CH641481A5 - Polymer film which is heat-sealable on both sides - Google Patents

Abstract

The polymer film (10) which is heat-sealable on both sides and has a flexible base layer (11) and heat-sealable outer layers (12, 14), is particularly suitable for closure parts of tear-open packs; the two outer layers (12, 14) have different heat-sealing temperatures, and the first outer layer (12) forms, during heat-sealing to itself, a peelable seal seam at a temperature at which the second outer layer (14) forms a non-peelable seal seam during heat-sealing to itself. <IMAGE>

Description

** WARNING ** beginning of DESC field could overlap end of CLMS **.

PATENT CLAIMS 1. Polymer film (10) that can be sealed on both sides with a flexible carrier layer (11) and heat-sealable outer layers (12, 14), in particular for closure parts of tear-open packs, characterized in that the two outer layers (12, 14) have different sealing temperatures and the outer layer (12 ) forms a peelable sealing seam on itself when heat-sealed at a temperature at which the other outer layer (14) forms a non-peelable sealed seam on itself when heat-sealed.

2. Film according to claim 1, characterized in that the carrier layer (11) is a foldable polymer film, in particular polyalkylene film, with a melting temperature of at least 1350C and a thickness in the range from 30 to 200 pm.

3. Film according to claim 1 or 2, characterized in that each of the heat-sealable outer layers (12, 14) is connected to the carrier layer (11) via an adhesion promoter layer (13, 15).

4. Film according to one of the claims 1-3, characterized in that the one outer layer (12) forms a peelable sealing seam when heat-sealed on itself at about 1100C and the other outer layer (14) does not form a heat seal on itself at about 1100C forms more peelable sealing seam.

5. Film according to one of claims 1-4, characterized in that the one outer layer (12) at least partially from a copolymer based on ethylene and vinyl acetate, the other outer layer (14) at least partially from a copolymer based on ethylene and acrylic acid consists.

6. Film according to claim 3, characterized in that the adhesive layers (13, 15) each have a thickness of 0.1 to 1 pm.

7. Film according to claim 6, characterized in that the adhesion promoter layers (13, 15) are those based on elastomeric polyurethane or based on crosslinked ethylene / vinyl acetate copolymer.

8. Film according to one of the claims 1-7, characterized in that the two heat-sealable outer layers (12, 14) each have thicknesses in the range from 4 to 15 pm and the one outer layer (12) has a smaller thickness than the other outer layer (14).

9. Film according to one of the claims 1-8, characterized in that the carrier layer (11) consists of a biaxially oriented polyalkylene film with a degree of crystallinity of at least 50%.

The invention relates to a polymer film which is sealable on both sides, which has a flexible carrier layer and heat-sealable outer layers and is particularly suitable for closure parts of tear-open packaging for pourable and preferably liquid packaging goods.

Heat-sealable polymer films are known and are commercially available under various trade names; This includes homogeneous sealing foils as well as those that are provided with heat-sealable cover layers on a polymer carrier layer.

The patent holder has also proposed closure lid films which are suitable as tear-open closures for disposable containers for packaging liquid or semi-liquid goods, such as yoghurt, and for those types of packaging which include a preformed container, e.g.

a deep-drawn or injection-molded plastic cup with an all-round rim and a peelable lid that can be peeled off the rim, offer extensive optimization.

On the other hand, the problem of zip fasteners for highly pourable goods such as drinks has not yet been optimally solved. Such disposable beverage packaging is known to be made of flexible material, e.g. laminated paper, to provide the existing wall of the container with a material weakening line intended to form a pouring point; this can e.g. be covered with a self-adhesive film and be covered with it after the first opening. However, this leads to difficulties which, depending on the system, more at the end-user level, the distributor level or the packaging or. Packaging production level.

The object of the invention is a polymer film of the type described at the outset, which is particularly suitable for closure parts of tear-open packaging in which a pourable and in particular liquid packaging material, e.g. a beverage is enclosed by a wall of flexible material that essentially encloses the material in a liquid-tight manner and the wall has a local weakening of material to form a pouring point when torn open.

