The invention relates to packaging material comprising a basic layer of greaseproof paper coated with a layer of plastic material. The invention is intended especially for use as a packaging material for food products.

Food packaging materials are required good barrier properties against gas, grease, aroma, water, and water vapour. Grease and aroma barriers primarily prevent evaporation of aroma or transmission of grease from the packaged product into surroundings, whereas water vapour barrier ensures that the product will not dry. Gas tightness prevents any influence of oxidation. To meet these requirements, following structures are used for instance in flexible packages for food products:

aluminum laminates, structures combining aluminum, polymer and paper, multi layer plastic laminates, polyolefin, polyamide, ethylene vinyl alcohol, etc. aluminated plastic laminates, oriented and aluminated polymers, polyolefin, polyethylene terephthalate, etc.

The barrier properties of these products against gas, grease, aroma, water and water vapour have usually been optimized by adapting the thickness of the layers, and they usually do operate well in a number of packaging structures in respect to the aforesaid protection requirements. However, creasing and folding on the one hand and aroma tightness in humid conditions on the other form two major problem areas. Creasing may, e.g., cause cracking of the aluminum which immediately results in considerable impairment of the oxygen tight properties. Another example is the barrier polymer, ethylene vinyl alcohol (EVOH), nowadays much used in multi layer structures, which considerably loses its oxygen tightness when the relative humidity is high. Furthermore, the existing oxygen and aroma barrier structures are almost without exception multi layer laminates whose recycling is practically impossible since it is not economically beneficial either to

separate or to screen the laminate layers. This is especially true of products containing aluminum foil.

The international publication WO 91/15410 introduces a gastight packaging material that provides a barrier against evaporation of aroma or transfer of oxygen, comprising a basic layer of greaseproof paper coated with polyethylene. The advantage of this packaging material is said to be gas tightness and good mechanical strength, e.g., when the material is folded in connection to packaging.

As already stated earlier, this is also a packaging material which is based on the combined effect of the protective properties of different layers. Although the packaging laminate in question does provide an adequately tight and mechanically strong structure for packaging different kinds of food products, the problem of recyclability remains because of the laminate structure of the package.

The only alternative for recycling is to treat packaging material as waste. To date, the focus of attention has been on the packaging properties of the packaging material, not on the after use properties.

The object of the present invention is to remove these defects and to present a packaging material with excellent barrier properties which, however, can be disposed after usage. In pursuing this aim, the packaging material in accordance with the present invention is primarily characterized in that the plastic of the layer covering the basic layer is biodegradable plastic.

Since the basic materials of the packaging material are biodegradable synthetic polymers and greaseproof paper made of naturally decomposing material (cellulose), the packaging material can be composted after usage. The packaging material combines two extremely important requirements: on one hand, good barrier properties against oxygen, aroma, grease, and water vapour; and on the other hand, biodegradability and compostability. There are many known biodegradable plastics whose oxygen tightness is not influenced by growing relative humidity, and who, in connection to lamination, close

the small pinholes of greaseproof paper which otherwise would impair oxygen tight properties.

In addition, the combination of a greaseproof paper and biodegradable plastic produces at least as good tightness as do the traditional materials. Further, it is possible to use combinations of different biodegradable plastics where the properties of different plastics are combined in an advantageous manner expressly for package use.

The invention has a number of embodiments, varying according to the application of the packaging material, and comprising various kinds of layers. These embodiments are described in detail undemeath. A characteristic shared by all these materials in question is that all the layers are biodegradable in appropriate environments after disposal. All the laminate structures described undemeath can be produced by the known methods of coextrusion and/or lamination.

In the following, the invention is described in more detail with reference to the enclosed figures of which

Fig. 1 shows a cross-sectional view of the basic idea of a packaging material in accordance with the present invention,

Fig. 2 is a second embodiment of the packaging material,

Fig. 3 is a third embodiment of the packaging material,

Fig. 4 is a fourth embodiment of the packaging material,

Fig. 5 is a fifth embodiment of the packaging material,

Fig. 6 is a sixth embodiment of the packaging material,

Fig. 7 is a seventh embodiment of the packaging material, and

Fig. 8 shows a schematic diagram of one preferred method for making a packaging material in accordance with the present invention.

