Sealable polypropylene film

Description

[0001] The present invention relates to a sealable polypropylene film, a sealable metallized polypropylene film and their use in laminates, as well as a method for producing bag packaging from these laminates or from these films.

[0002] Biaxially oriented polypropylene (boPP) films are used today as packaging films in a wide variety of applications. Polypropylene films are characterized by many advantageous properties such as high transparency, gloss, water vapor barrier, good printability, stiffness, puncture resistance, etc. In addition to transparent films, opaque polypropylene films have developed very successfully in recent years. Firstly, the special appearance (opacity and whiteness) of these films is particularly desirable for some applications. Secondly, opaque films offer users higher yields due to their reduced density. In some applications, the vacuole-containing base layer contributes to a further improvement of desired film properties.

[0003] Despite its many beneficial properties, there are still areas where polypropylene film must be combined with other materials to compensate for certain shortcomings. Polypropylene films, in particular, have not yet established themselves as the sole packaging material for moisture- and oxygen-sensitive products. For example, in snack packaging, both the water vapor barrier and the oxygen barrier play a crucial role. With a water absorption of just 3%, potato chips and other snack items become so sticky that consumers find them unpalatable. Additionally, the oxygen barrier must ensure that the fats contained in the snack items do not develop a rancid taste through photo-oxidation. Polypropylene film alone does not meet these requirements as a packaging material.

[0004] It is known that the barrier properties of boPP can be improved by metallization, which significantly reduces both water vapor and oxygen permeability. For example, the oxygen permeability of a transparent 20µm boPP film can be reduced to approximately 40 cm³ / m² per day by metallization and lamination with another 20µm transparent film (see VR Interpack 99 Special D28 "The Certain Crack").

[0005] For applications involving particularly sensitive products, even the barrier provided by metallized boPP films is insufficient. In such cases, lamination of a substrate with aluminum foil is preferred. This type of packaging is considerably more complex and expensive than composites made of metallized boPP film, but it offers an excellent oxygen barrier due to the lamination with high-density aluminum foil. For example, such aluminum foil laminates are used for instant soups and ready-made sauces (e.g., Maggi Fix products) and similar powdered products, which, due to their high fat content and large surface area, require particularly effective protection from light and oxygen.

[0006] An additional problem with pouch packaging for such powders is contamination of the sealing area. To produce the pouch packaging (four-side seal), three sides are sealed first, creating an open-top pouch. The pouch is then filled with powder, and powder dust inevitably settles in the area of ​​the fourth seal. Conventional powder packaging methods cannot effectively prevent this contamination of the sealing areas. This contamination frequently leads to sealing problems. The seals have reduced or no strength in the contaminated areas, and the seal's tightness is also compromised.

[0007] After the bags are filled on the packaging machine, the sealing seams of the closed bags are subjected to additional stress because several filled bags are picked up from the conveyor belt by a robotic gripper and tightly packed into a carton. The individual bags are held in place solely by the lateral pressure exerted by the gripper. To withstand this pressure, the sealing seams must have exceptionally high strength.

[0008] In the past, these problems could only be solved by laminating the respective composites with a special sealing film. Therefore, today's composite materials for such powders, in addition to the aluminum foil that ensures the barrier, include a special sealing film that maintains its seal even in the event of contamination and guarantees an increased burst pressure of the pouch packaging, as well as potentially other components.

[0009] In some applications, boPP films are metallized solely for visual appeal. The aim is to create the impression of high-quality packaging for the consumer, without actually providing an improved barrier. In these cases, the requirements for the metallized film are relatively undemanding. The metallized film only needs to have a uniform appearance and sufficient metal adhesion.

[0010] EP-A-1597073 describes a vacuole-containing, opaque, metallized polypropylene film with special barrier properties. According to this patent, opaque polypropylene films can also exhibit very good barrier properties after metallization if the metallized top layer is composed of a special propylene copolymer with a low ethylene content and has a minimum thickness of 4 µm. Due to these good barrier properties, these metallized opaque films can be used as a component of a laminate for instant soups.

[0011] EP 0 562 496 describes a biaxially oriented shrinkable film with a low-sealing top layer made of a blend. The blend contains a VLDPE and an ethylene alpha olefin plastomer. The base layer of the film can be composed of VLDPE, LLDPE, polypropylene, ethylene-propylene copolymer, ethylene butene-1 copolymer, or a blend of ethylene alpha olefin copolymers. It is described that additional intermediate layers of film reclaimed material may be applied. A combination of a polypropylene base layer and a soft intermediate layer is not mentioned in EP 0 562 496. EP 0 781 652 describes a peelable opaque film with a soft intermediate layer of statistical copolymers and a peelable top layer made of a polymer blend of two incompatible polymers. The film can be used as a lid film on PP containers and can be peeled off in a controlled manner without the film splitting or tearing.Bags and packaging made from these films are not mentioned.

[0012] The present invention was based on the objective of providing a sealable film suitable for the production of pouch packaging. The pouch packaging must provide particularly good protection for the contents against moisture and oxygen. The seal of the pouch packaging must exhibit high strength, which can be maintained even in the event of contamination in the seal area. The pouch packaging must withstand the overpressure of the package so that no pressure loss occurs over time. The seal must be mechanically stable against the pressure exerted by the gripping robot; that is, the packaging must not burst. All these properties must be ensured even if the sealing area becomes contaminated during packaging by the contents, for example, by powder.

[0013] The object of the present invention was therefore to provide a metallized film with special sealing properties. In addition, the film must exhibit excellent barrier properties after metallization, particularly against oxygen and water vapor. The other usual performance characteristics of the film with regard to its use as a laminate component should be retained.

[0014] The application as bag packaging therefore involves a complex set of requirements, meaning the film must simultaneously meet a whole range of requirements.

[0015] The problem underlying the invention is solved by a biaxially oriented, multilayer polypropylene film according to claim 1.

[0016] The problem is further solved by a bag packaging made from the laminates according to the invention or by a bag packaging which contains the film according to the invention.

[0017] The dependent claims specify preferred embodiments of the invention.

[0018] In the context of the present invention, the base layer is the layer of the film that constitutes more than 50%, preferably more than 65%, of the total film thickness. Intermediate layers are layers located between the base layer and the respective cover layers. The first sealable cover layer I forms an outer layer of the coextruded film, which, in the finished pouch packaging, forms the inside of this pouch. According to the invention, this first sealable cover layer I is in contact with the soft, first intermediate layer I. A second cover layer II can be applied directly to the base layer or to a second intermediate layer II. The surface of the second cover layer II is designed for metallization (metallization side of the film). In the case of lamination of the film according to the invention with another film, lamination is carried out against this metallization layer.

[0019] Within the scope of the present invention, it was found that prior art films containing vacuoles, while capable of providing a good barrier after metallization despite the vacuoles in the base layer, do not achieve sufficient maximum seal strength. In particular, pouch packaging made from these films bursts too frequently.

[0020] The present invention therefore starts with known metallized transparent, i.e., vacuole-free, coextruded films, which generally exhibit acceptable to good barrier properties after metallization. Various modifications of the coextruded sealing layer of these known films were investigated within the scope of the present invention in order to improve the sealing properties of these metallized films. However, the problem could not be satisfactorily solved by this method.

[0021] Surprisingly, it was found that the barrier and sealing properties of the films according to the invention are improved when the transparent film has an additional, soft intermediate layer bonded to the first sealable top layer I. The soft intermediate layer I significantly reduces the impact of powder contamination on the quality of the seal. The resistance of the seal to the internal pressure of the packaging is improved, allowing the internal pressure of the pouch packaging to be increased considerably without the packaging bursting during processing. Despite the significantly increased internal pressure, no substantial pressure losses occur; that is, the pressure loss of a pouch is greatly reduced. Furthermore, this measure improves the barrier properties of the metallized films according to the invention compared to similarly structured films without a soft intermediate layer.

