A paperboard structure, a package and use of the package

Abstract

According to an example aspect of the present invention, there is provided a paperboard structure, comprising: a support layer comprising paperboard; a filler layer on top of and in direct contact with the support layer, the filler layer comprising an inorganic filler and a polyolefin; and a plastic coating layer on top of the filler layer and forming the outermost layer of the paperboard structure, the plastic coating layer comprising a polyolefin.

Claims

1. A paperboard structure, comprising: a support layer comprising paperboard; a filler layer on top of and in direct contact with the support layer, the filler layer comprising an inorganic filler and a polyolefin; and a plastic coating layer on top of the filler layer and forming the outermost layer of the paperboard structure, the plastic coating layer comprising a polyolefin.

2. The paperboard structure according to claim 1, wherein the inorganic filler is in the form of particles.

3. The paperboard structure according to claim 1, wherein the inorganic filler is in the form of particles having an average particle size of 0.01 to 3 μm.

4. The paperboard structure according to claim 1, wherein the inorganic filler is an acid-sensitive inorganic filler.

5. The paperboard structure according to claim 1, wherein the polyolefin comprises polyethylene.

6. The paperboard structure according to claim 1, wherein the plastic coating layer consists of polyethylene.

7. The paperboard structure according to claim 1, wherein the thickness of the filler layer is 5 to 100 μm.

8. The paperboard structure according to claim 1, wherein the thickness of the plastic coating layer is 5 to 50 μm.

9. The paperboard structure according to claim 1, wherein the combined dosage produced by the filler layer and the plastic coating layer is 12 to 40 g per m.sup.2 of the support layer.

10. The paperboard structure according to claim 1, wherein the amount of inorganic filler in the filler layer is in the range of 5 to 70 wt-%.

11. The paperboard structure according to claim 1, wherein the amount of inorganic filler in the filler layer is at least 20 wt-%.

12. The paperboard structure according to claim 1, obtained by an extrusion coating method.

13. A package comprising the paperboard structure according to claim 1.

14. The package according to claim 13, further comprising side seams in which an acidic dispersion adhesive has been used.

15. The package according to claim 14, wherein the dispersion adhesive has a pH below or equal to 4.5.

16. The package according to claim 13, wherein the package stores acidic contents therein, and wherein the acidic contents comprise acidic liquids, acidic flowable materials, or acidic solid foods.

17. The package according to claim 16, wherein the acidic contents have a pH below or equal to 4.5.

18. The paperboard structure according to claim 1, wherein the paperboard is a multi-ply paperboard having a grammage of at least 150 g/m.sup.2.

19. The paperboard structure according to claim 1, wherein the inorganic filler is in the form of particles having an average particle size of 0.5 to 2 μm.

20. The paperboard structure according to claim 4, wherein the inorganic filler comprises carbonate-containing filler material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] FIG. 1 illustrates schematically a paperboard structure in accordance with at least some embodiments of the present invention.

EMBODIMENTS

Definitions

[0038] In the present context, the term “acid-sensitive” refers to materials or compounds that are susceptible of reacting with or being attacked by acidic compounds.

[0039] In the present context, the term “polyolefin” refers to an unmodified polyolefin. For example, the term “polyethylene” refers to an unmodified polyethylene.

[0040] We have unexpectedly observed that particular inorganic fillers with relatively high loadings can be incorporated in layered paperboard structures without sacrificing good sealing properties.

[0041] Particularly, we have found a new paperboard structure comprising acid-sensitive inorganic fillers and/or acid-sensitive pigments. The structure according to the invention provides good sealing properties and simultaneously reduces or avoids migration of filler particles onto the outermost surface of the structure (i.e. the top surface).

[0042] In the present paperboard structure, acid-sensitive pigments may be incorporated in the filler layer which is located below the plastic coating layer.

[0043] Other acid-sensitive materials or additives that may be added in the filler layer include any carbonate salt.

[0044] Some embodiments of the present invention provide the advantage that the acid-sensitive material does not migrate on the outermost surface of the paperboard structure and thus into contact with the ambient environment or with the contents of the package.

[0045] In preferred embodiments, an acid-sensitive filler and a polyolefin are used in the filler layer, and by means of applying a plastic coating layer comprising or consisting of a polyolefin on top of the filler layer it is possible to effectively prevent any contact between the filler and acidic contents of the package.

[0046] We have observed that the incorporation of acid-sensitive materials in accordance with some embodiments of the present invention does not negatively affect the heat-sealing properties, particularly during cup forming.

[0047] At least some embodiments of the present invention improve the strength of side seams in paperboard packages. In such seams, aqueous dispersion adhesives are typically used. These adhesives may be acidic, which makes the seam sensitive to alkaline fillers in the paperboard material.

[0048] FIG. 1 illustrates a paperboard structure in accordance with at least some embodiments of the present invention.

[0049] The structure comprises a support layer 1, a filler layer 2, and a plastic coating layer 3, as a cascade.

