PAPERBOARD-BASED MATERIAL

Abstract: The invention relates to a paperboard-based material used particularly for producing dishes, such as cups, bowls, plates or the like, the material comprising a core layer (1) which is liquid proof at least for a short period of time and is formed of at least one paperboard layer (2) and at least one other material layer (3). According to the invention, the material also comprises a dry-formed material layer (4) attached to one surface of the core layer (1).

Description: PAPERBOARD-BASED MATERIAL BACKGROUND OF THE INVENTION The invention relates to a paperboard-based material used particularly for producing cups, bowls, plates and the like, the material comprising a core layer which is liquid-proof at least for a short period of time and consists of at least one paperboard layer and at least one other material layer. The material described above is typically used for producing various dishes intended for liquids, such as cups and bowls, the material comprising a paperboard layer and a layer attached thereto which is liquid proof at least for a short period of time. Such materials are not as liquid proof as proper liquid packaging boards which can be used for storing liquids even for long periods and which comprise several plastic layers and barrier layers to ensure that they are liquid and gas proof. When dishes are produced from paperboard-based material, spe- cial structural solutions are needed to make the dishes suitable for hot liquids, too. For example, a coffee cup needs to be provided with ears which allow to handle the cup containing hot coffee safely. Such special structural solutions cannot, however, be applied to other kinds of dish, such as plates, bowls or the like. Thus the outer surface of a dish containing food or liquid heats up considerably when food or liquid is heated in a microwave oven, for example. In that case microwaves do not heat up the material of the dish itself, but heating results from heat transmission from the food or liquid. The outer surface of such a dish may be so hot after heating in the microwave oven that it cannot be handled safely with bare hands. BRIEF DESCRIPTION OF THE INVENTION The object of the present invention is to provide a paperboard- based material which is used particularly for producing dishes, such as cups, bowls, plates and the like, and the outer surface of which does not heat up to a dangerous extent even when the dish is filled with hot liquid or food or when these are heated up in a microwave oven. This is achieved with the paperboard-based material of the invention which is characterized in that, in addition to the core layer, the material comprises a dry-formed material layer attached to one surface of the core layer. Preferably this dry-formed material layer contains at least 50% of cellulose fibre and is bound with a binder. This dry- formed material layer can be attached to the core layer surface either by ex- trusion lamination or dispersion lamination. Usually the material layer providing short-term liquid impermeability is made of synthetic polymer and/or biopolymer. Particularly when biopolymer, also called bioplastic, is used, the dish will also be well- suited for recycling and may even be a biodegradable, i.e. com- postable, product. One surface of the paperboard material according to the invention consists of a dry-formed material layer which is porous and contains rather a lot of air. Thus heat transmission does not cause the outer surface of the material to heat up to a dangerous extent even when the dish made of it is filled with hot liquid or food or these are heated in the dish in a microwave oven. BRIEF DESCRIPTION OF THE DRAWINGS In the following, the paperboard-based material of the invention will be described in greater detail with reference to the accompanying drawing, in which the figure shows a cross-section of a preferred embodiment of the mate- rial according to the invention. DETAILED DESCRIPTION OF THE INVENTION The figure shows a cross-section of a preferred embodiment of the paperboard-based material according to the invention. The cross-section comprises a paperboard layer 2 and a material layer attached to one surface thereof, e.g. a layer 3 of synthetic polymer and/or biopolymer which renders the core layer 1 formed by the paperboard layer 2 and layer 3 liquid proof at least for a short period of time. The paperboard layer 2 may consist of pure solid board the basis weight of which may be e.g. 210 g/m 2 . Layer 3 may consist of LPDE the basis weight of which may be e.g. 10 to 30 g/m 2 . In principle, the structure of the core layer 1 corresponds to the structure of the conventional paperboard-based material used for producing dishes. According to the invention, a dry-formed material layer 4 is attached to one surface of the core layer 1. Most preferably this dry-formed material layer contains at least 50% of cellulose fibre and is bound with a binder. As is well known, in dry-forming fibres are spread evenly onto a moving wire on which the material is formed by means of air flow. In dry-forming it is possible to use very different fibres which are spread onto the wire by means of one or more formers. The material of the invention, however, primarily contains cellulose fibres and secondarily artificial fibres, such as plastic fibres or the like, depending on the desired properties of the material. In dry-forming either binder fibres are scattered into the material or binder is sprayed into the material on the wire, and in the following heat treatment step the binding agents bind the material layer on the wire so that it forms a uniform web. Such a dry- formed material layer is relatively porous, thus containing rather a lot of air. In the paperboard-based material of the invention the thickness of the dry-formed material layer 4 used may be e.g. 0.3 to 2 mm and the basis weight 30 to 100 g/m 2 . As appears from the figure, between the core layer 1 and the dry- formed layer 4 there is a material layer 5 by means of which the dry-formed layer 4 and the core layer 1 are attached to each other. This material layer 5 may be e.g. a layer of synthetic polymer and/or biopolymer formed by extrusion lamination. It may be made of LPDE the basis weight of which is e.g. 10 to 30 g/m 2 . Layer 5 may also be a material layer which is spread or sprayed onto the surface of the core layer 1 and by means of which the dry-formed layer 4 is attached to the core layer 1. This procedure is called dispersion lamination. The dry-formed layer 4 can also be attached in a manner which differs from the dispersion and extrusion lamination procedures described above. In this method the surface layer of the dry-formed material layer con- tains, at least on the side to be attached to the core layer 1 , adhesive latex by means of which the core layer and the dry-formed layer can be attached to each other. In that case there is no need for a separate material layer 5, but the core layer 1 and the dry-formed layer 4 can be directly attached to each other. Other materials could also be used at least on the surface of the dry- formed material layer to be attached to the core layer 1 to attach these layers together. The paperboard-based material according to the invention has been described above only by means of some preferred embodiments and it is to be understood that the detailed structure as well as the layer or layers providing liquid impermeability, the paperboard-based layer and the dry-formed layer can be modified without deviating from the scope of protection defined in the appended claims. Thus there may be one or more layers providing liquid impermeability and their material composition may vary according to the desired properties. The detailed composition and basis weight of the paperboard layer may also differ. Furthermore, the fibre content of the dry-formed layer and the way of binding it may vary as well as the way in which it is attached to the core layer. One significant property of the paperboard-based material of the invention is that, if desired, it can be provided with a composition which is suitable for recycling, i.e. of pulpable quality. Thus the invention can be modified considerably without affecting the implementation of the inventive concept, i.e. the fact that by arranging a relatively porous dry-formed material layer as the outer layer of the material from which a dish is to be formed the surface of the dish can be prevented from heating up when there is hot food or liquid next to the surface opposite to the material.