[0022] The metallized film according to the invention thus offers improved sealing properties compared to known transparent metallized films, in particular sealing seams with exceptional mechanical strength and an improved barrier after metallization against both water vapor and oxygen. This film can therefore be used particularly advantageously for the production of pouch packaging for water vapor- and oxygen-sensitive powdered products. The pouch packaging made from the film according to the invention is further characterized by low pressure losses and higher burst strength.

[0023] The film according to the invention is characterized, among other things, by the fact that it contains essentially no vacuoles. Thus, all layers of the films according to the invention are essentially vacuole-free, i.e., all layers of the film, in particular the base layer, contain no vacuole-initiating fillers. Since the film contains no vacuoles, it does not exhibit a reduced density compared to the components from which it is composed. In the context of the present invention, "vacuole-free" therefore means that the density of the film corresponds to the density of the starting materials and their respective proportions in the film. "Essentially vacuole-free" means, in particular, that the density of the film is reduced by a maximum of 5%, and more specifically by a maximum of 2%, compared to the calculated density. The calculated density is the density that is determined from the density of the components and their proportions in the film.Transparent embodiments of the film according to the invention thus have a density of 0.86 to 0.92g / cm 3< , preferably of 0.88 to 0.92g / cm 3< , in particular of 0.90 - 0.92g / cm 3< , which essentially corresponds to the density of polypropylene (0.90 - 0.92g / cm 3< ). Base layer

[0024] The base layer of the multilayer film according to the invention essentially contains polyolefin, preferably propylene polymers, and optionally other conventional additives in effective amounts, as well as optionally pigments.

[0025] The base layer contains at least 50 wt.%, preferably 60 to 99 wt.%, particularly 70 to 98 wt.%, polyolefins, based on the weight of the base layer, wherein the base layer contains at least 50 wt.%, based on the weight of the base layer, polypropylene. The polyolefins of the base layer are generally non-soft polymers, the characteristics of soft polymers being explained in more detail in connection with intermediate layer I. The propylene polymers contain 90 to 100 wt.%, preferably 95 to 100 wt.%, particularly 98 to 100 wt.%, propylene units and have a melting point of 150 to 170°C, and generally a melt flow index of 1 to 10 g / 10 min, preferably 2 to 8 g / 10 min, at 230°C and a force of 21.6 N (DIN 53735). Isotactic propylene homopolymer with an atactic content of 15 wt.% and less, copolymers of ethylene and propylene with an ethylene content of 5 wt.-% or less, copolymers of propylene with C4-C8 olefins with a C4-C8 olefin content of 5 wt.% or less, terpolymers of propylene, ethylene, and butylene with an ethylene content of 10 wt.% or less and with a butylene content of 15 wt.% or less are preferred propylene polymers for the base layer, with isotactic propylene homopolymer being particularly preferred. The stated wt. percent refer to the respective polymer.

[0026] Furthermore, a mixture of the aforementioned propylene homo- and / or copolymers and / or terpolymers and other polyolefins, in particular monomers with 2 to 6 carbon atoms, is suitable, wherein the mixture contains at least 50 wt.%, in particular at least 75 wt.%, propylene polymer.

[0027] In a further embodiment, the base layer can additionally contain opacifying pigments, i.e., opaque pigments, whereby the polymer content is reduced accordingly. These embodiments have a white, opaque appearance, i.e., they are opaque, but vacuole-free, since pigments essentially do not initiate vacuoles. Pigments are added in an amount of at most 25 wt.%, preferably 0.5 to 15 wt.%, and in particular 2 to 10 wt.%, based on the weight of the base layer. It is essential to the invention that the pigments essentially do not initiate vacuoles, since the film as a whole must be vacuole-free. "Optical" within the meaning of the present invention means a light transmittance of the film of (ASTM-D 1003-77) at most 70%, preferably at most 50%.

[0028] For the purposes of the present invention, pigments are incompatible particles that do not substantially lead to vacuole formation when the film is stretched. The coloring effect of the pigments is caused by the particles themselves. To prevent the pigments from forming vacuoles, they must have a mean particle diameter in the range of 0.01 to a maximum of 1 µm. The term "pigments" includes both so-called "white pigments," which color the films white, and optionally, "colored pigments," which give the film a colored or black color. Generally, the mean particle diameter of the pigments is in the range of 0.01 to 1 µm, preferably 0.01 to 0.7 µm, and particularly 0.01 to 0.4 µm.

[0029] Common pigments include materials such as aluminum oxide, aluminum sulfate, barium sulfate, calcium carbonate, magnesium carbonate, silicates like aluminum silicate (kaolin clay) and magnesium silicate (talc), silicon dioxide, and titanium dioxide, among which white pigments such as calcium carbonate, silicon dioxide, titanium dioxide, and barium sulfate are preferred. Titanium dioxide is particularly preferred. Various modifications and coatings of TiO₂ are known in the prior art.

[0030] For opaque embodiments with pigments, such as TiO₂, for example in the base layer and / or the first intermediate layer I, the density of the film is increased by the addition of TiO₂ compared to the density of polypropylene. For these embodiments of the film according to the invention, the density is preferably in the range of 0.91 to 0.95 g / cm³, in particular 0.92 to 0.94 g / cm³. This density of the opaque embodiment of the film is also essentially not reduced compared to the calculated density, i.e., the aforementioned density is also at most 5%, preferably at most 2%, below the calculated density, which is calculated from the density of the components and their proportion in the film. Soft intermediate layer I

[0031] The multilayer film according to the invention comprises at least one first, soft intermediate layer I applied between the base layer and the sealable top layer I. According to the invention, this soft intermediate layer I is composed of polyolefins that are softer than the polyolefins of the base layer. Various criteria can be used for selecting a soft polyolefin, for example, the melting point Tm, the softening point, the characteristics of the second heating curve of a DSC measurement, and / or the width of the melting range, the crystallinity, or the Shore hardness of the polyolefins. The soft intermediate layer I can be composed of one or more soft polymers. Preferably, the soft polymers are also mixed with other non-soft polymers, i.e., with polymers that do not meet the criteria for soft polymers described below.Such mixtures, which contain several soft polyolefins or soft and non-soft polyolefins, are hereinafter collectively referred to as "mixtures".

[0032] Soft polyolefins differ from "non-soft" polyolefins in their melting behavior. Soft polyolefins begin to soften at comparatively lower temperatures, so the melting process is a more continuous process that occurs over a very wide temperature range. In DSC measurements, soft polyolefins exhibit a second heating curve that rises continuously from 20 to 70°C (A), reaches an initial local maximum (softening point B) at a temperature above 90°C, and then transitions into the actual maximum of the heating curve (C), the melting point Tm. Once all components of the soft polyolefin or mixture have melted, the heating curve falls back to the baseline (D). The melting range of the soft polyolefin or mixture is the range between the softening point (B) and the melting point (C) and is, in effect, the temperature range in which the actual melting process takes place.

[0033] In contrast, non-soft polyolefins exhibit a second heating curve that only begins to rise at a temperature of 110 to 140°C (X) and then typically ascends steeply to a maximum Y (melting point Tm). Here, too, the heating curve then falls back to the baseline (Z) once all components have melted. A separate softening point is generally not discernible in the DSC curve of non-soft polyolefins or is so superimposed by the melt peak that no separate first maximum occurs or is discernible. Thus, the heating curves of non-soft polyolefins effectively lack a distinct softening point and a melt range as defined above.

[0034] The parameters "melting point", "softening point" and "melting range" are determined by means of DSC measurement and from the 2nd heating curve of the DSC measurement of the soft polymer or the mixture, whereby heating and cooling is carried out at a rate of 10K / min.

[0035] Figure 1This schematically compares the second heating curve of a soft polyolefin or mixture with the second heating curve of a non-soft isotactic propylene homopolymer. In this schematic example, the heating curve of the soft polymer begins to rise at a temperature of approximately 40°C (A). The DSC curve then shows a continuous slope, i.e., an ever-increasing distance from the baseline (BL). The softening point (B) is clearly visible as the first maximum at approximately 105°C, before the second maximum at approximately 135°C (melting point (C)). The heating curve then drops to the baseline at approximately 161°C, as the polyolefin is then completely melted and the melting process is complete (D). In this schematic example, the width of the melting range is therefore approximately 30°C.

