TECHNICAL FIELD The present invention relates to a thin and heat-sealable paper-based packaging laminate for a packaging container for a liquid food product. The invention is especially directed on such a laminate that is cost-effective yet sufficiently strong and durable, and that can be formed and sealed into a packaging container of a simple and flexible shape. Moreover, despite the low thickness of the laminate, it should have sufficient barriers for food products, such as a light-barrier for light- sensitive food products, and an outer appearance that is acceptable from a customer and consumer point of view. The laminate is especially well adapted for containers for ultra high temperature (UHT) treated food products or aseptic food packaging containers.

PRIOR ART AND PROBLEMS

In the market, a need exists of hygienic packaging containers for liquid or flowing food products, which packaging containers have an acceptable shelf -life at ambient conditions. Such containers can be of aseptic type and/or of the type intended for ultra high temperature (UHT) treated food products or others. They must also be sufficiently cost-effective for their intended market, and hence the packaging laminate of which they are formed should be beneficially thin and cost-effective. It does not have to be able to be formed into a self-supporting shape with dimension and grip stability, but may simply be formed into a simple and flexible shape, such as a pillow-shape e.g. However, one thing that it must have is an adequate light-barrier, to prevent a light-sensitive food product in the container from being spoiled and/or exhibiting off-flavour.

A problem in connection with thin and cost-effective paper-based packaging laminates, is that the paper layer is too thin to constitute an adequate light-barrier. Therefore, some kind of dedicated light-barrier has to be included in the laminate.

It is known in connection with packaging materials based purely on plastics to incorporate carbon black as a light-barrier.

A problem in connection with the use of carbon black as a light-barrier in a layer of a laminate, which layer is positioned further to the intended inside of the laminate than is the paper layer, is however that its black colour will be partly visible through the thin and white, but not fully opaque, paper layer, which gives the laminate and container an uneven, greyish appearance that is not accepted by consumers. It would however be very uneconomic to use a thicker paper to solve this problem.

Though it might be possible to conceal the black colour either by coating the paper layer with a composition comprising a pigment, or by printing a coloured ink on the paper layer, such solutions are costly and inconsistent with the low cost profile desired for the packaging laminate/container to be competitive.

Furthermore, while it might be possible to conceal the black colour by adding a white pigment to the plastics of the outermost heat-sealable layer of the laminate, such a solution leads to certain problems. Such problems include problems at start-up and shutting down of the converting line for manufacturing the laminate, since the white pigment deposits on process equipment. Accordingly, if the production in the line is to be temporarily shifted to another product, extensive cleaning has to be performed and the first few hours of the production of the second product will anyhow result in a product that is "contaminated" in its outermost layer by the white pigment, giving it an unacceptably patchy appearance. Moreover, having a white pigment in the outermost heat-sealable layer means that a printed design must be positioned on top of that plastic layer, whereby advanced or more environmentally unfriendly printing methods have to be used. Also, a protective lacquer needs to be applied on top of the printed design to protect it from scratches and wear during handling. Moreover, if there are flaws in the print, the entire laminate has to be discarded which means unnecessary waste of material.

BRIEF SUMMARY OF THE INVENTION

The present invention has for its object to provide a thin and heat-sealable paper-based packaging laminate for a packaging container for a liquid or flowing food product, such as a milk product, which laminate is sufficiently thin and thereby cost-effective, to be competitive, yet having adequately good properties in terms of

hygiene, sealability, strength, light-barrier and appearance of a packaging container formed from the laminate. Also, it should be beneficial from a converting point of view, avoiding or at least diminishing the problems in that connection, mentioned above. These and other objects are achieved by a thin packaging laminate for a packaging container for a liquid food product, having the following structure of layers, in order from an outside to an inside of the laminate:

- an outer heat-sealable layer consisting of a thermoplastic material,

- a thin paper layer, - a laminate layer consisting of a thermoplastic material having a white pigment included therein,

- an inner heat-sealable layer consisting of a thermoplastic material having a dark pigment included therein.

