FI112186B - Multilayer, light-drawable, polyamide-containing foil with improved crack strength - Google Patents

Abstract

The invention relates to a multilayer, readily thermoformable film, having the sequence arrangement ABCD, in particular for packaging objects with sharp edges, where - the sequence A comprises at least one copolyamide based on caprolactam and/or a mixture of an aliphatic polyamide with copolyamide based on caprolactam, and/or amorphous polyamide, - the sequence B contains at least one layer of olefinic (co)polymers, - the sequence C contains at least one layer of copolyamide based on caprolactam and/or a mixture of an aliphatic polyamide with a copolyamide based on caprolactam, and/or an aromatic polyamide, and the C:A thickness ratio is from 1.5 to 4, - the sequence D contains at least one layer of olefinic (co)polymers which, as outer layer, comprises a heat-sealable material, and the thicknesses are in the D:B ratio of from 3 to 10, preferably from 4 to 7.

Description

112186

The present invention relates to a multilayer, easily heat-mouldable polyamide-containing film which, due to its improved puncture resistance and, at the same time, its good deep-drawing properties (particularly thermoplastic extrusion), is suitable. The packaging must guarantee the safe protection of the packaged product 10 on its way to the consumer. Sharp edged foods are particularly at risk because shelf life is not guaranteed due to mechanical damage to the surrounding film. This requires special procedures for environmental and economic reasons.

Various multilayer composites with two separate layers of PA are already known in the art. They are characterized by good deep tensile properties and increased buckling strength (Kunststoffe 79, 9, 818-822 (1989)). The puncture resistance can be improved as desired by using disproportionately large thicknesses of the polyamide layer 20 and thus also thicker films. However, in this case, the thermoplasticity is greatly reduced as the molding resistance increases. Environmental and economic reasons are against increasing the thickness of the polyamide layers; Higher thicknesses, on the one hand, do not contribute to the reduction of the packaging material and, on the other hand, lead to an increase in the film price due to the use of relatively expensive polyamide.

EP 465 931 discloses a multilayer film stretched in at least one direction with 1 to 4 layers of polyamide as packaging material. The at least one Γ: 30 polyamide layer contains 50 to 95% by weight of crystalline PA and, 5 to 50% by weight of amorphous PA. The stretched film has characterized by a uniform thickness. However, this film is not deep enough to pull because it is already stretched at least in one direction. Therefore, this film cannot be used!!> T>! 35 for most deep-water applications.

»I» »» 2 112186

JA 4,164,641 and JA 4,216,933 disclose composite films comprising one or more layers of PA MXD6, one layer of a soaped ethylene-vinyl acetate copolymer, one layer of a further 5-polyethylene and one heat-sealable layer. Films having layers consisting of m-xylylenediamine and adipic acid based PA MXD6 or a mixture of PA MXD6 and another polyamide have the disadvantage that they can only be formed at high temperatures due to their high rigidity. In addition, due to their low formability, they can withstand only small punching loads.

In all of these sources, well structures are mentioned as having the common drawback of not being able to simultaneously meet the requirements of (a) easy thermoforming and (b) high puncture resistance.

Composite films with thick polyamide layers can only be deep-drawn through the long-lasting action of high molding temperatures. Therefore, the speed of the packing apparatus decreases and the number of cycles to be performed is reduced. The optical properties of the film are also reduced.

·, Reducing the thickness of the polyamide layers would result in half. 25 lower penetration resistance.

; The aim is therefore to provide a multilayer »♦; butter with improved puncture resistance and thermoforming ♦ suitable for packing products with sharp edges.

', · 30 Requirements to be met are: 1. Thermoforming

Usually the film is heated before packing- !! and deep drawing in specially shaped recesses. Low molding temperature and high residual film packing at critical points, especially in the recess, are desirable. Low molding temperatures can significantly increase the speed of packaging machines and significantly reduce the thermal load on the film. The film remains transparent and almost all traces of the heating plates on the other side of the film are avoided.

