Heat-sealable multilayer film with a low gas-permeability and its use as packaging material

Sealing multilayer film with low gas permeability and its use as a packaging material

The invention relates to a sealable stretched multilayer film, the gas barrier properties of which are particularly well suited as a packaging film for goods which require low gas permeability and aroma protection.

The use of composite films made of polyolefins with a sealable ethylene homo- or copolymer layer as packaging films has long been known. Attempts have also been made to improve the gas permeability of such composite films by incorporating a layer of saponified ethylene vinyl acetate. Thus, DE application 2 644 209 describes a composite film made of an adhesive layer of polypropylene, a modified polyolefin, a layer of saponified ethylene vinyl acetate copolymer and optionally a heat-sealable polyolefin layer. However, these composite films have the disadvantage that their unsatisfactory sliding properties at higher unloading speeds lead to erroneous pattern seams, erroneous rolls and adhesion to parts of the unloading equipment due to abrasion.

The multilayer films according to the invention can eliminate these disadvantages and provide a packaging material which, due to its excellent sliding and machine travel, is also suitable for high-speed packaging machines and which, due to its low gas permeability, is particularly suitable for perishable foodstuffs.

The invention relates to a heat-sealable multilayer film consisting of a bi-directionally stretched polypropylene film as a base film, at least one surface of which optionally has a layer combination oriented in at least one direction, consisting of

A) a heat-sealable surface layer made of polyethylene or an ethylene copolymer containing at least 3% by weight of ethylene;

B) an adhesive layer made of modified polyolefin;

C) a gas barrier layer made of a saponified ethylene-vinyl acetate copolymer containing 50-80 mol% of vinyl acetate units, of which at least 90% is saponified;

D) an adhesive layer made of modified polyolefin, and

E) a layer made of a polyethylene or ethylene copolymer containing at least 3% by weight of ethylene. The multilayer film is characterized in that layer A contains an additive combination consisting of

a) from 0.3 to 1% by weight, based on the weight of the layer to be sealed, of long-chain aliphatic amines,

(b) 0.1 to 0.7% by weight, based on the weight of the layer to be sealed, of a dispersed thermoplastic polymer incompatible with a polyethylene or ethylene copolymer having a softening point not exceeding 50 ° C above or below the softening point of the polyethylene or ethylene copolymer, and

c) from 0.1 to 1.2% by weight, based on the weight of the layer to be sealed, of polydialkylsiloxane, and that the second surface of the base film optionally has layer A, layer combination AE or BC or a layer consisting of a mixture of layers B and C polymers.

The invention also relates to the use of such a multilayer film as a packaging material, preferably as a food packaging material.

The core film polypropylene is preferably isotactic polypropylene having a density of 0.90 to 0.91 g / m 2 and a melt index of 1 to 4 g / m min at a temperature of 230 ° C and a pressure of 2.16 kp / cm³ (DIN 53 735).

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The polymer of the sealable layer consists of an ethylene homopolymer or copolymer, preferably using HD polyethylene or a stylistic ethylene / propylene copolymer containing 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. p-% ethylene.

The density of the layer polymer to be sealed should be

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0.895 to 0.960 g / cm and a melt index of 1-7 g / 10 min at a temperature of 190 ° C and a pressure of 2.16 kp / cm 2 and 125-148 ° C depending on the type of melting point of the crystallites (viewed under a polarizing microscope).

As component a) of the additive combination, long-chain aliphatic tertiary amines which are optionally simply unsaturated, preferably tertiary amines having from 12 to 18 carbon atoms in the aliphatic residue and which are substituted by two hydroxy-C1-4 alkyl groups are used. N, N-bis- (2-hydroxyethyl) -^c12-16^-alkylamines are particularly preferred.

The thermoplastic polymer other than the seamless polymer should have a softening point of not more than 50 ° C above or below the softening point of the seamless polymer, and should be dispersed as seamless polymer particles having a size of preferably 0.01 to 4, particularly preferably 0.1 -2 ^ im. The dispersion of the different polymer is carried out by conventional, known methods. Preferred are thermoplastic resins such as high molecular weight HD polyethylene, preferably having a softening point of about 129 ° C, ethylene methacrylic acid copolymer (90-99 ° C), polylaurine actamide (& 180 ° C), acrylonitrile-butadiene methacrylate copolymer (Ali 80 ° C), & 185 ° C). Very particularly preferred are ethylene-methacrylic acid copolymers, which may be wholly or partly as alkali metal or zinc salts, or polylaurine lactamide.

