MXPA99008588A - Biaxially oriented polypropylene film, its use and procedure for its production - Google Patents

Abstract

The invention relates to a biaxially oriented polypropylene film having a good processing performance and, after it has been metallized, it is a very good barrier against oxygen, and is composed of at least one base layer, where the delta flat orientation p of the movie is greater than 0.01

Description

BIAXIALLY ORIENTED POLYPROPYLENE FILM, ITS USE AND PROCEDURE FOR ITS PRODUCTION DESCRIPTIVE MEMORY The invention relates to a biaxially oriented propylene film composed of at least one base layer. The film has a good processing performance and good optical properties and, after metallizing it or covering it with oxidic materials, it is a very good barrier against oxygen. The invention also relates to the use of the film and a process for producing it. Biaxially oriented polypropylene films are used in packaging and industrial sectors, especially where there is a need for their useful properties, ie good optical properties, high mechanical resistance, good barrier action, in particular with respect to gases, good dimensional stability at warm it up and an excellent ability to lay flat. In packaging applications for food and beverages, a high barrier effectiveness is usually required against gases, water vapor and flavors (having the same importance as low permeability). A known method for producing packages of this type consists of the aluminum mentalization of the high vacuum of the plastic films used for this purpose. Other methods consist of coating the films with oxidic materials (for example SiOx or AlxOy) or with water-soluble glass. In essence, the coatings used are transparent. The effectiveness of the barrier against the mentioned substances depends essentially on the type of polymers in the film and the quality of the barrier layers applied. In this way, a very high barrier effectiveness against gases, such as oxygen and flavors, is achieved in the biaxially oriented polyester films. A highly effective barrier against water vapor is made even better with metallized biaxially oriented polypropylene films. There are other applications where both a very effective water vapor barrier as well as an acceptable oxygen barrier are desired. In the prior art, there is not sufficient background of the detailed basis for the barrier effect in the oxidically coated or metallized polypropylene films as well as the way to improve them. The clearly important variables are the surface of the substrate, the type of substrate polymer and its morphology. It is generally assumed that soft substrate surfaces result in better barrier properties. The thesis of H. Utz (Technische Universitat München, 1995: "Barriereeigenschaften aluminiumbedampfter Kunststoffolien" [barrier properties of metallized plastic films with aluminum]) provides detailed research results on the influence of the substrate surface on barrier properties in various plastic films. Thus, an object of the present invention is to provide a biaxially oriented co-extruded polypropylene film that also has good optical properties. After metallizing or covering it with oxidic materials, when compared to the prior art, the film should also be a better barrier against oxygen as well as having a simple procedure in addition to having a simple production. The gloss, at least on the surface must be covered with steam, must be greater than 120, and the turbidity of the film must be less than 3.0. In the present invention, low oxygen permeability means that less than 30 cm3 of oxygen per square meter per day must diffuse through the metallized film when exposed to air at a pressure of 1 bar. In terms of other properties, the film should at least be as good as packaging films of its kind. It must, for example, have a simple and profitable production, and a simple procedure (that is, not en bloc, for example) in conventional machinery. The objective is achieved by a biaxially oriented polypropylene film (OPP film) having one or more layers and with at least one base layer B with at least 80% by weight of thermoplastic polypropylene in its composition, and the film has a flat delta p orientation that is greater than 0.0138. In order to achieve the desired oxygen permeability of the metallized films according to the invention, the delta p flat orientation of the film of the present invention must be greater than the previous value. This value is given by delta p = 0.0138. Therefore, to achieve good oxygen barriers in OPP metallized films, a high delta p flat orientation is required. If the plane orientation delta p is less than the value established above, the barrier is deficient, with respect to the sense of the present invention. If the plane delta p orientation of the film is greater than the value established above, the barrier is good with respect to the direction defined in the present invention. In a preferred embodiment of the film of the present invention, the flat orientation delta p of this new film is greater than 0.0140, and in a particularly highly preferred embodiment is greater than 0.0143. In the preferred and particularly preferred embodiments, the novel film is, in the metallized form, a very good oxygen barrier. It has also proven to be useful in achieving a good refractive index (ND) barrier in the thickness direction of the film that is less than the previous value. This value is? ND = 1 -495.

According to the invention, the film has at least one layer structure. It therefore comprises a layer which is a base layer B and comprises the pigments necessary for processing the film. However, the film can also have a two-layer structure. It therefore comprises layers which are a base layer B and an outer layer A. In a preferred embodiment of the invention the film has a three-layer structure and has, on the one hand of layer B (= base layer) layer A , and on the other side of layer B, another layer C made of polypropylene. In this case, at least one of the two outer layers, but preferably both outer layers, consist of pigments required for the production and processing of the film. In principle, a variety of materials for various layers can be used as starting material. However, it is preferred for the. production of individual layers that are based on polypropylene starting materials. The base layer of the new film having more than one layer comprises polyolefins, preferably propylene polymers, and other additives, if desired, in effective amounts in each case. The base layer generally comprises at least 50% by weight of the propylene polymers, preferably from 75 to 100% by weight, in particular from 90 to 100% by weight, based in each case on the base layer. The propylene polymer generally contains from 90 to 100% by weight of propylene units, preferably from 95 to 100%, in particular from 98 to 100% by weight, and generally has a melting point of 120 ° C or higher, preferably from 150 to 170 ° C, and generally has a melt flow index of 0.05 to 8 g / 10 min, preferably 2 to g / 10 min, at 230 ° C and with a force of 21.6N (DIN 53 735). The preferred propylene polymers for the base layer are isotactic propylene homopolymers with an atactic ratio of 15% by weight or less, ethylene-propylene copolymers with an ethylene content of 10% by weight or less, copolymers of propylene with a C4-C8 olefins with an a-olefin content of 10% by weight or less, and terpolymers of propylene, ethylene and butylene with an ethylene content of 10% by weight or less, and with a butylene content of 15% by weight or less, and with a butylene content of 15% by weight or less, and particular preference is given to the isotactic propylene homopolymer. The percentages by weight given refer to the respective polymer. A mixture of homo- and / or copolymers and / or terpolymers and other propylene polyolefins mentioned above, in particular made of monomers having from 2 to 6 carbon atoms, are also suitable if the mixture comprises at least 50% by weight of propylene polymer, in particular at least 75% by weight. Other polyolefins which are suitable in the polymer mixture are polyethylenes and in particular HDPE, LDPE and LLDPE if the proportion of these polyolefins, based on the polymer mixture, does not exceed 15% by weight in each case.