2. Puncture resistance

All experience to date indicates that increasing the thickness of the polyamide layer or layers improves puncture resistance. Therefore, the aim should be to improve the tensile strength of the tel-10, even if the thickness of the polyamide layers remains the same, so that the thermoplasticity is not impaired. The energy (work) applied to the film in relation to the total thickness of one or more layers of polyamide is particularly suitable as a criterion.

Surprisingly, the above requirements were met by a multilayer, easily thermoplastic polyamide-containing film. The film according to the invention is particularly suitable for packaging sharp-edged products. For a membrane assembly having a sequence of 20 ABCDs, the sequence is characterized in that: - sequence A consists of at least one caprolactam * · '·' amamine-based copolyamide or a mixture of an aliphatic polyamide * with caprolactam-based copolyamide or amorphous: - polyamide: · olefinic (co) polymers, · · sequence C contains at least one layer consisting of caprolactam-based copolyamide or 4. # aliphatic polyamide-based caprolactam-based ».! 30 with a copolyamide or aromatic polyamide, and a C: A ratio of 1.5 to 4, - the sequence D contains at least one olefinic (co) polymer layer consisting of a sealing material and a thickness ratio of D: B of 3 to 10. , edul- * '. 35 added 4-7.

4, 112186

Sequence A contains a PA6-based copolyamide or a mixture of an aliphatic polyamide such as PA6, PA66, PA610, PA611, PA612, PA11 or PA12 with a PA6-based copolyamide or amorphous polyamide.

Sequence B contains at least one layer of olefinic (co) polymers. Layer B can act as a coupling layer between layers A and C, which performs its attachment function even after thermoforming. Particularly suitable functional groups for this task are the 10 PE and PP copolymers.

Sequence C consists of a PA6-based copolyamide or a mixture of an aliphatic polyamide such as PA6, PA66, PA610, PA611, PA612, PA11 or PA12, a PA6-based copolyamide or an aromatic polyamide. With 15 din. The thickness ratio C: A should be in the range of 1.4 -4. The layers contained in Sequence C may be prepared by coextrusion, adhesive lamination or extrusion coating, or by a combination of said manufacturing methods.

Furthermore, positioning the sequence C between two polyolefins results in a mutual barrier of water vapor so that the natural barrier properties of the polyamide, particularly with respect to oxygen, are not significantly impaired by the action of moisture. This is of particular advantage because the sequence C is thicker than the sequence A and the barrier properties of the membrane are thus clearly improved and more independent of climate change.

Sequence D contains at least one layer of olefinic (co) polymers. The outer layer is used. Sealing. It may be polyethylene, an ethylene-vinyl acetate copolymer, an ethylene-acrylic acid copolymer, an ethylene-methacrylic acid copolymer or ionomer, or a mixture of said polymers. The thickness ratio D: B is in the range of from about 10 to about 10, preferably from 4 to 7.

• · • · · • 5 112186

The film composition of the invention has surprisingly succeeded in meeting the specific requirements of thermoforming and puncture resistance. The film is very deep-drawn even at low temperatures, 70 to 5 90 ° C. The residual thickness of the film at the corners of the recess, which must be considered as particularly critical points, has been greatly improved. Even after forming, the film remains transparent throughout the recess.

The polymers used are illuminated after the given precursors and comparative examples. Polyamides are denoted by the letter "A" and polyethylene by the letter "B".

Example 1

Multilayer film having the following composition: 15 (A1 + A2) B3 (A1 + A2) / (A1 + A3) B1 / B2 8% 13% 23% 56%

The layer thickness portions are based on a film thickness of 320 µm. The film is prepared by coextrusion and extrusion-20 coating. In the mixture of polymers A1 and A2, the weight ratio A1: A2 is 85:15, and in the mixture of polymers A1 and A3 the weight ratio A1: A3 is 90:10.

Example 2 ♦. Multilayer film having the following composition: (A1 + A2) B4 (A1 + A2) B4 / B1 / B2 9% 9% 22% 60%

The layer thickness portions are based on the film thickness: 30 to 320 µm. The film is prepared by coextrusion and extrusion coating. In the mixture of polymers Al and A2, the weight ratio Al: A2 is 85:15. The polyamide layers (A1 + A2) are bonded by a thinner coupling layer compared to Example 1. As shown in Table 1, the puncture resistance of the film of Example 2 6 112186 is quite high but still slightly lower than that of the film of Example 1.

