A packaging laminate and a method of producing the same

Technical field

The present invention relates to a packaging laminate comprising a layer of paper or paperboard and outer, liquid-tight coatings of polyolefin, of which the one polyolefin coating contains light-absorbing carbon particles, hi particular, the present invention relates to such a packaging laminate for a packaging container for a liquid food, such as milk or yoghurt.

The present invention also relates to a method of producing such a packaging laminate.

Background art

Dairy produce, in particular milk and yoghurt, are extremely sensitive to light and are destroyed or deteriorate rapidly if they are exposed to visible light. A packaging laminate comprising a layer of paper or paperboard certainly has per se inherent light barrier properties which are sufficient to exclude or prevent the penetration of such harmful light, however on condition that this layer is produced from an unbleached pulp. The problem with packaging laminates which have one or more such unbleached paper or paperboard layers or a combination of both bleached and unbleached layers, e.g. a duplex paper, is however that they do not always satisfy the requirements stipulated by the authorities on recycling. For example, in certain countries it is totally forbidden to use unbleached fibres alone or in combination with bleached fibres, since paper or paperboard on such markets must be totally free of unbleached fibres in order to satisfy such government requirements. On the other hand, a packaging laminate comprising one or more layers of bleached paper or paperboard has insufficient light barrier properties to prevent the penetration of harmful visible light, unless it is supplemented with at least one additional layer to compensate for the otherwise insufficient light tightness. To this end, it is known in the art to provide at least one of the outer polyethylene coatings of the packaging laminate, normally that which is intended to be turned to face inwards in the package, with light-absorbing particles of carbon in a sufficient quantity to raise and maintain the requisite barrier properties of the package against visible light.

A packaging laminate with supplementary tightness properties against visible light is described in, for example, WO 2006/073341. The packaging laminate has a paper- or paperboard layer which, on its one side, displays a first outer coating of polyolefin and, on its other side, displays a second outer coating of polyolefin which, for purposes of increasing light tightness, contains light-absorbing particles of carbon. The particle-containing polyolefin coating is laminated to the paper- or paperboard layer by means of an extruded lamination layer. In order to conceal the blackened particle-containing polyolefin coating when the packaging laminate, by fold forming and theπnosealing, is reformed into a packaging container, the packaging laminate is therefore folded in such a manner that the black coating is turned to face inwards in the package.

If the particle-containing polyolefin coating, for some reason, contains such light-absorbing particles in an excessively large quantity, it may be necessary to supplement the packaging laminate with at least one additional layer and/or to provide at least some of the material layers already included in the packaging laminate with visual properties in order to conceal the black polyolefin coating so that it can neither be seen nor even discerned from the outside of the package. According to WO 2006/073341, the extruded lamination layer between the paper- or paperboard layer and the black polyolefin coating is provided with such supplementary visual properties by an admixture of light-reflecting white particles of titanium dioxide. By the admixture of the light-reflecting white particles in the lamination layer, the package is given a both "purer" and whiter appearance, at the same time as the printability of the package for decorative artwork and the like is improved as a result of its increased contrast WO 2006/073344 describes a further example of a prior art packaging laminate in accordance with the above. This prior art packaging laminate has a relatively thin paper- or paperboard layer which, on its one side, displays a first outer coating of polyolefin and, on its other side, displays a second outer coating of polyolefin which, for purposes of increasing light barrier properties, includes light- absorbing particles of carbon. The particle-containing blackened polyolefin coating is laminated to the paper- or paperboard layer by means of an extruded lamination layer. According to WO 2006/073344, the black polyolefin coating is concealed in

that the first-mentioned polyolefin coating is supplemented with light-reflecting particles of titanium dioxide.

Yet a further packaging laminate of the above-described type is previously known from WO 2006/073343. This prior art packaging laminate includes a relatively thin paper- or paperboard layer which, on its one side, has a first outer coating of polyolefin and, on its other side, has a second outer coating of polyolefin which, for purposes of improving light barrier properties, contains light-absorbing particles of carbon. The particle-containing polyolefin coating is laminated to the paper- or paperboard layer by means of an extruded lamination layer. According to WO 2006/073343, both the first mentioned outer polyolefin coating and the extruded lamination layer are supplemented with light-reflecting particles of titanium dioxide in order to conceal the black polyolefin coating.

