Method for manufacturing a packaging material

Abstract

The invention relates to a polymer-coated packaging material, a method of manufacturing the same, and products, such as a disposable drinking cup, made from the material. The packaging material comprises a fibrous base (1) of paper or board, an innermost polymer layer (2) containing a blend of (i) 10 to 25 wt-% of a low-density polyethylene (LDPE) and (ii) 75 to 90 wt-% of a second polyethylene with a higher melt viscosity, said second polyethylene being selected from linear low-density polyethylene (LLDPE) and high-density polyethylene (HDPE), and an outer layer (3) of more than 90 wt-% of HDPE. An outermost layer (4) of a polymer blend similar to that used for the innermost layer (2) may be provided for heat-sealing. The layers (2, 3 and 4) may be brought and adhered to the fibrous base (1) by coextrusion. To maximize renewability of the materials HDPE and LLDPE as used for the structure are of biologic origin.

Claims

1. A method of manufacturing a packaging material, comprising coextrusion onto a fibrous base an inner polymer layer containing a blend of (i) 10 to 25 wt-% of a low-density polyethylene (LDPE) and (ii) 75 to 90 wt-% of a second polyethylene with a higher melt viscosity, said second polyethylene being selected from linear low-density polyethylene (LLDPE) and high-density polyethylene (HDPE), and an outer layer of more than 90 wt-% of HDPE.

2. The method of claim 1, wherein at least one of the HDPE and LLDPE as used for the structure are of biologic origin.

3. The method of claim 1 wherein in said blend the low-density polyethylene (LDPE) has a melt index of at least 7.5 g/10 min (190 C., 2.16 kg) and said second polyethylene has a melt index of at most 7.2 g/10 min (190 C., 2.16 kg).

4. The method of claim 1 wherein the inner polymer layer of said blend is an adhesive layer in direct contact with the fibrous base.

5. The method of claim 1 wherein there is a layer of said blend coextruded as an outermost heat-sealable layer.

6. The method of claim 4 wherein there is a layer of said blend coextruded as an outermost heat-sealable layer, and wherein the same blend is used for the inner adhesive layer and the outermost heat-seal layer.

7. The method of claim 1 wherein said polymer blend contains at least 80 wt % of LLDPE or HDPE of biologic origin and 10 to 20 wt-% of LDPE.

8. The method of claim 1 wherein the weight of the inner adhesive layer is at most 15 g/m.sup.2.

9. The method of claim 1 wherein the weight of the outermost heat-seal layer is at most 15 g/m.sup.2.

10. The method of claim 1 wherein the weight of said outer HDPE layer is at most 15 g/m.sup.2.

11. A packaging material made by the method of claim 1.

12. A drinking cup made by heat-sealing from the packaging material made by the method of claim 1.

13. The method of claim 1 wherein said polymer blend contains 80 to 85 wt-% of LLDPE or HDPE of biologic origin and 15 to 20 wt-% of LDPE.

14. The method of claim 1 wherein the weight of the inner adhesive layer is at most 10 g/m.sup.2.

15. The method of claim 1 wherein the weight of the outermost heat-seal layer is at most 10 g/m.sup.2.

16. The method of claim 1 wherein the weight of said outer HDPE layer is at most 10 g/m.sup.2.

17. A packaging material comprising (i) a fibrous base of paper or board, (ii) an innermost adhesive layer of a blend of (i) 10 to 25 wt-% of a low-density polyethylene (LDPE) and (ii) 75 to 90 wt-% of a second polyethylene with a higher melt viscosity, said second polyethylene being of biologic origin and selected from linear low-density polyethylene (LLDPE) and high-density polyethylene (HDPE), (iii) a middle layer of more than 90 wt-% of HDPE of biologic origin, and (iv) an outermost heat-sealable layer of a blend of (i) 10 to 25 wt-% of a low-density polyethylene (LDPE) and (ii) 75 to 90 wt-% of a second polyethylene with a higher melt viscosity, said second polyethylene being of biologic origin and selected from linear low-density polyethylene (LLDPE) and high-density polyethylene (HDPE), said layers having been brought by coextrusion onto said fibrous base.

18. The packaging material of claim 17, wherein the same blend is contained in said innermost and outermost polymer layers.

19. The packaging material of claim 17 wherein the weight of each one of the innermost, middle and outermost polymer layers is at most 15 g/m.sup.2.

20. The packaging material of claim 17, wherein the fibrous base is coated with polymer layers similarly on both sides.

21. The packaging material of claim 17 wherein the weight of each one of the innermost, middle and outermost polymer layers is at most 10 g/m.sup.2 and the total weight of the polymer layers is at most 20 g/m.sup.2.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows the multilayer structure of a packaging material according to the invention,

(2) FIG. 2 shows the multilayer structure of a second packaging material according to the invention,

(3) FIG. 3 shows the multilayer structure of a third packaging material according to the invention, and

(4) FIG. 4 shows the multilayer structure of a fourth packaging material according to the invention.