[0036] In contrast, the heating curve for the non-soft polymer begins to rise at significantly higher temperatures, for example, at approximately 130°C. The melting process then starts relatively quickly, the DSC curve rises steeply, and leads directly to the melting point at 162°C (Y). The melting process is complete at 168°C (Z). The heating curve then falls back to the baseline. The predominantly crystalline propylene homopolymer does not show a discernible, separate softening point in the DSC curve. Therefore, a melting range as defined above cannot be derived from the second heating curve of the DSC measurement. In fact, the melting process takes place within a much narrower temperature range between the steep rise and fall of the melting peak, here approximately 155–162°C, corresponding to a range of 7°C.

[0037] In general, the soft polyolefin or mixture of the intermediate layer I has a melting point Tm (point C in Fig. 1) in the range of at most 150°C, preferably 70 to 140°C, particularly 80 to 130°C.

[0038] The soft polyolefin or mixture of the intermediate layer generally has a lower melting point Tm than the polyolefin of the base layer. The melting points Tm of the base layer and the intermediate layer I should advantageously differ by at least 10°C. Preferably, the melting point Tm of the soft polyolefin or mixture of the intermediate layer I is 15 to 60°C, and particularly 30 to 50°C, lower than the melting point Tm of the polyolefin of the base layer.

[0039] Alternatively or additionally, the softening point can also be used. Soft polyolefins exhibit a softening point in the DSC curve. This softening point of the soft polyolefin or mixture (point B in Fig. 1) is generally in a range of 80 to 120°C, preferably 90 to 110°C, whereas the polyolefin of the base layer does not have a separate softening point in the 2nd heating curve.

[0040] Additionally, it is advantageous that the polyolefin or mixture of the intermediate layer I has a wide melting range (BC). This means that in the second heating curve of the soft polyolefin or mixture, a separate softening point (B) is clearly discernible, i.e., different from the melting point of the soft polymer, and that this softening point and the melting point of the soft polyolefin or mixture are at least 60 K, preferably 10 to 50 K, apart.

[0041] Soft polyolefins or mixtures according to the present invention are characterized in that their heating curve begins to rise in a range of 20 to 70°C, preferably 25 to 60°C, whereas the analogous rise in non-soft polyolefins only begins in a range of 110 to 140°C.

[0042] Another selection criterion for soft polymers is the melting enthalpy. The enthalpy of soft polymers is lower than that of the polymers in the base layer. The enthalpy is determined from the cooling curve of the DSC measurement as the area under the crystallization peak. The enthalpy of soft polymers is generally in the range of 40 to 65 J / g, preferably 50 to 60 J / g. The typical cooling curve of a soft and a non-soft polymer is shown in Figure 2 depicted.

[0043] According to the invention, the first intermediate layer I contains at least 40 wt.%, preferably 60 to 100 wt.%, in particular 75 to 99 wt.% of a soft polyolefin, in each case based on the weight of the intermediate layer I, wherein different soft polyolefins can optionally be mixed together.

[0044] If necessary, additives can be added to the intermediate layer I in effective amounts. Furthermore, polymers that do not meet the criteria for a soft polyolefin may also be included. Their proportion should be chosen so that the mixture of soft and non-soft polymers meets the requirements for soft polyolefins described above; that is, the polymer mixture should then fulfill the aforementioned requirements regarding melting point, softening point, melting range, characteristics of the second heating curve, and enthalpy.

[0045] Soft polyolefins that meet the criteria described above include, for example, polyolefins made from olefins with 2 to 10 carbon atoms, among which the polymers listed below, consisting of ethylene, propylene, and butylene units, are preferred. Soft polyolefins are preferably polyethylenes, propylene copolymers and / or propylene terpolymers, as well as propylene homopolymers with low crystallinity.

[0046] Suitable propylene copolymers or terpolymers generally consist of at least 50 wt.% propylene and ethylene and / or butylene units as comonomers. Preferred copolymers are statistical ethylene-propylene copolymers with an ethylene content of 2 to 10 wt.%, preferably 5 to 8 wt.%, or statistical propylene-butylene-1 copolymers with a butylene content of 4 to 25 wt.%, preferably 10 to 20 wt.%, in each case based on the total weight of the copolymer, or statistical ethylene-propylene-butylene-1 terpolymers with an ethylene content of 1 to 10 wt.%, preferably 2 to 6 wt.%, and a butylene-1 content of 3 to 20 wt.%, preferably 8 to 10 wt.%, in each case based on the total weight of the terpolymer. These copolymers and terpolymers generally have a melt flow index of 3 to 15 g / 10 min, preferably 3 to 9 g / 10 min (230°C, 21.6N DIN 53735) and a melting point of 70 to 145°C, preferably 90 to 140°C (DSC).

[0047] Suitable soft propylene homopolymers preferably have an isotacticity of less than 95% and a xylene-soluble content of at least 3 to 10 wt.%, preferably 4 to 7 wt.%. Propylene homopolymers contain 98 to 100 wt.%, preferably 99 to 100 wt.% propylene units and have a melting point of 150 to 162°C, preferably 155 to 160°C, and generally a melt flow index of 1 to 10 g / 10 min, preferably 2 to 8 g / 10 min, at 230°C and a force of 21.6 N (DIN 53735).

[0048] Suitable polyethylenes include, for example, HDPE, MDPE, LDPE, LLDPE, and VLDPE, with HDPE and MDPE types being particularly preferred. The HDPE generally has a minimum viscosity index (MFI) (50 N / 190 °C) of greater than 0.1 to 50 g / 10 min, preferably 0.6 to 20 g / 10 min, measured according to DIN 53 735, and a viscosity index, measured according to DIN 53 728, Part 4, or ISO 1191, in the range of 100 to 450 cm³ / g, preferably 120 to 280 cm³ / g. The crystallinity is 35 to 80%, preferably 50 to 80%. The density, measured at 23 °C according to DIN 53 479, Method A, or ISO 1183, is in the range of >0.94 to 0.96 g / cm³. The melting point, measured by DSC (maximum of the melting curve, heating rate 20 °C / min), lies between 120 and 140 °C. Suitable MDPE generally has an MFI (50 N / 190 °C) of greater than 0.1 to 50 g / 10 min, preferably 0.6 to 20 g / 10 min, measured according to DIN 53 735.The density, measured at 23 °C according to DIN 53 479, method A, or ISO 1183, is in the range of >0.925 to 0.94 g / cm³. The melting point, measured with DSC (maximum of the melting curve, heating rate 20 °C / min), is between 115 and 130 °C.

[0049] In another embodiment, polymers with very low crystallinity or predominantly amorphous character can be used as soft polymers for the intermediate layer I, for example, elastomers or heterophase copolymers. Such polymers are available, for example, under the trade names Adflex (Basell), Koattro (Basell), or Vistamaxx (ExxonMobil). Sealable top layer I

[0050] According to the invention, a sealable first top layer I is applied to the soft intermediate layer I described above. The sealable top layer I generally contains at least 80 wt.%, preferably 90 to <100 wt.%, sealable olefinic polymers or mixtures thereof. Suitable polyolefins are, for example, polyethylenes, propylene copolymers and / or propylene terpolymers.