Comparative Example 3

Multilayer film having the following composition: AI B1 / B2 / B1 AI B1 / B2 12% 46% 15% 27%

The layer thickness portions are based on a film thickness of 10,385 µm. The polyamide layers are PA6 based and are made as single films and then glued together with polyethylene layers produced by coextrusion. The sealing layer is an ethylene-vinyl acetate copolymer having an acetate content of 3% by weight.

Compared to all other samples, the film of Comparative Example 3 has the highest thickness. The polyamide layers are relatively far apart.

Comparative Example 4

Multilayer film with the following composition: B6 / B4 AI B4 / B1 25% 36% 39% • i · (·

The layer thickness portions are based on the film thickness * 25 350 µm. The film is symmetrical in composition. The film is made as a blow film, and the joint between the polyamide and the polyethylene is achieved by means of a coextruded coupling layer '' (B4). Compared to all other models, the film of Comparative Example 3 has the highest polyamide layer thickness.

: 30 Comparative Example 5

Multi-layer film having the following composition: * - 1 AI B4 AI B4 / B1 / B4 / B5 13% 3% 13% 71% • 1 »1 1 = · • i 7 112186

The layer thickness portions are based on a film thickness of 320 µm. The film assembly is asymmetric. The film is made by coextrusion and extrusion lamination. The PA6 layers are bonded together by a thin polyolefin coupling-5 layer. The sealing layer consists of an ionomer. Comparative Example 6

Multilayer film having the following composition: (A1 + A2) B4 (A1 + A2) B4 / B1 / B2 10 22% 4% 22% 52%

The layer thickness portions are based on a film thickness of 250 µm. The film assembly is asymmetric. The film is made by coextrusion and extrusion lamination. As in Reference Example 5, the polyamide layers are bonded together by a coextruded coupling layer.

The following abbreviations are used to designate the polymers: Al: A semi-crystalline, aliphatic polyamide consisting of caprolactam (PA6) having a density of 1.14 g / cm 3 and a melting point of crystallites of about 219 ° C.

; A2: Cyclic, partially aromatic polyamide, containing about 50% by weight of hexamethylenediamine and about *. 50% by weight of a mixture of isophthalic acid and terephthalic acid in a ratio of 2: 1. The density is 1.19 g / cm3 and the glass transition temperature! about 125 ° C.

A3: Semi-crystalline aliphatic polyamide based on caprolactam and laurine lactam (PA6 / 12) and containing about 10% by weight of lauric lactam. The density is, · 30 1.1 g / cm3 and the melting point of the crystallites is 200 ° C.

B1: polyethylene (PE-LD) having a density of 0.915 g / cm3, ·. and the crystallites have a melting point of 104 ° C.

* <* f. t B2: copolymer (EVA) of ethylene and vinyl acetate (about 3-5% w / w). The density is 0.925 g / cm 3 and the melting point of the crystalline crystals is 102 ° C.

β 112186 Β3: copolymer of ethylene and methylene acrylate, having a density of 0.94 g / cm3 and a melting point of the crystallites of 99 ° C.

B4: Coextrudable Coupling Agent Based on Linear Low Density Polyethylene (PE-LLD) 5. The coupling agent is chemically modified with maleic anhydride. The density is 0.92 g / cm 3 and the melting point of the crystallites is 125 ° C.

B5: Copolymer of ethylene and methylene acrylate, the chain molecules of which have been crosslinked by Na ion bond (ionomer). The density is 0.94 g / cm 3 and the melting point of the crystallites is 94 ° C.

B6: Linear Low Density Polyethylene (PE-LLD) with a density of 0.92 g / cm 3 and a melting point of the crystallites of 15,121 ° C.

The puncture test is performed according to internal instructions. It is designed to evaluate films that are subject to sharp-edged objects. Measure the force and distance required to pass the needle through the membrane-20 membrane. Puncture work is defined by the force and distance integral.