In a preferred embodiment of the novel film the propylene polymer of the base layer is peroxidically degraded. This can give yet another improvement in the barrier properties of the metallized films. A measure of the degree of degradation of the polymer is the degradation factor A, which gives the relative change in the melt flow index (MFI) (in accordance with DIN 53 735) of the polypropylene, based on the starting polymer. A = MFH / MFI2 MFI1 = melt flow rate of the propylene polymer before adding the organic peroxide. MFI2 = melt flow index of the peroxidically degraded propylene polymer. The degradation factor A the propylene polymer used generally is in the range of 3 to 15, preferably 6 to 10. The particularly preferred organic peroxides are the dialkyl peroxides, where it is understood that the alkyl radicals are the lower alkyl radicals straight chain or branched saturated usually having up to 6 carbon atoms. Particular preference is given to 2, 5-dimethyl-2, 5-di (tert-butylperoxy) hexane and di-tert-butyl peroxide. The base layer can generally contain effective amounts in each case of stabilizers and neutralizing agents, and also, if desired, lubricants, antistatics and / or hydrocarbon resins. Hydrocarbon resins in particular can be used to improve the barrier properties of metallized films. Preferred resins in particular are hydrocarbon resins. The hydrocarbon resins can be hydrogenated to some degree or completely. The possible resins in principles are synthetic resins or resins from natural sources. It has proven to be particularly advantageous to use resins with a softening point higher than 80 ° C (measured in accordance with DIN 1995-U4 or ASTM E-28). Preferred are those with a softening point between 100 and 180 ° C, in particular between 120 and 160 ° C. The resin is preferably incorporated into the film in the form of a masterbatch, which is added to the extruder (for example single screw or cascade extruder). Some examples of master batches are those comprising from 30 to 70% by weight, preferably 50% by weight, of a propylene homopolymer and between 70 and 30% by weight, preferably 50% by weight, of hydrocarbon resin. The percentage weight data are based on the total weight of propylene polymer and hydrocarbon resin. Among various resins, preference is given to hydrocarbon resins and specifically to petroleum resins, styrene resins, cyclopentadiene resins and terpene resins. These resins are described in Ullmanns Enzykiopádie der techn. Chemie [Ullman's Encyclopedia of Industrial Chemistry] Fourth Edition, Volume 12, pages 525-555. Petroleum resins are those hydrocarbon resins that are prepared by polymerizing petroleum materials from decomposition to depth in the presence of a catalyst. These petroleum materials usually consist of a mixture of resin-forming substances, for example styrene, methylstyrene, vinyltoluene, indene, methylindene, butadiene, isoprene, piperylene and pentylene. Styrene resins are styrene homopolymers or copolymers of styrene with other monomers, for example methylstyrene, vinyltoluene and butadiene. The cyclopentadiene resins are cyclopentadiene homopolymers or cyclopentadiene copolymers obtained from coal-tar distillates and fractionated petroleum gas. These resins are prepared by keeping the materials, which consist of cyclopentadiene, at high temperature for a long period. Depending on the reaction temperature, dimers, trimers or oligomers can be obtained. Terpene resins are polymers of terpenes, that is hydrocarbons of the formula C10H16 present in almost all essential oils and in resins containing vegetable oil, or are terpene resins modified from phenol. Specific examples of terpenes that may be mentioned are pinene, α-pinene, dipentene, limonene, myrcene, camphene and the like. The hydrocarbon resins can also be those known as modified hydrocarbon resins. The modification is generally carried out by the reaction of the starting materials prior to the polymerization, by the introduction of specific monomers or the reaction of the polymerized product, in particular, for hydrogenation or partial hydrogenation reactions.