[0051] Propylene copolymers or terpolymers are generally composed of at least 50 wt.% propylene and ethylene and / or butylene units as comonomers. Preferred copolymers are statistical ethylene-propylene copolymers with an ethylene content of 2 to 10 wt.%, preferably 5 to 8 wt.%, or statistical propylene-butylene-1 copolymers with a butylene content of 4 to 30 wt.%, preferably 10 to 25 wt.%, in each case based on the total weight of the copolymer, or statistical ethylene-propylene-butylene-1 terpolymers with an ethylene content of 1 to 10 wt.%, preferably 2 to 6 wt.%, and a butylene-1 content of 3 to 20 wt.%, preferably 8 to 10 wt.%, in each case based on the total weight of the terpolymer. These copolymers and terpolymers generally have a melt flow index of 3 to 15 g / 10 min, preferably 3 to 9 g / 10 min (230°C, 21.6N DIN 53735) and a melting point of 70 to 145°C, preferably 90 to 140°C (DSC).

[0052] With regard to the use of the film as pouch packaging for powdered products, a mixture of the described propylene copolymers and / or propylene terpolymers is preferred for the sealable top layer I. These top layer mixtures are particularly advantageous with respect to the sealing properties of the film. Surprisingly, impurities do not interfere with sealing, or only to a minor extent, when the sealing layer I is composed of a mixture of the described propylene copolymers and / or propylene terpolymers.

[0053] In a particularly preferred embodiment, the top layer I has a sealing start temperature (SIT) of less than 110°C, preferably 75 to 105°C, and more specifically 80 to 100°C. Surprisingly, it was found that the low SIT, in combination with the soft intermediate layer I and the vacuole-free structure of the film, has a positive effect in the "bag packaging" application. The seal is only minimally affected by impurities, and the burst strength and mechanical strength of the seal are significantly improved when all three features are combined in a single film. In particular, the film according to the invention and the bag packaging made from the film according to the invention exhibit significantly improved seal strength.Low sealing initiation temperatures in packaging films are normally desirable when high processing speeds are achieved in the production of packaging from the films, for example, in HFFS and VFFS wrapping machines. However, since packaging speeds in the production of pouch packaging are generally significantly slower than, for example, on HFFS machines, there was no reason for a person skilled in the art to design the sealing layer I in such a way that the film exhibits a low sealing initiation temperature. Furthermore, the effect of the low sealing initiation temperature, in conjunction with the soft intermediate layer I and the vacuole-free structure of the film, on the mechanical strength of the seal was unpredictable. In particular, it was not foreseeable what positive effects on the pouch packaging would be achieved by the combination of features.

[0054] Propylene copolymers and propylene terpolymers particularly suitable for these embodiments with low SIT include, for example, C3C4 copolymers with a butylene content of 10 to 30 wt.%, preferably 12 to 28 wt.%, or C2C3C4 terpolymers with an ethylene content of 1 to 10 wt.%, preferably 2 to 6 wt.%, and a butylene-1 content of 3 to 20 wt.%, preferably 8 to 10 wt.%, in each case based on the total weight of the terpolymer or mixtures thereof. These polymers are, for example, marketed under the trade names Mitsui Tafmer XM 7080, Mitsui Tafmer XM 7070, and ExxonMobil Vistamaxx 3980 FL.

[0055] The sealable top layer I is preferably not pretreated by corona, flame, or plasma. It has been found that an untreated surface of the sealing layer I positively influences the properties of the pouch packaging; in particular, pressure losses in the pouch packaging are lower with an untreated sealing layer I than with a pouch packaging with a corona- or otherwise treated sealing layer.

[0056] In a further embodiment, the sealing layer I can additionally contain polyethylene, generally in an amount of 10 to 40 wt.%, preferably 15 to 35 wt.%, based on the sealing layer I. Suitable polyethylenes are, for example, HDPE, MDPE, LDPE, LLDPE, and VLDPE, with HDPE and MDPE types being particularly preferred. The HDPE generally has a minimum viscosity index (MFI) (50 N / 190 °C) of greater than 0.1 to 50 g / 10 min, preferably 0.6 to 20 g / 10 min, measured according to DIN 53 735, and a viscosity index, measured according to DIN 53 728, Part 4, or ISO 1191, in the range of 100 to 450 cm³ / g, preferably 120 to 280 cm³ / g. The crystallinity is 35 to 80%, preferably 50 to 80%. The density, measured at 23 °C according to DIN 53 479, method A, or ISO 1183, is in the range of >0.94 to 0.96 g / cm³. The melting point, measured with DSC (maximum of the melting curve, heating rate 20 °C / min), is between 120 and 140 °C.Suitable MDPE generally has a melt flow index (MFI) (50 N / 190 °C) of greater than 0.1 to 50 g / 10 min, preferably 0.6 to 20 g / 10 min, measured according to DIN 53 735. The density, measured at 23 °C according to DIN 53 479, Method A, or ISO 1183, is in the range of >0.925 to 0.94 g / cm³. The melting point, measured by DSC (maximum of the melting curve, heating rate 10 °K / min), is between 115 and 130 °C. Second top layer II / Metallized top layer

[0057] The film has a second top layer II on the side opposite the soft intermediate layer I / sealable top layer I, which is intended for metallization. This top layer II can be applied directly to the transparent or pigmented base layer, or the film may have a second intermediate layer 11 between the second top layer II and the base layer.

[0058] The second top layer (II) generally contains at least 80 wt.%, preferably 90 to <100 wt.%, olefinic polymers or mixtures thereof. Suitable polyolefins include, for example, propylene copolymers and / or propylene terpolymers, as well as the propylene homopolymers already described in connection with the base layer.

[0059] Suitable propylene copolymers or terpolymers generally consist of at least 50 wt.% propylene and ethylene and / or butylene units as comonomers. Preferred copolymers are statistical ethylene-propylene copolymers with an ethylene content of 2 to 10 wt.%, preferably 5 to 8 wt.%, or statistical propylene-butylene-1 copolymers with a butylene content of 4 to 25 wt.%, preferably 10 to 20 wt.%, in each case based on the total weight of the copolymer, or statistical ethylene-propylene-butylene-1 terpolymers with an ethylene content of 1 to 10 wt.%, preferably 2 to 6 wt.%, and a butylene-1 content of 3 to 20 wt.%, preferably 8 to 10 wt.%, in each case based on the total weight of the terpolymer. These copolymers and terpolymers generally have a melt flow index of 3 to 15 g / 10 min, preferably 3 to 9 g / 10 min (230°C, 21.6N DIN 53735) and a melting point of 70 to 145°C, preferably 90 to 140°C (DSC).

[0060] Furthermore, for the second cover layer II, propylene polymers with a low ethylene content and a high melting point can be used. These polymers are known per se as mini-copolymers. For these embodiments, propylene-ethylene copolymers with an ethylene content of 0.5 to 3.0 wt.%, in particular 0.8 to 2.5 wt.%, preferably 1.0 to <2 wt.%, are especially preferred. Their melting point is preferably in the range of 150 to 155°C and the enthalpy of melting preferably in the range of 90 to 100 J / g. The melt flow rate is generally 3 to 15 g / 10 min, preferably 3 to 9 g / 10 min (230°C, 21.6 N DIN 53 735).

[0061] To improve metal adhesion, the surface of the second cover layer II is generally subjected to a surface tension increase process using corona, flame, or plasma, as is known per se. Typically, the surface tension of the treated, unmetallized cover layer II is then in the range of 35 to 45 mN / m. Alternatively or additionally, the surface of cover layer II can be subjected to plasma treatment immediately before metallization to further improve the barrier properties of the metallized film and the metal adhesion.

[0062] In addition to this main component, the second coating layer (II) may contain common additives such as antiblocking agents, stabilizers, and / or neutralizing agents in effective amounts. With regard to metallization, additives that impair metallizability should not be present in coating layer II. This applies, for example, to migrating lubricants or antistatic agents. Second intermediate shift II

[0063] In a further embodiment according to the invention, the film has a second intermediate layer II, which is placed between the metallizable, second cover layer II and the base layer.

[0064] This second intermediate layer II can, in principle, be composed of the polymers described for the second top layer II, with the aforementioned propylene homopolymers or the described mini-copolymers being preferred. In general, the second intermediate layer II contains at least 80 wt.%, preferably 95 to 100 wt.%, and in particular 98 to <100 wt.% propylene polymers, the composition of the second top layer II and the second intermediate layer II generally not being identical.