This object is achieved according to the invention in that the two outer layers of the polymer film have different sealing temperatures and one outer layer - also referred to below as the inner welding layer or I layer - forms a still peelable sealing seam on itself when heat-sealed at a temperature at which the other outer view - hereinafter also referred to as the outer welding layer or A-layer - forms a non-peelable sealing seam when heat-sealing itself. A seal temperature of around 110C can serve as a reference, but this reference is only preferred and is not generally critical.

As is customary in the plastic sealing technology, such a heat seal is understood to be peelable, the strength of which is significantly lower than the strength of the weakest point of the material composite in the seal.

A polymer film with a coating suitable for forming peelable seals is also referred to in packaging technology as a peel effect film or peel film.

On the other hand, the general criterion of a heat seal in the strict sense (here to distinguish it from the peel effect as a non-peelable seal) is that the strength of the seal is at least about the same as, and preferably greater than, the strength of the weakest point in the seal united material composite.

The absolute strength values of seals are therefore not suitable for general characterization here, especially since the reproducibility is questionable when using non or poorly defined counter surfaces and the results of seal strength tests are relativized by the test methodology.

Since the above-given characteristics of films according to the invention are each based on a given film and the relative sealing strengths which can be determined directly thereon, it is not subject to the objection of indeterminacy or of the dependence on a specific test method.

The criterion of the formation of peelable sealing seams on the one outer layer (I layer) of films according to the invention is applied to itself when heat-sealed, i.e. I-layer on I-layer, is of particular importance because this outer layer of the film can actually be sealed with itself when used as intended

and is intended to form an at least partially peelable sealing seam, as explained in more detail below.

The other outer layer (A-layer) is normally only sealed to itself for test purposes (A-layer on A-layer), because this layer is in particular intended to be used to cover part of the outer surface of a container wall in the chartteristic, i.e. not peelable to be connected way.

Accordingly, the designations used here, sometimes without qualification, mean heat seal seam, heat seal layer, heat seal connection, heat seal compound, etc.

only the ability to form thermal bonds and / or fusions, typically at temperatures in the range from 50 to 200 C, in particular 80 to 180 C, and usually also at light to medium contact pressures, e.g. in the range of 0.1 to 10 bar / cm2 (0.1 to 10 kg / cm2) or surface pressures of 1. 10-2 to 1 N / mm2.

The drawings serve to further explain the invention on the basis of schematic representations of preferred embodiments. Show it: Fig. 1 shows the sectional view of a preferred Layer structure of a film according to the invention, the covering layers being exaggeratedly thick, and Fig. 2 is a sectional view of a zipper made with the film of Fig. 1, the layer thicknesses not being drawn to scale for better illustration.

The polymer film 10 of FIG. 1 is constructed from a carrier layer 11 and has two heat-sealable outer layers 12, 14, which according to a preferred embodiment of the invention are each connected to the carrier layer 11 by an adhesion promoter layer 13 or 15.

The term polymer is understood here in the same sense as plastic and similar to plastic (i.e. also including regenerates), but does not exclude the use of monomeric or non-polymeric components such as fillers, pigments, stabilizers, plasticizers and the like. The use of metal foils, for example to reinforce the carrier layer 11, is not in itself excluded, but is less preferred.

The carrier layer 11 is always flexible, as is the entire polymer film 10 which is sealable on both sides, which is understood here as the ability for manual refolding onto itself without breaking (under normal conditions). In general, the backing layer 11 is foldable and has fold number values of over 102, e.g. 105, is moisture-proof in the sense that the wet tensile strength is approximately the same as the dry tensile strength, and - like the components of all coatings of the carrier layer 11 used here - consists of physiologically harmless material. It is often expedient if the carrier layer 11 (and the entire film 10) has a certain bending stiffness, e.g. a Taber bending stiffness value of at least 0.5 and an impact strength (according to DIN 53 448) in the range from 300 to 900 mJ / mm2. The carrier film 11 preferably has an elastic modulus (according to DIN 53 457) of more than 20 kg / mm2 , in particular in the range from 25 to 60 kg / mm2, and a practically uniform thickness in the range from 30 to 200 Sm, in particular from 60 to 120 Sm.

