Method and arrangement for manufacturing a web-shaped packaging laminate

#The present invention relates to a method for manufacturing a web-shaped packaging laminate, in which a film of polymer material is extruded down into a nip between a cooling roll and a counter-roll, and the said film of polymer material is joined together in the nip, directly or indirectly, with at least one other layer of the packaging laminate. The invention also relates to an arrangement for implementing the method.

#Packaging laminates for packagings, for example packagings intended for liquid foods, are usually constructed from a number of layers, where each layer has its particular function. Thus, for example, a core layer, which is normally made from a fibre-based material, such as cardboard, or a polymer-based material, provides the packaging to be manufactured from the laminate with strength, gripping stability and dimensional stability. One or more polymer layer(s) provide(s) liquid tightness, and a barrier layer made of, for example, aluminium foil provides an oxygen barrier. The types of layer just mentioned are usually incorporated into the laminate in the form of prefabricated web-shaped materials, the polymer layer(s) normally being extruded as a film of molten polymer material down into a nip between a cooling roll and a counter-roll, for example a rubberized impression roll. At the same time, at least one of the other prefabricated layers, usually at least the core layer, is guided into the nip so as there to be joined together over essentially its whole surface with the film of polymer material.

#Other types of layer are instead incorporated into the laminate by virtue of at least one prefabricated layer in the laminate being coated with a water-based composition which comprises a dry substance content. After drying, that is to say removal of the water, the dry substance remains and then forms a layer. Such layers may be, for example, layers which provide the packaging laminate with an improved characteristic in respect of aroma barrier, gas barrier, gloss, grippability, scavenging effect, adhesion or capacity for being easily delaminated for recycling. The dry matter content may comprise, for example, polyvinyl alcohol, ethylene vinyl alcohol, ethylene acrylic acid, ethylene methacrylic acid, ascorbic acid, vitamin E, Fe or Fe2+ compounds, carboxymethylcellulose, polyvinyl acetate or starch and also possibly nanoparticles. One problem with forming such water-based layers in the laminate is being able to make them thin but still with the requisite properties. Another problem is that expensive, bulky and complicated coating equipment is necessary for their production, which is a sufficiently great problem as far as creating a completely new line for producing packaging laminate is concerned, and an even greater problem when it is desired to supplement an existing line with coating equipment for producing such a coated layer in the packaging laminate. The only solution today is to arrange the coating equipment off-line, that is to say outside the ordinary production line, which in turn gives rise to logistical problems etc. and increased production costs.

#The invention will be described below with reference to FIG. 1 which shows diagrammatically an arrangement according to the invention.

#Component 1 in FIG. 1 symbolizes a rotatable cooling roll which is normally cooled internally by means of a cooling medium (cooling liquid). The cooling roll 1 has a shell made of metal, usually steel, and preferably has an engraved surface, for example of the screen roller type, which means that its surface is capable of holding a greater quantity of water-based composition in a surface layer than a completely smooth surface does. It is also conceivable according to the invention, however, for the roll to have a completely smooth surface or a surface which varies only slightly from a completely smooth surface, for example by virtue of being matt-ground.

#A counter-roll 2, for example a rubberized impression roll, bears against the cooling roll 1 in a position around its horizontal centre line, in a nip, with an adjustable nip pressure. A web 4 of at least one layer in the laminate to be manufactured, usually a core layer which may already have been laminated together with a barrier layer, is fed into this nip. Also fed into the nip, between the web 4 and the cooling roll 1, is a film 5 of molten polymer material extruded from an extruder 3. In the nip, the web 4 is joined together with the molten polymer film 5 over essentially the whole of their mutually facing surfaces. During the continued contact with the surface of the cooling roll 1, when the laminate of the web 4 and the film 5 runs around the cooling roll 1, the film 5 is cooled and consequently solidifies/crystallizes.

#According to the invention, an arrangement 6 for covering the cooling roll 1 with a surface layer of a water-based composition 7 comprising a dry matter content is arranged on the opposite side to the nip, in a position around the horizontal centre line of the cooling roll 1. The arrangement 6 is shown here as comprising two rolls which transfer the composition 7 to the surface of the cooling roll. However, as mentioned above, many other configurations are conceivable. The covering of the water-based composition on the cooling roll 1 should of course be made as wide as the web 4 being fed into the nip and the film 5. In the nip, the surface layer present on the cooling roll will then be transferred to the polymer film 5 while this is still hot and formable. In this way, a layer of the water-based composition is formed on the polymer film, which layer will form part of the finished packaging laminate. The transfer according to the invention affords the possibility of making the layer of the water-based composition so thin that, after drying, it takes on the nature of a skin.