FI78642B - PAO BAERARFOLIEN KASCHERAD LAMINATFOLIE. - Google Patents

Abstract

1. Multi-layer film comprising a single- or mul-.

Description

78642

Laminate film deposited on a carrier film -Pä bärarfolien kascherad laminatfolie

The present invention relates to multilayer films comprising a single or multilayer carrier film and a laminate film formed of polyolefins or olefin copolymers deposited on the carrier film by coating, the layers of the laminate film being made of polyolymers having varying mechanical impact to olefin.

Multilayer films are known and are widely used, for example, in food packaging. These films comprise a carrier film and a second single- or double-layer film layered therewith. Thus, EP patent publication 0.008.934 discloses a blown two-layer laminate film in which the layers are joined by a fusion joint and in which the inner layers of the blown layer are joined together by an adhesive layer. Usually, the carrier film is heat-resistant, biaxially stretched and possibly lacquered. It is preferably made of cellophane, polyester, polyamide, polypropylene or aluminum, or consists of several individual films of said substances. in the finished package, the carrier film forms the outer layer and therefore must be of good pressure.

The film deposited on the carrier film forms the inside of the finished package, therefore, in the case of a laminate film, this film must be highly weldable and have a low coefficient of friction to ensure good machinability in packaging machines.

However, for many applications, this well structure has not yet proven satisfactory, especially as the puncture resistance, especially in vacuum packs, 2 78642 is not yet sufficient, and as a result there are significant weaknesses such as loss of tightness, leading to spoilage of many foods. However, to improve low puncture strength with increased film thickness, it is not possible because many packaging machines can only process films with a certain maximum thickness. This maximum thickness for coffee packaging machines is at most 110 μm.

Therefore, multilayer films have already been made from the carrier film and the coextruded polyethylene laminate films coated thereon. The coextruded polyethylene laminate films used usually comprise two layers, one of which is usually composed of copolymers of polyethylene having high mechanical impact resistance, i.e. high toughness, the other of LD polyethylene (homopolyethylene). Alternatively, a layer formed of polyethylene having high mechanical impact resistance was then coated, however, preferably an LDPE layer with a carrier film. Although puncture resistance could be increased with this system, these multilayer films still have shortcomings so that they cannot be used satisfactorily in all areas. A disadvantage of such a multilayer film is the low smoothness at higher processing temperatures, so that interference often occurs, especially in high-speed packaging machines. This is mainly due to the different coefficients of thermal expansion in each layer of the laminate film and the different film thicknesses in each layer of the laminate film, so that these act as if they were bimetallic and thus make the film web prone to warping. This is particularly pronounced with a multilayer laminate film having a high mechanical impact polyethylene layer between the carrier film and the LDPE film.

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On the other hand, if a layer of high mechanical impact polyethylene is used as the lower layer, whereby the LDPE layer is coated on a carrier film, although the susceptibility of the multilayer film web to curvature is reduced, processing difficulties occur due to the high mechanical impact polyethylene layer. The addition of lubricants to the polyethylene from which this layer is made is only possible to some extent, as these substances migrate to other layers and reduce the deposition strength.

Another disadvantage of known multilayer films is their insufficient "dead-fold" behavior, which is understood as the ability of the film to remain in the position in which it was folded, with little or no backward elasticity. "Dead-fold" behavior is important, for example, in vacuum-packed coffee packs, where it is important that, for example, a pre-folded film in the shape of a box retains its box shape after removal of the extraction mandrel normally used for wrapping, thus allowing the filling material to be used neatly.

It is an object of the present invention to provide a multilayer film comprising a carrier film and a laminate film coated on this carrier film, which together eliminate these disadvantages and in particular provide high puncture strength, as well as good smoothness even at higher temperatures with excellent "dead-fold" properties and if necessary, good slip resistance to metal on the opposite side of the carrier film.

This object is solved according to the invention by a multilayer film, the features of which are set out in claim 1.

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Preferably, the blown, coextruded laminate film is formed of two layers; however, for different applications, it may also be appropriate to use 3- to 5-layer hoses and combine them into a 6- or 10-layer membrane. In this way, other layers can be used, e.g. for the additional use of polyvinyl alcohol (as a gas barrier).

The outer layers are melted on the surface with the inner layers during extrusion. The inner layers are pressed together using heat and pressure with a pair of press rollers. The pre-compressed, multilayer hose is preferably electrically pretreated on one side in a known manner and also coated on a single or multilayer carrier grease in a known manner.

