A LAMINATED PACKAGING MATERIAL AND A METHOD OF PRODUCING THE MATERIAL

Abstract: A packaging laminate comprising a paper or board layer (11) and an outer plastic layer (12) disposed on the one side of the paper or board layer (11) and with an interjacent thin metal coating (13). The metal coating (13) is produced by vacuum deposition on the plastic layer (12) and imparts to the packaging laminate (10) good grease resistance which effectively prevents grease- or oil-containing products from penetrating into the paper or board layer (11) from the metal-coated plastic side (12). Preferably, the other side of the paper or board layer (11) is also protected by a plastic layer (14) which prevents liquid and other moisture from penetrating into the paper or board layer (11) from the non-metal-coated plastic side of the packaging laminate (10). The packaging laminate (10) is primarily intended for packaging containers for such oil- or grease-containing products, for example, cooking oil.

Description: A LAMINATED PACKAGING MATERIAL AND A METHOD OF PRODUCING THE MATERIAL TECHNICAL FIELD The present invention relates to a laminated packaging material of the type which has a core layer of paper or board and a layer of plastic disposed on the one side of the core layer. The present invention also relates to a method of producing the laminated packaging material, as well as a packaging container produced from the packaging material. Moreover, the present invention relates to use of the laminated packaging material for a packaging container for products of oil or grease. BACKGROUND ART In packaging technology, use is often made of packages of the single- use disposable nature for packing and transporting foods, and a very large group of these so-called single use disposable packages is produced from a laminated packaging material (packaging laminate) comprising a core layer of paper or board and a plastic layer disposed on one side of the core layer. Most generally, the other side of the core layer is also covered by a plastic layer. The composition of the packaging laminate is based on the concept of providing the best possible protection for the product which is to be packed, at the same time as the packaging material should be easy to produce and easy to reform, or convert, into packages using rapid, modern packaging and filling machines which produce finished packages on a rational, industrial scale. A packaging laminate consisting solely of paper or board and plastic, as described above, makes possible the production of mechanically strong and configurationally stable packaging containers possessing good tightness properties vis-a-vis liquids, but generally lacks tightness properties against gases and is therefore unsuitable for packaging containers for gas-sensitive products, in particular products which are sensitive to oxygen gas. Moreover, such packaging laminate lacks resistance to grease, with the result that products of oils, fats or greases can penetrate into the paper or board layer of the packaging laminate which thereby suffers from a deterioration in quality or becomes weakened and acquires an unappetisingly dirty appearance because of oil or grease spots which are readily visible through the outer plastic layer of the packaging laminate. In order to supplement the packaging laminate with tightness properties against gases, in particular oxygen gas, and with grease resistance properties, it is known in the art to provide the packaging laminate with one or more additional layers of a material possessing the desired properties. A known packaging laminate with grease resistance uses a core layer comprising a grease resistant paper or grease resistant board with outer plastic layers disposed on both sides of the core layer. A packaging laminate of this type is described, for example, in European Patent Application published under number EP 0 313 356. The prior art packaging laminate offers great resistance to fatty and greasy products which cannot, or can only very slowly, penetrate into and through the grease resistant core layer of the packaging laminate. The disadvantage inherent in the prior art packaging laminate is, however, that it requires a paper or board of a special quality which is expensive and therefore contributes in making the costs of the packaging laminate unnecessarily high. OBJECTS OF THE INVENTION One object of the present invention is, therefore, to realise a new laminated material or packaging laminate without the consequential difficulties and drawbacks of the type inherent in the above-described prior art packaging laminates. A further object of the present invention is to realise a packaging laminate possessing superior grease resistance, without the employment of expensive or energy-consuming material layers. Still a further object of the present invention is to realise a packaging laminate possessing superior grease resistance and good gas tightness properties. Yet a further object of the present invention is to realise a simple and easily produced packaging laminate possessing superior grease resistance and superior gas tightness properties. SOLUTION These and other objects and advantages will be attained according to the present invention by means of a laminated material or packaging laminate of the type described by way of introduction which has been given the characterizing feature that the plastic layer displays a metal coating on that side of the plastic layer facing towards the core layer. As a result of the packaging laminate's metal coating, which may be made very thin, the packaging laminate according to the present invention acquires excellent grease resistance which effectively prevents products of oils, fats or greases from penetrating into and through the packaging laminate from that side of the core layer on which the metal-coated plastic layer is