Heat-sealable multilayer film with a low gas-permeability and packaging material made therefrom.

The present invention relates to a sealable, stretched multilayer film which, owing to its gas barrier properties, is particularly suitable as packaging film for goods which require low gas permeability and aroma protection.

The use of composite films made of polyolefins with a sealable layer of ethylene homo- or copolymers as a packaging film has long been known. Attempts have also already been made to improve the gas permeability of such composite films by incorporating a layer of saponified ethylene vinyl acetate. For example, DOS 2 644 209 describes a composite film made of polypropylene, an adhesion promoter layer made of modified polyolefin, a layer made of saponified ethylene-vinyl acetate copolymer and optionally a heat-sealable layer made of polyolefins. However, these composite films have the major disadvantage that their unsatisfactory sliding properties at higher packaging speeds lead to faulty sealing seams, incorrect wraps and coverings on the machine parts of the packaging machines due to abrasion.

With the composite films according to the invention it is possible to overcome these disadvantages and to provide a packaging material which, owing to its excellent lubricity and machine compatibility, is also suitable for fast-working packaging machines and, owing to the low gas permeability, can be used in particular for perishable foods.

The invention therefore relates to heat-sealable composite films made from a biaxially stretched polypropylene film as the base film, an adhesion promoter layer made from modified polyolefin, a gas barrier layer made from saponified ethylene vinyl acetate copolymer and a heat seal layer made from olefin polymers, characterized in that the base film bears an optionally at least monoaxially oriented layer on one surface. which is composed of<ul id="ul0001" list-style="none"><li>A) a heat-sealable outer layer made of polyethylene or an ethylene copolymer with at least 3% by weight, preferably 4% by weight, of ethylene;</li><li>B) an adhesion promoter layer made of modified polyolefin;</li><li>_C.) a gas barrier layer of saponified ethylene-vinyl acetate copolymer with 50 to 80 mol% of vinyl acetate units, which are at least 90% saponified;</li><li>_D) an adhesive layer made of modified polyolefin and</li><li>E) a layer of polyethylene or an ethylene copolymer with at least 3% by weight, preferably at least 4% by weight of ethylene, layers A and B and / or D and E or layers B and C or C and D can be combined to form a layer by mixing the corresponding polymers and layer A is an additive combination consisting of<ul id="ul0002" list-style="none"><li>a) 0.3 to 1 wt .-% preferably 0.4 - 0.7 wt .-% based on the sealable layer of a long-chain aliphatic amine.</li><li>b) 0.1 to 0.7% by weight, preferably 0.15-0.5% by weight, based on the sealable layer of a dispersed thermoplastic polymer which is incompatible with the polyethylene or ethylene copolymer and has a softening point in the range of max. 50 ° C below or above the softening point of the polyethylene or ethylene copolymer ,.</li><li>c) 0.1 to 1.2% by weight, preferably 0.2-0.7% by weight, based on the sealable layer of a polydialkylsiloxane. contains and the base film optionally carries a layer A, a layer combination A to E or B and C or a layer of a mixture of the polymers of layers B and C on its other surface.</li></ul></li></ul>

The polypropylene of the core film is preferably an isotactic polypropylene with a density of 0.90 to 0.9₁ g / cm³ and a melt flow index of 1 to 4 g / 10 min at 230 ° C / 2.16 kp / cm² Pressure (according to DIN 53 735).

The sealing layer polymer consists of an ethylene homopolymer or copolymer, preferably a high-density polyethylene or random ethylene / propylene copolymer with at least 3% by weight of ethylene, preferably 94-96, particularly preferably 95% by weight of propylene and 4-6 , particularly preferably 5% by weight of ethylene is used.

The density of the sealing layer polymer should preferably be in the range of 0.895 to 0.960 g / cm³ and a melt flow index of 1 to 7 g / 10 min at 190 ° C / 2.16kp / cm² Pressure and a crystallite melting point depending on the type in the range of 125 to 148 ° C (under a polarizing microscope). *

Long-chain aliphatic tertiary amines, which are optionally monounsaturated, are preferably used as component a) of the additive combination, preferably tertiary amines, the aliphatic radical of which is one _C.Chain length of C₁₂ to C₁₈ and with two hydroxyalkyl (C₁-C₄) Groups are used. N, N-bis (2-hydroxyethyl) - (C₁₂-C₁₆) alkylamines are particularly preferred.