[0065] The embodiments with a combination of a second intermediate layer II and a second top layer II are advantageous with regard to the possible different additives used in the individual layers. For example, it is possible to add antiblocking agents only to the top layer II and to keep the intermediate layer II free of other additives. In general, however, both layers will contain stabilizers and neutralizing agents. In particular, the second intermediate layer II also contains essentially no vacuole-containing fillers. TiO₂ can be added without significant technical disadvantages, whereby the amount should be less than 10 wt%, based on the intermediate layer II, to ensure a smooth, metallizable surface.

[0066] The overall thickness of the film can vary within wide limits; preferred embodiments have a total thickness of 10 to 150 µm, preferably 12 to 100 µm, and particularly 15 to 50 µm. For the purposes of the present invention, the base layer is the layer that constitutes more than 50% of the total thickness of the film. Its thickness is the difference between the total thickness and the thickness of the applied top and intermediate layers.

[0067] The film according to the invention generally comprises at least four layers and always includes as essential layers the base layer (BS) and a first sealable top layer I (DSI), a first intermediate layer I (ZWSI), and a second metallizable top layer II (DSII), according to a structure DSI / ZWSI / BS / DSII. Optionally, the film comprises a second intermediate layer II ZWSII, according to a structure DSI / ZWSI / BS / ZWSII / DSII. Depending on the application, the film may also comprise further layers.

[0068] The thickness of the first sealable top layer I is generally 0.5 to 5µm, preferably 0.5 to 3µm, in particular 0.8 to 2.5µm.

[0069] The thickness of the first intermediate layer I is 1.0 to 12µm, preferably 1.5 to 10µm, particularly 2.0 to 7.0µm.

[0070] The thickness of the second metallizable cover layer II is generally 0.5 to 5µm, preferably 0.5 to 3µm, in particular 0.8 to 2.5µm.

[0071] The thickness of the second intermediate layer II is generally 0.5 to 10µm, preferably 0.8 to 8µm, and particularly 1.0 to 5.0 µm.

[0072] To further improve certain properties of the polypropylene film according to the invention, the base layer, intermediate layers, and / or top layer(s) can contain additives in an effective amount, preferably antistatic agents, antiblocking agents, lubricants, stabilizers, and / or neutralizing agents that are compatible with the polymers of the layers, with the exception of the generally incompatible antiblocking agents. All quantities specified below in weight percent (wt%) refer to the respective layer to which the additive may be added.

[0073] In general, all layers of the film preferably contain neutralizing agents and stabilizers in effective amounts.

[0074] The usual stabilizing compounds for ethylene, propylene, and other olefin polymers can be used as stabilizers. Their addition amount is between 0.05 and 2 wt%. Phenolic stabilizers, alkali / alkaline earth starates, and / or alkali / alkaline earth carbonates are particularly suitable. Phenolic stabilizers are preferred in an amount of 0.1 to 0.6 wt%, especially 0.15 to 0.3 wt%, and with a molar mass of more than 500 g / mol. Pentaerythrityl tetrakis-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate or 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene are particularly advantageous.

[0075] Neutralizing agents are preferably calcium stearate and / or calcium carbonate and / or synthetic dihydrotalcite (SHYT) with a mean particle size of no more than 0.7 µm, an absolute particle size of less than 10 µm, and a specific surface area of ​​at least 40 m² / g. Generally, neutralizing agents are used in amounts of 50 to 1000 ppm, based on the coating thickness.

[0076] Antiblocking agents are added to the top layer I to be metallized and / or the sealable top layer II, with embodiments containing antiblocking agents in both top layers being preferred. Suitable antiblocking agents are inorganic additives such as silicon dioxide, calcium carbonate, magnesium silicate, aluminum silicate, calcium phosphate, and the like, and / or incompatible organic polymers such as polyamides, polyesters, polycarbonates, and the like, or cross-linked polymers such as cross-linked polymethyl methacrylate or cross-linked silicone oils. Polymethyl methacrylate, silicon dioxide, and calcium carbonate are preferred. The average particle size is between 1 and 6 µm, particularly 2 and 5 µm. The effective amount of antiblocking agent is in the range of 0.1 to 5 wt.%, preferably 0.5 to 3 wt.%, and particularly 0.8 to 2 wt.%.

[0077] Lubricants are preferably added to the base layer, the first intermediate layer I, and / or the first top layer I. Lubricants include higher aliphatic amides, higher aliphatic acid esters and metal soaps, as well as polydimethylsiloxanes. The effective amount of lubricant is in the range of 0.01 to 3 wt.%, preferably 0.02 to 1 wt.%, based on the respective top layer. The addition of 0.01 to 0.3 wt.% aliphatic amides, such as erucamide, or 0.02 to 0.5 wt.% polydimethylsiloxanes, especially polydimethylsiloxanes with a viscosity of 5,000 to 1,000,000 mm² / s, is particularly suitable.

[0078] Antistatic agents are optionally added to the base layer, the first intermediate layer I, and / or the first top layer I. Preferred antistatic agents are glycerol monostearate, alkali alkanesulfonates, polyether-modified, i.e., ethoxylated and / or propoxylated polydiorganosiloxanes (polydialkylsiloxanes, polyalkylphenylsiloxanes, and the like), and / or essentially straight-chain and saturated aliphatic tertiary amines with an aliphatic residue of 10 to 20 carbon atoms substituted with alpha-hydroxy (C1-C4) alkyl groups, wherein N,N-bis-(2-hydroxyethyl) alkylamines with 10 to 20 carbon atoms, preferably 12 to 18 carbon atoms, in the alkyl residue are particularly suitable. The effective amount of antistatic agent is in the range of 0.05 to 0.5 wt.%.

[0079] All the above figures in wt.% refer to the weight of the respective layer in which the additive is contained.

[0080] The invention further relates to a method for producing the multilayer film according to the invention using the coextrusion process known per se, wherein the stenter process is particularly preferred.

[0081] In this process, the melts corresponding to the individual layers of the film are co-extruded through a flat die, the resulting film is drawn off on one or more rollers for consolidation, the film is then stretched (oriented), the stretched film is thermofixed and, if necessary, plasma-, corona- or flame-treated on the surface layer intended for treatment.

[0082] Specifically, as is typical in extrusion processes, the polymer or polymer mixture of the individual layers is compressed and liquefied in an extruder, whereby any additives may already be contained in the polymer or polymer mixture. Alternatively, these additives can also be incorporated via a masterbatch.

[0083] The melts are then pressed together and simultaneously through a flat die (wide slot die), and the pressed multilayer film is pulled off on one or more take-off rollers at a temperature of 5 to 100 °C, preferably 10 to 50 °C, where it cools and solidifies.

[0084] The resulting film is then stretched lengthwise and crosswise to the extrusion direction, which orients the molecular chains. Longitudinal stretching is preferably carried out at a temperature of 80 to 150 °C, expediently using two rollers rotating at different speeds according to the desired stretch ratio. Crosswise stretching is preferably carried out at a temperature of 120 to 170 °C using a suitable clamping frame. The longitudinal stretch ratios are in the range of 4 to 8, preferably 4.5 to 6. The crosswise stretch ratios are in the range of 5 to 10, preferably 7 to 9.

[0085] The stretching of the film is followed by heat setting (heat treatment), during which the film is held at a temperature of 100 to 160 °C for approximately 0.1 to 10 seconds. The film is then wound up using a conventional winding device. These processes are known in the art and are frequently described in film patents.

[0086] Preferably, after biaxial stretching, the surface of the cover layer II is / are treated with plasma, corona, or flame using one of the known methods. The treatment intensity is generally in the range of 35 to 50 mN / m, preferably 37 to 45 mN / m, and particularly 39 to 40 mN / m.