[0050] The lowermost layer, i.e. the support layer, is made of a paperboard material. The fibre matrix of the paperboard material may comprise bleached or unbleached hardwood pulp, bleached or unbleached softwood pulp, bleached or unbleached mechanical pulp, bleached or unbleached chemi-mechanical pulp or recirculated broke pulp used in paperboard production, or mixtures thereof. In particular, mutual mixtures of the above described bleached and unbleached pulps, respectively, and mechanical or chemi-mechanical pulps, are possible. Recirculated broke pulp may also be used in any of the abovementioned pulps, mechanical pulps and chemi-mechanical pulps.

[0051] In some embodiments, paperboard is a single-ply or multi-ply paperboard material. In one embodiment, paperboard has a grammage of at least 150 g/m.sup.2.

[0052] In preferred embodiments, the paperboard structure is folding boxboard.

[0053] The middle layer, i.e. the filler layer, comprises an inorganic filler, preferably an alkaline inorganic filler or an acid-sensitive inorganic filler.

[0054] Examples of alkaline or acid-sensitive fillers include: calcium carbonate, ground calcium carbonate (GCC), precipitated calcium carbonate (PCC), and other carbonate fillers.

[0055] In some embodiments, the inorganic filler is calcium carbonate, ground calcium carbonate, precipitated calcium carbonate or kaolin.

[0056] The filler layer may also comprise pigments, such as acid-sensitive pigments. Examples of acid-sensitive pigments include carbonate pigments.

[0057] The filler layer is in direct contact with and placed directly on top of the support layer. The filler layer is preferably homogeneous in the sense that the filler is distributed throughout the filler layer, across its entire thickness.

[0058] In a preferred embodiment, the filler layer comprises or consists of a mixture of an alkaline inorganic filler and a polyolefin.

[0059] In one embodiment, the filler layer comprises or consists of a mixture of a carbonate-containing filler and a polyolefin in the form of microparticles or nanoparticles.

[0060] The filler may be in the form of particles, for example particles with an average size in the range of 0.01 to 3 μm, for example 0.5 to 2 μm. Advantageously, the average size of the filler particles is in the range 1 to 2 μm. If the average particle size is larger than 5 μm, the structure of the above-lying plastic coating layer may weaken.

[0061] In one embodiment, the thickness of the filler layer is 5 to 100 μm, preferably 5 to 50 μm.

[0062] In one embodiment, the amount of inorganic filler in the filler layer is in the range of 5 to 70 wt-%, preferably 10 to 60 wt-%.

[0063] In one embodiment, the amount of inorganic filler in the filler layer is at least 20 wt-%.

[0064] The plastic coating layer forms the topmost layer of the structure. Advantageously, the plastic coating layer is not in direct contact with the support layer.

[0065] In one embodiment, the plastic coating layer comprises or consists of polyolefin, such as polyethylene.

[0066] In a preferred embodiment, the plastic coating layer does not contain any inorganic filler.

[0067] In one embodiment, the thickness of the plastic coating layer is 5 to 8 μm.

[0068] In one embodiment, the combined dosage produced by the filler layer and the plastic coating layer is 12 to 40 g per m.sup.2 of the support layer, preferably 12 to 30 g per m.sup.2 of the support layer.

[0069] In a preferred embodiment, the paperboard structure consists of the following three layers: the support layer, the filler layer, and the plastic coating layer in this order.

[0070] The filler layer and the plastic coating layer are preferably applied by an extrusion coating method, for example co-extrusion coating, on the support layer.

[0071] The paperboard structure can be used for manufacturing packages for food industry. The package according to the invention may be for example a paper cup for acidic beverages or a package for yoghurt.

[0072] The package is particularly advantageous in holding acidic contents, such as acidic liquids, acidic flowable materials or acidic food. Examples of acidic contents include: acidic beverages, soda, citrus fruit juice, wine, yoghurt, crushed tomatoes. In one embodiment, the pH of the acidic contents is below 4.5.

[0073] The paperboard structure according to the invention is advantageous in paperboard packages comprising acidic materials, such as acidic adhesives. In one embodiment, the pH of an adhesive in a seam of the paperboard package is below 4.5.

[0074] The entire package or only a part of it may be formed of a paperboard material that comprises the paperboard structure according to the present invention. Preferably, all parts of the package that are in contact with the contents of the package are made of a paperboard material that has the paperboard structure according to the present invention.

[0075] It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.

[0076] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment.

[0077] As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. In addition, various embodiments and example of the present invention may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations of the present invention.

[0078] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.

[0079] While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.

[0080] The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of “a” or “an”, i.e. a singular form, throughout this document does not exclude a plurality.

INDUSTRIAL APPLICABILITY

[0081] The present invention is industrially applicable for example in the manufacturing of paperboard packages for food industry.

ACRONYMS LIST

[0082] FCM Food Contact Material

REFERENCE SIGNS LIST

[0083] 1 support layer [0084] 2 filler layer [0085] 3 plastic coating layer

CITATION LIST

Patent Literature

[0086] WO 2017/091391 A1