Examples of suitable materials for the carrier layer 11 are polyalkylenes, such as polyethylene and polypropylene, polyester, copolystyrene and the like plastics for the production of clear films. Thremoplastics are preferred, especially those with melting temperatures of at least about 135 C.

High density polyethylene (# 0.94) is particularly preferred; A preferred example for the carrier layer 11 is a film made of low-pressure polyethylene with a density of 0.950 to 0.965 g / cm 3 and a molecular weight (weight average) in the order of 100,000 to 200,000, preferably as a blown film with an inflation ratio of 1: 3 to Made 1: 6. High-pressure polyethylenes (relatively low density) are generally comparatively less cheap. The polymer mass of the film for the backing layer 11 can be mineral filler or pigment such as TiO2, e.g. in proportions of up to about 20% by weight.

Polyalkylenes, including polyethylene, which are biaxially - e.g. by blowing or other stretching processes - and have a significant degree of crystallinity, e.g. of more than 50%.

The heat-sealing layers 12, 14 are preferably not applied directly to the carrier layer 11, but only after this - if appropriate after the layer 11 has been pretreated in a conventional manner electronically, electrically, mechanically or chemically to improve the adhesion - on one or both sides with thin, e.g. 0.1 to 1 micron thick adhesive layers 13, 15 have been provided, which have elastomer components, preferably with a certain cross-linkability, e.g. Made of polyurethane.As is customary for adhesion promoters or so-called primer layers, corresponding prepolymers or polymer-forming multicomponent mixtures in solution or emulsion form can be used for this and after application to the carrier layer 11 to effect a certain - i.e. crosslinking can also be heated to an elastic layer.

Instead of polyurethanes, other elastomers in a thin layer are also suitable for layers 13, 15, e.g.

Copolymers of ethylene and vinyl acetate, acrylate, acrylic acid or the like. Application quantities of approximately 0.1 g of adhesion promoter polymer per m2 for each side of the carrier layer 11 are to be mentioned as an example. Suitable adhesion promoter preparations with the properties mentioned are technically available under various brand names.

The backing layer 11 can first have an adhesive layer 13 (or 15) on one side, then the subsequent sealing layer 12 (or 14) and then on the other side the corresponding adhesive layer 15 (or 13) and finally the other sealing layer 14 (or 12). Alternatively, both sides of the carrier layer 11 can first be provided with the two adhesion promoter layers 13, 15 in any order and then, likewise in any order, coated with the sealing layers 12, 14.

While different layer thicknesses can be expedient for the sealing layers 12, 14, the use of adhesive layers 13, 15 of different thicknesses usually brings no particular advantages, i.e. both layers 13, 15 can be approximately equally thin, e.g. in the range given above.

The heat seal layer 12 or I layer, as explained, must have a different sealing temperature, which is usually significantly higher than that of the heat seal layer 14 or A layer. There is usually a clear difference if the I-layer is practically non-sticky at the sealing temperature at which the A-layer is sticky.

A sealing temperature difference of at least about 10 C is sufficient for this in many cases. The selection of a predetermined sealing temperature is a technical measure in itself and therefore does not require any special explanations. For example, different types of hot-melt adhesive resins or identical, but somewhat different components in terms of degree of polymerization, melt index or similar parameters can be used for the heat-sealing layers 12, 14.

Moreover, the layer 12 must be capable of forming peelable seals when it is sealed on itself.

For this purpose, heat seal layers 12 in the form of preferably uniform and coherent, relatively thick, e.g. 0.5 to 10 micrometer thick layers based on copolymers of ethylene and vinyl acetate have been found to be suitable. Such copolymers, also called EVA polymers, are technically under different brand names, e.g. AC Copolymer 400 (Dow Chemical), Ultrathene (U.S. Industrial Chemicals), Montothene (Monsanto Chemicals), Elvax (Du Pont de Nemours), etc., and can also contain wax components in different proportions to control the peel strength of the heat seal compounds available with them.