Other hydrocarbon resins used are styrene homopolymers, styrene copolymers, cyclopentadiene homopolymers, cyclopentadiene copolymers and / or terpene polymers with a softening point higher than 100 ° C in each case. In the case of unsaturated polymers, hydrogenated products are preferred. Particular preference is given to the use of cyclopentadiene polymers with a softening point of 140 ° C and above in the base layer. If its structure does not have more than one layer, the film consists of at least one external layer A, which has been applied to the base layer B mentioned above. For this outer layer in principle, use may be made of the polymers that were used for the base layer. In addition to these other materials may also be present in the outer layer, in which case, the outer layer is then preferably composed of a mixture of polymers, a copolymer or a homopolymer. The same applies to the outer layer C of a film that has three or more layers. The outer layer A (and layer C, if present) is (are) generally composed of α-olefins having from 2 to 10 carbon atoms. The outer layer generally consists of a propylene homopolymer or a copolymer of ethylene and propylene, or ethylene and butylene, or propylene and butylene, or ethylene and another α-olefin having from 5 to 10 carbon atoms, or propylene and other oolefin having from 5 to 10 carbon atoms, or a terpolymer of ethylene and propylene and butylene, or ethylene and propylene and another a-oleofin having from 5 to 10 carbon atoms, or a mixture made of two or more homogen -, co- and terpolymers mentioned or a combination made of two or more mentioned homo-, co- and terpolymers, if desired mixed with one or more of the aforementioned homo-, co- and terpolymers. The outer layer particularly preferably consists essentially of a propylene homopolymer or a copolymer of ethylene and propylene, or ethylene and 1-butylene, or propylene and 1-butylene, or a terpolymer of ethylene and propylene and 1-butylene, or a mixture made of two or more of the preferred homo-, co- and terpolymers particularly mentioned or a combination made of two or more of the above-mentioned particularly preferred homo-, co- and terpolymers, if desired mixed with one or more of the homo- , co- and terpolymers mentioned, and preference is given in particular to propylene homopolymers or either ethylene-propylene copolymers with an ethylene content of 1 to 10% by weight, preferably 2 to 8% by weight, or copolymers randomized propylene-1-butylene with a butylene content of 4 to 25% by weight, preferably 10 to 20% by weight, based in each case on the total weight of the copolymer, or random ethylene-propylene terpolymers o-1-butylene with an ethylene content of 1 to 10% by weight, preferably 2 to 6% by weight, and a content of 1-butylene of 3 to 20% by weight, preferably 8 to 10% by weight , based in each case on the total weight of the terpolymer or a mixture made of an ethylene-propylene-1-butylene terpolymer and a propylene-1-butylene copolymer with an ethylene content of 0.1 to 7% by weight and a content of propylene of 50 to 90% by weight and a content of 1-butylene of 10 to 40% by weight, based in each case on the total weight of the polymer mixture.

