 2. The second dispersion coating layer 3 forms a second inside layer. The polymer preferably is a copolymer of polyethylene and polypropylene. The polyolefin may be present in an amount in a range from ≥90 wt % to ≤100 wt %, based on the dry solid content of the layer. The second dispersion coating layer 3 may be free of pigments. The second dispersion coating layer 3 will be in contact with the content of a container produced from the paperboard.

[0065] On the second side of the paperboard, the top ply 1b is coated with a third dispersion coating layer 4. The dispersion coating layer 4 forms the printing surface of the heat-sealable paperboard. The paperboard may be printed directly on the dispersion coating layer 4. The third dispersion coating layer 4 comprises a polyolefin in an amount in a range from ≥50 wt % to ≤100 wt %, based on the dry solid content of the layer. The third dispersion coating layer 4 further may comprise a latex and pigment, together being present in an amount in a range from ≥0 wt % to ≤50 wt %, based on the dry solid content of the layer.

[0066] In an alternative embodiment, the third dispersion coating layer 4 comprises a polyolefin in an amount in a range from ≥95 wt % to ≤100 wt %, based on the dry solid content of the layer, and is preferably free of pigment. The paperboard may be printed directly on such a dispersion coating layer 4. The material of such embodiment is particularly suitable for the manufacture of the sides of heat-sealed product packages for cold and hot liquids or food, and frozen food.

[0067] The heat-sealable paperboard as shown in FIG. 2 comprises a paperboard substrate 1, a first dispersion coating layer 2, forming a first inside layer and second dispersion coating layer 3 will be in contact with the content of a container produced from the paperboard as described for FIG. 1. On the second side of the paperboard, the top ply 1b is coated with a third dispersion coating layer 4. The third dispersion coating 4 comprises a latex and pigment. The latex preferably is selected from styrene-butadiene latex, styrene-acrylate latex, or a mixture thereof. The pigment preferably is selected from clay or talc. A fourth dispersion coating layer 5 comprising a polyolefin is coated on the third dispersion coating layer 4. The fourth dispersion coating layer 5 forms the outer surface of the heat-sealable paperboard. The polymer preferably is a copolymer of polyethylene and polypropylene. The polyolefin may be present in an amount in a range from ≥90 wt % to ≤100 wt %, based on the dry solid content of the layer. The fourth dispersion coating layer 5 may be free of pigments. The second dispersion coating layer 3 will be in contact with the content of a container produced from the paperboard. The material as shown in FIG. 2 is particularly suitable for the manufacture of the bottom of a heat-sealed product package for cold and hot liquids or food, and frozen food.

[0068] The material as shown in FIG. 1 and FIG. 2 is particularly suitable for the manufacture of heat-sealed product packages for cold and hot liquids or food, and frozen food.

EXAMPLE 1

[0069] In order to evaluate the packaging material of the invention, a test series was performed in which the barrier properties, the stretch at break and the static coefficient of friction of packaging material manufactured in accordance with the invention was evaluated in a laboratory trial using a rod coater.

[0070] A first dispersion coating composition (Dispersion 1) was prepared according to the table 1. All percentages calculated as dry solid content (wt %). A second dispersion coating (Dispersion 2) was prepared comprising 100 wt % co-polymer of polyethylene and polypropylene, as calculated on the dry solid content.

[0071] The coating compositions were coated by use of a rod coater on a paperboard Cupforma Natura (baseboard) of different grammages from 195 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. In all the samples 1-4, the dispersion 1 were coated on a first side (reverse side) of the paperboard to form first, innermost coating layer with a grammage of 7 gsm, whereupon the dispersion 2 were coated onto said first inner coating layer forming a second coating layer with a grammage of 7 gsm. Sample 1 and 2 were further coated on the second side (print side) of the baseboard with Dispersion 2 forming a third coating layer of 5 gsm. Sample 3 were further coated on the second side with dispersion 1 forming a third coating layer with a grammage of 7 gsm whereupon dispersion 2 were coated onto said third coating layer forming a fourth coating layer with a grammage of 7 gsm.

[0072] The samples were thus prepared to show the following coating structures:

Sample 1 and 2: Dispersion 2/Baseboard/Dispersion 1/Dispersion 2

Sample 3: Dispersion 2/Dispersion 1/Baseboard/Dispersion 1/Dispersion 2

Sample 4: Baseboard/Dispersion 1/Dispersion 2

[0073]

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

[0074] As a reference, a first reference sample (Ref Board 1) was prepared by coating a paperboard baseboard (Tambrite 240 gsm) with Dispersion 1 to provide a coating layer of 7 gsm. A second reference sample (Ref Board 2) was prepared by providing a paperboard baseboard (Tambrite 240 gsm) with a first coating layer of Dispersion 1 (5 gsm) and a second dispersion coating layer (10 gsm) comprising 100 wt % styrene-acrylate latex onto said first coating layer.

[0075] The properties of the packaging materials of the invention and the reference board are summarized in table 2. The water absorption (COBB600) is measured on the first side/reverse side (RS) of the coated paperboard samples.

TABLE-US-00002 TABLE 2 Sample Sample Sample Sample Ref Ref 1 2 3 4 Board 1 Board 2 Baseboard 214 214 195 295 240 240 Grammage [g/m.sup.2] Stretch at 5.63 6.22 6.57 5.32 3.81 3.60 break CD [%] Static 0.410 0.397 0.332 0.477 0.661 0.843 coefficient of friction (mean) Cobb600 RS 3.5 1.5 2.0 2.3 84.0 6.1 [g/m2] PTS reject 11.2 11.1 — — — — level [%]

[0076] As can be seen in table 2, the packaging materials made in accordance with the invention shows a low water absorption, a high stretch at break, a low static coefficient of friction and a low PTS reject level.