disposed. As a result of the metal coating, the packaging laminate according to the present invention will moreover be given improved gas tightness properties, in particular oxygen gas tightness, thus rendering the packaging laminate eminently suitable for packages for oxygen gas sensitive grease- and oil-containing products, for example cooking oil. Since the metal coating effectively prevents the penetration of grease- and oil-containing products, it also functions as an efficient protection for the paper or board layer which lies well concealed in the packaging laminate behind the protective metal coating, and, as a result, cannot be reached by such products from the metal-coated plastic side of the packaging laminate. This in turn entails that the packaging laminate according to the invention places no particular demands on the paper quality in the core layer, but any optional commercially available and economical paper or board quality, respectively, may in practice be employed in a packaging laminate according to the present invention. Further practical and advantageous characterizing features of the packaging laminate according to the present invention are set forth in appended Claims 2 to 7. FURTHER OBJECTS OF THE INVENTION AND THEIR SOLUTIONS A further object of the present invention is to realise a simple and uncomplicated method of producing the laminated packaging material according to the invention. This object is attained according to the present invention by means of the method as defined in appended Claim S. Yet further objects of the present invention are to realise a packaging container filled with grease- or oil-containing products, and to propose the use of laminated packaging material according to the present invention for such a packaging container in accordance with appended Claims 10 and 11, respectively. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING The present invention will now be described in greater detail hereinbelow, with particular reference to the accompanying Drawing, in which: Fig. 1 schematically illustrates a cross section through a laminated packaging material according to the present invention; and Fig. 2 schematically illustrates a method of approach for producing the laminated packaging material employing the method according to the present invention. Before the description of the present invention continues, it should first be noted that the embodiment which is shown on the Drawing is not intended in any way to restrict the scope of the invention, but is shown merely for the purposes of illustrating the present invention in a simple and readily comprehensible manner. It will be obvious to a person skilled in the art that numerous different modifications and variations are possible without departing from the inventive concept as herein disclosed. Thus, such modifications and variations lie within the scope of and are encompassed by the appended Claims. DESCRIPTION OF ILLUSTRATIVE EMBODIMENT Referring to the Drawing, Fig. 1 thus schematically illustrates a cross section of a laminated packaging material (packaging laminate) according to the present invention, carrying the general reference numeral 10. The packaging laminate 10 comprises a core layer 11 and an outer plastic layer 12 which is disposed on the one side of the core layer and which, in the illustrated embodiment, lies above the core layer 11. Between the core layer 11 and the outer plastic layer 12, there is disposed a coating of metal 13 which, by a conventional vacuum deposition technique, is deposited on and bonded to the outer plastic layer 12. Preferably, the packaging laminate 10 includes a further outer plastic layer 14 which is provided on the other side of the core layer 11, i.e. on that side which, in the illustrated embodiment, is turned to face downwards. The outer plastic layer 12 with ine vacuum-deposited metal coating 13 is laminated or bonded to the subjacent core layer 11 by means of a layer of adhesive or sealing plastic 15 disposed between the core layer 11 and the metal coating 13 and capable of binding with good adhesion (high adhesive strength) to both the metal coating 13 and the core layer 11, for the formation of a mechanically strong and durable sealing joint or seam between the two surrounding laminate layers 13 and 14. The core layer 11 consists of a fibre material, for example paper or board, of any optional commercially available quality, without any demands that the fibre material possess any specific chemical and/ or optic properties. However, one requirement which the core layer 11 must satisfy is that it must impart to the packaging laminate 11 the requisite mechanical rigidity and strength sc as to make possible the production of dimensionally stable packaging containers from the packaging laminate 10. According to the present invention, the core layer 11 may thus consist of conventional paper or board qualities which are normally employed in packaging technology for producing consumer packages of the single-use nature (single-use disposable packages) for liquid foods. Such conventional paper and board qualities are well known to persons skilled in the art and, therefore, need no detailed description here. The outer plastic layer 12 on the upper side of the packaging laminate 10 in Fig. 1 may, in principle, consist of any known plastic material whatever which imparts to the packaging laminate 10 tightness properties against liquids, but preferably consists of a thermoplastic material which, in addition to good liquid-tightness properties, also possesses the advantageous property that it may be sealed by so-called heat sealing under which facing plastic layers are, by the supply of heat and pressure, brought to surface fusion with one another for the formation of liquid-tight, mechanically strong and durable sealing joints or seams between the plastic