The propylene homopolymer used in the outer layer consists predominantly (at least 90%) of propylene and has a melting point of 140 ° C or higher, preferably 150 to 170 ° C. Isotactic homopolypropylene with a n-heptane-soluble fraction of 6% by weight or less, based on isotactic homopolypropylene, is preferred. The homopolymer generally has a melt flow index of 0.5 to 15 g / 10 min, preferably 2.0 to 10 g / 10 min. The copolymers that are used in the outer layer and described above usually have a melt flow index of 2 to 20 g / 10 min., preferably from 4 to 15 g / 10 min. The melting point is on a scale of 120 to 140 ° C. The terpolymers used in the outer layer have a melt flow index in the range of 2 to 20 g / 10 min, preferably 4 to 15 g / 10 min, and a melting point in the range of 120 to 140 ° C. The combination made of co- and terpolymers and described above has a melt flow index of 5 to 9 g / 10 min and a melting point of 120 to 150 ° C. All the melt flow rates given above are measured at 230 ° C and with a load of 21.6 N (DIN 53 735). If so desired, polymers of the outer layer may have been peroxidically degraded in the manner described above for the base layer, and in principle, the same peroxides are used. The degradation factor for the outer layer polymers is generally on a scale of 3 to 15, preferably 6 to 10. Here, too, the peroxide degradation of the outer layer materials can have a favorable effect on the barrier after of metallization. If so desired, hydrocarbon resins may also be added to the outer layer (s) in the manner described above for the base layer. The outer layers generally comprise from 1 to 40% by weight of resin, in particular from 2 to 30% by weight, preferably from 3 to 20% by weight. The embodiments having resin-containing outer layers are particularly advantageous with respect to their optical properties, such as brightness and transparency. Here also, the addition of hydrocarbon resins can have a favorable effect on the barrier after the metallization of the films. The outer layers comprising resin generally must comprise antiblocking agents to ensure that they progress adequately through the machinery. The new film comprises at least the base layer described above. If the film has more than one layer it also comprises at least one outer layer A and, if so desired, also another outer layer C. The outer layer C is accommodated on the opposite side of the base layer B. If so desired , there may also be one or more intermediate layers applied between the base and outer layers. The preferred embodiments of the film have three layers. The structure, thickness and composition of a second outer layer can be chosen independently of the outer layer already present. Similarly, the second outer layer may consist of one of the polymers or polymer blends described above, but does not have to be the same as the first outer layer. However, the second outer layer may also comprise other polymers commonly used for an outer layer. The thickness of the outer layer or layers is greater than 0.1 μm, preferably in the range of 0.2 to 5 μm, in particular 0.4 to 3 μm, and if there are external layers on both sides, their thickness may be identical or different. The total thickness of the polyolefin film of the present invention having more than one layer can vary widely and depends on the application for which it was created. It is preferred that the base layer have from 3 to 100 μm, in particular from 8 to 60 μm, constituting from about 50 to 96% of the total thickness of the film. The density of the film is generally 0.9 g / cm.sup.3 or more preferably 0.9 to 0.97 g / cm.sup.3 In order to improve the adhesive properties of the outer layer (s), at least one surface of the film must be treated by corona discharge or of flame. If desired, identical or different treatments of this type can be carried out on both surfaces. For yet another improvement of certain properties of the polyolefin film of the present invention, either the base layer or the outer layer (s) may comprise an amount effective in each case of other additives, preferably antistatic and / or antiblocking agents and / or lubricants and / or stabilizers and / or neutralizing agents, compatible with the propylene polymers of the base layer and the outer layer (s), except for the antiblocking agents, which are generally incompatible. All amounts given in percentages by weight (% by weight) in the description below are based on the respective layer or layers to which the additive may be added. Preferred antistats are alkali metal alkan sulphonates, polydiorganosiloxanes (polydialkylsiloxanes, polyalkisenylsiloxanes and the like) modified with polyether (ie ethoxylated and / or propoxylated) and / or the essentially straight-chain aliphatic amines and saturated with an aliphatic radical having 10 at 20 carbon atoms with substitution by hydroxyalkyl groups of C1-C4, N, N-bis (2-hydroxyethyl) alkylamines having from 10 to 20 carbon atoms, preferably from 12 to 18 carbon atoms, in the alkyl radical are particularly suitable. Effective amounts of antistatics are in the range of 0.005 to 0.5% and a preferred antistatic is 0.005 to 0.5% by weight of glycerol monostearate. To achieve good barrier values and good metal addition, it is useful to keep the antistatic ratio low if possible, or even to avoid the antistatic altogether. Suitable antiblocking agents are inorganic additives, such as silica, calcium carbonate, magnesium silicate, aluminum silicate, calcium phosphate and the like and / or incompatible organic polymers, such as polyamides, polyesters, polycarbonate and the like. Preferred are benzoguanamine-formaldehyde polymers, silica and calcium carbonate. The effective amounts of antiblocking agents are in the range of 0.001 to 2% by weight, preferably 0.01 to 8% by weight. The average particle size is from 1 to 6 μm, in particular from 2 to 5 μm. Globular particles, such as those described in EP-A-0 236 945 and DE-A-38 01 535, are particularly suitable. The antiblocking agents are preferably added to the outer layers. The lubricants are amides of higher aliphatic acids, esters of higher aliphatic acids, waxes and metal soaps and also polydimethylsiloxanes. Effective amounts of lubricants are in the range of 0.001 to 3% by weight preferably 0.002 to 1% by weight. The addition of higher aliphatic acid amides in the range from 0.001 to 0.25% by weight in the base layer and / or in the outer layers is particularly suitable. A particularly suitable amide of an aliphatic acid is erucamide. To achieve good barrier values and good metal adhesion is useful, in the case of being able to substantially eliminate the lubricants. The stabilizers that can be used are the usual stabilization compounds for polymers of ethylene, propylene polymers and other α-olefin polymers. The amounts of these added are from 0.005 to 2% by weight. Phenolic stabilizers, alkali metal / alkaline earth metal stearates and / or alkali metal / alkaline earth metal carbonates are particularly suitable. Phenolic stabilizers are preferred in amounts of 0.1 to 0.6% by weight, in particular of 0.15 to 0.3% by weight and with molar masses above 500 g / mol. Particularly useful are pentaerythritol tetrakis-3- (3,5-di-tert-butyl-4-hydroxyphenyl) -propionate or 1,3,5-tritymethyl-2,4,6-tris (3,5 -di-tert-butyl-4-hydroxybenzyl) benzene. The neutralizing agents preferably are calcium stearate and / or calcium carbonate of average particle size not greater than 0.7 μm, absolute particle size less than 10 μm and a specific surface area of not less than 40 m2 / g. In order to achieve the mentioned properties of the film, in particular the permeability values after the metallization of the films, it has been further proved that it is useful for the surfaces of the film to have suitable properties and topographies. For the films of the present invention, it is useful for at least one of the two surfaces of the film to be described by the parameters indicated below a) average roughness Ra b) static / sliding friction coefficient μ of this side with respect to itself and c) number of elevations / protrusions N / mm2. It is useful if the film is structured in such a way that on one of its external surfaces mentioned above a) the Ra value is from 20 to 300 nm b) the coefficient of friction of static / sliding μc of this layer with respect to itself is less than 0.55 c) the number of elevations / protrusions Nc / mm2 is expressed by equations 2-Bh2 * log h / μm <; log Nc / mm2 < Ah3-Bh3 * log h / μm (1) 0.05 μm < h < 1.0 μm Ah2 = -1,000 Bh2 = 3.70 Ah3 = 2.477 Bh3 = 2.22 Ad2-Bd2 * log d / μm < log Nc / mm2 < Ad3-Bd3 * log h / μm (2) 0.2 μm < d < 10 μm Ad2 = 1,700 B = 3.86 Ad3 = 4,700 Bd3 = 2.70 In a preferred embodiment Ra is from 30 to 250 nm, in particular from 35 to 200 nm. In a preferred embodiment the coefficient of static friction / slip μc of this layer with respect to itself is smaller than 0. 50, in particular less than 0.40. In a preferred embodiment the constants Ah2 to Bh3 in equation (1) have the values Ah2 = -0.523, Bh2 = 3.523, Ah3 = 2.300 and Bh3 = 2.3, and in a particularly preferred embodiment the values are Ah2 = 0.00, Bh = 3,300, Ah3 = 2,000 and Bh3 = 2,400, and very particularly preferable Ah2 = 1,420, Bh2 = 2,500, Ah3 = 2,000 and Bh3 = 3,000. In a preferred embodiment the constants Ad2 to Bd3 in equation (2) have the values Ad2 = 2.00, Bd2 = 3.630, Ad3 = 4.40 and Bd3 = 2.70, and in a particularly preferred embodiment the values are Ad2 = 2.400, Bd2 = 3.720 , Ad3 = 4,000 and Bd3 = 2,600, and very particularly preferable Ad2 = 3,400, Bd2 = 2,400, Ad3 = 4,000 and Bd3 = 3,300. For the films described in the present invention in addition, it has been proven to be useful for the surface of the film, which will subsequently be metallized or coated with oxidic materials, obey the following conditions: log N / mm2 < 1.4-2.5 * log h / μm (3) where 0.05 μm < h < 1.00 μm log N / mm2 < 3.4-2.4 * log d / μm (4) where 0.2 μm < d < 10 μm N in number / mm2. h in μm d in μm If so desired, there may also be an intermediate layer between the base layer and the outer layer (s). Again, this may be composed of the polymers described for the base layers. In a particularly preferred embodiment it is composed of the polypropylene used for the base layer. It can also comprise the usual additives described.