The invention also relates to a packaging container formed from such a laminate.

By the content of a dark pigment, preferably a black pigment such as carbon black, in the inner heat-sealable layer, the laminate and the container formed thereof achieves an adequate light-barrier for the food contents of the container not to be spoiled by exposure to light. By the content of a white pigment, such as titanium dioxide (TiO ₂ ), in the thermoplastic laminate layer, the laminate and the container formed thereof achieves an acceptably white appearance despite the inner dark pigmented layer.

In a preferred embodiment, the thermoplastic laminate layer with white pigment included therein is directly bonded to the paper layer, i.e. without any intermediate layers.

A special advantage of including the white pigment solely in the laminate layer, and in no other layers, is that a printed design can be positioned directly on the paper layer, where it is protected but not concealed by the fully transparent outer heat-sealable thermoplastic layer. Also, less costly and more environmentally friendly printing techniques can be used when printing directly on the paper layer, such as flexography with water-based ink. Moreover, there will be less depositing of white pigment on process equipment than would be the case if the white pigment was

included in the outer heat-sealable layer, and even if the converting line is temporarily shifted to produce a second laminate remaining white pigment will not be a problem since it will be positioned in a more central layer of the laminate, beneath the paper layer, were it is less visible than in an outer layer.

DETAILED DESCRIPTION OF THE INVENTION

According to one aspect of the invention, said outer heat-sealable layer consists of an extruded polyethylene material with a density of 880-970 kg/m ³ , preferably 910-930 kg/m ³ . It may have a weight of 8-25 g/m ² , preferably 10-20 g/m ² , and even more preferred 10-15 g/m ² . It may be composed of several preferably co-extruded part-layers, whereof at least the outermost is heat-sealable.

According to another aspect of the invention, said thin paper layer consists of bleached kraft paper having a weight of 30-80 g/m ² , preferably 40-70 g/m ² , and even more preferred 40-60 g/m ² . It has a basis weight and strength sufficient, together with the other layers, to give an adequate laminate strength. Most preferred, a paper layer of about 50 g/m ² is used, which gives a number of advantages over an even thinner paper layer. For example, there will be less problems with curl and wrinkles, an improved opacity will be achieved due to the material being somewhat denser (because more short fibres and/or fillers may be used since there is no demand for increased strength compared to a thinner paper), a wider choice of suitable papers is available, the sealing window may in certain cases be increased since the increased amount of paper can receive and distribute excessive heat so that local overheating of plastic sealing layers is avoided, etc. Moreover, the stiffness of the resulting packaging container will be improved. Of course, other types of flexible papers of similar thickness and properties can be used. It is also conceivable to use a multilayer paper.

According to yet another aspect of the invention, said thermoplastic of the laminate layer is a polyethylene material with a density of 880-970 kg/m ³ , preferably 910-930 kg/m ³ . It may have a weight of 8-50 g/m ² , preferably 10-40 g/m ² , and even more preferred 15-30 g/m ² . The white pigment is included in this layer at a content of at least 2 %, preferably at least 5 %, and even more preferred at least 8 %, but 20 %, preferably 15 %, and even more preferred 12 % at the most, by weight. Suitably,

said white pigment is titanium dioxide, although other types of white pigment are conceivable. Since it is difficult to include larger contents of the white pigment in the thermoplastic laminate layer, the layer must be made thicker, at the upper end of the above given ranges, if there is a need of a large total amount of white pigment to conceal the dark pigment in the inner heat-sealable layer. Also, the laminate layer may be composed of several preferably co-extruded part-layers, in which case the white pigment may be included in one or more, or all, of these part-layers.

