FI88131B - FOERSEGLINGSBARA FLERSKIKTSFOLIER OCH DERAS ANVAENDNING FOER FOERPACKNING AV LIVSMEDEL - Google Patents

Description

1 83131

Sealing multilayer films and their use for food wrapping

The present invention is directed to multilayer coils which are particularly suitable as packaging wells because of their sufficient sealing strength at relatively low sealing temperatures.

Temperatures.

It is known that multilayer films based on a polypropylene film and sealing layers of polymers such as ionomer resins (e.g. Surlyn) can be sealed at relatively low temperatures with sufficient strength. This also applies to multilayer films with sealing layers of ethylene / vinyl acetate copolymers.

15 However, both known multilayer films have the disadvantage that, after the electronic pre-treatment required for printing the films, they can no longer be sealed with sufficient strength. If, although only one sealing layer of the double-sided multilayer film is pre-treated electrically, the pre-treated multilayer film can thus no longer be used for numerous wrapping packages; namely, not in packages where the sealing of the pretreated film must be done against a pretreated or untreated film surface.

25 Surprisingly, it can now be used asymmetrically. The multilayer films according to the invention having the structure eliminate this drawback and multilayer films which can be printed and sealed without difficulty are made available.

The present invention thus relates to a non-heat-sealed, at least uniaxially oriented, optionally printable, asymmetrically structured multilayer film consisting of a propylene polymer film as a base layer and two outer sealing layers, one or more of which is sealed. a vinyl acetate copolymer and, if desired, acrylic acid derivatives or it: is formed therefrom and the second sealing layer (2) contains 20 0131 ethylene / acrylic acid copolymer and, if desired, acrylic acid derivatives or is formed, whereby this sealing layer can be printed if desired.

It is understood by the asymmetrical structure that the chemical compositions of the outer sealing layer are different. Due to this asymmetrical structure, these multilayer films according to the invention also provide joint seams with sufficient sealing strength at relatively low temperatures when one of their surfaces is printed.

The base layer of the sealable multilayer films according to the invention consists essentially of a propylene polymer containing up to 10% by weight of other O-olefins having up to eight carbon atoms, preferably ethylene.

Preferably, isotactic polypropylene having a density of 0.9 to 0.91 g / cm and a melt index of 1 to 4 g / 10 min at a temperature of 230 ° C and a pressure of 21.6 N (according to DIN 53735) is used. The base layer may contain 3-15% by weight, preferably 8-12% by weight of additives incompatible with the propylene polymer, preferably an inorganic additive such as calcium carbonate, silica, sodium aluminum silicate and, or titanium dioxide, making the film opaque.

As the ionomer resins for the preparation of the sealing layer (1), known copolymers obtained from α-olefins, QtV3-unsaturated monocarboxylic acids and, if desired, derivatives of these CK, β-unsaturated monocarboxylic or monohydric acids, preferably anhydrides, can be used. esters of alcohols in which the carboxyl groups have been neutralized to at least 10 mol% by metal ions. Monovalent, divalent or trivalent ions of the metals of groups I-III, IVa and Vili of the Periodic Table of the Elements are particularly suitable for salt formation (cf. "Handbook of Chemistry and Physics", Chemical Rubber Publishing Co., 37th edition, page 392). .

3 88131

Suitable monovalent metal ions include sodium, potassium, lithium, cesium, silver, mercury and copper ions. Suitable divalent metal ions include beryllium, magnesium, calcium, strontium, barium, copper, cadmium, mercury, tin, lead, iron, cobalt, nickel and zinc ions. Suitable trivalent metal ions include aluminum and iron ions. Preferably zinc ions and / or sodium ions are used for neutralization. the isomeric resin should be composed of at least 50 mole% of 10 cX-olefin, preferably ethylene. Preferred ionomer resins contain 1 to 25 mole% of β-β-unsaturated monocarboxylic acid, with at least 10%, preferably 30% of the carboxyl groups being neutralized with metal ions. Copolymers containing more than 80% by weight of the multilayer films of the invention are particularly preferred. mol% of ethylene and less than 20 mol% of acrylic acid and optionally acrylic acid derivatives neutralized at least 10%, preferably at least 30% by zinc ions (Surlyn 1705). ), ethylene / vinyl acetate copolymers having a vinyl acetate content of 2 to 10% by weight, preferably 6 to 9% by weight and a melt index in the range of 0.5 to 3 g / 10 min at 190 ° C can also be used. at a temperature of 21.6 N 25 (DIN 53735), preferably in the range of 1-2 g / 10 min.

Copolymers obtained from ethylene and acrylic acid and, if desired, acrylic acid derivatives such as acrylonitrile or lower aliphatic alcohols (C 1 -C 4) acrylic alcohols (C . Copolymerization of this sealing layer does not involve or mainly involves ionomer resins. Thus, the carboxyl groups are substantially or not at all neutralized.