layers. Examples of appropriate heat-sealable plastics which may be employed for the outer plastic layer 12 in the packaging laminate 10 according to the present invention are: LDPE (Low Density Polyethylene), HDPE (High Density Polyethylene), PP (Polypropylene) and PET (PolyEthylene Terephthalate). The metal coating 13 on the outer plastic layer 12 between the core layer 11 and the outer plastic layer 12 in the packaging laminate 10 according to the present invention is, as has already been mentioned, a metal film produced by conventional vacuum deposition, and bonded by good adhesion (high adhesive strength) to the outer plastic layer 12 serving as substrate for the metal film. The present invention is not restricted to any one particular of several known and commercially available vacuum deposition techniques for producing the metal coating 13, although the so-called CVPD (Chemical Vapour Plasma Deposition) technique has given positive and purposeful results in practical experiments which have been carried out in accordance with the present invention. In order not to unduly burden the description with details and facts relating to such previously known deposition techniques, reference is made to the literature available in this area which accurately describes and explains the principles for these techniques. Using such known vacuum deposition techniques, it is possible to produce extremely thin, but still very dense and tight metal coatings and, according to the present invention, the thickness of the metal coating 13 may vary within a relatively wide span between in themselves very low limit values. A practically well-functioning thickness range for the metal coating 13 is from 100 Angstrom (A) to 800 Angstrom (A), preferably 300 - 500 Angstrom (A), for example 400 Angstrom (A). The material in the metal coating 13 may be of any suitable metal or other inorganic chemical compound which, in a very thin layer, can be deposited on the outer plastic layer 12 by vacuum deposition. The expression "metal" as employed in this description and in the appended Claims thus encompasses both "pure" metals and other such inorganic chemical compounds. An example of a preferred metal is aluminium which, at such a slight thicknesses as 100 - 800 Angstrom (A), gives dense, tight continuous coatings possessing good tightness properties against gases, in particular oxygen gas, and the desired protection against penetration of oil and grease. A metal coating 13 of aluminium moreover imparts to the packaging laminate 10 according to the present invention a beautifully silver sheen appearance through the transparent outer plastic layer 12 from the upper side of the packaging laminate 10 in Fig. 1. An example of one such other inorganic chemical compound as may be employed in the coating 13 is a silicon compound possessing the general chemical formula SiOχ, where x may vary between 1.5 and 2.2. In order further to improve the appearance of the packaging laminate, the packaging laminate 10 according to the present invention may be dέcor printed in patterns on the outer plastic layer 12, the dέcor print being freely optional in its patterns and colours in order to provide, in a decorative and attractive way, information about the product which is packed in a packaging container produced from the packaging laminate 10. As has been pointed out above, it is desirable and occasionally necessary to protect the core layer 11 from liquid which may readily penetrate into the absorbent paper or board material and render the packaging laminate slack and unusable. From the upper side of the packaging larr late 10 in Fig. 1, the core layer 11 is totally concealed and protected against both liquids and grease and oil, as a result of the outer plastic layer 12 and the metal coating 13, respectively. In order to protect the core layer 11 also from the under side of the packaging laminate 10 in Fig. 1 against the penetration of, at least liquid and other moisture, the packaging laminate 10 according to the present invention is preferably provided with an additional plastic layer 14 on the other side of the core layer 11. The material in this additional plastic layer 14 may be any optional plastic possessing tightness properties against liquid, but is preferably a thermoplastic which may readily be sealed to the other outer plastic layer 12 by heat sealing in order to make possible the production of liquid-tight, mechanically strong and durable sealing joints or seams during reforming of the packaging laminate into dimensionally stable packaging containers. Examples of suitable thermoplastics for the plastic layer 14 are those which were already mentioned in connection with the plastic layer 12. The packaging laminate 10 is produced according to the present invention in the manner which is schematically illustrated in Fig. 2. In order to facilitate a comparison with Fig. 1, the same reference numerals as in Fig. 1 have also been employed in Fig. 2 for identical or corresponding parts. A web of plastic 12 (corresponding to the outer plastic layer 12 in Fig. 1) is unreeled from a magazine reel 12' (in the left-hand part of Fig. 2), and is led into a treatment or coating station carrying the general reference designation A in which the plastic web 12 is coated on its one side with a thin coating of metal, e.g. aluminium (corresponding to the metal coating 13), by conventional vacuum deposition technology. From the station A, the thus unilaterally metal-coated plastic web 12 is led further to a lamination station carrying the general reference designation B where the plastic web is united with and bonded to a paper or board web (corresponding to the paper or board layer 11), with the aid of an adhesive or a sealing plastic 15 which is applied between the two webs 12 and 13 by means of an extruder 16 disposed above the webs and extruding