Method of producing a heat-resistant polymer-coated oven board, an oven board obtainable by the method, a food tray and a food package

Abstract

The invention covers a method of producing a heat-resistant polymer-coated oven board, the resulting oven board, a food tray and a food package, which comprise such board and withstand heating in a range or microwave oven. According to the invention the coated oven board (1) is made by adhering a premade heat-resisting film (4) comprising polyethylene terephthalate (PET) or its derivate, such as glycol-modified PET known as PETG, to a board base (2) by extrusion lamination, in which an adhesive layer (3) comprising polyamide (PA) is extruded between the heat-resisting film and the board base. To improve the strength and barrier properties, the film (4) may be an extruded multilayer film and/or the film may be stretch-orientated to bring about crystallization in PET.

Claims

1. A method of producing a polymer-coated oven board, comprising: adhering a pre-made solid heat-resisting film comprising polyethylene terephthalate (PET) or its derivate and having a weight of 10-20 g/m.sup.2 to a board base by extrusion lamination, in which an adhesive layer comprising a molten polyamide (PA) is extruded between the pre-made solid heat-resisting film and the board base.

2. The method of claim 1, wherein the polymer-coated oven board forms a surface layer of the product.

3. The method of claim 1, wherein the board base is similarly coated on its both sides.

4. The method of claim 1, wherein the adhesive layer comprises high-barrier polyamide (HBPA).

5. The method of claim 1, wherein the weight of the adhesive layer is 3-15 g/m.sup.2.

6. The method of claim 1, wherein the heat-resisting film comprises PET, PETG, or both.

7. The method of claim 6, wherein the heat-resisting film comprises of a plurality of coextruded layers of PET and PETG.

8. The method of claim 6, wherein the heat-resisting film includes an innermost PA layer, which is adhered to the extruded adhesive PA layer at the extrusion lamination step.

9. The method of claim 1, wherein the heat-resisting film is stretched before the extrusion lamination step.

10. The method of claim 1, wherein the weight of the adhesive layer is 5-10 g/m.sup.2.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is illustrated by means of examples, with reference to the attached drawings, in which

(2) FIG. 1 shows manufacture of a polymer-coated board according to the invention, and

(3) FIGS. 2 to 6 show examples of coated board structures according to the invention.

DETAILED DESCRIPTION

(4) FIG. 1 shows a process according to the invention for manufacturing an ovenable coated packaging board 1, which comprises a board base, and inner coating layer of polyamide (PA) and an outer coating layer of polyethylene terephthalate (PET). The process is one of extrusion lamination, in which a layer 3 of melted PA is extruded between a board base 2 and a premade solid PET film 4 to form a bond between the same. The film 4 may be a monolayer or multilayer film, and may be stretch-orientated before incorporation into the board product 1.

(5) According to FIG. 1 a web of paperboard 2 and a web of PET film 4 are drawn from respective rolls 5, 6 to a nip 7 formed by a drive roll 8 and a chill roll 9, and PA melt 3 is extruded from a nozzle 100 to meet the board and film webs 2, 4 at the nip 7. The chill roll 9 cools the melted PA, and the rolls 8, 9 together press the layers 2, 3, 4 to form the finished board product 1.

(6) FIG. 2 shows the structure of the board product 1 made in accordance with the process of FIG. 1 at its simplest. The board base 2 has an inner coating layer 3 of PA and an outer coating layer 4 of PET. In the figure the borderline 10 between the extruded inner layer 3 and the outer film layer 4 has been emphasized merely for the sake of illustration; in practice there is a smooth adhesive bonding between the layers 3, 4.

(7) FIG. 3 corresponds to FIG. 2 but shows HBPA and PETG as alternative materials for the extruded and premade film layers 3, 4. Of course combining PA with PETG or HDPA with PET for the two layers 3, 4 is also possible.

(8) The weight of the paperboard base 2 may vary in the range of about 120 to 250 g/m.sup.2. Use of a heavier cardboard for the base 2 is also possible. The board base 2 may comprise chemical or mechanical pulp or combinations of the same, usually as a multilayer structure customary to the art.

(9) The weight of the extruded adhesive layer 3 may vary in the range of about 3 to 15 g/m.sup.2, preferably 5 to 10 g/m.sup.2. The weight of the outer film layer 4 may vary in the range of about 10 to 30 g/m.sup.2, preferably 10 to 20 g/m.sup.2.

(10) FIG. 4 shows an embodiment according to the invention, in which the premade outer film consists of two layers 4, 4 bonded to each other. The materials of the film are PET and PETG. PETG has better moldability, and therefore forms the outermost layer 4 in the finished product. The combined weight of the film layers 4, 4 preferably fits within the above range of about 10 to 30 g/m.sup.2.

(11) Even the material according to FIG. 4 has been manufactured in the manner shown in FIG. 1. The film has been prepared by coextrusion of the PET and PETG layers and solidifying the film, for subsequent use in the process of the present invention.

(12) FIG. 5 shows a further embodiment according to the invention, in which the premade outer film consists of three layers 4, 4, 4 bonded to each other. The materials of the film layers are PETG, PET and PETG in this order.

(13) FIG. 6 shows a still further embodiment according to the invention, in which the premade outer film consists of layers 4, 4 of PA and PETG. PA bonds excellently to the extruded innermost PA layer 3, and PETG forms the preferred material for the outer surface of the coated board.

(14) The coating layers are principally designed to form the contact layer with food in a food tray or container, and withstand heating in a range or microwave oven. The coated board may thus be formed to food trays, in which there is coating at least on the inner food-contact side of the tray, or sealed food containers, in which there is coating at least on the food-contacting inner surface of the container. However, it may be desirable to provide similar coating also to the outside of the tray or container.