[0087] For the alternative corona treatment, the film is passed between two conductor elements serving as electrodes. A high voltage, usually alternating current (approximately 10,000 V and 10,000 Hz), is applied between the electrodes to induce spray or corona discharges. These discharges ionize the air above the film surface, causing it to react with the molecules of the film surface and resulting in the formation of polar inclusions within the essentially nonpolar polymer matrix. Treatment intensities are within the usual range, with 37 to 45 mN / m being preferred.

[0088] The coextruded multilayer film is provided with a metal layer, preferably of aluminum, on the outer surface of the second cover layer II using methods known per se. This metallization takes place in a vacuum chamber in which, for example, aluminum is vaporized and deposited on the film surface. In a preferred embodiment, the surface of cover layer II to be metallized is subjected to plasma treatment immediately before metallization. The thickness of the metal layer generally correlates with the optical density of the metallized film; that is, the thicker the metal layer, the higher the optical density of the metallized film. In general, the optical density of the metallized film according to the invention should be at least 2, and in particular 2.5 to 4.The metallized film can be used directly for the production of pouch packaging, for example for packaging potato flakes, coffee powder, etc.

[0089] The film according to the invention is characterized by excellent barrier properties after metallization. The water vapor permeability of the metallized film according to the invention is generally < 0.5 g / m² / day at 38°C and 90% relative humidity, preferably in the range of 0.05 to 0.3 g / m² / day. The oxygen permeability is preferably < 50 cm³ / m² / day bar, more preferably 5 to 30 cm³ / m² / day bar, and particularly 5 to 25 cm³ / m² / day bar.

[0090] In a preferred embodiment, the metallized film according to the invention is laminated with a further, preferably biaxially oriented, film, wherein the lamination is carried out against the metallized side of the metallized film according to the invention. The further film is preferably printed so that the pouch packaging has an attractive appearance. In principle, polyester films or boPP films (transparent or opaque boPP films) can be used for the further film. Lamination of the metallized film against paper is also possible. Preferably, the metallized film according to the invention is laminated against an opaque multilayer boPP film, which has a vacuole-containing base layer and a printable top layer.Suitable examples include four-layer films with a top layer on one surface of the base layer, suitable for lamination against the metal layer, and a combination of a homopolymer intermediate layer, optionally modified with TiO₂, and a printable top layer applied to the opposite surface of the base layer. These laminates are characterized by a particularly attractive surface gloss of the finished printed laminate and can be advantageously used for the production of pouch packaging.

[0091] The film according to the invention is characterized by exceptional sealing properties, in particular by the unusually high seal strengths achieved. When sealing the first cover layer I against itself at 130°C, 10 N / cm² and 0.5 s, the maximum seal strength is at least 6 N / 15 mm, preferably 6.5 to 10 N / 15 mm.

[0092] Pouch packaging comprising the film according to the invention exhibits excellent burst pressure. If the pouch packaging can be manufactured without significant contamination of the seal, it exhibits a burst pressure in the range of 300 to 1000 mbar, preferably 350 to 900 mbar, and particularly 400 to 800 mbar. Even if the seal is contaminated with dust, the pouch packaging still has a burst pressure of 150 to 400 mbar, preferably 200 to 350 mbar, and particularly 250 to 350 mbar. The average pressure drop of the pouch packaging is preferably less than 1 mbar for uncontaminated seals and 3 to 15 mbar for pouches with a contaminated seal.

[0093] The following measurement methods were used to characterize the raw materials, films, and bags: Melting flux index

[0094] The melt flow index was measured according to DIN EN ISO 1133-1. Water vapor and oxygen permeability

[0095] Water vapor permeability is determined according to DIN 53 122 Part 2. The oxygen barrier effect is determined according to draft DIN 53 380 Part 3 at a relative humidity of 50%. Determination of ethylene content

[0096] The ethylene content of the copolymers was determined by 13C NMR spectroscopy. Measurements were performed using a Bruker Avance 360 ​​nuclear magnetic resonance spectrometer. The copolymer to be characterized was dissolved in tetrachloroethane to obtain a 10% mixture. Octamethyltetrasiloxane (OTMS) was added as a reference standard. The nuclear magnetic resonance spectrum was measured at 120°C. The spectra were evaluated as described in J.C. Randall, Polymer Sequence Distribution (Academic Press, New York, 1977). Melting point, melting range, enthalpy of fusion, softening point ISO 11357-3

[0097] The aforementioned parameters of the polyolefins are determined from a DSC curve of the respective polymer or polymer blend. In DSC measurement, a defined amount of heat per unit time is supplied to the polymer or polymer blend at a specific heating rate, and the heat flow is plotted against the temperature. This means the change in enthalpy is measured as the deviation of the heat flow from the baseline. The baseline (BL) is the (linear) portion or beginning of the curve where no phase transitions occur and therefore no slope is observed. Here, there is a linear relationship between the amount of heat supplied and the temperature. In the region where melting occurs, the heat flow increases by the necessary melting energy, and the DSC curve rises and deviates from the baseline.In the area where most of the crystallites melt, the curve passes through a maximum and, after all the crystallites have melted, falls back to the baseline.

[0098] The melting point, as defined in the present invention, is the highest maximum of the second heating curve of the DSC measurement (point C or Y in the curve). Figure I ). The start of the second heating curve, according to the present invention, is the temperature at which the second heating curve deviates from the baseline and the rising curve begins (point A or X in ). Figure 1 Accordingly, the end is the temperature at which the curve has fallen back to the baseline (point D or Z in the graph). Fig 1 The softening point is the point at which the second heating curve reaches a first local maximum (point B in Figure 1 ) reached. This softening point does not occur in non-soft propylene homopolymers. The melting range is the distance between points B and C in the second heating curve.

[0099] The DSC measurement is performed with a 2 to 6 mg sample in a differential calorimeter with a heating and cooling rate of 10 K / 1 min in the range of 20 to 200 °C. First, an initial DSC curve is recorded, and then the sample is cooled. Subsequently, a second heating curve is recorded under the same conditions and evaluated as described above to determine the melting range, melting point, and softening point. The enthalpy is calculated from the cooling curve ( Figure 2 ) certainly. Metal adhesion

[0100] The surface-treated films were metallized 14 days after production (short-term assessment) and 6 months after production (long-term assessment). Adhesion to the metal was assessed using an adhesive tape test. If no paint or metal could be removed with the tape, the adhesion was rated as very good; if significant removal of paint or metal occurred, the adhesion was rated as poor. Determination of the seal opening temperature

[0101] The Brugger HSG / ET sealing device produces sealed samples (seal seam 20 mm x 100 mm) by sealing the top layer I of the film against itself at different temperatures using two heated sealing jaws with a sealing pressure of < 10 N / cm² and a sealing duration of 0.5 s. Test strips 15 mm wide are cut from the sealed samples. The T-seal strength, i.e., the force required to separate the test strips, is determined using a tensile testing machine at a pull-off speed of 200 mm / min, with the seal plane forming a right angle to the pull direction. The sealing start-up temperature (SIT) is the temperature at which a seal strength of at least 0.5 N / 15 mm is achieved. Maximum seal strength

[0102] The Brugger HSG / ET sealing device produces sealed samples (seal seam 20 mm x 100 mm) by sealing the top layer I of the film against itself using two heated sealing jaws at a temperature of 130°C and a sealing pressure of < 10 N / cm² for a sealing time of 0.5 s. Test strips 15 mm wide are cut from the sealed samples. The T-seal strength, i.e., the maximum force required to separate the test strips, is determined using a tensile testing machine at a pull-off speed of 200 mm / min, with the seal plane forming a right angle to the pull direction. The maximum seal strength is the maximum of the curve recorded during this test. Light transmission

[0103] Light transmission is measured in accordance with ASTM D 1003. density

[0104] The density is determined according to DIN EN ISO 1183-1, method A. Surface tension

[0105] The surface tension was determined using the inkjet method according to DIN ISO 8296. Inspection of the bag packaging Manufacturing the four-sided bag without contamination