The thermoplastic polymer incompatible with the sealing polymer should have a softening point in the range of max. 50 ° C below or above the softening point of the sealing polymer and dispersed in the sealing polymer, preferably with a particle size of 0.01 to 4 microns, particularly preferably from 0.1 to 2 microns. The incompatible polymer is dispersed in the sealing compound by customary, known methods. Thermoplastic resins such as high molecular weight are preferably suitable _PHigh density polyethylene with a softening point, preferably around 129 ° C, ethylene-methacrylic acid copolymer (90 to 99 ° C), polylaurine lactamide (≈ 180 ° C), acrylonitrile-butadiene-methacrylate copolymers (≈ 80 ° C), polyethylene vinyl alcohol Copolymers (≈ 185 ° C). Ethylene / methacrylic acid copolymers, which may optionally be wholly or partly in the form of alkali metal salts or Zn salts, or polylaurine lactamide, are very particularly preferred.

The polydialkylsiloxane used as additive component C should be from 10^{5 -}10⁶ mPas preferably one _Vhave a viscosity of at least 1 million mPas at 20 ° C. Polydimethylsiloxane is very particularly preferably used.

The gas barrier layer consists of an ethylene / vinyl acetate cop^qlymerisat, preferably from 50 to 80 mol%, particularly preferably from 60 - 75 mol%. Vinyl acetate units, which are at least 90%, preferably more than 95%, saponified.

The intrinsic viscosity [µ] of the polymer, measured in a solvent mixture of 85% by weight phenol and 15% by weight water, should preferably be between 0.07 and 0.17 l / g, particularly preferably between 0.09 and 0, 15 1 / g lie.

Modified polyolefins are used to produce the adhesion promoter layer. These are preferably polyolefins with carboxyl groups, such as polypropylene or polyethylene, which contain at least one monomer from the group of the α, β-monounsaturated dicarboxylic acids, such as Contain maleic acid, fumaric acid, itaconic acid or their acid anhydrides, acid esters, acid amides and acid imides grafted on, copolymers of ethylene with α, β-monounsaturated carboxylic acids, such as acrylic acid, methacrylic acid and / or their metal salts (Zn, Na) and / or their alkyl (C.₁-C₄) esters or corresponding graft polymers onto polyolefins such as polyethylene or polypropylene or saponified copolymers already described which have been graft-polymerized with a monomer of the abovementioned unsaturated acids.

Particularly preferred are polyolefins such as propylene or copolymers of propylene and ethylene with a maximum of 1.0% by weight grafted on α, β-monounsaturated dicarboxylic acid anhydride such as maleic anhydride or their saponified copolymers.

If the adhesion promoter polymer is incorporated either into the sealable layer A or into the gas barrier layer C, up to 40% by weight, preferably 25 to 30% by weight, based on layer-forming polymers, of the modified polyolefin are used to produce the corresponding polymers.

By using the additive combination according to the invention, it is possible not only to produce multilayer films with very good machinability and very good lubricity, but also to dispense with the usual electrical pretreatment of the film, which is known to worsen the film's sliding properties. There is also no scratching or clouding of the film, as occurs with spacers based on inorganic powder. Surprisingly, there is also no impairment of the adhesive properties of the film, for example with a tear strip, although this was to be feared when using polyalkylsiloxanes.

It was therefore not to be expected that the desired improvement of the known multilayer films would be achieved with the additive combination according to the invention, especially since the use of known lubricants, such as saturated or unsaturated fatty acid amides, as well as higher molecular weight substituted fatty acid amides with melting points between 70 and 150 ° C, e.g. Erucic acid amides, oleic acid amides, alkyl di-fatty acid amides, N, N-polyethoxylated fatty acid amides do not provide sufficient lubricity on the high-speed packaging machines.

The invention also relates to the use of the multilayer films according to the invention as packaging material for oxygen-sensitive foods.

