GB2123747A

GB2123747A - Packaging material

Info

Publication number: GB2123747A
Application number: GB08230894A
Authority: GB
Inventors: Piero Francesconi
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-07-09
Filing date: 1982-10-27
Publication date: 1984-02-08
Also published as: SE8303914D0; CH655074A5; DK318983D0; DE3323629A1; IT1192473B; BE897222A; IT8209466A0; DK318983A; SE8303914L; GB2123747B

Abstract

A composite film is made up of least a first layer 3 providing desirable mechanical characteristics and acting as a support which is produced from a mixture of low-density linear polyethylene and ethylenevinyl acetate with a vinyl acetate content of about 12% by weight and a second layer 5, serving to provide vapour and gas permeability suited to the particular use together with tackiness for self-sealing, the second layer comprising ethylenevinyl acetate with a vinyl acetate content of about 30% by weight together with an addition of ionomer resin and of anti-fog material as customarily employed in thermoplastic films for wrapping foodstuffs. Such film as cold-stretch properties and may have thermo- shrink properties. <IMAGE>

Description

SPECIFICATION Packaging material This invention relates to a self-sealing, transparent, cold-stretch film for use in the packaging (or wrapping) of foodstuffs such as fresh meat, fruit, vegetables, cheese, and including the whole range of deep-frozen foods. Such film can be used either manually or on semi-automatic and automatic machines, and it suitable for supermarkets, other stores, and pre-packaging centres. The film has been devised to avoid the problems arising from possible transfer of harmful or unpleasant substances to the packaged foodstuffs from the wrapping material.

According to the present invention there is provided a self-sealing, transparent, cold-stretch film comprising at least two superimposed different layers of adhered thermoplastic material, a first layer comprising a mixture of low-density linear polyethylene (LLDP) and of ethylenevinyl acetate (EVA) with a vinyl acetate content of about 12%, and the second layer comprising ethylenevinyl acetate (EVA) with a vinyl acetate content of about 30%, together with the addition of a percentage of ionomer resin (in order to vary the permeability characteristic) and with an anti-fog material as conventionally employed in thermoplastic films for wrapping food-stuffs.

Advantageously, the low-density, linear polyethylene of the first layer is of low grade and a limited proportion thereof may be conventional, low-density, low-grade polyethylene.

An intermediate, third, layer may be interposed between said first and second layers to provide a barrier against the passage of gases and vapours or to impart to the composite film precise accurate permeability characteristics. The intermediate layer may be a layer of polyvinylidene chloride or polyamide resin (nylon).

The invention will now be described, by way of example, with reference to the accompanying diagrammatic drawing, in which: Figure 1 is a section, to a much enlarged scale, of a fragment of film in accordance with the invention; Figure 2 is a section similar to that of Figure 1 but incorporating an intermediate layer; and Figures 3 and 4 are respectively perspective and side views of a fresh-meat package wrapped with film in accordance with the invention, before sealing the package.

Referring now to Figure 1 , film according to the invention, generally indicated by reference numeral 1, comprises at least two layers 3 and 5 laid one upon the other and adhered together over the whole area so that it is impossible for the layers to separate. The overall film thickness, bearing in mind that the use of the film is of the so-cailed "throwaway" kind, for wrapping portions, even of moderate weight, of fresh foods, is thin, for example usually ranging from 10 to 25 Mm. Greater thicknesses may be employed, for example, for packages of higher weight and of larger size or for packages which are to be handled over and over again with higher risk of tearing.As for stretch films of heavily plasticized PVC conventionally employed, film according to the invention can be employed for packaging foods placed on open, small, trays 7, as illustrated in Figures 3 and 4; or, as in the case of pieces of cheese having comparatively rigid consistency, the film can be used without a tray.

In both cases, the film is stretched (manually by the operator, or by suitable means on semiautomatic or automatic machines) in both width and length directions on the top surface of the food to be packaged and turned down below the tray or the food item having solid consistency, by pulling or overlapping for some length of its edge portions, such as those indicated by 9, 11 and 13, which are then pressed with the aid of a heated plate against the bottom 7F of the tray (or against the lower surface of the piece having comparatively rigid consistency) so that the edge portions adhere together and thus keep the film in tension and seal the package.

