DISPOSABLE BOARD CONTAINER AND USES OF BOARD

Abstract

The invention relates to a disposable container of fibrous board comprising a bottom (3) and an upward mantle (2) heat-sealed thereto. The material for both the bottom and the mantle is a polymer coated fibrous board, in which the coating covers at least the inner surfaces of the container. According to the invention the material comprises a fibrous board base (8) such as paperboard or cardboard, an extruded inner coating layer (9) of a blend of polyethylene (PE) and polypropylene (PP), and an extruded outer coating layer (10) of polypropylene-olefin copolymer (PP-c). The inner coating layer (9) secures adhesion with the board base (8) and the outer coating layer (10) is for liquid-proof heat-sealing between the bottom (3) and the mantle (2) of the container. The container is in particular a microwave ovenable cup or food tray.

Claims

1. A disposable board container comprising a bottom and a mantle extending upwards therefrom, said bottom and mantle being made from a polymer coated fibrous board and joined by heat-sealing, there being a coating of polymer at least on inner surfaces of the container, wherein said board comprises: i. a fibrous board base, ii. an extruded inner coating layer of a blend of polyethylene (PE) and polypropylene (PP), and iii. an extruded outer coating layer of propylene-olefin copolymer (PP-c).

2. The container of claim 1, wherein the polypropylene (PP) in the inner coating layer is propylene homopolymer.

3. The container of claim 1, wherein said blend of the inner coating layer contains 20 to 50 wt-% of PE and 50 to 80 wt-% of PP.

4. The container of claim 1, wherein the weight of the inner layer is 5 to 15 g/m2, and the weight of the outer layer (10) is 5 to 15 g/m2.

5. The container of claim 1, wherein the outer surface of the container is provided with at least one heat-sealable coating layer of PP-c or a blend of PE and PP.

6. The container of claim 5, wherein the inner and outer surfaces of the container are similarly coated with layers of polymer.

7. The container of claim 1, which is a microwave-ovenable food tray.

8. The container of claim 1, which is a disposable drinking cup.

9. (canceled)

10. (canceled)

11. The container of claim 1, wherein the weight of the inner layer is about 10 g/m.sup.2.

12. The container of claim 1, wherein the weight of the outer layer is about 10 g/m.sup.2.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Reference is made to the enclosed drawing, in which

[0020] FIG. 1 shows a paperboard drinking cup in a partially sectional view,

[0021] FIG. 2 is a sectional view of the heat-sealed joint between the bottom and mantle of the cup according to the prior art,

[0022] FIG. 3 is a sectional view of the joint between the bottom and mantle of the cup according to the invention,

[0023] FIG. 4 is a sectional view of the polymer coated board used for the cup as shown in FIGS. 1 and 3, and

[0024] FIGS. 5 and 6 show two further embodiments of boards useful for cups according to the invention.

DETAILED DESCRIPTION

[0025] FIG. 1 shows a drinking cup 1 made from a polymer coated fibrous material, such as paperboard. The cup 1, which has the conventional basic configuration, comprises a mantle 2 shaped as a truncated cone and a circular flat bottom 3. The mantle 2 has an upright seal 4, and the bottom 3 is sealed together with the mantle along its circumference. At the upper end of the mantle 2 a bead or a mouth roll 5 running around the mouth of the cup has been formed by mechanical moulding with the aid of heat and moisture. If desired, a separate lid may be provided for closing the mouth of the cup, for instance such as described in WO 2005/077768 A1.

[0026] The mantle 2 and the bottom 3 of the cup have a coating of polymer at least on the inner surfaces of the cup 1. The coating is liquid-tight, shielding the board base against wetting and enabling liquid-proof non-leaking sealing of the parts 2, 3. Preferably the drinking cup 1 has a polymer coating also on its outer surfaces.

[0027] As seen in FIG. 1, a circumferential downward rim 6 has been formed to the bottom 3 of the cup 1 by means of a compression-moulding press. The lower end of the mantle 2 has been bent accordingly to form an upward rim 7, forming a narrow track which fits the downward rim 6 of the bottom 3. Heat-sealing of the adjacent triple board layers at the lower end of the cup by means of the coating polymer seals the cup from its bottom.

