METHOD FOR MANUFACTURING A PACKAGING MATERIAL AND A PACKAGING MATERIAL MADE BY THE METHOD

Abstract

The invention relates to a method of manufacturing a heat-sealable packaging material, the method comprising the steps of: providing a paperboard substrate comprising a top ply, applying a first dispersion barrier layer on the top ply, wherein the first dispersion barrier layer comprises a latex having a first glass transition temperature, and applying a second dispersion barrier layer on the first barrier layer, wherein the second dispersion barrier layer comprises a latex having a second glass transition temperature, wherein the second glass transition temperature is higher than the first glass transition temperature, wherein the grammage of the second dispersion barrier layer is lower than the grammage of the first dispersion barrier layer, and wherein the second dispersion barrier layer comprises pigments. The invention further relates to a respective heat-sealable packaging material.

Claims

1. A method of manufacturing a heat-sealable packaging material, the method comprising the steps of: providing a paperboard substrate comprising a top ply, applying a first dispersion barrier layer on the top ply, wherein the first dispersion barrier layer comprises a latex having a first glass transition temperature, and applying a second dispersion barrier layer on the first barrier layer, wherein the second dispersion barrier layer comprises a latex having a second glass transition temperature, wherein the second glass transition temperature is higher than the first glass transition temperature, wherein the second dispersion banner layer has a grammage lower than the grammage of the first dispersion barrier layer, and wherein the second dispersion barrier layer comprises pigments.

2. The method according to claim 1, wherein the first glass transition temperature is in a range from 10 C. to 15 C.

3. The method according to claim 1, wherein the second glass transition temperature is in a range from 10 C. to 40 C.

4. The method according to claim 1, wherein the first dispersion barrier layer is applied in an amount in a range from 4 g/m.sup.2 to 25 g/m.sup.2.

5. The method according to claim 1, wherein the second dispersion barrier layer is applied in an amount in a range from 3 g/m.sup.2 to 20 g/m.sup.2.

6. The method according to claim 1, wherein the first dispersion barrier layer comprises pigments in an amount in a range from 0 wt % to 40 wt %, based on the dry solid content.

7. The method according to claim 6, wherein the second dispersion barrier layer comprises pigments in an amount in a range from 30 wt % to 70 wt %, based on the total solid content.

8. The method according to claim 1, wherein the second dispersion barrier layer comprises latex in an amount in a range from 50 wt % to 90 wt %, based on the dry solid content of the layer.

9. The method according to claim 1, wherein the average particle size of the latex in the second dispersion barrier layer is smaller than the average particle size of the latex of the first dispersion barrier layer.

10. A heat-sealable packaging material made by the method of claim 1.

11. A heat-sealable packaging material comprising: a paperboard substrate comprising a top ply, a first dispersion barrier layer on the top ply, wherein the first dispersion barrier layer comprises a latex having a first glass transition temperature, and a second dispersion barrier layer on the first barrier layer, wherein the second dispersion barrier layer comprises a latex having a second glass transition temperature, wherein the second glass transition temperature is higher than the first glass transition temperature, wherein the second dispersion barrier layer has a grammage lower than the grammage of the first dispersion barrier layer, and wherein the second dispersion barrier layer comprises pigments.

12. The heat-sealable packaging material according to claim 10, wherein the first dispersion barrier layer has a KIT barrier in a range from 6 to 12.

13. The heat-sealable packaging material according to claim 10, wherein the second dispersion barrier layer comprises pigments in an amount in a range from 30 wt % to 70 wt %, based on the total solid content.

14. A heat-sealed package or a package sealed by ultrasonic made from the packaging material made by the method according to claim 1.

15. The method according to claim 1, wherein the first glass transition temperature is in a range from 10 C. to 10 C.

16. The method according to claim 1, wherein the second glass transition temperature is in a range from 15 C. to 30 C.

17. The method according to claim 1, wherein the first dispersion barrier layer is applied in an amount in a range from 5 g/m.sup.2 to 15 g/m.sup.2.

18. The method according to claim 1, wherein the second dispersion barrier layer is applied in an amount in a range from 5 g/m.sup.2 to 15 g/m.sup.2.

19. The method according to claim 1, wherein the first dispersion barrier layer comprises pigments in an amount in a range from 5 wt % to 20 wt %, based on the dry solid content.

20. The method according to claim 1, wherein the second dispersion barrier layer comprises latex in an amount in a range from 60 wt % to 80 wt %, based on the dry solid content of the layer.

Description

[0050] Further features of the present invention will become apparent from the examples and figures, wherein:

[0051] FIG. 1 is a schematic drawing of a packaging material according to an embodiment of the invention.