The polydialkylsiloxane used as additive component C should have a viscosity of 10 to 10 mPa, preferably at least 10 mPa at 20 ° C. Polydimethylsiloxane is very particularly preferred.

The gas barrier layer consists of an ethylene-vinyl acetate copolymer which preferably contains 50-80 mol%, particularly preferably 60-75 mol% of vinyl acetate units which are at least 90%, preferably more than 95%, saponified.

The intrinsic viscosity number of the polymer, measured in a solvent mixture containing 85% by weight of phenol and 15% by weight of water, should preferably be 0.07 to 0.17 l / g, particularly preferably 0.09 to 0.15 l / g.

Modified polyolefins are used to make the adhesive layer. These are preferably polyolefins having carboxyl groups, such as, for example, polypropylene or polyethylene, grafted with at least one monomer which is o (β-simply unsaturated dicarboxylic acid, such as maleic acid, fumaric acid, itaconic acid or their acid anhydride, acid diester, : copolymers of ethylene and ¢ (, / 3simply unsaturated carboxylic acids, such as acrylic acid, methacrylic acid and / or their metal salts (Zn, Na) and / or their C 1-4 alkyl esters; grafted with monomers formed by the above-mentioned unsaturated acids.

Particularly preferred are polyolefins, such as polypropylene or copolymers of propylene and ethylene, having up to 1.0% by weight of grafted C 1-4 monounsaturated dicarboxylic anhydrides, such as maleic anhydride, or saponified blend polymers thereof.

When the adhesive polymers are incorporated into either the embossable layer A or the gas barrier layer C, a modified polyolefin of up to 40% by weight, preferably 25-30% by weight, based on the polymers forming the layer, is used to prepare the corresponding polymer.

By using the additive combination according to the invention, multilayer films can be produced which have very good machine permeability and slipperiness, and in addition, conventional electrical pretreatment is avoided, which is known to impair the sliding properties of the film. Also, no tearing or clouding of the film is observed, as is the case with the use of spacers based on inorganic powders. Surprisingly, there is also no deterioration in the adhesiveness of the film, for example in the case of tear strips, although this was to be feared with the use of polalkylsiloxanes.

Thus, the additive combination of the invention was not expected to achieve the desired improvement over known multilayer films, especially when the addition of known lubricants such as saturated or unsaturated fatty acid amides or , Ν-ethoxy fatty acid amides, no excellent slipperability is achieved in high speed packaging machines.

The invention further includes the use of a multilayer film according to the invention as a packaging material for oxygen-sensitive foods.

The incorporation of additives into the polymers used in the sealable layer can be done by mixing, and the multilayer film can be prepared conventionally, such as by lamination or coextrusion.

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It is advantageous to add the additives directly to the sealable layer polymer, as this avoids the laborious method of adding additives (Additiv-Masterbatch-Technik).

It is further preferred to apply the layer combination to the base film at the end of the stretching process separately from the extrusion of the polypropylene film.

Conventional stretching methods can be used for bidirectional stretching. Longitudinal stretching is preferably performed in a ratio of 5: 1 to 7: 1 and transverse stretching in a ratio of 7: 1 to 10: 1.

In the multilayer film according to the invention, the thickness of the polypropylene base film should preferably be 20-50 [mu] m, and the thickness of the layer combination preferably 2-6 [mu] m, particularly preferably 3.5-5 [mu] m, the embossing layer having a thickness of 0.8-2 [mu] m, particularly preferably 1 [mu] m. the thickness is 0.1 to 1 μm, preferably 0.4 to 0.6 μm, and the thickness of the gas barrier layer is 0.2 to 1.2 μm, particularly preferably 0.6 to 0.8 μm.

Layers B and D or A and E are preferably similar in structure.

The passage of the packaging is evaluated according to machine-specific criteria such as feed, wrapping and non-adhesion, and unless any interference with other properties occurs when the film is unloaded at high speeds, the film meets the requirements. Even the slightest disturbance means that the film is unsuitable. It is assumed that interference is avoided by adjusting the packaging machine as well as possible before the test.

The stability of the seams is the force required to remove the seam made under the conditions defined below (50 N / cm2 / 0.5 s, 130 ° C smooth pattern jaws). The stability of the joints is given in newtons (N) and is measured with a 15 mm wide test strip.

The antistatic properties of the film are measured by an ash test. The ash test is performed when the film is charged in a certain way by brushing with a wool cloth three times in one direction.

The film is sufficiently antistatic when the charged film does not attract cigarette ash from a distance of 3 cm.

Oxygen permeability is measured in accordance with DIN 63 380. Turbidity is measured according to ASTM D 1003-52.