The specimen is cut into a circular specimen with a diameter of 80 mm. It is tensioned in the specimen holder, which is attached to a tensile testing machine. Moving transverse beam. A needle is attached to the force transducer on the 25a. The diameter of the needle at the tip is 1 mm. It has a conical shape and an angle of 90 °. Measurement shall always be carried out on at least five samples.

Thermoplasticity is estimated by deep drawing machines, which are commonly used in the packaging industry. The tensioned membrane web on each of its long sides is preheated with a heating plate. By suctioning air from the surface of the structured sheet to the membrane, a good heat transfer is achieved. The heating of the film can be done from the seam side or from the opposite side of the seam layer.

The membrane, heated at a plate temperature of 70-100 ° C, is sucked in by means of a differential pressure into a recess 5 having an edge dimension of 115 x 185 mm. The depth of the recess ranges from 50 to 100 mm.

The results of deep drawing of film are evaluated by the following criteria: (a) marks on the film by the heating plate, (b) formation of cavity, (c) transparency of film and cavity, and (d) residual thickness at recess angles considered particularly critical.

15 Grading factors include (a) visible marks on the film by the heating plate, (b) incomplete cavity, (c) film or cavity turbidity, and (d) less than 15% of the film thickness at the corners of the cavity.

20 The film is scored according to the above criteria. A rating of "+" means that the film meets all requirements. with respect to the foregoing. An unsatisfactory result is marked with "o" for only one criterion. If unsatisfactory results are obtained for more than 25 points, the film shall be graded »I _ Il

Table 1 Film comparison

Punch Distance Punch Energy Deep Draw-30 (mm) N'cm / mmrPA Results: Example 1 8.4 89 + * ·, Example 2 7.0 75 +

Comparative Example 3 6.4 73 p

Comparative Example 4 6.6 68 o 35 Comparative Example 5 5.4 65

Comparative Example 6 6.7 65 + 112186 10

In order to compare different films, the puncture energy for each film is calculated for the total thickness of the polyamide layers. The puncture energy at the breaking point of the film can thus be expressed as independent of the thickness of the polyamide layers. The comparison would be incorrect if only the energy required for fracture was reported.

t * · I · »· I I» I ·

Claims (8)

1. A multilayer, lightly thermoformable film having the sequence ABCD, specifically designed for packaging sharp-edged products, characterized in that - the sequence A consists of at least one caprolactam-based copolyamide or a mixture of aliphatic polyamide with caprolactam-based The sequence C contains at least one layer consisting of a caprolactam-based copolyamide or a mixture of an aliphatic polyamide with a caprolactam. based copolyamide or an aromatic polyamide and the thickness ratio C: A is 1.5-4. The sequence D contains at least one layer of olefinic (co) polymers which as outer layer consists of sealing material, and the thickness ratio D: B is 3-20. , preferably 4-7. * 2. Foil according to claim 1, characterized in that the thickness of the sequence C is 30 - 150 μτη, preferably 50 I - 10 0 μτη. : 3. Foil according to claims 1 and 2, characterized in that the thickness of the sequence D is 100 - 250 μια, preferably 150 - 200 μτη. Foil according to any of claims 1-3, characterized in that the sequence B contains an acid-modified polyolefin which acts as a coupling medium for the sequences A and C. · (ί 5. A film according to any one of claims 1-4, characterized in that the film structure ABCD or one or more of the sequences A, B, C and D is produced by co-extrusion or adhesion lamination or extrusion lamination. 14 112186 Foil according to any of claims 1-5, characterized in that the sealing material contained in the sequence D is polyethylene or ethylene vinyl acetate copolymer or ethylene acrylic acid copolymer or ethylene methylene acrylic acid copolymer or ionomer. A film according to any one of claims 1-6, characterized in that the film surface located on the opposite side of the sealing layer and / or the other layer is provided with printing. Foil according to any one of claims 1-7, characterized in that the toluene is used for packaging sharp-edged foods, such as e.g. coarse salt products, mussels, etc. • · * 1 i * · * · »·» · ·