The additives can be incorporated into the sealing layer polymer by mixing and the multilayer film can be produced by customary methods such as lamination or melt extrusion.

It is advantageous to add the additives directly to the sealing layer polymer, since this avoids a complex additive masterbatch technique.

It is also advantageous to apply the layer combination to the base film separately from the polypropylene film extrusion in a later stage of the stretching process.

The usual stretching methods can be used for biaxial stretching. The longitudinal stretching is preferably carried out in a ratio of 5: 1 to 7: 1 and the transverse stretching in a ratio of 7: 1 to 10: 1.

In the multilayer film according to the invention, the polypropylene base film should preferably have a thickness of 20 to 50 μm and the layer combination preferably a thickness of 2 to 6 μm, particularly preferably 3.5 to 5 μm, the sealing layer having a thickness of 0.8 to 2 μm, particularly preferably 1 μm Adhesion promoter layer has a thickness of 0.1 to 1 µm, preferably 0.4 to 0.6 µm, and the gas barrier layer has a thickness of 0.2 to 1.2 nm, particularly preferably 0.6 to 0.8 µm.

Layers B and D or A and E are preferably constructed identically.

Test methods

The packaging run is assessed according to the criteria set by the machine personnel, such as feed, wrapping and freedom from abrasion. If there are no problems with these features when packing at the higher speed level, the film meets the requirements. An occasional malfunction means that the film is unsuitable. It is assumed that malfunctions due to optimal adjustment of the_Packungsmaschine be excluded before the trial run.

Seal strength is understood as the force that is required to hold one under defined conditions (50 _{N /}cm²/ 0.5 sec, 130 ° C, smooth sealing jaws) to separate the sealed seam. The seal strength is given in Newtons (N) and is based on a 15 mm wide test strip.

The antistatic behavior of a film is assessed after the ash test. The ash test is carried out after a certain charge of the film - by rubbing three times with a woolen cloth in one direction.

The film is sufficiently antistatic if cigarette ash is not attracted to a charged film from a distance of 3 cm.

The measurement of the 0₂Permeability is carried out according to DIN 53 380.

The turbidity is measured according to ASTM D 1003-52.

The coefficient of friction is determined in accordance with DIN 53 375.

example 1

To produce a layer combination were used for the layer _A in 98.7% by weight of a propylene-ethylene copolymer with 4.5% by weight of ethylene, the density 0.90 g / cm³, with the melt index 5 g / 10 min at 230 °_{C /}2.16 kp / cm² and the crystallite melting point 140 ° C. 0.5% by weight of N, N-bis (2-hydroxyethyl) - (C₁₂-c₁₆) -alkylamine, 0.5% by weight of an ethylene-methacrylic acid copolymer, in which the carboxyl groups are partly present via Zn salts, with a melt index of 5 g / 10 min at 190 ° C / 1 kp / cm² and the melting point of 99 ° C and 0.3 wt .-% of a polydimethylsiloxane with a density of 0.985 g / cm³ at 20 ° C and a viscosity of 10⁶ m. Pa. s incorporated at 20 ° C and with a modified polypropylene such as a saponified copolymer with 0.7 wt .-% grafted maleic anhydride and a melt index of 5 g / 10 min at 250 ° C / 216 kp / cm² for the adhesion promoter layers and an ethylene / vinyl acetate copolymer with 55 mol% vinyl acetate units, which are 96% saponified, for the gas barrier layer and the above-mentioned propylene-ethylene copolymer for layer E, co-extruded according to conventional methods with the base film made of polypropylene density 0.905 g / cm³, with the melt index of 2 g / 10 min at 230 ° C / 2.16 kp / cm and the softening range from 160 to 166 ° C and stretched, so that a composite film with a longitudinal stretching ratio of 5: 1 and a transverse stretching in Ratio 10: 1 was obtained.

The layer structure and the properties of the finished film are listed in the following tables.