[0106] Two sheets of foil, each measuring 160 x 150 mm, are cut out and placed together with their sealing side (top layer I) facing each other. All four edges are sealed using a Brugger heat sealer at a temperature of 140°C, a pressure of 52 N / cm², and a contact time of 2 seconds. Production of the four-sided bag with dust contamination in the sealing area

[0107] Two sheets of foil, each measuring 160 x 150 mm, are cut out and sprinkled with standard wheat flour on the sealing side (top layer I). Excess flour is blown off using compressed air. The two floured sealing sides (top layer I) are then placed together. All four edges are sealed using a Brugger heat sealer at a temperature of 140°C, a pressure of 52 N / cm², and a contact time of 2 seconds. Burst and leak tests

[0108] The burst and leak tests of the bags are carried out using the methods described below. For this purpose, each bag to be tested is pierced in the center with the test head of the Skye tester (for example, the Skye 2500SL from Mocon). An expansion limiter, set to a height of 20 mm, prevents the bag from inflating excessively and ballooning. Burst test

[0109] Each bag to be tested is inflated on the Skye tester with a pressure increase of 10 mbar / s until it bursts. The highest internal pressure a bag reaches is recorded as the burst pressure (maximum overpressure). This test is performed on at least 10 bags. Leakage test

[0110] The bag is pre-inflated to a pressure of approximately 50-60% of the burst pressure determined in the previous burst test. Once this pre-inflated pressure is reached, the pressure loss is measured and recorded over a period of 30 seconds. This test is also performed on at least 10 bags. In some comparative examples, the bags fail during this leak test. This means that no overpressure remains before the 30 seconds have elapsed, and the Skye Tester automatically shuts off.

[0111] The invention will now be explained by the following examples. Example 1:

[0112] A five-layer pre-film was extruded from a slot die at an extrusion temperature of 240 to 270°C using the co-extrusion process. This pre-film was first laid off and cooled on a cooling roller. It was then oriented longitudinally and transversely and finally fixed in place. The surface of the second top layer (II) was pre-treated with corona to increase surface tension. The five-layer film had the following structure: first top layer (I) / first intermediate layer (I) / base layer / second intermediate layer (II) / second top layer (II). The individual layers of the film had the following composition: First top layer I (1.5 µm):

[0113] Approximately 30 wt% propylene-butylene copolymer with a butylene content of 25 wt% (based on the copolymer) and a melting point of 75 °C; and a melt flow index of 7.0 g / 10 min at 230 °C and a load of 2.16 kg; approximately 60 wt% ethylene propylene-butylene terpolymer with a melting point of 135 °C and a melt flow index of 5.5 g / 10 min at 230 °C and a load of 2.16 kg; 0.13 wt% polymethyl methacrylate (PMMA) First intermediate layer 1 (4µm):

[0114] Approximately 50 wt% propylene homopolymer (PP) with an n-heptane soluble content of approximately 4 wt% (based on 100% PP) and a melting point of 163 °C; and a melt flow index of 3.3 g / 10 min at 230 °C and a load of 2.16 kg; and approximately 50 wt% ethylene propylene butylene terpolymer with a melting point of 135 °C and a softening point of 103 °C and a melt flow index of 5.5 g / 10 min at 230 °C and a load of 2.16 kg. Base layer:

[0115] Approximately 100 wt% propylene homopolymer (PP) with an n-heptane soluble content of about 4 wt% (based on 100% PP) and a melting point of 163 °C; and a melt flow index of 3.3 g / 10 min at 230 °C and a load of 2.16 kg Second top layer II (1.0 µm):

[0116] 99.7 wt% propylene-butylene copolymer with a butylene content of 5 wt% (based on the copolymer) and a melting point of 140 °C; and a melt flow index of 5.5 g / 10 min at 230 °C and 2.16 kg load; 0.3 wt% antiblocking agent with a mean particle diameter of approx. 4 µm (Sylobloc 45)

[0117] All layers of the film also contained stabilizer and neutralizing agent in usual quantities.

[0118] Specifically, the following conditions and temperatures were chosen for the production of the film: Extrusion: Extrusion temperature approx. 250 -270°C Cooling roller: Temperature 30°C, Longitudinal extent: T = 125 °C Longitudinal extension around the Factor 5 Cross-section: T = 165 °C Transverse extension around the Factor 9 Fixation T = 143°C

[0119] The film was surface-treated on the surface of the second cover layer II using corona treatment and exhibited a surface tension of 40 mN / m on this side. The film had a thickness of 30 µm and a transparent appearance. Example 2

[0120] A film was produced according to Example 1. In contrast to Example 1, a second interlayer with the following composition was inserted: Second interlayer II (1.5 µm): approximately 100 wt.% propylene homopolymer (PP) with an n-heptane soluble content of approximately 4 wt.% (based on 100% PP) and a melting point of 163 °C; and a melt flow index of 3.3 g / 10 min at 230 °C and a load of 2.16 kg. Example 3

[0121] A film was produced according to Example 1. In contrast to Example 1, the composition of the first intermediate layer I was changed. The first intermediate layer I now had the following composition: First intermediate layer I (4 µm): Approximately 50 wt% propylene homopolymer (PP) with an n-heptane soluble content of about 4 wt% (based on 100% PP) and a melting point of 163 °C; and a melt flow index of 3.3 g / 10 min at 230 °C and a load of 2.16 kg; and approximately 50 wt% propylene-butylene copolymer with a butylene content of 25 wt% (based on the copolymer) and a melting point of 75 °C; and a softening point of a melt flow index of 7.0 g / 10 min at 230 °C and a load of 2.16 kg. Example 4

[0122] A film was produced according to Example 2. In contrast to Example 2, TiO₂ pigments were added to the base layer. The base layer now had the following composition: Approximately 97 wt% propylene homopolymer (PP) with an n-heptane soluble content of approximately 4 wt% (based on 100% PP) and a melting point of 163 °C; and a melt flow index of 3.3 g / 10 min at 230 °C and 2.16 kg load; 3.0 wt% TiO2 via masterbatch P87286, supplier Schulman GmbH, Hüttenstraße 211, D-54578 Kerpen. Example 5

[0123] A film was produced according to Example 1. In contrast to Example 1, the composition of the intermediate layer I was changed as follows: Approximately 70 wt% propylene homopolymer (PP) with an n-heptane soluble content of approximately 4 wt% (based on 100% PP) and a melting point of 163 °C; and a melt flow index of 3.3 g / 10 min at 230 °C and a load of 2.16 kg (DIN 53 735) and approximately 30 wt% polyethylene (MDPE; density 0.924 g / cm³) with a melting point of 125 °C and a softening point of 114 °C and a melt flow index of 0.15 g / 10 min at 190 °C and a load of 2.16 kg Comparative example 1

[0124] A film was produced according to Example 1. In contrast to Example 1, CaCO3 and TiO2 were added to the base layer. The base layer now had the following composition: approx. 93% by weight Propylene homopolymer (PP) with an n-heptane soluble content of approximately 4 wt% (based on 100% PP) and a melting point of 163 °C; and a melt flow index of 3.3 g / 10 min at 230 °C and a load of 2.16 kg 4.0 wt.% CaCO3 of type ®< Omyalite 90T, supplier of masterbatches: Multibase, ZI du Giers, F-38380 Saint-Laurent-du-Pont, France; 3.0 wt.% TiO 2 via masterbatch P87286, supplier Schulman GmbH, Hüttenstraße 211, D-54578 Kerpen.