The above-described prior art packaging laminates are produced by a lamination process where a prefabricated, particle-containing polyolefin film is laminated to one side of a paper- or paperboard web by means of a lamination layer of polyolefin which is extruded between the film and the web and where, finally, the other side of the web is coated with a polyolefin coating by extrusion.

One drawback inherent in the production of these prior art packaging laminates is that a polyolefin mixture containing particles requires excessively meticulous process monitoring and complicated extrusion equipment in order to ensure a unitarily uniform distribution of particles throughout the entire lamination- and polyolefin layers, respectively. Such a unitary particle distribution requires int. al. a good mixture of polyolefin and particles, which, not without considerable difficulties, may be achieved without the employment of a complicated extruder screw. Further, the thorough mixing requires particular monitoring and adjustment of the viscosity of the polyolefin melt in order to make for a uniform flow of the melt through the extruder. An admixture of particles, and also other solid matter in the molten polymer, moreover increases the risk of excessive wear and damage to particularly sensitive parts of the process equipment, at the same time as it normally also requires at least one separate pre-treatment or compatibility operation of the particles in order to render them compatible with the relevant polyolefin.

There is thus a need in the art for a packaging laminate for foods, in particular liquid dairy produce, which ensures the requisite protection against product-harmful

UV radiation, but which at the same time may be produced by a simple lamination process without requirements on excessively meticulous process monitoring or complicated process equipment.

Objects of the invention

One object of the present invention is thus to satisfy the above-mentioned need in the art. A further object of the present invention is to realise a packaging laminate of the above described type from which may be produced cost-effective packaging containers with requisite product protection for foods, in particular liquid dairy produce.

Still a further object of the present invention is to realise a packaging laminate for a flexible cushion- or bag-like packaging container for liquid dairy produce such as milk or yoghurt, possessing superior tightness properties against product-harmful

UV radiation.

Yet a further object of the present invention if to realise a simple method of producing a packaging laminate for flexible, cost-effective packaging containers possessing the requisite product protection for foods, in particular liquid dairy produce.

These and other objects and advantages will be attained according to the present invention by means of a packaging laminate as claimed in independent Claim

1 and by means of a method as claimed in independent Claim 11, respectively. Expedient and preferred embodiments of the packaging laminate and the method according to the present invention have been given the characterising features as set forth in appended subclaims 2 to 10 and 12 to 15, respectively.

Brief summary of the invention According to one aspect of the present invention, there will thus be realised a packaging laminate comprising a layer of paper or paperboard and outer, liquid-tight coatings of polyolefin, of which the one polyolefin coating contains light-absorbing

particles of carbon. The packaging laminate is characterised in that the paper- or paperboard layer includes light-reflecting particles which are embedded in and spread throughout the entire paper or paperboard layer.

As a result of the light-reflecting white particles in the paper- or paperboard layer, the fibre layer thus "assumes" the role of concealing the black polyolefin coating, but with the advantageous consequence that both the lamination layer and the one outer polyolefin coating can be extruded from "pure" polyolefins, i.e. polyolefins without an admixture of particles. As a result of this role assumption, there is thus made possible a simple production of the packaging laminate according to the invention, without the requirement on the superior light tightness and "pure" and whitish appearance of the packaging laminate being jeopardized.

The quantity of light-reflecting white particles in the paper- or paperboard layer may vary within broad limits, but should in each individual case be sufficiently great to render the black carbon particles in the particle-containing polyolefin coating practically completely invisible through the paper- or paperboard layer. Preferably, the quantity should be sufficiently great also to impart to the packaging laminate a contrast-improving whitish background and thereby improved printability for printing ink which, for decorative and/or informative purposes is to be printed on the packaging laminate. In practice, it has proved to be advantageous if the quantity of light-reflecting particles is at least 7 weight %, counting on the total weight of the fibre layer, in order to impart to the packaging laminate both the requisite light tightness and the desired whitish appearance and printability with a good contrast effect. On the other hand, the quantity of light-reflecting particles should not be greater than approx. 20 weight %, counted on the total weight of the fibre layer, since the fibre layer will, in increasing quantities, become steadily more brittle and progressively lose mechanical strength properties. One preferred quantity of light-reflecting particles in the fibre layer is therefore between 7 and 20 weight %, counted on the total weight of the fibre layer. One preferred example of light-reflecting particles for use in the packaging laminate according to the present invention consists of particles of titanium dioxide.

Examples of polyolefins which may be employed in the outer coatings in the packaging laminate according to the present invention are polyethylene and polypropylene. Preferably, the polyolefin is selected from the group essentially comprising low density polyethylene (LDPE), linear low density polyethylene (LLDPE) and metallocene polyethylene (mPE).