The decisive factor of the multilayer film according to the invention is the symmetrical structure of the coextruded laminate film connected to the carrier film and compressed into at least four layers of tubing. The symmetrical structure provides a substantially better smoothness compared to the two-layer laminate films with asymmetrical structures used so far, even with larger temperature differences during processing. The previously mentioned bimetallic effect does not occur, because due to the symmetrical structure, the forces leading to the curvature of the film on one side or the other are reversed.

The use of a multilayer film according to the invention, consisting of a carrier film and a coextruded and compressed laminate film with outer layers A, A 'and inner layers B, B', has, compared to previously known film structures, a substantially higher puncture strength is obtained, or with the same puncture strength, the total thickness of the laminate film can be kept substantially lower, thus achieving considerable material savings as well as great advantages in processing machines.

The higher puncture strengths are mainly explained by the fact that the inner layers B, B 'are joined by compression and not by fusion, and further by the fact that at least one of the blown, coextruded laminate film layers or at least two extruded hose layers is made of polyolefin or olefin copolymer. In addition, the puncture strength is improved so that between the layers A, B and A ', B', due to the rotation of the blow head, a certain leveling in the strength in the machine direction and in the transverse direction is obtained.

For the purpose of the invention, it is important that a highly compressible polyethylene or ethylene copolymer with high mechanical impact resistance is selected for the inner layers B, B 'of the laminate film under pressure and heat.

By compression is meant, for the purposes of the present invention, the adhesion between the layers B, B ', which enables the mechanical release of both layers. Preferably, the bond adhesion achieved by pressing the layers B, B 'is at most 100 cN / cm.

In contrast, for the outer layers A, A ', well-weldable raw materials with a low coefficient of friction with respect to the metal are selected.

The production of deep-drawn, coextrudable laminate films requires that the composite film of the invention be blown in an unstretched state.

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Within the scope of the invention, it has proved expedient to use a coextruded laminate film in which either the inner layers B, B 'are made of polyethylene or ethylene copolymers or the outer layers A, A' of polyolefin or olefin copolymers with a mechanical impact resistance of . Ethylene vinyl acetate copolymers EVA with a vinyl acetate content of up to 35% have proven to be advantageous for the production of coextruded laminate film layers. Copolymers with a vinyl acetate content of 3 to 10% by weight and a melt index of 0.2 to 4.0, preferably 0.5 to 1.5, are very particularly suitable. These copolymers can be used both in the outer layers A, A * and also in the inner layers B, B '. Depending on whether ethylene vinyl acetate copolymers are used in the outer or inner layers, they may include lubricating agents or anti-adherents. It is preferable to use ethylene vinyl acetate copolymer layers as inner layers B, B ', since this type of plastic adheres well when pressed, and on the other hand due to its softness and poor friction values with respect to metal and suitable for manufacture. However, it is also possible to use it as outer layers A, A 'when the above-mentioned disadvantages are not decisive and, on the other hand, excellent weldability is necessary.

Inner coatings made of vinyl acetate copolymers with a vinyl acetate content of 20 to 28% by weight have proved to be particularly advantageous for the production of hot-loaded vacuum deep-drawing packages, because the very soft nature of these inner layers starting points that would result in partial detachment of the layers.

Particularly preferred for the outer layers is LLDPE (linear-low-density polyethylene) having a specific gravity of 0.918 to 0.945, preferably 0.922 to 0.930. This polyethylene has a melt index of 0.2 to 4.0. LLDPE having a melt index of 0.8 to 1.5 is preferred.

This polyethylene group can be used with or without a lubricant, it may optionally contain a silicate as an anti-adhesive.

The impact resistance of LLDPE reaches a peak value of 175 cN, which makes such LLDPE suitable for the purposes of the invention.

For the production of heat-loaded films, in particular vacuum deep-drawing packages, outer layers made of HD polyethylene (low-pressure polyethylene) and polypropylene, very particularly preferably an unstretched film (PPUG) made of polypropylene copolymers, preferably 1-4% by weight, have been added. ethylene. These outer layers are particularly suitable in combination with inner layers containing 20 to 28% by weight of vinyl acetate, which are made of ethylene vinyl acetate.