a thin film of the adhesive or sealing plastic, respectively, to the metal-coated side of the plastic web 12. The converging webs 11 and 12 with interjacent adhesive or sealing plastic 15 are led into and through the nip between two non-slip cooling rollers 17, 17 rotating beneath the extruder 16 and, with light pressure towards one another, compressing the two webs during cooling, for the formation of the finished, well-integrated packaging laminate 10 according to the present invention. Even though the foregoing production process has been described as a continuous, unbroken process, it need not be carried out in-line as illustrated. Instead of leading the metal-coated plastic web 12 from the treatment/ coating station A direct to the lamination station B, it can if desired, be rolled up for temporary storage or transport before being laminated to a paper or board web. Such may be the case when, for example, the coating station A and the lamination station B are located geographically apart from one another. From the finished, laminated packaging material 10 according to the present invention, dimensionally stable consumer packages of the single-use type are produced, for example Tetra Brik® for oil- and grease-containing products, for example cooking oil which, with good shelf life, may be stored in the packages without the packaging material of the packages running the risk of being destroyed or damaged by the packed products and without the appearance of the packages being impaired or harmed as a result of oil or grease spots deriving from products which have penetrated through the core layer of the packaging material. While it has not been stated in the foregoing, it is obvious for reasons that will readily be appreciated, that the packaging material in a packaging container according to the present invention (in particular when it is to be employed for packing oil- and grease-containing products) should be disposed such that the metal-coated outer plastic layer is to be turned to face outwards and form the outside of the packaging container, whereby the paper or board layers of the packaging material lie well concealed from view behind the protective, preferably silver shining metal coating. As will have been apparent from the foregoing disclosures, the present invention, as defined in the appended Claims, realises an efficient and economical packaging laminate for packages for oil- and grease- containing products, the packaging laminate being moreover easy to produce employing already extant, conventional apparatuses and techniques. In particular, the present invention realises a packaging laminate from which consumer packages of the single-use type for such products may be manufactured with the aid of modern, rapid packaging machines which produce packages on a rational, industrial scale. The perhaps most important contribution to the state of the art is that the present invention makes possible the production of paper or board-based packaging containers which afford good protection to the packed oil- or grease-containing products without requiring special, expensive paper or board qualities, respectively.

Claims: WHAT IS CLAIMED IS: 1. A laminated packaging material comprising a core layer (11) of paper or board and a layer (12) of plastic disposed on the one side of the core layer, characterized in that the plastic layer (12) displays a metal coating (13) on that side of the plastic layer (12) facing towards the core layer. 2. The laminated packaging material as claimed in Claim 1, characterized in that the metal coating (13) is applied to the plastic layer (12) by conventional vacuum deposition techniques. 3. The laminated packaging material as claimed in Claim 1 or 2, characterized in that the vacuum-deposited metal coating (13) has a thickness of 100 - 800 Angstrom (A). 4. The laminated packaging material as claimed in any of Claims 1 to 3, characterized in that the vacuum-deposited metal coating (13) consists of aluminium. 5. The laminated packaging material as claimed in any of the preceding Claims, characterized in that the plastic layer (12) consists of a material which has been selected from among the group consisting of LDPE (Low Density Polyethylene), HDPE (High Density Polyethylene), PP (Polypropylene) and PET (PolyEthylene Terephthalate). 6. The laminated packaging material as claimed in any of the preceding Claims, characterized in that the plastic layer (12) is provided with printed dέcor. 7. The laminated packaging material as claimed n any of the preceding Claims, characterized in that the other side of the core layer (11) also displays a plastic layer (14). 8. A method of producing a laminated packaging material as claimed in Claim 1, characterized in that the one side of a plastic web (12) is coated with metal by a conventional vacuum deposition technique; and that the thus metal-coated plastic web is laminated to a paper or board web (11) with the metal-coated side of the plastic web (12) facing towards the paper or board web (11). 9. The method as claimed in Claim 8, characterized in that the metal- coated plastic web is laminated to the paper or board web by means of an adhesive or a sealing plastic (15) which is applied between the two webs. 10. Packaging containers of a laminated packaging material according to Claim 1 and filled with products from oil or grease, in which the paper or board layer (11) of the laminated packaging material (10) forms the inside of the packaging container. 11. Use of a laminated packaging material according to any of Claims 1 to 7 for a packaging container for products from oil or grease.

Inventors: KJELGAARD TOM, KJELGAARD, TOM
Applicants: KJELGAARD TOM, TETRA LAVAL HOLDINGS & FINANCE, KJELGAARD, TOM, TETRA LAVAL HOLDINGS & FINANCE S.A.
Application year: 1995
Main classification: B32B27
IPC codes: B32B15, B32B27, B65D65, B65D85