Examples of polyolefins which may be employed in the lamination layer in the packaging laminate according to the present invention are polyethylene and polypropylene. Preferably, the polyolefin is selected from the group essentially comprising low density polyethylene (LDPE), linear low density polyethylene (LLDPE) and metallocene polyethylene (mPE).

According to another aspect of the present invention, there will be realised a method of producing a packaging laminate comprising a layer of paper or paperboard and outer, liquid-tight coatings of polyolefin of which the one contains light- absorbing particles of carbon. The method is characterised in that a prefabricated film of polyolefin containing light-absorbing carbon particles is laminated to one side of a web of paper or paperboard by means of a lamination layer of polyolefin which is extruded between the film and the web, and that the uncoated side of the web is coated with a coating of polyolefin by extrusion.

The method according to the present invention enjoys the advantage that it may be carried out without any requirements on excessively meticulous process monitoring or complicated extrusion equipment and that it may readily be carried out using only simple process equipment.

Further objects, advantages and details of the present invention will be apparent from the following description of the invention with reference to the accompanying Drawings.

Brief description of the accompanying Drawings

Fig. 1 schematically illustrates a cross section of a packaging laminate according to the present invention; and Fig. 2 schematically illustrates the production of the packaging laminate of

Fig. 1 in the method according to the present invention.

Detailed description of preferred embodiment and accompanying Drawings

Even though the invention will be described with particular reference to the accompanying Drawings, it is not restricted exclusively to these illustrated embodiments. It will be obvious to a person skilled in the art that individual details in the illustrated and described embodiments may be modified with the guidance of the description, without departing from the inventive concept as herein disclosed. The inventive concept is therefore defined only by the appended Claims.

Fig. 1 thus schematically illustrates a cross section of a packaging laminate according to the present invention carrying the generic reference numeral 10. The packaging laminate 10 has a thin layer 11 of paper or paperboard and outer, liquid- tight coatings 12 and 13 of polyolefin of which the one coating 12 contains light- absorbing carbon particles in a quantity sufficient to impart to the packaging laminate 10 the requisite tightness properties against light, in particular UV radiation. The particle-containing coating 12 is laminated to the paper- or paperboard layer 11 by means of a lamination layer 14 of polyolefin.

The paper- or paperboard layer 11 preferably has a grammage or carrier weight of approx. 50-70 g/m ² and can be kraft paper.

The particle-containing coating 12 may include a polyolefin of polyethylene or polypropylene, and is preferably a polyethylene which has been selected from the group essentially comprising low density polyethylene (LDPE), linear low density polyethylene (LLDPE) ₅ very low density polyethylene (VLDPE), ultra low density polyethylene (ULDPE) and metallocene polyethylene (mPE). Preferably, the particle-containing coating 12 has a coating weight (surface weight) of approx. 15-30 g/m ² . The quantity of light-absorbing carbon particles in the coating 12 should lie within the range of approx. 0.2-3 g/m ² .

The extruded lamination layer 14 may include a polyolefin of polyethylene or polypropylene and is preferably a polyethylene which has been selected from the group essentially comprising low density polyethylene (LDPE), linear low density polyethylene (LLDPE), very low density polyethylene (VLDPE), ultra low density polyethylene (ULDPE) and metallocene polyethylene (mPE). The lamination layer 14 preferably has a coating weight (surface weight) of 10-30 g/m ² .

The particle-free coating 13 may, like the coating 12, include a polyolefin of polyethylene or polypropylene and is preferably a polyethylene which has been selected from among the group essentially comprising low density polyethylene (LDPE), linear low density polyethylene (LLDPE), very low density polyethylene (VLDPE), ultra low density polyethylene (ULDPE) and metallocene polyethylene (mPE). The coating 13 preferably has a coating weight (surface weight) of approx. 10-20 g/m ² .

In order to conceal the coating 12 blackened by the carbon particles and render it invisible through the paper- or paperboard layer 11, the paper- or paperboard layer 11 contains light-absorbing white particles, preferably titanium dioxide particles, which are embedded in and spread throughout the entire fibre layer 11.