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The copolymers preferably contain 1 to 20% by weight of acrylic acid and, if desired, acrylic acid derivatives, in particular 3 to 10% by weight of acrylic acid and optional acrylic acid derivatives. Copolymers containing 6-9% by weight of acrylic acid are particularly preferably used. The melt index of the sealing layer materials should be in the range 1-20, preferably in the range 3-15 and particularly preferably in the range 5-10 g / 10 min at 190 ° C and 21.6 N measured according to DIN 53735.

The multilayer films according to the invention may contain, in addition to the base layer and the outer sealing layers, further layers, such as a gas barrier layer and, if desired, adhesion-promoting layers. Known polymers can be used to prepare the gas barrier layer, preferably ethylene / vinyl acetate copolymers containing 40-85 mol%, preferably 60-75 mol% of vinyl acetate units saponified at least 90%, preferably more than 95 molar. %: isesti. The intrinsic viscosity numbers (^) of the polymers, measured in a solvent mixture containing 85% by weight of toluene and 15% by weight of water, should preferably be between 0.07 and 0.17 l / g, particularly preferably between 0.09 and 0.15 l / g. g.

In addition to the ethylene / vinyl alcohol copolymers described above, other polymers having gas barrier properties, such as polyvinyl alcohol or polyamides, can be used to prepare the gas barrier layer, in particular the oxygen and / or odor impermeable layer. Particularly preferred are blends containing the above ethylene / vinyl alcohol copolymers and 10-60% by weight of said polymers. Polyamide-6 and -12 are particularly suitable as polyamides.

Also suitable are the mixtures described in EP 0 064 330 A 1 and 0 063 006 A 1, in which case mixtures of ethylene / vinyl alcohol copolymers and polyamides which additionally contain suitable plasticizers are used for the preparation of the gas barrier layers.

5 88131

If the multilayer films according to the invention contain gas barrier layers, sufficient bond strength is generally achieved only by means of adhesion-transmitting layers. Modified polyolefins are preferably used to make these adhesion-promoting layers. These are, in particular, homo- or copolyolefins containing carboxyl groups, such as, for example, polypropylene or polyethylene, which contain at least one monomer from the group consisting of O-, monounsaturated dicarboxylic acids, such as maleic acid, fumaric acid, itaconic acid or acid anhydrides, acid esters, acid amides or acid imides inoculated are further suitable Copolymers of ethylene with o, β-unsaturated carboxylic acids such as acrylic acid, methacrylic acid and / or their metal salts (zinc, sodium) and / or their al-k With C4 esters or corresponding graft polymers of said monomers in polyolefins such as polyethylene or polypropylene or partially saponified ethylene / vinyl acetate copolymers which, if desired, are graft polymerized with the monomer of the above acids and which are saponified to a small degree.

Particularly preferably, polyolefins, such as polypropylene or copolymers of propylene and ethylene, containing up to 1% by weight of grafted, α (β-simply unsaturated dicarboxylic acid anhydrides, such as maleic acid or if desired mixed with 30 polyolefins.

Adhesion-mediating polymers can also be added to the sealable layer or the gas barrier layer. It is possible to add conventional additives and auxiliaries, such as lubricants, anti-clogging agents and anti-static agents, to the layers of the multilayer films according to the invention in conventional amounts.

Thus, polyorganosiloxanes or mixtures thereof having a kinematic viscosity of at least 100 mm / s at 25 ° C can be added. Suitable siloxane-polydiorganosi are polydialkylsiloxanes, polyalkyylivinyy-polydimethylsiloxane, olefiinimodifioidut siloxane, poly-eetterimodifioidut siloxane and olefin / polyether-modified silicone oils, silicone oils etoksimodifioidut 10 and alcohol-silicone oils, polydialkylsiloxanes, wherein the alkyl groups have preferably 1 to 4 carbon atoms.

Polydimethylsiloxane is particularly suitable. Preferably, the kinematic viscosity of the polydiorganosiloxanes should be at least 10 mm / s at 25 ° C, preferably at least 10 mm / s. It is further possible to add known unsaturated fatty acid amides, saturated fatty acid amides, such as stearic acid amide, erucic acid amide, in addition to thermoplastic polymers, which are incompatible with the polymers of the film materials, such as polyamide-12 or inorganic extenders, such as SiC such as long chain aliphatic tertiary amines which, if desired, may be simply unsaturated, such as ethoxylated tertiary amines, N, N-bis (hydroxyethyl) - (C 1 -C 2 alkyl) diamines are particularly preferably added. ·

The multilayer films according to the invention can be produced by conventional methods, such as lamination, coating and / or melt (co) extrusion.

The monolayer films according to the invention are oriented at least in one direction; they are preferably subjected to bidirectional stretching. In this case, the length elongation ratio is preferably 5: 1 to 7: 1 and the transverse elongation ratio 7: 1 to 10: 1.