The coefficient of friction is measured according to DIN 53 375.

Example 1

To prepare the layer combination, 98.7% by weight of a propylene-ethylene copolymer with 4.5% by weight of ethylene and a density of 0.90 g / cm 3, a melt index of 5 g / 10 min (230 ° C, 2, 16 kp / cm²) and a melting point of crystallites of 140 ° C, 0.5% by weight of N, N-bis- (2-hydroxyethyl) -C 1-2 alkylamine, 0.5% by weight of an ethylene-methacrylic acid copolymer with carboxyl groups partly as zinc salts and a melt index of 5 g / 10 min (190 ° C, 1 bp / cm²) and a melting point of 99 ° C, as well as 0.3% by weight of a polydimethylsiloxane having a density of 0.985 g / cm , 7% by weight grafted with maleic anhydride and having a melt index of 5 g / 10 min (250 ° C, 216 kp / cm²), and a gas barrier layer-forming ethylene vinyl acetate copolymer containing 55 mol% of vinyl acetate units which were 96% saponified and the above-mentioned layer E-forming propylene ethylene copolymer was incorporated into a base film of polypropylene formed by polypropylene. / cm², melt index 2 g / 10 min (230 ° C, 2.16 kp / cm²) and a softening point of 160-166 ° C, and stretched to give a composite film stretched longitudinally in a ratio of 5: 1 and transversely in a ratio of 10: 1.

The layer structure and properties of the finished film are given in the tables below.

Example 2

To prepare the layer combination, 99.0% by weight of a propylene-ethylene copolymer containing 4.5% by weight of ethylene and having a density of 0.90 g / cm 3 was mixed for layer A.³ and crystallites melting point 140 ° C, 0.5 wt% N, Nbis- (2-hydroxyethyl) -Ci 2-16^-alkyl^am1.2% by weight of polylaurine lactamide with a density of 1.01 g / cm, a viscosity (according to DIN 52 729) of 250 and a melting point range of 176-180 ° C, and 0.3% by weight of polydimethylsiloxane with the density was 0.985 g / cm³ At 20 ° C and a viscosity of 10⁶ mPa at 20 ° C, co-extruded and attached by conventional methods to a base film of polypropylene having a density of 0.905 g / cm 2, a melt index of 2 g / 10 min (230 ° C; 2.16 kp / cm²) and a softening range of 160 to 166 ° C, and stretched to give a composite film stretched 5: 1 in the longitudinal direction and 10: 1 in the transverse direction.

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

Example 3

To prepare the layer combination, 98.3% by weight of a propylene-ethylene copolymer containing 4.5% by weight of ethylene and having a density of 0.90 g / cm 3 was combined for layer A.³, melt index 5 g / 10 min (230 ° C, 2.16 kp / cm²) and melting point of crystallites 140 ° C, 0.5% by weight, N, N-bis- (2-hydroxyethyl) -C12-6^alkyl^ainii^ofi^a· 0.5% by weight of an ethylene-methacrylic acid copolymer with carboxyl groups partly as zinc salts and a melt index of 5 g / 10 min (190 ° C, 1 kp / cm²) and a melting point of 99 ° C, and 0.7% by weight of polydimethylsiloxane having a density of 0.985 g / cm³ At 20 ° C and a viscosity of 10θ mPa.s at 20 ° C, and this mixture was co-extruded with a modified propylene-ethylene copolymer such as a saponified blend polymer containing 0.5% by weight of grafted maleic anhydride and having a melt index of 10 g / 10 min ( 250 ° C, 2.16 kp / cm²) and used to make the adhesive layer, the ethylene vinyl acetate copolymer used to make the gas barrier layer containing 55 mol% of vinyl acetate units that were 96% saponified and the above propylene ethylene copolymer used to make layer E the density was 0.905 g / cm² melt index 2 g / 10 min (230 ° C, 2.16 kp / cm^z) and a softening temperature of 160-166 ° C, and stretched to obtain a composite film stretched longitudinally in a ratio of 5: 1 and transversely in a ratio of 10: 1.