In the following figures, the basic layer of greaseproof paper is marked with a reference number 1 , and the layer of biodegradable plastic covering is marked with a reference number 2. In cases where the plastic layer is comprised of sublayers these have been marked with a reference number 2 and a small letter representing each sublayer.

The basic layer 1 of the packaging material is greaseproof paper. Greaseproof paper is a known wrapping paper for food products and, compared to other papers made of cellulose-based pulp, it provides excellent barrier properties against grease, it is a good oxygen barrier and a gas barrier, and it thus also prevents evaporation of scent and aroma. This is accomplished by a high degree of beating of the fibrous pulp creating a tight structure. The above-mentioned properties of paper may have been further improved by calendering and by finishing with naturally decomposing surface sizing chemicals such as carboxymethyl cellulose (CMC) and starch.

The basis weight of greaseproof paper may vary but is typically 30 — 100 g/m ² . The raw material used is usually sulphite pulp or sulphate pulp whose degree of beating is high. Spruce sulphite pulp is a traditional raw material because of its excellent beatability properties. The degree of tightness (grease tightness) for the paper layer in question, expressed in Linden, may be 30—600 s, preferably 100—600 s.

The plastic layer 2 covering the basic layer 1 is thinner and improves the gas tightness of the packaging material, and particularly provides a water vapour barrier for the packaging material. The plastic layer is noticeably thinner than the basic layer 1 with a basis weight varying below the weight limits of the basic layer 1. As will be stated in the following, the basic layer 1 may either be laminated on only one side with a layer 2 of biodegradable plastic, or both sides of the basic layer 1 may be laminated. Furthermore, the layer of biodegradable plastic may comprise two or more sublayers with varying properties. In

addition to the above-mentioned layers, the packaging material may comprise other layers which are all similarly compostable.

The concept of biodegradable plastic is used for all such plastic materials whose polymer chain degrades as result of microbial activity, that is, it has a chemical structure which is inherently decomposable under suitable conditions, such as in a compost, contrary to e.g. polyethylene which has been blended with suitable materials for breaking its mechanical structure under compost conditions. In addition, these plastics can be molded when fluid, e.g., by extrusion, into a thin foil of only some micrometers thick.

Figure 1 presents the simplest form of packaging material. The basic layer of greaseproof paper 1 has been coated by coextrusion or lamination with a layer 2 of biodegradable plastic. Suitable plastics are polyhydroxybutyrate (PHB), hydroxybutyric/hydroxyvaleric copolymer (HB/HB), that is, generally some polyhydroxyalkanoate containing hydroxybutyrate, as well as polycaprolactone (PCL), polylactic acid i.e. polylactide (PLA), cellulose ester, or some other suitable biodegradable plastic, such as a synthetic polyester, or a combination of these plastics.

Figure 2 shows a packaging material with a basic layer 1 laminated also on the opposite side with a layer 2 of biodegradable plastic. This layer may also be of some of the above-mentioned plastics. These plastic layers may be identical or different in their construction.

Figure 3 presents a packaging material with a layer 2 of biodegradable plastic comprised of two sublayers; layer 2a which is in direct contact with the basic layer 1 and is an adhesive layer; and layer 2b whose primary function is to provide a barrier layer. Thus, the packaging material also has excellent heat-sealing properties, appropriate friction, and other aforesaid protective properties essential in materials for food product packaging. Polylactide is well suitable for layer 2a and hydroxybutyrate based polyhydroxyalkanoate for layer 2b, especially HB/HV.

Figure 4 shows a packaging material with a basic layer 1 covered with a plastic layer 2 comprised of three sublayers 2a, 2b and 2c made of biodegradable plastic. Again, the inner layer 2a is an adhesive layer; the middle layer 2b provides an actual barrier layer which prevents transmission of different substances; and the outer layer 2c, which also forms the surface of the packaging material, is mainly chosen according to good surface properties such as heat-sealability, friction etc. For barrier, adhesion and surface properties, a good solution is obtained with the combination of inner layer 2a of polylactide, middle layer 2b of polyhydroxyalkanoate, especially HB/HV, and outer layer 2c of polylactide.

Instead of polylactide, also cellulose ester or a synthetic biodegradable polyester can be used.