The quantity of light-reflecting white particles in the paper- or paperboard layer 11 may vary within broad limits but should, in each individual case, be sufficiently great to make the black carbon particles in the particle-containing polyolefin coating practically completely invisible through the paper- or paperboard layer 11. Preferably, the quantity should also be sufficiently great to impart to the packaging laminate 10 a contrast-improving whitish background against printing ink which, for decorative and/or informative purposes, is to be printed on the packaging laminate 10.

In practice, it has proved advantageous that the quantity of light-reflecting white particles be at least 7 weight %, counted on the total weight of the fibre layer, in order to impart to the packaging laminate 10 both the requisite light tightness and the desired whitish appearance and printability with a good contrast effect. On the other hand, the quantity of light-reflecting white particles should not be greater than approx. 20 weight %, counted on the total weight of the fibre layer 11, since the fibre layer 11 will, with increasing quantities, become increasingly brittle and progressively lose mechanical strength properties. A preferred quantity of light- reflecting white particles in the fibre layer 11 is therefore between 7 and 20 weight %, counted on the total weight of the fibre layer 11.

The packaging laminate 10 in Fig. 1 is produced in the manner which is schematically illustrated in Fig. 2. From the left in the figure, a web 20 of paper

containing light-reflecting particles is unwound from a magazine reel (not shown), at the same time as a web or film 21 of polyolefϊn containing light-absorbing carbon particles is unwound from a magazine reel (not shown) to the right in the figure. Both of the webs 20 and 21 converge with one another and are led together through the nip between two rotary cooling rollers 22, 23 at the same time as a lamination film 24 of polyolefin is extruded between the webs 20 and 21 by means of an extruder 25 in order to laminate them to one another. After passage through the nip between the two cooling rollers 22, 23, the laminated webs 20 and 21 are led via a bending roller 26 to a coating station at A where the uncoated side of the paper web 20 is coated with a film 27 of polyolefin which is extruded on the web by means of an extruder 28 for the formation of the packaging laminate for further transport and handling.

In practice, the light-reflecting particles in the paper web 20 may be titanium dioxide, of which the quantity of these titanium dioxide particles must be at least 7 weight %, counted on the total weight of the paper web 20. The quantity of titanium dioxide particles should not, however, be greater than approx. 20 weight %, counted on the total weight of the paper web 20, since the web 20 progressively loses mechanical strength properties on increasing quantities of particles. The practical quantity range for the light-reflecting particles is thus from approx. 7 to 20 weight % within which range the paper web 20 effectively conceals the black colour of the carbon particles in the subjacent polyolefin film 21, at the same time as the light- reflecting particles impart to the packaging laminate a pure whitish appearance and good printability.

Both the particle-containing polyolefin film 21 and the lamination film 24 as well as the particle-free polyolefin film 27 may include polyethylene or polypropylene but preferably include a polyethylene which has been selected from the group essentially comprising low density polyethylene (LDPE), linear low density polyethylene (LLDPE) and metallocene polyethylene (mPE). Most preferred as the polyolefin is a low density polyethylene (LDPE). Preferred coating quantities (surface weights) of the material layers included in the packaging laminate are apparent from the table below:

As was mentioned previously, from the packaging laminate according to the present invention there are produced flexible, thin-walled packaging containers for the transport and storage of liquid dairy produce, e.g. milk and yoghurt, by fold forming and thermosealing of the packaging laminate in a per se known manner.

From, for example, a web of the packaging laminate, such cushion- or bag- like packages are produced in that the web is first reformed into a tube by thermosealing along the longitudinal edges of the tube. The tube is filled with the pertinent product and is divided into filled cushion-shaped packages by repeated thermoseals transversely of the longitudinal axis of the tube. The cushion-shaped packages are thereafter separated from one another by incisions or cuts through the transversely sealed tube zones.

One well-known example of such a cushion-shaped flexible package is the previously mentioned Tetra Fino® package in which liquid dairy produce such as milk and yoghurt may be reliably transported and stored without the risk of penetration of harmful UV radiation.

Even though the present invention has been described in detail with reference to the accompanying Drawings, it is not restricted exclusively to these illustrated and described embodiments. For a person skilled in the art, with the guidance of the foregoing description, it will be obvious that numerous modifications and alterations are possible without departing from the inventive concept. All such modifications and alterations are thus encompassed by the inventive concept as this is defined by the appended Claims.

Industrial application

The packaging laminate according to the present invention is particularly applicable for flexible, thin-walled packaging containers for liquid dairy produce, such as for example milk and yoghurt, but may naturally be employed to pack and transport also other types of liquid foods, e.g. juice, wine, cooking oil etc.