To form the I layer 12, the EVA polymer, optionally in a mixture with waxes, can be applied in a conventional manner as an emulsion or as a melt onto the carrier layer 11 optionally provided with an adhesion promoter layer 13 and optionally dried under heat. Application thicknesses of 4 to 8 g of solids per m2 of coating area can be mentioned as examples of suitable I-layers 12.

For the other heat-seal layer or A-layer 14, what has been said above applies first and the requirement that this layer not primarily like the I-layer 12 for sealing with itself, but for the formation of solid, that is to say preferably non-peelable, seals with the wall material Packaging container is determined, as shown in Fig. 2 in a schematic sectional view.

From the packaging container, e.g. consists of conventional materials for disposable beverage packaging, only a wall part 27, which is usually located on the top of the container, is drawn. On these is a double layer 2 formed by folding onto itself from film 20 according to the invention, e.g. in the form of a strip 15 to 30 mm wide and 100 to 200 mm long. A corresponding strip, possibly pre-folded at the kink 29, is first covered over about half its length with the A layer, i.e. the heat-sealing layer 24 - which corresponds to the layer 14 from FIG. 1 - sealed onto the wall 27 in order to form the sealing layer 240 in the form of a firm, practically non-peelable connection.

The wall 27 is provided with a material weakening 270, preferably after the formation of the sealing layer 240, but in any case before the formation of the peelable sealing layer 220 ~, e.g. a more or less closed perforation line or punch, for example in the form of an oval, a disk or the like.

Preferably, at the same time, an analog and in this case congruent material weakening 205 is also applied in the lower layer 201 of the double layer 2 which bears against the wall 27 or has already been sealed over 240. However, one can also first form the material weakening 270 in the wall 27 and then the lower layer 201 of the film strip 20, optionally provided beforehand or subsequently with the material weakening 205, to form the heat seal 240 in a corresponding correspondence (congruence or congruence) of the material weakenings 270, Connect 205 to wall 27. Congruence of the material weakenings here means that the area delimited by material weakening 205 of film layer 201 must cover the pouring opening - the area delimited by material weakening 270 of the wall, ie the same size as or larger than it can be.

The upper layer 202 of the film 20 can now be folded back and sealed onto the lower layer 201 around the kink 29, so that the inner sealing layer 220 is formed. This layer 220 is formed from self-sealed sealing layer 22 and is peelable. The upper layer 202 is expediently somewhat longer than the lower layer 201 of the double-layer strip 2 and, as shown, forms a protruding or protruding grip part 28.

The peelable seal 220 comprises or covers the material weakening areas 205, 270, e.g. as a coherent layer or as an approximately U-shaped sealing seam, the leg ends of which lie in the kink 29. If desired, the area of the seal 220 directly above the material weakenings 205, 270 can be reinforced, e.g. by locally increased sealing temperature, if a stronger seal than peelable seal is desired in this area, for example in order to reliably tear open a comparatively less pronounced material weakening 270 of the wall 27.

In any case, the seal 220 forms a liquid-tight seal of the container enclosed by the wall 27 in the area of the weakening of the material provided for the tear-open point until the first actuation of the tear-off seal of FIG. 2 by peeling off the seal connecting the layers 201, 202.

To open the closure, the protruding part 28 is gripped and the upper layer 202 is thus pulled upwards. As a result, the seal 220 is peeled from left to right in the drawing. Since lower layer 201 has material weakening 205 and / or locally ~ i.e. in the area directly above the weakening 270 of the wall 27 - is more firmly connected to the upper layer 202, when the seal 220 is peeled off, a composite piece consisting of the wall part 271 (defined by material weakening) and the film part 210 with the region of the sealing layer 240 lying in between pivoted upwards with the layer 202 of the film 20 from the position shown in FIG. 2. As a result, a pouring opening in the container wall 27 corresponding to the wall part 271 is cleared.