In order to comply with the use requirements briefly hereinbefore described, films according to the invention have stretch or extensibility and tackiness characteristics at least equal to the ones of plasticized PVC film used up to now, without having the inconvenience which PVC presents of likely transfer to the packaged foods even of small traces.(estimated as parts per million) of substances suspected of being harmful, such as vinyl monomer, and DOA or other plasticizers.Such extensibility and tackiness are obtained by manufacturing the two different layers 3 and 5 with the first layer, acting as a support, which provides for the required mechanical characteristics of the film, that is, the extensibility in conjunction with the tear or split resistance, and the second layer which provides for the tackiness to make the film self-sealing as well as for the characteristic of the appropriate permeability to gases and vapours. For satisfactory storage of fresh food-stuffs, it is usually necessary that the film which has to wrap them to be only partially gas and vapour-proof, while for aesthetic purposes it is necessary that no condensates be evident on the inside of the film which covers the packaged foodstuff.

To achieve the above-mentioned characteristics, each layer is produced from different mixtures of thermoplastic materials, the overall composition being the result of predetermined components being metered within a certain range of individual constituents.

The first layer of the film is produced from a mixture of a low-density, linear polyethylene (which is commonly indicated by the abbreviation L.L.D.P.) and ethylenevinyl acetate (EVA) having a comparatively low vinyl acetate content, that is, about 12% by weight. All percentages herein expressed are by weight.

The second layer is essentially made up of ethylenevinyl acetate (EVA) with a comparatively high vinyl acetate content, that is, about 30%; this second layer may be even of 100% of EVA, but for practical applicationvs it is preferable to mix the EVA with a percentage of ionomer resin, such as SURLYN (Registered Trade Mark) and a percentage of anti-fog material as customarily employed in thermoplastic films for wrapping foodstuffs. The ionomer resin which is employed in the mixture of the second layer is usually an ethylene copolymer with acrylic or metacrylic acid, in the molecuie of which ionic bonds take place for the presence of zinc and sodium atoms. The ionomer resin gives the film, in a more or less marked way, the characteristics of gas and vapour permeability mentioned above for the storage of fresh foods.

The low-density linear polyethylene of the first layer mixture should be of a rather low grade (or melt index), preferably grade 1. In addition, this linear polyethylene may be partly replaced, in order to lower the cost of the product, by conventional, low-density, polyethylene having characteristics suitable for producing thin films, and thus also having a low grade (or melt index).

The ranges between which the component percentages of the first and second layers may vary so that the film shall present cold-extensibility and self-sealing properties as well as the desired permeability to gases and vapours, are as follows: First layer Low-grade, low-density, linear polyethylene 20% to 50% Low-grade, low-density, conventional polyethylene 0% to 40% EVA with about 12% of vinyl acetate 20% to 50% Second layer EVA with about 30% of vinyl acetate 50% to 90% lonomer resin (such as SURLYN (Registered Trade Mark) or the like) 0% to 40% "Anti-fog" material 7% to 12% Disregarding cost, technically excellent results are obtained with the following percentages;; First layer Low-grade, low-density, linear polyethylene 50% EVA with about 12% of vinyl acetate 50% Second layer EVA with about 30% of vinyl acetate 50% lonomer resin (such as SURLYN (Registered Trade Mark) or the like) 40% "Anti-fog" material 10% From the economic point of view, quite favourable results are obtained from the standpoint of functionality, in particular for use in packaging and fresh-foods storage, together with a manufacturing cost which makes the product competitive on the market, with the following percentages:: First layer Low-grade, iow-density, linear polyethylene 35% Low-grade, low-density, conventional polyethylene 35% EVA with about 12% of vinyl acetate 30% Second layer EVA with about 30% of vinyl acetate 50% lonomer resin (such as SURLYN (Registered Trade Mark) or the like) 40% "Anti-fog" material 10% Films in accordance with the invention still have acceptable working characteristics with the percentage content of the first layer components corresponding to the lowest possible cost, while, as it is apparent from the above, the second layer composition is determined mainly in relation to the use to which the film is assigned and permits only partial variations in order to lower costs.

Cold-extensible films in accordance with the invention may be manufactured, for example, to provide a barrier against the passage of gases and vapours, with three layers, that is, with an intermediate layer 1 5 (Figure 2) interposed between the two different layers hereinbefore described.

The intermediate layer, having a barrierfunction, may be constituted by a thin film of polyvinylidene chloride PVDC) or by a thin film of polyamide resin (e.g. Nylon).