The total thickness of the multilayer films according to the invention is preferably 10 to 100 micrometers, particularly preferably 7 to 831 31 20 to 50 micrometers, the base layer having a thickness of 20 to 50 micrometers and the heat-sealable layers having a thickness of 0.8 to 2 micrometers, particularly preferably 1.2 to 1, 5 micrometers.

The multilayer films according to the invention are suitably suitable as packaging materials, in particular as wrapping films, preferably for foodstuffs, and can be printed and provided with tear strips for this purpose.

The following test methods are used to determine the values in the following examples: The haze is determined according to ASTM 10 Method D 1003-52. To determine the gloss of the film, a photoelectric gloss meter (Dr. B. Lange, Berlin) was used, comprising a low voltage incandescent lamp and a condenser, which illuminates the sample at a 45 ° angle and another 45 ° branch with a slit dimmer and a photocell. A finely adjustable display device (microammeter) is connected to the device, which also includes a power supply for the incandescent lamp of the constant voltage regulator. Gloss is determined as the percentage of light regularly reflected at a 45 ° angle in 20% using a surface-silvered mirror as a 100% standard.

When testing gloss, a polished black glass plate is placed on the gloss meter as an intermediate standard because the silver mirror standard is not resistant to airborne contamination. This corresponds exactly to 5% of the gloss of the surface silver-coated mirror glass plate.

The galvanometer display of the photometer of the gloss meter is adjusted with an adjustment potentiometer via a black glass intermediate standard to improve the reading accuracy of the scale interval. The film to be tested is placed transversely according to the optical axis of the gloss meter in the direction of travel on a matte black photographic paper evenly under the gloss meter and the measurement is performed at five perfect points. The Gal vanometer reading is divided by 10 and averaged.

To determine the strength of the joints, the sealing strength is tested using a sealing pressure of 50 N / cm. In this case, the sealing strength is understood to mean the force required to separate the joint produced under the specified conditions (pressure 50 N / cm and sealing time 0.5 s) at the temperatures shown in the table. The sealing strength is expressed in newtoe for a 15 mm wide test strip.

5 To determine the scratch resistance, the turbidity formed using an Ulbricht ball is measured. In this case, the turbidity of the film is measured before and after scratching. Scratching takes place using 40 g of dust-free silicon carbide, which is sprinkled for a certain time 45 ° with respect to the horizontal on the film obtained by Kalliste-10.

Example 1

According to a conventional method, a polypropylene base film having a density of 0.905 g / cm, a melt index of 3.3 g / 10 min at 230 ° C and 21.6 N and a melting range of 160-166 ° C is applied to a surface (A ) as a sealing layer consisting of an ethylene / acrylic acid copolymer precipitate whose carboxyl groups have been neutralized with zinc ions and on the other surface (B) an ethylene / acrylic acid copolymer containing 3 mol% of acrylic acid and the compound is thus stretched that a longitudinal ratio of 5: 1 and a transverse stretch ratio of 10: 1 are obtained in the composite film.

In this case, the thickness of the base film is 17.4 micrometers and the thicknesses of the sealing layers are 1.3 micrometers in each case.

25 Before determining the sealing strength, gloss and scratch resistance, the sealing layer of ethylene / acrylic acid copolymer is electrically pretreated (corona treatment). The measurement results are shown in Table 1.

Example 2 (Comparative) As shown in Example 1, a multilayer film is prepared, however, an ethylene / acrylic acid copolymer having carboxyl groups neutralized with zinc ions is applied to both surfaces of the polypropylene base film. According to Example 1, another sealing layer is treated electrically. The measurement results are shown in Table 1.

9 80131

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Claims (7)

1. Heat-sealable, at least monoaxially oriented, optionally printable multilayer film of non-symmetrical structure, characterized in that it consists of a film of propylene polymer as the base layer and of two sealing layers of which one of the sealing layers ( an ionomer resin or an ethylene / vinyl acetate copolymer and 2) the second sealing layer (2) contains a copolymer of ethylene and acrylic acid and, if desired, of acrylic acid derivatives. Multilayer film according to claim 1, characterized in that the sealing layer (2) is printable. Multilayer film according to at least one of the preceding claims 1-2, characterized in that the base layer consists essentially of propylene polymer containing no more than 10% by weight of other α-olefin having a maximum of 8 carbon atoms. 4. Multilayer foil according to at least one of the preceding claims 1-3, characterized in that it contains a sealing layer (1) of ethylene / acrylic acid copolymer, whose carboxyl groups are at least partially neutralized with zinc ions and another sealing layer ( 2) of ethylene / acrylic acid copolymer. Multilayer film according to at least one of the preceding claims 1-4, characterized in that it also comprises other layers. Multilayer film according to at least one of the preceding claims 1-5, characterized in that it is biaxially stretched. Use of a multilayer film according to any of claims 1-5 for packaging of food.