The above-mentioned composite part consisting of wall part 271 and film part 210 remains connected to the upper layer 202 (via the seal 220) and can serve as a comparatively effective, but mostly no longer liquid-tight, use seal by the upper film layer 202 with the composite part 271 still attached to it , 210 is returned to the starting position of FIG. 2.

The functional parameters of the sealing layers 12, 22 of the new polymer films can be understood from the preferred use of a polymer film according to the invention for tear-off closures, particularly as regards the relative strength of the seals which can be achieved therewith. Accordingly, a comparatively firmer seal in the layer 240 is appropriate for zippers according to FIG. 2 and can be adapted to the respective requirements by the composition and thickness of the A layers 14, 24. The thicknesses of both layers 12, 14 and 22, 24 can e.g. in the range from 0.5 to 15 μm, but preferably such that the I layers (12, 22) are thinner than the A layers (14, 24). This can expediently be checked via the amount stacked up per unit area, e.g. 4 to 8 g of solids per m2 of coating for the I layers (12, 22) according to the above examples and 10 to 15 g of solids per m2 of coating for the A layers (14, 24).

Known and technically obtainable preparations which are known per se can be used as heat sealants for the A layers 14, 24. Those based on copolymers of ethylene and acrylic acid or methacrylic acid or the corresponding lower alkyl esters or alkali metal salts of the acids mentioned have proven to be particularly suitable.

Specific examples are the products available under the brand names SURLYN (Du Pont), LUPOLEN, types A-2910 MX and A-2710 HX (BASF) and ZETAFAX (Dow).

The sealants suitable for the A layers 14, 24, like those for the I layers 12, 22, can generally also be dispersions, e.g. aqueous dispersions with approx.

40% by weight of solids, or partly from melts, for example by extrusion.

Suitable coating methods and systems for such methods are known to the person skilled in the art and can be used to produce the layers 12-15 described above.

For many applications it is advantageous if the finished polymer film 10, 20 according to the invention has a basis weight of 50 to 120 g / m 2. The lower limit is mostly due to the manufacturing technology, the upper limit to the application technology or economic reasons and values outside the range just mentioned can also be realized.

Examples of the production of polymer films according to the invention are given below. The transfer symbols refer to FIG. 1.

Example 1 (a) Production of the Carrier Layer 11 Commercially available low-pressure polyethylene granules with a density of 0.950 g / cm3 and a molecular weight of 130,000 (degree of crystallinity 70%) were processed with the addition of 3% by weight of TiO2 with an inflation ratio of 1: 4 to give a blown film with a thickness of 90 micrometers, namely at extruder temperatures of 190 to 2300C (screw) or 2200C (nozzle) and with an output of 180 kg / hour. The blown film slit on both sides of the extruder was electronically treated, cut open and wound up after the separation on the top and bottom in a conventional manner to improve adhesion.

(b) Application of the adhesion promoter layer 15 The carrier layer 11 was provided on one side continuously and uniformly with an emulsion-like primer preparation based on polyurethane in an application amount of 0.5 g / m 2. The adhesion promoter layer was dried at 70 to 900C.

(c) Application of the A sealing layer 14 After cooling to room temperature, a heat sealant based on ethylene / acrylic acid copolymer was coated onto the adhesive layer 15 obtained in (b) by continuously and uniformly applying an emulsion of the copolymer in an application amount of 12.5 g / m 2 and in a continuous furnace at approx. 800C dried.

(d) applying the adhesion promoter layer 13 After cooling to room temperature, an adhesion promoter layer as described in paragraph (b) and applied in the same amount per area was applied to the still uncoated side of the backing layer 11 of the film obtained in accordance with paragraph (c).