Particularly preferred has been a copolymer of ethylene methacrylic acid crosslinked with sodium or zinc ions, also known as an ionomer resin, manufactured by Dupont under the trade name Surlyn. Since the mechanical impact resistance of the sodium crosslinked ionomer resin is up to 450 cN, this raw material is preferably used for the production of inner layers B, B '. In addition to excellent mechanical impact resistance, this raw material is characterized by very good compression properties, oil resistance and good extrudability.

In this application, all data on mechanical impact resistance are based on measurements according to ASTM D-1709-62, with a drop height of 650 mm and a film thickness of 25 μm.

For the purposes of the invention, it has proved advantageous for the inner layers B, B 'to be formed of polyethylene or ethylene copolymers which have a higher mechanical impact resistance than the outer layers A, A'. However, the invention is not limited to this arrangement.

LDPE is preferably used as the outer layer and the polyethylene, which has a less high mechanical impact resistance. It is easily available, has excellent machine driving properties as well as weldability properties, and is available on the market in a wide range of types, so that the outer layer important for the coextruded laminate film welding step, which forms an inner layer in the finished package, can be easily adapted to suitable packaging machines. LDPE having a density of 0.918 to 0.934, preferably 0.922 to 0.928 and a melt index of 0.2 to 4.0, preferably 0.7 to 2.0 is usually used.

From the above-mentioned raw materials, the following very particularly advantageous alternatives for producing the multilayer film according to the invention can be derived, without limiting the invention to these alternatives: 1. The outer layers A, A 'consist of LDPE to which anti-adhesion and anti-slip additives are added in ordinary amounts, inner layers B , B 'consist of ethylene-vinyl acetate copolymer. Such a multilayer film is particularly well suited for vacuum packaging of coffee, with excellent surface properties, good "dead-fold" behavior and, due to the inner layers made of ethylene-vinyl copolymer, excellent puncture resistance.

2. The outer layers A, A 'consist of LLDPE, the inner layers B, B' of ethylene vinyl acetate copolymer. This option has even greater puncture strength and, moreover, is deep-drawn.

3. The outer layers A, A 'consist of an ethylene vinyl acetate block copolymer, the inner layers B, B' consist of an ethylene methacrylic acid copolymer crosslinked with sodium ions. Due to this structure, the multilayer film according to the invention has excellent penetration strength, and particularly good deep drawability. Preferably, this film is used for packaging meat, cheese and nuts.

4. The outer layers A, A 'consist of HDPE or a copolymer of polypropylene with 2 to 3 mol% of ethylene, the inner layers consist of an ethylene vinyl acetate copolymer containing 20 to 30% by weight of vinyl acetate. Preferably, this film is used in prepared foods or so-called for the packaging of dog sausage, ie for packaged goods which have to be heated vigorously to prevent rapid spoilage.

As the carrier film, non-stretchable or biaxially stretched films based on polyamide, polyester, polypropylene and cellulane can be applied with an adhesive, optionally further coated with an aluminum film.

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For non-deep-drawn packages, such as vacuum coffee packages, the total thickness of the known multilayer films is about 100 .mu.m. The proportion of the carrier film, which may consist of two layers, is then about 15-25 .mu.m. When the usual thicknesses of non-deep-drawn coated films are 25 to 100 μm, most often 50 to 75 μm, and it is not possible to produce coextruded single layers of laminate film with an average thickness <10 μm, the use of the multilayer film according to the invention , that the coextruded composite film or compressed hose preferably consists of four layers.

Preferably, the thickness of the layers A, A 'is 1/2 to 4/5 of the total thickness of the coextruded laminate film or compressed hose, while the total thickness of the layers B, B' must not be less than 1/5 or more than 1/2 of the total thickness. The total thickness of the compressed hoses made in this way is min. 40 - max. 500 μm, with a preferred thickness range of 70 to 100 μm for non-deep drawn films, while deep drawing films also have larger thicknesses, and the preferred range is 80 to 25 μm.

The multilayer films of the invention can be used in many areas of the packaging industry, however, they have proven to be particularly suitable in the area of puncture-prone vacuum packs, namely 1) deep-drawn vacuum packs, especially for meat, cheese and nuts. A, A 'are ethylene vinyl acetate copolymer and the inner layers B, B' are metal ion crosslinked ethylene methacrylic acid copolymer, 11 78642 2) in non-deep-drawn vacuum packs, in particular coffee or similar oxygen sensitive lacquered stretched polyester film or polyamide film and coextruded laminate film with outer layers A, A 'of ethylene-vinyl acetate copolymer and inner layers B, B' of sodium ion crosslinked ethylene methacrylic acid copolymer, or outer layers A, A 'LLDPE and inner layers B, B' ethylene vinyl acetate copolymer.