[0125] The film now had a white opaque appearance and, due to vacuole formation in the base layer, a reduced density of 0.75 g / cm 3< . Comparative example 2

[0126] A film was produced according to Example 1. In contrast to Example 1, the soft first intermediate layer I was omitted, resulting in a film with only three layers: a base layer, a first layer, and a second top layer. Comparative example 3

[0127] A film was produced according to VB2. In contrast to VB1, the following mixture was used for the top layer I: Approximately 50 wt.% propylene-butylene copolymer with a butylene content of 25 wt.% (based on the copolymer) and a melting point of 75 °C; and a melt flow index of 7.0 g / 10 min at 230 °C and a load of 2.16 kg; approximately 50 wt.% ethylene-propylene-butylene terpolymer with a melting point of 135 °C and a melt flow index of 5.5 g / 10 min at 230 °C and a load of 2.16 kg; 0.13 wt.% polymethyl methacrylate (PMMA) Comparative example 4

[0128] A film was produced according to Example 1. In contrast to Example 1, CaCO3 and TiO2 were added to the intermediate layer II. The intermediate layer now had the following composition: approximately 93 wt.% propylene homopolymer (PP) with an n-heptane soluble content of about 4 wt.% (based on 100% PP) and a melting point of 163 °C; and a melt flow index of 3.3 g / 10 min at 230 °C and a load of 2.16 kg (DIN 53 735). 4.0 wt.% CaCO3 of type ®< Omyalite 90T, supplier of masterbatches: Multibase, ZI du Giers, F-38380 Saint-Laurent-du-Pont, France; 3.0 wt.% TiO 2 via masterbatch P87286, supplier Schulman GmbH, Hüttenstraße 211, D-54578 Kerpen.

[0129] The film now had a white opaque appearance and, due to vacuole formation in the intermediate layer, a reduced density of 0.90 g / cm 3< .

[0130] All films, according to the examples and comparative examples, were coated with an aluminum layer on the surface of the first cover layer I in a vacuum metallizing system. To improve metal adhesion, the surface was subjected to plasma treatment immediately before coating.

[0131] Four-sided pouches were produced from the metallized films as described in the test methods "Testing of Pouch Packaging". The properties of the metallized films according to the examples and comparative examples, and the properties of the pouches produced therefrom, are summarized in Table 1. It is shown that the films according to the invention, according to Examples 1, 2, and 3, exhibit excellent barrier properties against water vapor and oxygen, while simultaneously maintaining good sealing properties despite contamination when used as pouches for powdered products. The pouches show significantly improved burst resistance and reduced pressure loss. Example Thickness µm Density of the film [g / cm³< ] Max. seal strength ** at 130 °C, 10 N / cm² < , 0.5 sec. [N / 15 mm] Burst pressure (max. overpressure) [mbar] Average pressure loss [mbar] Burst pressure (max. overpressure) Contaminated seal area [mbar] Average pressure drop [mbar] Contaminated seal area WDD 38°C 90% rel. Humidity *** [g / m 2 < *day] OTR 23°C, 50% rel. Humidity *** [cm 3< / m 2< *Day g*bar] Example 1 30 0,91 7,9 561 - 631 0,8 187 - 296 10,6 0,125 17,8 Example 2 30 0,91 7,8 572 - 617 0,5 200 - 291 9,8 0,140 21,4 Example 3 30 0,91 8,7 601 - 720 0,3 273 - 386 5,5 0,155 27,0 Example 4 30 0,92 7,6 533 - 611 0,9 177 - 285 13,2 0,173 30,1 Example 5 30 0,91 7,2 492 - 573 1,4 153 - 285 11,1 0,162 25,4 VB 1 30 0,75 2,9 112 - 264 4,0 82 - 154 23,7 **** 0,254 89,3 VB 2 30 0,91 5,0 214 - 243 1,7 108 - 151 51,1 ***** 0,168 34,2 VB 3 30 0,91 4,6 220 - 289 1,4 123 - 148 43,4 ****** 0,181 31,5 VB 4 30 0,90 2,7 131-211 2,1 98 - 139 44,1 ******* 0,225 40,4 ** Sealing of the non-metallized top layer I against itself *** after metallization of top layer II **** only 1 bag out of 10 passes the test ***** 6 bags out of 10 fail during the test ****** 4 bags out of 10 fail during the test ******* only 1 bag out of 10 passes the test

Claims

1. Biaxially oriented, multilayer polypropylene film comprising at least three layers consisting of • a base layer, and • a first intermediate layer I, and • a first heat-sealable top layer I applied onto said intermediate layer I, wherein • substantially all layers of the film are free of voids and the density of the film is at most 5% lower than the calculated density of the film, characterized in that a) the base layer contains at least 50 wt.%, based on the weight of the base layer, of polypropylene, wherein the polypropylene has a melting point of from 150 to 170°C and contains from 90 to 100 wt.% propylene units, and b) the thickness of the first intermediate layer I is from 1.0 to 12 µm, and c) the first intermediate layer I is a soft intermediate layer containing at least 40 wt.% of a soft polyolefin or a mixture of the soft polyolefin with a further polyolefin, wherein the soft polyolefin or the mixture exhibits, in a DSC measurement, a second heating curve which rises from 20 to 70°C (A), reaches a first local maximum at a temperature of >90°C, and then merges into the actual maximum of the heating curve (C), corresponding to the melting point Tm, and d) the thickness of the first heat-sealable top layer I is from 0.5 to 2.5 µm, and e) the first heat-sealable top layer I has a seal initiation temperature of <115°C, determined as described in the description, f) the film comprises, on the opposite side, a second top layer II, and the surface of the second top layer II is metallized.

2. Film according to claim 1, characterized in that the film is transparent and has a density in the range from 0.86 to 0.92 g / cm3.

3. Film according to claim 1 or 2, characterized in that the film contains pigments, preferably TiO2, and the density of the film is in the range from 0.91 to 0.95 g / cm3.

4. Film according to one of claims 1 to 3, characterized in that the second heating curve of the soft polymer or the mixture of the first intermediate layer exhibits, in a DSC measurement, a softening point (B), and the softening point (B) is in the range from 80 to 120°C.

5. Film according to one of claims 1 to 4, characterized in that the melting point (C) of the soft polymer or polymer mixture is in the range from 70 to ≤150°C.

6. Film according to one of claims 1 to 5, characterized in that the melting point (C) of the soft polymer or mixture is in the range from 70 to ≤150°C and is from 10 to 50°C higher than the softening point (B).

7. Film according to one of claims 1 to 6, characterized in that the melting point (C) of the soft polymer or mixture of intermediate layer I is from 15 to 60°C lower than the melting point (Y) of the polypropylene of the base layer.

8. Film according to one of claims 1 to 7, characterized in that the soft polymer of the intermediate layer is polyethylene, a propylene copolymer, a propylene terpolymer, an elastomer, a heterophasic polymer blend, and / or a propylene homopolymer having an isotacticity of <95%.

9. Film according to claim 8, characterized in that the surface of the first top layer I is not pretreated by corona, plasma, or flame treatment.

10. Film according to claim 9, characterized in that the surface to be metallized is plasma-treated immediately before metallization and the optical density of the metal layer is at least 2.5.

11. Use of a film according to one of claims 1 to 10 for producing a laminate with a further biaxially oriented polypropylene film, characterized in that the metallized film is laminated with the metallized side facing a second BOPP film.

12. Use according to claim 11, characterized in that the second BOPP film of the laminate comprises a void-containing base layer.

13. Use of a film according to one of claims 1 to 10 for producing a pouch package.

14. Use according to claim 11, 12, or 13, characterized in that the packaged product of the pouch package is in powder form.

15. Pouch package comprising a film according to one of claims 1 to 10, characterized in that the pouch package has a burst pressure of at least 200 mbar, preferably from 220 to 1000 mbar.

16. Pouch package comprising a film according to one of claims 1 to 10, characterized in that the pouch package has an average pressure loss of less than 15 mbar, wherein the pressure loss is measured over a period of 30 seconds.

17. Film according to one of claims 1 to 10, characterized in that the first heat-sealable top layer I is sealed to itself at a temperature of 130°C under a pressure of 10 N / cm2 for 0.5 s, and the resulting seal seam exhibits a maximum seal seam strength of more than 6 N / 15 mm, wherein, for determining the seal seam strength, the maximum force required for separating sealed samples from 15 mm wide test strips using a tensile testing machine at 200 mm / min is measured.