Films in accordance with the invention either made in two layers or with an intermediate layer interposed between the two layers, can be manufactured according to conventional co-extrusion processes for producing co-extruded thin films. However, it is preferable to produce such a film by coextrusion and blow process utilizing the method and equipment described in Italian Patent Application for Industrial Invention filed on 9th May, 1980, No. 9426 A180 in the name of Gaspare PULEO.

It will be further apparent that films according to the invention, in two layers only, or with the addition of an intermediate layer, can be manufactured by forming the layers separately and then matching them by means of the conventional methods and equipment for the production of matched films.

Films in accordance with the invention can be made to have thermo-shrink properties by using known processes for particular uses in the field of the foodstuffs storage.

The advantages of films in accordance with the invention are clearly evident; they effectively replace the cold-stretch PVC film for the storage of fresh (or deep-frozen) foodstuffs without presenting the inconvenience of transferring traces of harmful components to the foods with which the film comes in contact. By rigorous experiment, films in accordance with the invention have been found to be chemically inert and do not cause any transfer of even minimum traces of any material. Even subjected such films to a transfer test in vegetable oil, which is the most severe test, the transfer is zero.

Claims

1. A self-sealing, transparent, cold-stretch film comprising at least two superimposed different layers of adhered thermoplastic material, a first layer comprising a mixture of low-density linear polyethyiene (LLDP) and of ethylenevinyl acetate (EVA) with a vinyl acetate content of about 12%, and the second layer comprising ethylenevinyl acetate (EVA) with a vinyl acetate content of about 30%, together with the addition of a percentage of ionomer resin (in order to vary the permeability characteristic) and with an anti-fog material as conventionally employed in thermoplastic films for wrapping foodstuffs.

2. A film according to claim 1, wherein the low-density linear polyethylene of the first layer is of low-grade and a limited proportion of it is replaced with conventional low-grade low-density polyethylene.

3. A film according to claim 1 or claim 2, wherein mechanical characteristics such as stretchability, flexiblity at low temperatures, and tear resistance, and the characteristics of tackiness for the purposes of the self-sealing capacity and relative vapour and gas permeability, are obtained by the following ranges of percentage contents of the components: First layer Low-grade, low-density, linear polyethylene 20% to 50% Low-density conventional polyethylene 0% to 40% EVA (with about 12% vinyl acetate) 30% to 50% Second layer EVA (with about 30% vinyl acetate) 50% to 90% lonomer resin 0% to 40% Anti-fog material 7% to 12%

4.A film according to any one of the preceding claims, wherein the following percentage contents of the various components are used: First layer Low-grade, low-density, linear polyethylene 50% EVA (with about 12% vinyl acetate) 50% Second layer EVA (with about 30% vinyl acetate) 50% lonomer resin 40% Anti-fog material 10%

5. A film according to any one of claims 1, 2 or 3, wherein the following percentage contents of the components are used: First layer Low-grade, low-density, linear polyethylene 35% Low-density, conventional polyethylene 35% EVA (with about 12% vinyl acetate) 30% Second layer EVA 9 with about 30% vinyl acetate) 50% lonomer resin 40% Anti-fog material 10%

6.A film according to any one of the preceding claims, comprising a third, intermediate, layer interposed between said first and second layers in order to provide an additional barrier against the passage of gases and vapours or to impart to the film precise permeability characteristics.

7. A film according to claim 6, wherein the intermediate layer is a film of polyvinylidene chloride.

8. A film according to claim 6, wherein the intermediate layer is a film of polyamide resin (nylon).

9. A process for the manufacture of film according to any one of the preceding claims, comprising co-extruding the materials of the film to form the composite.

10. A process for the manufacture of a film according to any one of claims 1 to 8, wherein the film is produced by a co-extrusion and blow process using the method and equipment of Italian Patent Application filed on 9th May 1 980 under No. 9426 A/80 by Gaspare PULEO.

11. A process for the manufacture of a film according to any one of claims 1 to 8, comprising the steps of forming the film of the first and second layers and the intermediate layer and matching and adhering these layers together to form the composite.

12. A process for the manufacture of a film according to any one of claims 1 to 8, wherein a known process is applied to impart thermo-shrink characteristics to the composite film.

13. A composite film comprising a first layer of low-density, linear polyethylene and ethyienevinyl acetate with a minor proportion of vinyl acetate therein and a second layer of ethylenevinyl acetate with a minor proportion of vinyl acetate higher than the proportion thereof in the ethylenevinyl acetate of the first layer, together with an ionomer resin.

14. A self-sealing, transparent, cold-stretch film, for packaging foods and other materials.