In order to further clarify the invention, it will be described in more detail with reference to the accompanying Figures 1-3, without limiting the invention to the embodiments shown in the figures.

Figure 1 shows a schematic cross-section of a two-layer coextruded blow hose.

Figure 2 shows the same hose in cross-section, but in a compressed state.

Figure 3 shows in schematic form a multilayer film according to the invention, in which the hose shown in Figure 2 is coated on a single-layer, polyamide carrier film.

In Figure 1, the letters A and B denote the outer and inner layers of the coextruded laminate film 1.

Figure 2 shows a press hose 1 'made by pressing together a laminate film 1. The layers A, A' are connected at point 3 by a fusion joint with the layers B, B '. Along the line 4, the inner layers B, B 'are pressed together. Reference numeral 2 denotes a page on which an electrical pretreatment was performed before coating.

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In Fig. 3, reference numeral 6 denotes a carrier film made of polyamide coated on a hose 1 'compressed by means of an adhesive 5.

The following examples are intended to further illustrate the invention without limiting the invention to these embodiments.

Example 1:

To make multilayer vacuum deep drawing films, two-layer blown, coextruded laminate films of various thicknesses are made and finally the blown hose is pressed together. The outer layers A, A 'of this four-layer laminate film consist of an ethylene copolymer having a vinyl acetate content of 4.2% by weight, a mechanical impact resistance of 145 cN and a melt index of 0.8. Both inner layers B, B 'consist of an ethylene methacrylic acid copolymer crosslinked with sodium ions with a mechanical impact resistance of 450 cN and a melt index of 1.4. The total thickness of both outer layers A, A 'is 2/3, the total thickness of both inner layers B, B' is 1/3 of the total thickness of the hose pressed together. In one series of experiments, compressed hoses with the total thickness of 80, 100, 120, 140, 160, 180, 200, 220 and 240 μm of the structure described above were prepared.

The compressed tubing was coated with carrier films made of unstretched polyamide 6, the thickness of the carrier film being half the thickness of the compressed tubing.

In a comparative experiment, one of the multilayer films of the invention described above, with a total thickness of 240 [mu] m, was compared with a known deep-drawing film 13,78642 having a total thickness of 300 [mu] m and consisting of a 100 [mu] m thick unstretched polyamide film and 8 % of vinyl acetate-containing ethylene copolymer, and the individual layers were 100 .mu.m thick, in a packaging test in which curved meat sausage was packaged. Despite the reduction in thickness by 60 and despite the lower proportion of vinyl acetate, the multilayer film according to the invention showed better deep-drawing behavior (especially cleanly drawn corrugation) and lower permeation leakage than the previous film.

In another comparative experiment, the multilayer film of the invention described in Example 1 with a total thickness of 360 μm was compared with a conventional multilayer film whose individual layers were made as a raw material polyamide / LDPE / LDPE / polyamide / LDPE and a total thickness of 365 μm. This multilayer film comprised two polyamide / polyethylene laminate films joined by melt extrusion with polyethylene into a five-layer film. Such films are used to package durable sausages known as "pepper slices". An equally good packaging result was achieved despite a slightly reduced overall thickness, the real advantage being that the film according to the invention has substantially lower production costs, namely only one coating step instead of the three required by the previous film.

Example 2;

To make a multilayer film for vacuum packaging, a 12 μm thick metallized polyester film is used as the carrier material and three different two-layer laminate films are made by blow molding, the resulting hoses are compressed together and coated with the carrier film.

I: The two outer layers A, A 'of the compressed laminate film consist of LDPE having a mechanical impact resistance of 86 cN, a sulfur content of 2.0, both inner layers B, B' of an ethylene vinyl acetate copolymer containing 5% by weight of vinyl acetate, and having a mechanical impact resistance of 150 cN and a melt-dexl of 2.0.

II: Both outer layers consist of LLDPE with a mechanical impact resistance of 175 cN, melting 1.0, both lower layers being as described in I.

III: The two outer layers A, A1 consist of an ethylene polymer with a vinyl acetate content of 3% by weight and a mechanical impact resistance of 150 cN and a melt index of 2.0. Both layers B, B 'consist of a sodium ion crosslinked ethylene methacrylic acid copolymer with a mechanical impact resistance of 450 cN and a melt index of 1.4.