[0028] The heat-sealed joint between the bottom 3 and the mantle 2 of the cup is shown in an enlarged scale in FIGS. 2 and 3. In FIG. 2, which represents the prior art, the material for both the bottom 3 and mantle 2 parts of the cup comprises a paperboard base 8 and a monolayer coating 9 of a blend of PE and PP. Typically the weight of the board base 8 is about 170-250 g/m.sup.2 and the weight of the polymer coating 9 is about 20 g/m.sup.2. At the heat seal adjacent coating layers 9 of said blend are sealed together, but as noted already, the seal between PE+PP layers tends to be deficient due to the middlemost board layer belonging to the bottom 3 restricting conduction of heat to the seal area.

[0029] In FIG. 3, which represents the invention, the material for both the bottom 3 and mantle 2 parts of the cup comprises a paperboard base 8 and a coextruded double layer coating, in which the inner layer 9 comprises a blend of PE and PP and the outer layer 10 comprises a propylene copolymer (PP-c). Suitable weights are 170-250 g/m.sup.2 for the board base 8, 5-15 g/m.sup.2 for the inner coating layer 9, and 5-15 g/m.sup.2 for the outer coating layer 10. Each inner coating layer 9 secures an excellent adhesion to the paperboard base 8 and the adjacent heat-sealed outer coating layers 10 form a liquid-proof seal between the bottom 3 and mantle 2 parts of the cup.

[0030] FIG. 4 is a sectional view of the triple-layer 8, 9, 10 material for the cup as shown in FIG. 3. FIGS. 5 and 6 are sectional views of two further cup materials suitable for use in the invention. In both cases the double layer coating 9, 10 for the inner surfaces of the cup is the same as in FIGS. 3 and 4. However, in FIG. 5 the reverse side of the material forming the outer surface of the cup is provided with a monolayer coating 11 of a blend of PE and PP, suitably of a weight of 10-20 g/m.sup.2. In FIG. 6 the reverse side of the material forming the outer surface of the cup is provided with a double layer coating of an inner layer 11 of PE+PP and an outer layer 12 of PP-c, preferably so that the material is similarly polymer coated on both sides.

[0031] The cup 1 according to the invention as depicted in FIGS. 1 and 3-6 is suitable for heating in a microwave oven and works as a drinking cup as well as a premade food container closed with a peelable lid of paper, plastic or metal. The cup could be modified to a food tray of a round, oval or rectangular configuration without changing its basic structure. In general any modifications within the metes and bounds of the appended claims belong to the scope of the invention as described herein.

Examples

[0032] Paperboard was extrusion coated by coextrusion of an inner layer of 10 g/m.sup.2 of WG341C (a blend of PP and PE) and an outer layer of 10 g/m.sup.2 of TD109CF (a propylene alfa olefin copolymer by Borealis AG developed for the manufacture of unoriented films in particular and having a reported melting point of 128-132 C.). As a reference representing the prior art, the same paperboard was extrusion coated by a monolayer of 20 g/m.sup.2 of WG341C. The coated materials were turned to cups of the type shown in FIG. 1 by heat-sealing, the material forming both the bottom and the mantle of the cup and the polymer coating being on the inner surfaces of the cup.

[0033] For the double-layer coated material according to the invention a heat-sealing temperature of 400 C. was needed to achieve non-leaking heat-seal between the bottom and the mantle of the cup. For the monolayer coated reference material a heat-sealing temperature of 490 C. was required for a seal, which was still of inferior quality.

[0034] A corresponding pair of coated materials was produced, in which both sides of the fibrous board base were identically coated, and the materials were turned to cups by heat-sealing. The required heat-sealing temperatures for a seal between the bottom and the mantle of the cup were 430 C. (invention) and 530 C. (prior art), respectively.

[0035] The heat-sealing temperatures are close to those needed for heat-sealing of conventional LDPE-coated cups, which means that advantageously the same sealing apparatus can be applied for cups according to the invention as for said conventional cups.

[0036] In view of the above detailed description of the present invention, other modifications and variations will become apparent to those skilled in the art. However, it should be apparent that such other modifications and variations may be effected without departing from the spirit and scope of the invention.