(e) Applying the 1 seal layer 12 The side of the film which had been primed in accordance with paragraph (d) and cooled to room temperature was coated on this side with a heat sealant based on ethylene / vinyl acetate copolymer by continuously and uniformly applying an emulsion of the copolymer in an amount of 6 g / m 2 and in a continuous furnace dried at 800C. After cooling to room temperature, the finished film 10 can be rolled up and stored.

The film obtained was cut into rectangular test strips 3 cm wide and 17 cm long. A test strip was folded on itself with the I-layer 12 facing in such a way that one layer protruded approximately 2 cm above the other layer, and then sealed onto itself in some areas. The sealing jaw was covered with a TEFLON separating layer. The sealing temperature was 110 C, the sealing pressure 2 kg / cm2 and the sealing time 1 sec.

After cooling, the seal could be peeled off smoothly.

With the same seal of another folded test strip on itself, but with the A-layer 14 turned inwards, the seal obtained is no longer peelable; Attempts to forcibly separate the A-A seal lead to the tearing of the carrier layer.

Another 7 cm long test strip was sealed with sealing layer 14 onto an approximately 2 mm thick polystyrene foam composite film (110 ° C., 1 sec, 2 kg / cm 2).

The composite supported on the polystyrene side was provided with an oval material weakening (approx. 1 cm wide, approx. 3 cm long, four webs offset by approx. 900 with a web width of approx. 0.5 mm) using an oval punch punch; then the part of the strip which was still free was folded back onto the part of the strip which had already been welded to the polystyrene layer and sealed to itself at 1100 ° C. (1 sec, 2 kg / cm ') on the sealing layers 12, 12.

The zip fastener obtained is liquid-tight before the first tear-open and can be closed repeatedly dust-tight after the first peeling of the I-I seal.

If desired, the I-I sealing of the layers 12, 12 directly above the oval weakening of the material can be strengthened by resealing at 1300C (1 sec, 2 kg / cm2).

Attempts to separate the seal between the test strip and the polystyrene layer led to the destruction of the material.

Example 2 The procedure was as in Example 1, but with reversal of the coating sequence, i.e. with the sequence of steps (a), (d), (e), (b), (c). The film obtained was the same as in Example 1.

Example 3 The procedure was as in Example 1 or 3, but with the modification of step (e) as follows: The I-seal layer 12 was coated onto the adhesion-promoting layer 13 by means of a slot extruder with a heat sealant based on ethylene / vinyl acetate copolymer from the melt in an application amount of 6 t 2 g / m 2. The melting temperature was 100 to 150 C, the die temperature 1800 C.

Again, practically equivalent results were obtained as in Examples 1 and 2, respectively.

Substantially equivalent results were also obtained if the amount of primer applied in steps (b) and (d) varied in each case between 0.1 and 1 g / m 2 and / or the polyurethane primer was obtained using one based on crosslinkable ethylene / vinyl acetate Copolymer was replaced.

Even if the application quantities were varied between 10 and 15 g / m2 in step (c) and between 4 and 8 g / m2 in step (e), practically equivalent results were achieved.

Claims (9)