The thickness of the intermediate layer is generally greater than 0.3 μm, preferably from 0.5 to 15 μm, in particular from 1.0 to 10 μm and very particularly preferably from 1.0 to 5 μm. In the particularly useful three-layer embodiment of the film of the present invention, the thickness of the outer layer (s) A (and C) is generally greater than 0.1 μm, preferably from 0.2 to 3.0 μm, advantageously from 0. 2 to 2.5 μm, particularly from 0.3 to 2 μm and very particularly preferably from 0.3 to 1.5 μm, and the outer layers A and C may have identical or different thicknesses. The invention furthermore also relates to a process for producing the film of the present invention having more than one layer by a coextrusion process known per se. For the purposes of the present invention, the method is to coextrude, through a die of flat film, the molten materials corresponding to the individual layers of the film, to obtain the resulting film in one or more rolls to solidify it, and then biaxially stretching (orienting) the film to heat-fix the biaxially stretched film, if desired, to corona-treat the surface layer created for corona discharge treatment. The biaxial stretching (orientation) is generally carried out sequentially and preference is given to the sequential biaxial stretching that begins with longitudinal stretching (machine direction), followed by transverse stretching (perpendicular to the machine direction). The polymer or polymer mixture for the individual layers is usually first compressed and plasticized in an extruder as in the co-extrusion process, where the polymer or polymer mixture can at this time contain any added additive. In particular, the resins are preferably added in the form of a master batch. The melted materials are subsequently extracted simultaneously through a die of flat film and the coextruded film is then removed in one or more lifting rolls, after which it cools and solidifies. The resulting film is then stretched longitudinally and transversely in the direction of extrusion, and this causes the orientation of the molecular chains. Longitudinal stretching is usefully developed with the help of two rollers running at different speeds corresponding to the desired stretch ratio, and the transverse stretch with the help of a tension frame. The longitudinal stretching ratios according to the invention are from 4.0 to 9, preferably from 4.5 to 8.0. The cross-stretch ratios should subsequently be chosen correspondingly, preferably giving a scale of 5.0 to 11.0. After biaxial stretching of the film, heat fixation (heat treatment) continues, where the film is maintained at a temperature between 100 and 160 ° C for about 0.1 to 10 sec. The film is then rolled up in a conventional manner using a winding equipment. It has been found to be particularly useful for the lifting rolls which cool and solidify the extruded film which are maintained at a temperature between 10 and 100 ° C, preferably between 20 and 70 ° C, by means of a cooling and heating circuit. The temperatures at which the longitudinal and transverse stretching are carried out can vary on a relatively broad scale and depend on the composition of the mixture of the base cap and, respectively, the mixture of the outer layer, and on the desired properties of the movie. In general, the longitudinal stretch is preferably carried out at 80 to 150 ° C and preferably the transverse stretch at 120 to 170 ° C. As mentioned above, one or both surfaces of the film can be treated by corona or flame discharge by one of the known methods after biaxial stretching, if desired. The intensity of the treatment is generally in a range from 37 to 50 mN / m, preferably from 38 to 45 mN / m. A useful method for corona discharge treatment is to pass the film between two conductors that function as electrodes, where the voltage that is applied between the electrodes, mainly an alternating voltage (of approximately 5 to 20 kV and of 5 to 30 kHz) , is high enough to allow corona discharge. The corona discharge ionizes the air on the surface of the film and this reacts with the surface molecules in the film in such a way as to produce polar inclusions in the matrix of the essentially non-polar polymer. For flame treatment with a polarized flame (see US-A-4,622,237) a direct voltage is applied between a burner (negative pole) and a cooling roller. The magnitude of the applied voltage is 400 to 3000 V, preferably 500 to 2000 V. The voltage applied increases the acceleration of the ionized atoms and the kinetic energy with which they impact the surface of the polymer. It is easier to break the chemical bonds within the polymer molecule, and the formation of free radicals is done more quickly. The thermal stress on the polymer is much less than in the standard flame treatment, and the films can be obtained with even better sealing properties on the treated side than on the untreated side. In the case of metallization of the film, the metal layer is preferably composed of aluminum. However, other materials that can be applied as a coherent and thin layer are also suitable. A particular example of a suitable material is silicon, which unlike aluminum gives a transparent barrier layer. The oxidic layer is preferably composed of oxides of elements of major groups 2o, 3o. or 4th. of the periodic table, in particular magnesium, aluminum or silicon oxides. The metallic or oxidic materials that are generally used are those that can be applied under reduced pressure or vacuum. The thickness of the applied layer is generally from 10 to 100 nm. An advantage of the invention is that the production costs of the new film are comparable with those of the prior art. The other important properties of the film of the present invention for processing and use have essentially not changed or been improved. further, the recycled material can always be reused in the production of the film in concentrations of 20 to 50% by weight, based on the total weight of the film, without any significant adverse effect on the physical properties of the film. The film is very suitable for packing food and other consumer items that can be damaged by contact with light and / or air. In summary, after having metallized or coated with oxidic materials the film of the present invention is an excellent oxygen barrier. In addition, it has the good processing performance desired and with high brightness and low turbidity. The brightness of the film is greater than 120. In a preferred embodiment the gloss is greater than 125, and a particularly preferred embodiment is greater than 130. The film, therefore, is particularly suitable for printing or metallizing. The high gloss of the film is transferred to the printed or applied metal layer and thus provides the film with the desired appearance, effective for advertising purposes. The turbidity of the film is less than 3.0. In a preferred embodiment the turbidity of the film is less than 2.5, and a particularly preferred embodiment is less than 2.0. Once the surface A has been metallized, the film has a permeability value of less than 30 gm "2 d" 1 barias "1, preferably less than 27 gm" 2 d "1 barias" 1 and preferably in particular less than 23 g " gm "2 d" 1 barias "1. The coefficient of friction in at least one surface of the film is less than 0.6 In a preferred embodiment this coefficient of friction of the film is less than 0.55, and in a particularly preferred embodiment is less than 0.50 Table 1 below shows once again the most important properties of the film according to the invention.