DETAILED DESCRIPTION

(5) The packaging material shown in FIG. 1 comprises a fibrous base 1, an inner adhesive layer 2 in direct contact with the fibrous base 1, the adhesive layer 2 comprising a blend of (i) 10 to 25 wt-% of a low-density polyethylene (LDPE) of a lower melt viscosity and (ii) 75 to 90 wt-% of a second polyethylene of a higher melt viscosity, and an outer layer 3 of HDPE. In the blend forming the inner adhesive layer 2 the low-density polyethylene (LDPE) preferably has a melt index of at least 7.5 g/10 min (190 C., 2.16 kg), or more preferably of at least 15 g/10 min (190 C., 2.16 kg), and the second polyethylene preferably has a melt index of at most 7.2 g/10 min (190 C., 2.16 kg). The second polyethylene may be linear low-density polyethylene (LLDPE) or high-density polyethylene (HDPE). HDPE and LLDPE as used in the structure are of renewable biologic origin. The fibrous base 1 may be paper, paperboard or cardboard of a weight of 40 to 500 g/m.sup.2, preferably board of a weight of 170 to 350 g/m.sup.2. The inner adhesive layer 2 and the outer HDPE layer 3 have been brought onto the fibrous base 1 by coextrusion. The weight of each one of the coextruded polymer layers 2, 3 may be e.g. 3 to 15 g/m.sup.2, preferably 5 to 10 g/m.sup.2.

(6) The packaging material according to FIG. 2 differs from the material shown in FIG. 1 in that it even comprises an outermost layer 4 of a polymer blend, which is similar to, preferably the same as the blend used for the innermost adhesive layer 2. The outermost layer 4 is useful as a heat-sealing layer as the material is turned into containers such as disposable drinking cups for instance. The three layers 2, 3, 4 have been brought onto the fibrous base 1 by coextrusion.

(7) The weight of each one of the coextruded polymer layers 2, 3, 4 may be e.g. 3 to 12 g/m.sup.2, preferably 5 to 10 g/m.sup.2.

(8) The packaging material according to FIG. 3 differs from the material shown in FIG. 2 in that it even comprises a heat-sealing layer 4 on the opposite side of the fibrous base 1. Preferably this heat-sealing layer 4 is of a polymer blend, which is the same as the blend used for the innermost and outermost layers 2, 4 on the reverse side of the fibrous base, the latter forming the inside as the material is turned into a drinking cup.

(9) The packaging material according to FIG. 4 comprises a coextruded multilayer structure 2, 3, 4; 2, 3, 4 on both sides of the fibrous base 1. These multilayer structures may both correspond to that described above in connection with FIG. 2. The material of FIG. 4 is suitable for heat-sealed product packages shielded against water vapour penetration from both the inside of the package, i.e from a moist product, and from the outside of the package, i.e. from humid ambience.

Examples

(10) 20 wt-% of extrusion grade LDPE of petroleum oil origin was dry blended with film grade bio-HDPE of sugar cane origin to form a polymer blend. This polymer blend was co-extruded together with 100 wt-% bio-HDPE onto a paperboard surface so that the polymer blend formed an adhesion layer in-between the paperboard surface and the HDPE layer. The grammage of the adhesion layer was 8 g/m.sup.2 and the grammage of HDPE layer was 7 g/m.sup.2. So, in total coating, there was 1.6 g/m.sup.2 LDPE and 13.4 g/m.sup.2 HDPE. Coating weight of 15 g/m.sup.2 was achieved with good runnability, acceptable neck-in and good adhesion to the paperboard.

(11) A series of tests were carried out by extruding onto a paperboard base double or triple layer coatings according to the invention, as well as monolayer coatings as comparative examples. Extrusion grade oil-based LDPE, film grade bio-HDPE, and film grade bio-LLDPE (bio-HDPE and bio-LLDPE made from sugar cane by Braskem, Brazil) were used for the tests. The neck-in in extrusion and heat-sealing temperature of the finished material were measured, and adhesion to the board base was evaluated on a scale 1 (no adhesion) to 5 (perfect adhesion). The results are presented in the following table 1.

(12) TABLE-US-00001 TABLE 1 Thick- Heat Adhe- Neck- nesses sealing sion in Structure g/m.sup.2 (m) ( C.) (0-5) (mm) Board/LDPE* 15 15 360 5 60 Board/LLDPE + 20% LDPE* 15 15 440 5 90 Board/LLDPE + 20% LDPE/HDPE/LLDPE + 20% LDPE 15 5/5/5 440 5 90 Board/LLDPE + 20% LDPE/HDPE/LLDPE + 20% LDPE 20 5/10/5 430 5 90 Board/HDPE + 20% LDPE/HDPE/HDPE + 20% LDPE 15 5/5/5 510 5 85 Board/HDPE + 20% LDPE/HDPE/HDPE + 20% LDPE 20 5/10/5 510 5 85 Board/HDPE + 20% LDPE/HDPE 15 10/5 490 5 85 Board/HDPE* 25 25 500 3.5 110 *comparative

(13) The comparative HDPE monolayer coating had the worst neck-in and adhesion in spite of the largest layer thickness. Thinner HDPE monolayers failed in extrusion altogether. Adding an inner layer of a blend of LLDPE or HDPE with 20 wt-% of LDPE improved adhesion and diminished the neck-in, even though the total coating weights and thicknesses were reduced, and by addition of an outermost layer of the same blends considerably improved heat-sealability in case of LLDPE+LDPE.