PATENT CLAIMS 1. Polymer film (10) that can be sealed on both sides with a flexible carrier layer (11) and heat-sealable outer layers (12, 14), in particular for closure parts of tear-open packs, characterized in that the two outer layers (12, 14) have different sealing temperatures and the outer layer (12 ) forms a peelable sealing seam on itself when heat-sealed at a temperature at which the other outer layer (14) forms a non-peelable sealed seam on itself when heat-sealed. 2. Film according to claim 1, characterized in that the carrier layer (11) is a foldable polymer film, in particular polyalkylene film, with a melting temperature of at least 1350C and a thickness in the range from 30 to 200 pm. 3. Film according to claim 1 or 2, characterized in that each of the heat-sealable outer layers (12, 14) is connected to the carrier layer (11) via an adhesion promoter layer (13, 15). 4. Film according to one of the claims 1-3, characterized in that the one outer layer (12) forms a peelable sealing seam when heat-sealed on itself at about 1100C and the other outer layer (14) does not form a heat seal on itself at about 1100C forms more peelable sealing seam. 5. Film according to one of claims 1-4, characterized in that the one outer layer (12) at least partially from a copolymer based on ethylene and vinyl acetate, the other outer layer (14) at least partially from a copolymer based on ethylene and acrylic acid consists. 6. Film according to claim 3, characterized in that the adhesive layers (13, 15) each have a thickness of 0.1 to 1 pm. 7. Film according to claim 6, characterized in that the adhesion promoter layers (13, 15) are those based on elastomeric polyurethane or based on crosslinked ethylene / vinyl acetate copolymer. 8. Film according to one of claims 1-7, characterized in that the two heat-sealable outer layers (12, 14) each have thicknesses in the range from 4 to 15 pm and the one outer layer (12) has a smaller thickness than the other outer layer (14). 9. Film according to one of the claims 1-8, characterized in that the carrier layer (11) consists of a biaxially oriented polyalkylene film with a degree of crystallinity of at least 50%. The invention relates to a polymer film which is sealable on both sides, which has a flexible carrier layer and heat-sealable outer layers and is particularly suitable for closure parts of tear-open packaging for pourable and preferably liquid packaging goods. Heat-sealable polymer films are known and are commercially available under various trade names; This includes homogeneous sealing foils as well as those that are provided with heat-sealable cover layers on a polymer carrier layer. The patent proprietor has also proposed closure lid films which are suitable as tear-open closures for disposable containers for packaging liquid or semi-liquid goods, such as yoghurt, and for those types of packaging which include a preformed container, e.g. a deep-drawn or injection-molded plastic cup with an all-round rim and a peelable lid that can be peeled off the rim, offer extensive optimization. On the other hand, the problem of zip fasteners for highly pourable goods such as drinks has not yet been optimally solved. Such disposable beverage packaging is known to be made of flexible material, e.g. laminated paper, to provide the existing wall of the container with a material weakening line intended to form a pouring point; this can e.g. be covered with a self-adhesive film and be covered with it after the first opening. However, this leads to difficulties which, depending on the system, more at the end user level, the distributor level or the packaging or. Packaging production level. The object of the invention is a polymer film of the type described at the outset, which is particularly suitable for closure parts of tear-open packaging in which a pourable and in particular liquid packaging material, e.g. a beverage is enclosed by a wall of flexible material that essentially encloses the material in a liquid-tight manner and the wall has a local weakening of material to form a pouring point when torn open. This object is achieved according to the invention in that the two outer layers of the polymer film have different sealing temperatures and one outer layer - also referred to below as the inner welding layer or I layer - forms a still peelable sealing seam on itself when heat-sealed at a temperature at which the other outer view - hereinafter also referred to as the outer welding layer or A-layer - forms a non-peelable sealing seam when heat-sealing itself. A seal temperature of around 110C can serve as a reference, but this reference is only preferred and is not generally critical. As is common in the plastic sealing technology, a heat seal is understood to be peelable, the strength of which is significantly lower than the strength of the weakest point of the material composite in the seal. A polymer film with a coating suitable for forming peelable seals is also referred to in packaging technology as a peel effect film or peel film. On the other hand, the general criterion of a heat seal in the strict sense (here to distinguish it from the peel effect as a non-peelable seal) is that the strength of the seal is at least about the same as, and preferably greater than, the strength of the weakest point in the seal united material composite. The absolute strength values of seals are therefore not suitable for general characterization, especially since the reproducibility is questionable when using non or poorly defined counter surfaces and the results of seal strength tests are relativized by the test methodology. Since the above-given characteristic of films according to the invention is based in each case on a given film and the relative sealing strengths which can be determined directly thereon, it is subject to neither the objection of indeterminacy nor that of the dependence on a specific test method. The criterion of the formation of peelable sealing seams on the one outer layer (I layer) of films according to the invention is applied to itself when heat-sealed, i.e. I-layer on I-layer, is of particular importance because this outer layer of the film can actually be sealed with itself when used as intended ** WARNING ** End of CLMS field could overlap beginning of DESC **.