Example 2

To produce a layer combination, 99.0% by weight of a propylene-ethylene copolymer with 4.5% by weight of ethylene and a density of 0.90 g / cm were used for layer A³, with the melt index 5 g / 10 min at 230 ° C / 2.16 kp / c_m² and the crystallite melting point 140 ° C, 0.5 wt .-% N, N-bis- (₂-hydroxyethyl) - (c₁₂-C₁₆) -alkylamine, 0.2 wt .-% polylaurine lactamide with a density of 1.01 g / cm³, the viscosity number (according to DIN 53 729) 250 and the melting range of 176-180 ° C. and 0.3% by weight of a polydimethylsiloxane with a density of 0.985 g / cm³ at 20 ° C and a viscosity of 10⁶ m _Pa. s worked in at 20 ° C and co-extruded and by conventional methods with the base film made of polypropylene with a density of 0.905 g / cm³, with a melt index of 2 g / 10 min at 230 ° C / 2.16 kp / cm² and the softening range of 160 to 166 ° C and stretched so that a composite film with a longitudinal stretching in the ratio of 5: 1 and a transverse stretching in the ratio of 10: 1 was obtained.

The layer structure and the properties of the finished film are listed in the following tables.

Example 3

To produce a layer combination, 98.3% by weight of a propylene-ethylene copolymer with 4.5% by weight of ethylene and a density of 0.90 were used for layer A _G/cm³, with the melt index 5 g / 10 min at 230 ° C / 2.16 kp / cm² and the crystallite melting point 140 ° C, 0.5 wt .-% N, N-bis- (2-hydroxyethyl- (C₁₂-C₁₆) -alkylamine, 0.5% by weight of an ethylene-methacrylic acid copolymer, in which the carboxyl groups are partly present via Zn salts, with a density of 5 g / 10 min at 190 ° C./1 kp / cm² and the melting point of 99 ° C. and 0.7% by weight of a polydimethylsiloxane with a density of 0.985 g / cm³ at 20 ° C and a viscosity of 10⁶ m _Pa. s incorporated at 20 ° C and with a modified propylene / ethylene copolymer such as a saponified copolymer with 0.5% by weight of grafted maleic anhydride and a melt index of 10 g / 10 min at 250 ° C / 2.16 kp /_cm² for the _HAftvermitterschichten and an ethylene / vinyl acetate copolymer with 55 mol% vinyl acetate units, which are 96% saponified, for the gas barrier layer and the above-mentioned propylene-ethylene copolymer for the layer E, according to conventional methods with the base film made of density polypropylene 0.905 g / cm³, with a melt index of 2 g / 10 min at 230 ° C / 2.16 kp / cm² and the softening range of 160 to 166 ° C and stretched so that a composite film with a longitudinal stretching in the ratio of 5: 1 and a transverse stretching in the ratio of 10: 1 was obtained.

The layer structure and the properties of the finished film are listed in the following tables.<tables id="tabl0001" num="0001"><img file="EP0062815A2_D0001.tif" /></tables><tables id="tabl0002" num="0002"><img file="EP0062815A2_D0002.tif" /></tables>

Comparative Example 1

To produce a layer combination, 99.5% by weight of a propylene-ethylene copolymer with 4.5% by weight of ethylene, the density 0.90 g / c_m³, with a melt index of 5 g / 10 min at 230 ° C / 2.16 kp / cm³ and the crystallite melting point 140 ° C, 0.2 wt .-% N, N-bis (2-hydroxyethyl) - (C₁₂-C₁₆) -alkylamine and 0.3% by weight erucic acid amide and incorporated with a modified polypropylene, such as a saponified copolymer with 0.7% by weight grafted maleic anhydride and a melt index of 5 g / 10 min at 250 ° C./2.16 kp / cm² for the adhesion promoter layers and an ethylene / vinyl acetate copolymer with 55 mol% vinyl acetate units, which are 96% saponified, for the gas barrier layer and the above-mentioned propylene-ethylene copolymer for layer E, co-extruded according to conventional methods with the base film made of polypropylene density 0.905 g / cm³, with a melt index of 2 g / 10 min at 230 ° C / 2.16 kp / cm² and the _Eranged from 160 to 166 ° C and stretched so that a composite film with a longitudinal stretching in the ratio 5; 1 and a transverse stretching ratio of 10: 1 was obtained.

The layer structure and the properties of the finished film are listed in the following tables.