The total thickness of the compressed hose in all three alternatives was 85 μm, with the outer layers A, A * accounting for 2/3 of the thickness and the inner layers B, B '1/3, so that the total thickness including the adhesive and the carrier film was 100 μm.

As a reference material, the metallized polyester film forming the carrier film was coated with a 45 μm thick polyethylene film (LDPE) so that the total thickness of this film, including the adhesive, was 100 μm.

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In packaging experiments in which a vacuum packer with a 250 g coffee pack on an unloader machine, the films of the invention produced substantially less leakage.

Example 3;

In another experiment with 250 and 500 g coffee packs in a vacuum kettle hose bag machine, the films described below were used comparatively.

To prepare the multilayer film of the invention, a biaxially stretched 15 μm polyamide film coated with a 12 μm aluminum film was used, and this was coated into a tube-compressed co-extruded four-layer laminate film having an outer layer A, A 'of LDP 86 cN and a melt index of 0.8, and the inner layers B, B 'consisted of an ethylene vinyl copolymer with a vinyl acetate content of 5% by weight, a mechanical impact resistance of 150 cN and a melt index of 2.0. The thickness of each of the outer layers A, A 'together was 50 μm, the thickness of the inner layers B, B' together was 25 μm. The total thickness of the pre-coated multilayer film was 105.

For comparison, a conventional film was prepared from the same support materials as described above and coated with a 75 μm thick LDPE film having a mechanical impact resistance of 96 cN and a melt index of 0.8, resulting in a total thickness of 105 μm, including adhesive.

In a packaging test in which coffee was vacuum-packed, a 40% lower number of leaks was achieved with the film according to the invention.

Claims (7)

16,78642 A multilayer film consisting of a carrier film (6) and an associated blown, coextruded laminate film (1 '), the layers of which are made of polyolefins or olefin copolymers having different mechanical impact resistance, in which the coextruded outer (A, A ') and two inner layers (B, B') of uniform material and thickness, the outer layers (A, A ') being connected to the inner layers (B, B') by a fusion joint, characterized in that the inner layers (B, B ') ) is joined together by pressing that the polyolefin or olefin copolymer forming the at least one outer layer (A, A ') or the inner layer (B, B') has an mechanical impact resistance of> 100 cN, measured according to ASTM D 1709-62, and that the blown, coextruded laminate film is joined by coating on a single or multilayer carrier film (6). Multilayer film according to Claim 1, characterized in that either the outer layers (A, A ') or the inner layers (B, B') of the coextruded laminate film are made of a material with a mechanical impact resistance at least 25 cN higher than that of the coextruded laminate film (1 '). ) in other layers. Multilayer film according to Claim 1, characterized in that either the outer layers (A, A ') or the inner layers (B, B') of the coextruded laminate film are made of a material with a mechanical impact resistance of at least 50 cN higher than in the other layers of the coextruded laminate film. Multilayer film according to one of Claims 1 to 3, characterized in that the raw material for the inner layers (B, Β ·) of the coextruded laminate film 17 78642 is a metal ion-crosslinked ethylene methacrylic acid copolymer. Multilayer film according to one of Claims 1 to 4, characterized in that the inner layers (B, B ') of the coextruded laminate film are made of polyethylene or ethylene copolymer which has a higher mechanical impact resistance than the outer layers. Multilayer film according to one of Claims 1 to 5, characterized in that the polyethylene or ethylene copolymer from which the inner layers (B, B ') of the coextruded laminate film are made has a mechanical impact resistance of up to 450 cN, and a polyolefin or olefin copolymer having the outer layers (A, A ') are made with mechanical impact resistance up to 175 cN. Multilayer film according to one of Claims 1 to 6, characterized in that the laminate film coextruded for vacuum packaging consists of four layers with a total film thickness of 70 to 100 μm, the outer layers (A, A ') having a thickness of at most 4/5 and at least 1 / 2 and the thickness of the inner layers is not more than 1/2 and not less than 1/5 of the total thickness. Multilayer film according to one of the preceding claims 1 to 7, characterized in that the coextruded laminate film for the multilayer deep-drawing film consists of four layers with a total thickness of 80 to 100 μm, the outer layers (A, A *) having a thickness of 1/2 to 4. / 5 and the proportion of inner layers (B, B ') 1/5 to 1/2 of the thickness. ιβ 78642