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 and an extruded polymer layer (2) containing a blend of (i) 0 to 25 wt-% of a branched low-density polyethylene (LDPE) with a lower melt viscosity and (ii) 75 to 90 wt-% of a linear low-density polyethylene (LLDPE) with a higher melt viscosity. The packaging material of the invention comprises multilayer coatings, e.g. an adhesive innermost and a heat-sealable outermost layer (2, 4) of said blend and a vapor barrier middle layer (3) of at most 90 wt-% of high density polyethylene (HDPE). The layers (2, 3, 4) are 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 heat-sealable packaging material, comprising coextrusion onto a fibrous paper, paperboard or cardboard base, into direct contact with the same, a multilayer coating comprising an innermost polymer layer containing a blend of (i) 10 to 25 wt-% of a low-density polyethylene (LDPE) having a melt viscosity and (ii) 75 to 90 wt-% of a linear low-density polyethylene (LLDPE) having a higher melt viscosity than the LDPE, a middle vapour barrier polymer layer, and an outermost heat-seal layer of the same blend as said innermost layer, the innermost layer adhering the coating to said fibrous base and the outermost layer forming a heat-seal layer, wherein the outermost heat-seal layer excludes materials comprising more than 90 wt-% of high-density polyethylene (HDPE).

2. The method of claim 1, wherein said polymer blend contains 80 to 90 wt-% of said LLDPE and 10 to 20 wt-% of said LDPE.

3. The method of claim 1, wherein said LDPE has a melt index of at least 25 g/10 min (190 C., 2.16 kg) and that said LLDPE has a melt index of at most 10 g/10 min (190 C., 2.16 kg).

4. The method of claim 1, wherein the weight of each one of the innermost adhesive layer, the middle vapour barrier layer, and the outermost heat-sealable layer is at most 15 g/m.sup.2.

5. The method of claim 1, wherein a blend containing up to 90 wt-% of HDPE of biologic origin is used for said middle vapour barrier layer.

6. The method of claim 1, wherein LLDPE of biologic origin is used for said blend.

7. A heat-sealable packaging material comprising (a) a fibrous base of paper, paperboard or cardboard, (b) an innermost adhesive layer of a blend of (i) 10 to 25 wt-% of a low-density polyethylene (LDPE) having a lower melt viscosity and (ii) 75 to 90 wt-% of a linear low-density polyethylene (LLDPE) having a higher melt viscosity, the innermost layer being in a direct contact with said fibrous base, (c) a middle vapour barrier polymer layer, and (d) an outermost heat-sealable layer of a blend of (i) 10 to 25 wt-% of a low-density polyethylene (LDPE) having a melt viscosity and (ii) 75 to 90 wt-% of a linear low-density polyethylene (LLDPE) having a higher melt viscosity than the LDPE, said innermost, middle and outermost layers having been brought by coextrusion onto said fibrous base.

8. The packaging material of claim 7, wherein the weight of each one of the innermost, middle and outermost polymer layers is at most 15 g/m.sup.2, and the total weight of the polymer layers is at most 25 g/m.sup.2.

9. The packaging material of claim 7, wherein a blend containing up to 90 wt-% of HDPE of biologic origin has been used for said middle vapour barrier polymer layer.

10. The packaging material of claim 7, wherein LLDPE of biologic origin has been used for said blend with LDPE.

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

12. A drinking cup made by heat-sealing from the packaging material of claim 7.

13. The method of claim 1, wherein said polymer blend contains 80 to 85 wt-%, and 15 to 20 wt-% of said LDPE.

14. The method of claim 1, wherein said polymer contains about 80 wt-% of said LLDPE and about 20 wt-% of said LDPE.

15. The method of claim 1, wherein the weight of each one of the innermost adhesive layer, the middle vapour barrier layer, and the outermost heat-sealable layer is at most 10 g/m.sup.2.

16. The method of claim 1, wherein the weight of each one of the innermost adhesive layer, the middle vapour barrier layer, and the outermost heat-sealable layer is at most 5 g/m.sup.2.

17. The packaging material of claim 7, 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.

18. The packaging material of claim 7, wherein the weight of each one of the innermost, middle and outermost polymer layers is at most 5 g/m.sup.2, and the total weight of the polymer layers is at most 15 g/m.sup.2.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

DETAILED DESCRIPTION

(4) 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 branched low-density polyethylene (LDPE) of a lower melt viscosity and (ii) 75 to 90 wt-% of a linear low-density polyethylene (LLDPE) of a higher melt viscosity, a middle layer 3 of a blend of 50 to 90 wt-% of HDPE and 10 to 50 wt-% of LDPE or LDPE and outermost layer 4 of a polymer blend, which is similar to, preferably the same as the blend used for the innermost adhesive layer 2. In the blend forming the inner adhesive layer 2, and the outermost layer 4, the low-density polyethylene (LDPE) preferably has a melt index of at least 15 g/10 min (190 C., 2.16 kg) and the linear low-density polyethylene (LLDPE) preferably has a melt index of at most 10 g/10 min (190 C., 2.16 kg). 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 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. 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.

(5) The packaging material according to FIG. 2 differs from the material shown in FIG. 1 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.

(6) The packaging material according to FIG. 3 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. 1. The material of FIG. 3 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

(7) 20 wt-% of extrusion grade LDPE of petroleum oil origin was dry blended with 80 wt-% of film grade bio-LLDPE of sugar cane origin to form a polymer blend. A layer of this polymer blend having a coating weight of 15 g/m.sup.2 was extruded onto a paperboard surface into direct contact with the same. The coating layer was achieved with good runnability, acceptable neck-in and good adhesion to the paperboard.

(8) A series of tests was carried out in order to determine the performance of the above blend as an adhesion layer between paperboard and one or more outer polymer layers in a coextruded multilayer coating. Layers of 100 wt-% bio-HDPE were used for testing, but in regard of adhesion these do not differ significantly from blends of 50 to 90 wt-% of HDPE and 10 to 50 wt-% of LDPE or LLDPE within the scope of the invention. Extruded monolayer coatings, as well as coextruded multilayer coatings with an innermost HDPE+LDPE blend layer, were included as a comparison.

(9) 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.

(10) TABLE-US-00001 TABLE 1 Heat Thicknesses sealing Adhesion Neck-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

(11) 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 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.