The layer structure and properties of the finished film are given in the tables below.

table 1

<td></td><td>Example 1</td><td>Comparative Example 1</td><td>Example 2</td><td>Example ί</td>

<td>Layer structure and layer thickness</td><td>P / E-Copo 1</td><td>P / E-COpo 1</td><td>P / E-Copo 1</td><td>P / E-Copo 1</td>

<td>(.um)</td><td>HV 0.5</td><td>HV 0.5</td><td>PP 25</td><td>HV 0.5</td>

<td></td><td>EVAL 1</td><td>EVAL 1</td><td>P / E-Copo 1</td><td>EVAL 1</td>

<td></td><td>P / E-Copo 1</td><td>P / E-Copo 1</td><td></td><td></td>

<td></td><td>HV 0.5</td><td>HV 0.5</td><td></td><td>HV 0 ,!</td>

<td></td><td>PP 25</td><td>PP 25</td><td></td><td>P / E-Copo 1</td>

<td></td><td>P / E-Copo 1</td><td>P / E-Copo 1</td><td></td><td>PP 25</td>

<td></td><td></td><td></td><td></td><td>P / E-Copo 1</td>

<td></td><td></td><td></td><td></td><td>HV 0 /</td>

<td></td><td></td><td></td><td></td><td>EVAL 1</td>

<td></td><td></td><td></td><td></td><td>HV 0.5</td>

<td></td><td></td><td></td><td></td><td>P / E 1</td>

<td>Total-</td><td></td><td></td><td></td><td></td>

<td>thickness (μm).</td><td> 30</td><td> 30</td><td> 37</td><td> 33</td>

<td colspan="2">Seamable layer</td><td></td><td></td><td></td>

<td>additives (wt%)</td><td></td><td></td><td></td><td></td>

<td>Aliphatic amine</td><td> 0,5</td><td> 0,2</td><td> 0,5</td><td> 0,5</td>

<td>Ethylene Metacrvvli ·</td><td></td><td></td><td></td><td></td>

<td>acid copolymer</td><td> 0,5</td><td> —</td><td> —</td><td> 0,5</td>

<td>Polvlaurine lactate</td><td></td><td></td><td></td><td></td>

<td>midi</td><td> -</td><td> -</td><td> 0,2</td><td> —</td>

<td>Polydimethylsiloxane</td><td></td><td></td><td></td><td></td>

<td>saani</td><td> 0,3</td><td> -</td><td> 0,3</td><td> 0,7</td>

<td>Erucic acid amide</td><td> -</td><td> 0,3</td><td> -</td><td> -</td>

P / E-Copo = Propylene ethylene copolymer

HV = modified polyolefins with polyfunctional groups

EVAL = saponified ethylene-vinyl acetate copolymer

PP = polypropylene

II

Table 2

Example 1 Comparative Example 2 Example 3 Example 1

Film properties

<td>Coefficient of friction, film / membrane</td><td> 0,30</td><td> 0,48</td><td> 0,30</td><td> 0,27</td>

<td>Coefficient of friction, film / metal</td><td> 0,20</td><td> 0,35</td><td> 0,20</td><td> 0,17</td>

<td>Blurring (%)</td><td> 0,8</td><td> 2,8</td><td> 2,5</td><td> 3,0</td>

<td>Pattern stability (N / 15 mu)</td><td> 5</td><td> 5</td><td> 5</td><td> 5</td>

<td>Oxygen permeability (cm / m^Z .d.bar)</td><td> 20</td><td> 20</td><td> 1000</td><td> 8</td>

<td>Antistatic properties</td><td>sufficient</td><td>not enough</td><td>sufficient</td><td>sufficient</td>

<td>Features in the packaging machine</td><td>quite good</td><td>unsatisfactory manners</td><td>very ladies</td><td>very ladies</td>

Comparative Example 1

To prepare the layer combination, 99.5% by weight of a propylene-ethylene copolymer was obtained for layer A to give 4.5% by weight of ethylene and a density of 0.90 g / cm 3, a melt index of 5 g / 10 min (230 ° C, 2.16 kp / cm²) and a melting point of the crystallites of 140 ° C, 0.2% by weight of N, N-bis- (2-hydroxyethyl)^aalkylamine and 0.3 wt% erucic acid amide, and this mixture was co-extruded with a modified polypropylene such as a saponified blend polymer containing 0.7 wt% ok10 doped maleic anhydride and a melt index of 5 g / 10 min (250 ° C, 2, 16 kp / cm²), which was used to prepare the adhesive layer, the ethylene-vinyl acetate copolymer containing 550 mol% of vinyl acetate units 96% saponified used to prepare the gas barrier layer, and the above-mentioned propylene-ethylene copolymer used to prepare layer E were coupled to this. which was polypropylene with a density of 0.905 g / m 2², melt index 2 g / 10 min (230 ° C, 2.16 kp / cm²) and a softening temperature of 160-166 ° C, and stretched to give a composite film stretched 5: 1 longitudinally and 10: 1 transversely.

The layer structure and properties of the finished film are given in the tables above.