TABLE 1 ) Measured on the metallized film The methods named below were used to determine parameters for the starting materials and the films: (1) Optical density Macbeth TD-904 densitometer, from Macbeth (division of Kollmorgen Instrumens Corp.) was used. ) to measure the optical density. The optical density is defined as DO = -1g l / l, where I is the intensity of the incident light, l0 is the intensity of the transmitted light and I / lo is the transmittance. (2) Oxygen barrier The oxygen barrier of the metallized films was measured using an OX-TRAN 2/20 from Mocon Modern Controls (EUA) in accordance with DIN 53 380, part 3. (3) Determination of the plane delta p orientation The plane orientation is determined by measuring the refractive index with an Abbe refractometer using the internal operation specification 24.

Preparation of samples Sample size: sample length between 60 and 100mm. The width of the sample corresponds to the prism width of 10mm. To determine? MD and na (=? ND) the sample to be measured should be cut from the film; the leading edge of the sample must advance precisely in the transverse direction. To determine nTD and na (= nND) the sample to be measured must be cut from the film; the leading edge of the sample must advance precisely in the direction of the machine. Samples should be taken from the middle of the film's mesh. Care must be taken that the temperature of the Abbe refractometer is 23 ° C. Using a glass rod, a little diiodomethane (N = 1745) or diiodomethane-bromonaphthalene mixture is applied to the lower prism, completely clean before the measurement procedure. The refractive index of the mixture must be higher than 1,685. The cutting of the sample in the transverse direction first extends in its upper part, in such a way that the entire surface of the prism is covered. Using a paper cleaner, the film is pressed firmly flat on the prism, so that it is placed evenly and firmly on it. The excess liquid must be eliminated. Subsequently, a little test liquid is added dropwise. A second prism is turned over, placed in place and pressed firmly to make contact. The right side spline screw is used to move the indicator scale until a clear to dark transition can be seen in the field of view on a scale of 1.62 to 1.68. If the transition from light to dark is not evident, the colors are joined using the upper screw striated in such a way that only a clear area and a dark area are visible. The obvious transmission line is brought to the crossing point of the two diagonal lines (in the eyepiece) using the lower serrated screw. The value that is now indicated on the measurement scale is read and accessed to the text register. This is the refractive index? D in the direction of the machine. Now the scale is moved using the lower serrated screw until the visible scale in the eyepiece is 1.49 to 1.50. Then the refractive index na or nMD is determined (in the thickness direction of the film). To improve the visibility of the transition, which is only slightly visible, a polarization film is placed on the eyepiece. It moves until the transition is clearly visible. The same considerations apply as in the determination of? MD- If the transition from light to dark is not evident (colored), the colors are joined together using the upper serrated screw in such a way that the obvious transition can be observed. This obvious transition line is placed at the crossing point of the two diagonal lines using the lower serrated screw and the value indicated on the scale is read and accessed to the frame. The sample then moves, and the corresponding refractive indices? MD and na (=? ND) on the other side are measured and accessed in the appropriate box. After the determination of the refractive indexes, respectively in the direction of the machine and the thickness direction of the film, the sample strip that was cut in the machine direction is placed in the position and therefore the refractive indices nTD and na (= nND) are determine The strip is flipped, and the values for the B side are measured. The values for side A and side B are combined to give the average refractive indices. The orientation values are subsequently calculated from the refractive indices by the following formulas: delta n =? MD - GIJD delta p = (nMD + nTD) / 2-nND (4) Coefficient of friction The coefficient of friction is determined according to DIN 53 375, the coefficient is measured 14 days after production. (5) Surface tension The surface tension was determined using the "ink method" (DIN 53 364). (6) Turbidity The turbidity of the film was measured in accordance with ASTM-D 1003-52. Holz turbidity was determined by a method based on ASTM-D 1003-52, but to use the most effective measurement scale the measurements were made on four pieces of film spread one on top of the other, and a 1st slot diaphragm was used. place of a 4th small hole. (7) Brightness The brightness was measured in accordance with DIN 67 530. The reflectance was measured as an optical characteristic value for a film surface. Based on the ASTM-D 523-78 and ISO 2813 standards, the angle of incidence was set at 20 ° or 60 °. A beam of light hits the flat test surface at the established angle of incidence and is reflected and / or scattered from it. A proportional electric variable is shown by representing light rays striking the photoelectric detector. The measured value has no dimension and should be established along with the angle of incidence. (8) Determination of particle sizes on the film surface A scanning electron microscope (for example DSM 982 Gemini, Leo GmbH (Zeiss)) together with an image analysis system was used to determine the particle size distribution of the antiblocking agent (particle size distribution) on film surfaces. The amplification chosen in all cases was 1700. For these measurements the film samples are placed flat on a sample holder. Subsequently they are metallized obliquely at an angle α with a thin metallic layer (for example silver), in this case it is the angle between the surface of the sample and the direction of diffusion of the metal vapor. The particles of the antiblocking agent cast a shadow on this oblique metallization. Because the shadows in this stage are not electrically conductive, the sample can be metallized further with a second metal (eg gold), the metal vapor here is vertically impacted on the surface of the sample. Scanning electron microscope (SEM) images are taken from the surface of samples prepared in this way.