The inner heat-sealable layer suitably consists of a thermoplastic material in the group that consists of a polyethylene material, preferably with a density of 880- 970 kg/m ³ , preferably 910-930 kg/m ³ , a polypropylene, an ethylene vinyl acetate and a thermoplastic acrylic acid co-polymer (neutralised or non-neutralised). It may be composed of several preferably co-extruded part-layers, whereof at least the innermost is heat-sealable. Here, it should be noted that the term "innermost" refers to the layer that is outermost on the inside of the laminate, i.e. the layer that will be in contact with the contents of the packaging container formed there from. The inner heat-sealable layer may have a total thickness, depending on thermoplastic quality, of 10-45 g/m ² , preferably 13-35 g/m ² , and even more preferred 20-30 g/m ² . It suitably includes a content of dark pigment of 0.2-2 g/m ² , preferably 0.2-1 g/m ² , and even more preferred 0.3-0.8 g/m ² . However, since the dark pigment is not very expensive, and since it is quite easily included in the thermoplastic material, it is conceivable that it may be included at even larger contents, such as up to 3 or 4 g/m ² . Suitably, said dark pigment is carbon black. In case the inner heat-sealable layer is composed of several part-layers, the dark pigment may be included in one or more, or all, of these part-layers. Preferably, the inner heat-sealable layer is pre-manufactured prior to its incorporation in the packaging laminate, i.e. it constitutes a pre-manufactured film, suitably made by (co-)extrusion blowing, (co-)extrusion casting or (co-)extrusion coating. A blown or cast film has the advantage over an extruded layer that it has better strength and less oxidative degradated materials, because it is made at a lower temperature, and that it has a more controlled machine and cross directional properties.

Advantages of using a pre-manufactured film as the inner heat-sealable layer, and using a pre-manufactured paper layer as a bulk layer in the thin laminate according to the invention, are that it is easy to change film and/or paper quality, e.g. food contact layer grade, in the converting line, if needed, and that there are somewhat less demands on the accuracy of the extrusion thickness of the extruded layers (the outer heat-sealable layer and the laminate layer).

The packaging laminate has a total weight of 60-180 g/m , preferably 70-150 g/m , and even more preferred 75-125 g/m .

The invention also relates to a packaging container with a liquid or flowing food content, which container is formed of such a packaging laminate. It may for example have the shape of a flexible pillow with one longitudinal seal and two transversal seals at opposing ends of the container.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS The present invention will now be described in greater detail herein below, with reference to preferred embodiments and with reference to the accompanying Drawings. In the accompanying Drawings:

Fig. 1 is showing a cross-section of a laminate according to the invention, Fig. 2 shows a packaging container, formed from the laminate in Fig. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In Fig. 1, the preferred laminate according to the invention is generally denoted 10. It is composed of four layers 12, 13, 14 and 15. The paper layer 12 is made of bleached kraft paper and has a weight of about 50 g/m ² . The extruded outer heat- sealable thermoplastic layer 13 will constitute the outside of a packaging container formed from the laminate 10 and is made of low density polyethylene (LDPE), and has a weight of about 12 g/m ² . The inner heat-sealable thermoplastic layer 14 will be in contact with the food in the packaging container formed from the laminate 10. It is a film of extrusion blown linear low density polyethylene (LLDPE), and has a weight of 23 g/m . Of that weight, 0.4 g/m is carbon black, which gives layer 14 a black appearance and acts as a light-barrier. The black colour of layer 14 is concealed, as seen from the outside of the laminate 10, i.e. as seen from layer 13, by the extruded

laminate layer 15. The laminate layer 15 is made of low density polyethylene (LDPE), and has a weight of about 17 g/m ² . Of that weight, 12 % is TiO ₂ , which gives layer 15 a white and desirably opaque appearance, hence concealing the black inner heat-sealable thermoplastic layer 14. Fig. 2 shows a packaging container 20, made by a form-fill-seal process of the laminate shown in Fig. 1. It is of flexible pillow-shape, with one longitudinal seal 22 and two transversal seals 24a, 24b at opposing ends of the container.

By way of conclusion it should be observed that the present invention which has been described above with particular reference to the accompanying drawings, is not restricted to these embodiments described and shown exclusively by way of example, and that modifications and alterations obvious to a person skilled in the art are possible without departing from the inventive concept as disclosed in the appended claims.