Since layer 2 of biodegradable plastic usually forms the inner product contact layer in the embodiments listed above, we have taken into consideration, when selecting the plastic layer for layer 2 in figure 1 ; plastic layer 2 on the inner surface in figure 2; layer 2b in figure 3; and layer 2c in figure 4, that these layers are in direct contact with the material packaged.

In the following, we have described with reference to figures 5 — 7 packaging materials which comprise, in addition to the basic layer 1 and the layer 2 of biodegradable plastic, additional layers chosen primarily on the basis of the quality of the package.

Figure 5 shows a packaging material suitable for liquid products. The inner surface of the basic layer 1 is coated with a layer 2 of biodegradable plastic comprised of two sublayers 2a and 2b, whose properties are chosen mainly according to the properties required of the sublayers presented in figure 3. One surface of the basic layer 1 is, through a layer 2 of biodegradable plastic with appropriate adhesive properties, adhered to a paperboard layer 3 which forms the body of the packaging material. The paperboard may be of any quality used in liquid package paperboards. The basis weight may vary within 100 — 500 g/m ² .

Figure 6 presents a packaging material for use as a wrapping paper for butter and margarine, i.e., for use of a flexible package. The layer 2 of biodegradable plastic is applied only on one side of the basic layer 1 and, through this plastic material, the basic layer 1 is adhered to a layer 4 which is ordinary packaging paper and improves the strength of the material by being of kraftliner for example. Greaseproof paper is thus in direct contact with the packaged product. The quality of the biodegradable plastic is here chosen primarily on the basis of good adhesive properties, but if the water vapour barrier properties are important for the package, these properties can be more important in the choice of plastic.

Figure 7 shows a material similar to that in figure 6 but with a basic layer 1 of greaseproof paper laminated also on the inner surface with a layer 2 of biodegradable plastic. Such packaging material can be utilized in flexible packages, e.g., in packaging of snacks and potato crisps, with the advantage of good heat-sealing properties of the biodegradable plastic on the inner surface. One of the layers can be of PHB or HB/HV and the other of PLA. The purpose of layer 4 of ordinary packaging paper is to add strength to the material and provide protection from light. Furthermore, the outer surface of this layer provides an excellent printing surface. The paper can be for example

MG, SC or clay-coated SC. The flexible package we have described can well be used to replace, e.g., aluminum foil packages.

Figure 8 shows the principle for manufacturing some products in accordance with figures 1 — 7. Coextruder 5 comprises a known feed block 6 in which melted polymer material A, B, C, which will form the different layers, is fed. In this case the polymer material is biodegradable plastic. Feed block 6 then organizes the material into layers one upon another in desired order after which the forming die 7 spreads the layers into a foil of full width which forms the layer 2 of biodegradable plastic described above. Greaseproof paper is deposited from its own roll into the nip between the compactor roll 8 and support roll 9, into which nip also the foil from the extruder is led. Here, layer 2 of biodegradable plastic adheres to the surface of the basic layer 1 and the completed material is guided along the surface of

the support roll 9 for further preparation, e.g., reeling, or lamination on the other surface with similar equipment. A product in accordance with figure 6 can be produced by depositing the web which forms the additional layer 4 from its own roll 10 between the compactor roll 8 and the support roll 9, as illustrated with a broken line in the diagram.

Research on packaging material which combines a basic layer 1 of greaseproof paper and a layer 2 of biodegradable plastic has indicated that the packaging material exhibits excellent oxygen barrier properties. The OTR - values (oxygen transmission rate) of the greaseproof paper representing these properties may be above 1000 cm ³ /m ² , 24h, 1 bar. For the polymer layer alone, the OTR - values are accordingly 100 — 1000 expressed in the same standard units. Compared to the above values, the OTR - values for a layered product consisting of the basic layer and a biodegradable plastic layer are as low as 10 at the most, for example in the range of 1 — 10. This proves that, in addition to compostability, a packaging material in accordance with the present invention has at least as good properties as the packaging materials we already know.

The packaging material according to the present invention is particularly suitable for packaging of food products. These packages may be, depending on the quality of the material, various kinds of consumer or large-scale consumer packages. Suitable materials to be packaged include powders which contain grease - such as dry soups - as well as spices, snacks and liquids, in addition to food products, the packaging material may be utilized in packaging of pharmaceutics, cosmetics and toiletries, such as soap.