Samples of the antiblocking agent particles are visible due to the contrast between the materials. The sample is oriented in the SEM in such a way that the shadows run parallel to the lower edge of the image (address x). The SEM images are taken with this arrangement and transferred to an image analysis system, which is used to take precise measurements of the length of the shadows (in the x direction) and its maximum extension in the y direction (parallel to the vertical edge of the image). The diameter D of the particles of the antiblocking agent at the level of the surface of the sample is equal to the maximum extension of the shadow in the y-direction. The height of the particles of the anti-blocking agent, measured from the surface of the film, can be calculated from the metallization angle α and the length L of the shadows, with the background of the amplification V chosen from the SEM image: h = ( tan (a) * L)? / In this way, to achieve a sufficiently high level of statistical reliability, precise measurements are made on a few thousand particles of the antiblocking agent. Using the known statistical methods, the frequency distributions are subsequently produced for the diameters and heights of the particles. The class interval chosen for this is 0.2 μm for the diameter D of the particles and 0.05 μm for the height h of the particles. (9) Roughness The roughness Ra of the film was determined in accordance with DIN 4768 with a cut of 0.25 mm. (10) Melt flow index Melt flow index measurements were based on DIN 53 735, with a load of 21.6 N at 230 ° C and 50 N at 190 ° C, respectively. (11) Casting point DSC measurements, maximum cast curve, heating rate 20 ° C / min.

EXAMPLE 1 The coextrusion followed by stepwise orientation in longitudinal and transverse directions was used to produce a transparent film of two layers an AB structure and a total thickness of 20 μm. The thickness of the respective layers is given in table two. The outer layer A was a mixture made of: 84. 00% by weight of sotactic polypropylene with an MF1 of 4 g / 10 min, 16.00% by weight of a master batch made of 99.0% by weight of polypropylene with an M.FI of 4 g / 10 min, and 0.5% by weight weight of Sylobloc 44 (Grace colloidal Si02) and 0.5% by weight of Aerosil TT 600 (Sio2 in the form of Degussa chain) Base layer B: 89.8% by weight of polypropylene with an MFl of 4 g / 10 min, 0.2% by weight of N, N-bisetioxyalkylamine 10.00% by weight of a master batch made of 99.0% polypropylene with an MFl of 4 g / 10 min and 0.5% by weight of Sylobloc 44 (Grace's colloidal SiO2) and 0.5% by weight of Aerosil TT 600 (SiO2 in the form of Degussa's chain) The production conditions in the individual steps of the procedure were: Extrusion Temperatures Layer A 270 ° C Layer B 270 ° C Lifting roller temperature 30 ° C Die space width 1 mm Longitudinal stretching Temperature from 80 to 140 ° C Longitudinal stretching ratio 5.0 Transverse stretching Temperature 160 ° C Stretch ratio transversal 10.0 Fixation Temperature 150 ° C Duration 2s The film has very good optical properties and good processing performance (see table 3).

After producing the film (as in this example and in all the examples below) its side A was metallized with vacuum aluminum in an industrial metallizer. The coating speed was 8 m / s and the optical density was 2.6.

The film obtained the high oxygen barrier value required. The structure of the film and the properties achieved with the films that were produced in this way are given in tables 2 and 3 EXAMPLE 2 Co-extrusion followed by stepwise orientation in longitudinal and transverse directions was used to produce a three-layer clear film with ABA structures and a general thickness of 20 μm, similar to that of Example 1. The outer layer A is a mixture made of : 84. 00% by weight of sotactic polypropylene with an MFl of 4 g / 10 min, 16.00% by weight of a master batch made of 99.0% polypropylene with an MFl of 4 g / 10 min and 0.5% by weight of Sylobloc 44 H (Grace's colloidal SiO2) and 0.5% by weight of Aerosil TT 600 (SiO2 in the form of Degussa chain).

Base layer B: 89.8% by weight of polypropylene with an MFl of 4 g / 10 min, 0.2% by weight of N, N-bisetoxyalkylamine The process conditions for all layers were the same as those chosen for Example 1.

EXAMPLE 3 Coextrusion followed by stepwise orientation in longitudinal and transverse directions was used to produce a three layer transparent film with ABC structure and a general thickness of 20 μm. The only change compared to Example 2 was presented in outer layer A. External layer A is a mixture made of: 96. 0% by weight of isotactic polypropylene with an MFl of 4 g / 10 min, 4.00% by weight of a master batch made of 99.0% by weight of polypropylene with an MFl of 4 g / 10 min and 0.5% by weight of Sylobloc 44 H (Grace's colloidal SiO2) and 0.5% by weight of Aerosil TT 600 (SiO2 in the form of Degussa chain).