Claims: CLAIMS 1. A paperboard-based material used particularly for producing dishes, such as cups, bowls, plates or the like, the material comprising a core layer (1 ) which is liquid proof at least for a short period of time and is formed of at least one paperboard layer (2) and at least one other material layer (3), characterized in that the material also comprises a dry-formed material layer (4) attached to one surface of the core layer (1 ). 2. A material according to claim 1, characterized in that said at least one other material layer (3) is a layer of synthetic polymer and/or biopolymer. 3. A material according to claim 1 or 2, characterized in that the dry-formed material layer (4) is a layer containing at least 50% of cellulose fibre and bound with a binder. 4. Material according to any one of claims 1 to 3, character- i z e d in that the dry-formed material layer (4) contains, at least in the surface layer to be attached to the core layer (1), adhesive latex used for attaching the dry-formed material layer (4) and the core layer (1) to each other. 5. A material according to any one of claims 1 to 3, characterized in that the dry-formed material layer (4) and the core layer (1 ) are attached to each other by extrusion lamination (5). 6. A material according to any one of claims 1 to 3, characterized in that the dry-formed material layer and the core layer are attached to each other by dispersion lamination.

Inventors: KIISKI SEPPO, NEVALAINEN KIMMO, NIEMI TAPIO, PENTTINEN TAPANI, KIISKI, SEPPO, NEVALAINEN, KIMMO, NIEMI, TAPIO, PENTTINEN, TAPANI
Applicants: ENSO OYJ, KIISKI SEPPO, NEVALAINEN KIMMO, NIEMI TAPIO, PENTTINEN TAPANI, WALKISOFT FINLAND OY, KIISKI, SEPPO, NEVALAINEN, KIMMO, NIEMI, TAPIO, PENTTINEN, TAPANI
Application year: 1999
Main classification: B32B29
IPC codes: B32B27, B32B29, B65D1, C08L101, D21H27