[0052] The packaging material shown in FIG. 1 comprises a paperboard substrate 1, comprising a top ply 1a. The paperboard substrate may be a multilayer packaging paperboard further comprising at least a back ply 1b. The top ply 1a of the paperboard is coated with a first dispersion barrier layer 2, wherein the first dispersion barrier layer 2 comprises a latex having a first glass transition temperature. A second dispersion barrier layer 3 is arranged on the first barrier layer 2, wherein the second dispersion barrier layer 3 comprises a latex having a second glass transition temperature. The glass transition temperature of the latex of the second dispersion barrier 3 is higher than the glass transition temperature of the latex of the first dispersion barrier layer 2. The grammage of the second dispersion barrier layer 3 is lower than the grammage of the first dispersion barrier layer 2. The second dispersion barrier layer 3 further comprises pigments. The dispersion barrier layers are brought by dispersion barrier coating onto the paperboard substrate. The material as shown in FIG. 1 is particularly suitable for heat-sealed product packages.

EXAMPLE 1

[0053] In order to evaluate the packaging materials of the invention, a test series was performed in which the blocking behaviour of packaging material manufactured in accordance with the invention was evaluated in a laboratory trial using a rod coater.

[0054] Coating compositions (primer, heat seal 1, heat seal 2) were prepared according to the table 1:

TABLE-US-00001 TABLE 1 Solids Dispersion Dispersion Dispersion Raw material [%] 1 2 3 CHP 204 (Tg 10) 50 200 100 Acronal 728 (Tg 23) 50 200 Rheocarb 121 30 1 1 Hydragloss 90 72 100 100 NaOH 10 2 2 Total 303 303 Theoretical dry content [%] 56.9 56.9 50

[0055] CHP 204 is a SA Latex having a glass transition temperature of 10 C., Acronal 728 is a SA latex available from BASF having a glass transition temperature of 23 C. Rheocarb 121 is an acrylic thickener, and Hydragloss 90 is a kaolin clay pigment.

[0056] The coating composition was coated by use of a rod coater on uncoated paperboard Cupforma Natura, 232 g/m.sup.2, 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 (Chemi-Thermo-Mechanical Pulp).

[0057] The properties of the packaging material of two test runs is summarized in table 2:

TABLE-US-00002 TABLE 2 layer 1, coating layer 2, coating Heat seal grammage grammage Cobb600 (hot bar) run [gsm] [gsm] layer 1 layer 2 [g/m.sup.2] [ C.] 1 10 5 Dispersion 1 Dispersion 2 58 90 2 7 5 Dispersion 3 Dispersion 2 5 90

[0058] All test runs showed no or very little blocking tendency. This is a significant improvement over the previous, prior art, technique when using one, single latex, with a glass transition temperature (Tg) of around 10 in the coating and where we have observed a lot of problems related to blocking, and sometimes even the paperboard layers were not able to be separated after reel-up. In addition, as can be seen in table 2, the Cobb values observed were low, especially when using only latex with low glass transition temperature (Tg) as the first dispersion layer as in test run no. 2. Heat sealing was also was observed to be surprisingly good. At 100 all fibre tear.

EXAMPLE 2

[0059] A second test series was performed in which the blocking behavior of packaging material manufactured in accordance with the invention was evaluated in a production trial using an offline coater (roll applicator and metering rod).

[0060] The coating compositions of dispersion layers 1 and 2 were prepared according to the table 3:

TABLE-US-00003 TABLE 3 dispersion dispersion Raw material Solids [%] layer 1 layer 2 CHP 204 50 4500 Acronal 728 50 4500 6000 Rheocarb 121 30 40 40 Hydragloss 90 72 3000 NaOH 10 20 20 Total 9060 9060

[0061] In accordance with example 1, the latexes used were SA Latexes CHP 204 having a glass transition temperature of 10 C., and Acronal 728 having a glass transition temperature of 23 C. Also Rheocarb 121 being an acrylic thickener, and Hydragloss 90 being a kaolin clay pigment were used.

[0062] Three trials were run with rod application and an offline coater. The results are summarized in table 4:

TABLE-US-00004 TABLE 4 Base board coating grammage coating grammage grammage dispersion layer 1 dispersion layer 2 Cobb600 Trial # Baseboard [gsm] [gsm] [gsm] [g/m.sup.2] KIT # 1 Cupforma Natura 182 7 5 8 12 2 Cupforma Natura 213 11 7 5 12 3 Cupforma Special 312 6 5 5 12

[0063] As can be seen in table 4 from COBB and KIT values, all three trials using first and second dispersion layer according to the invention provided paperboard with high moisture and grease barrier values. Moreover, no problem with blocking was observed and satisfying heat-sealability.

[0064] Again, this provides important advantages compared to prior art methods causing severe blocking when the condition that the glass transition temperatures of the latex of the second dispersion layer is higher than the glass transition temperature of the latex of the first dispersion layer were not observed.