The outer layer C was a mixture made of: 84. 00% by weight of isotactic polypropylene with an MFl of 4 g / 10 min, 16.00% by weight of a master batch made of 99.0% polypropylene with an MFl of 4 g / 10 min and 0.5% by weight of Sylobloc 44 H ( Colloidal SiO2 from Grace) and 0.5% by weight of Aerosil TT 600 (SiO2 in the form of Degussa chain).

The process conditions for all layers were the same as those chosen for example 1.

EXAMPLE 4 Co-extrusion followed by stepwise orientation in longitudinal and transverse directions was used to produce a three-layer transparent film with structure ABC and a total thickness of 20 μm, in a manner similar to that of Example 2. The only change compared to Example 2 was in the outer layer A. The outer layer A was a mixture made of: 99. 0% by weight of isotactic polypropylene with an MFl of 4 g / 10 min, 1.00% by weight of a master batch made of 99.0% by weight of polypropylene with an MFl of 4 g / 10 min and 0.5% by weight of Sylobloc 44 H (Grace colloidal SiO2) and 0.5% by weight of Aerosil TT 600 (S¡O2 in the form of Degussa chain).

EXAMPLE 5 The coextrusion followed by stepwise orientation longitudinal and transverse directions was used to produce a three layer transparent film with an ABC structure and a total thickness of 20 μm. The only change compared with example 3 was in the conditions of the longitudinal stretch.

The production conditions for the individual procedure steps were: Extrusion Temperatures Layer A 270 ° C Layer B 270 ° C Layer C 270 ° C Elevator roll temperature 3 300 °° CC Dirt gap width 1 mm Longitudinal stretch Temperature from 80 to 135 ° C Longitudinal stretch ratio 5.0 Transverse stretch Temperature 160 ° C Transverse stretch ratio 10.0 Fixation Temperature 150 ° C Duration 2s EXAMPLE 6 Co-extrusion followed by stepwise orientation in longitudinal and transverse directions was used to produce a three-layer transparent film with structure ABC and a total thickness of 20 μm, in a manner similar to that of Example 3. The only change compared to Example 3 It was presented in outer layer A.

The outer layer A was a mixture made of: 86.0% by weight of polypropylene with an MFl of 4 g / 10 min, 4.00% by weight of a master batch made of 99.0% by weight of polypropylene with an MFl of 4 g / 10 min. and 0.5% by weight of Sylobloc 44 H (Grace's colloidal SiO 2) and 0.5% by weight of Aerosil TT 600 (SiO 2 in the form of Degussa chain). 10.0% by weight hydrocarbon resin (®Regalrez 1139 from Hercules Inc.) with a softening temperature of 140 ° C and a molecular weight of 2500 COMPARATIVE EXAMPLE Co-extrusion followed by stepwise orientation in longitudinal and transverse directions was used to produce a three-layer transparent film with an ABC structure and a total thickness of 20 μm. The only change compared with example 3 was the conditions for longitudinal stretching.

The production conditions for the individual procedure steps were: Extrusion Temperature Layer A 270 ° C Layer B 270 ° C Layer C 270 ° C Elevator roll temperature 3 300 °° CC Die space width 1 mm Longitudinal stretch Temperature from 80 to 143 ° C Longitudinal stretch ratio 5.0 Transverse stretch Temperature 160 ° C Transverse stretch ratio 10.0 Fixation Temperature 150 ° C Duration 2s TABLE 2 TABLE 3 4" 1) Measured in the unmetallized film Side A: metallic outer layer; the oxygen barrier was measured in the metallized film Side C: non-metallized outer layer

Claims (12)

NOVELTY OF THE INVENTION CLAIMS

1. - A biaxially oriented polypropylene film having one or more layers, with a base layer with at least 80% by weight composed of thermoplastic polypropylene, comprising internal and / or inert particles, characterized in that the flat orientation delta p of the film is greater than 0.0138.

2. The polypropylene film according to claim 1, further characterized in that the flat orientation delta p of the film is greater than 0.0140, preferably higher than 0.0143.

3. The polypropylene film according to claim 1 or 2, further characterized in that the oxygen permeability of the metallized film is less than 30 cm3 / m2 barias d.

4. The polypropylene film according to one or more of claims 1 to 3, further characterized in that the oxygen permeability of the metallized film is less than 27 cm3 / m2 barias d.

5. The polypropylene film according to one or more of claims 1 to 4, further characterized in that the film has at least one outer layer.

6. - The polypropylene film according to claim 5, further characterized in that the thickness of the outer layer (s) facing outward is from 0.1 to 4.0 μm.

7. The polypropylene film according to claim 5 or 6, which has a three-layer structure and is composed of the outer layer A that faces outwards, the base layer B and another outer layer C, which is applied to the side of the base layer B opposite the outer layer A.

8. The polypropylene film according to claim 7, further characterized in that the outer layers are pigmented.

9. The polypropylene film according to one or more of claims 5 to 8, further characterized in that the outer layers are pigmented differently.

10. A process for producing a biaxially oriented polypropylene film having one or more layers according to claim 1, further characterized in that the molten polypropylene material whose composition corresponds to the composition of the outer and base layers is fed to a The mono-or co-extrusion die is removed and the latter is drawn to a cooling roller, and the resulting pre-film is then oriented biaxially and fixed with heat, where the flat delta p orientation of the film is greater than 0.0138.

11. The process for producing a biaxially oriented polypropylene film according to claim 10, wherein the recycled materials are fed to the extrusion die in a concentration of 10 to 50% by weight, based on the total weight of the movie.

12. The use of the film according to one or more of claim 1 to 10 for packaging food and other consumer items.