MXPA00008984A - Sealable, biaxially oriented polypropylene film with improved barrier properties - Google Patents

Abstract

The invention relates to a multi-layer, sealable biaxially oriented polypropylene film consisting of a base layer and at least one sealable covering layer. The base layer contains between 1 and 15 weight%of a resin with a mean molecular weight Mw of between 600 and 1,500 and between 1 and 6 weight%of a wax with a mean molecular weight Mn of between 200 and 700. The n-heptane insoluble part of the polypropylene of the base layer has a chain isotactic index of at least 95%, as measured by 13C-NMR spectroscopy. The invention also relates to a method for producing said film and to its use.

Description

SEALABLE POLYPROPYLENE FILM. B I AXIALLY ORIENTED. WITH IMPROVED BARRIERS PROPERTIES The invention relates to a polypropylene film with improved barrier properties, relating to the passage of water vapor, and with improved mechanical properties. The improvement of the mechanical properties of films, especially films for packaging applications, has been of particular importance in recent times. From the point of view of costs and environmental f 10, the packaging industry is always looking for thin films that can leave similar machines and that may have similar or improved race properties, especially in relation to the passage of water vapor. However, the thin films have a disproportionate and damaging rigidity in the machine direction and, due to this, a retention in their travel through the machine substantially bad, especially in today's high-speed wrapping machines. With the reduction of film thickness, barrier properties decrease, also disproportionately. Due to the poor barrier properties, the thin films strongly reduce the protective effects of the film against drying and loss of content. The increase in the modulus of elasticity (modulus E) in the direction of the machine has always been a matter of great concern, since this mechanical property is directly dependent on the aptitude for technical application and, in such a way, directly influences the retention of treatment. The barrier biaxially oriented polypropylene films 5 (boPP), with respect to water vapor (WDD) and oxygen (SDD) decrease with the thickness of the film. In general, the usual thickness scale of boPP films (from 4 to 100 μm) is, for example, between the water vapor barrier (WDD) and the thickness (d), following a hyperbolic relationship (WDD.d). = constant). The constant depends substantially on the • 10 composition of the starting material and the stretching conditions. For the packaging films of boPP, according to the state of the art, the constant has an approximate value of: const = 28 g.μm / m2.d. The water vapor passing capacity will be measured in accordance with DIN 53 122. It is known that the modulus E of the boPP films is increased in the machine direction, either by means of process techniques or by modifications of the starting materials, or by combination of both possibilities. It is known to modify polypropylene films with different hydrocarbon resins, according to the state of the art. One such modification of starting materials allows the preparation of polypropylene films whose mechanical strength in the longitudinal direction is substantially improved compared to the films formed with unmodified starting materials; however, the longitudinal stretch value of the film can not be reached and its shrinkage in the longitudinal direction is eventually relatively high. In US-A-4,921,749 (corresponding to EP-A-0 247 898), a sealable boPP film with improved mechanical and optical properties is described. The sealing ability of the film and the possibility of letting water and oxygen vapor through are also improved. Complete improvements are obtained in the addition of a low molecular weight resin in the base layer. The resin portion then corresponds to between 3 and 30 percent in • 10 weight. The resin has a molecular weight substantially less than 5,000, preferably less than 1,000, and is, for example, 600. The softening point of the resin is between 120 and 140 ° C. EP-A-0 645 417 describes a biaxially oriented polypropylene film whose insoluble portion in n-heptane exhibits an index isotactic chain, measured by means of 13 C-NMR spectroscopy, of at least 95%. The basic layer contains from 1 to 15 weight percent of a natural or synthetic resin, whose softening point is between 70 and 170 ° C. US 5,155,160 describes the improvement of barrier properties by the addition of wax to non-oriented polypropylene films. As 20 waxes are described: paraffin wax and polyethylene wax, with molecular weight from 300 to 800. The barrier should be below 0.2 g / 645.16 cm2 / 24 hours. A continuous search continues to further improve the water vapor barrier of polypropylene films, for packaging, biaxially oriented. All previously known methods reduce the water vapor barrier not to the desired extent, or affect other essential properties of the film in a non-acceptable manner. Therefore, it is an object of the present invention to prepare a biaxially oriented polypropylene film, which is characterized by a good water vapor barrier and exhibits good properties mechanical. The film must be able to be prepared in a safe and constant procedure, at production speeds of up to 400 m / minute. Other • 10 physical properties of the film, which are necessary in view of its use as packaging films, are not negatively influenced. The films should have high gloss, no optical defect, in the form of granules or bladders, good scratch resistance, with a lower film thickness, in a problem-free packaging machine, and high speed; and a minimum of turbidity of the film. Additionally, the ability to seal the film should not be negatively influenced by the above. This purpose is achieved by means of a multilayer biaxially oriented polypropylene film, consisting of a base layer and at least one cover or coating layer; whose characteristic properties are that the base layer contains a combination of resin and wax, and the resin has a weight average molecular weight of 600 to 1500, and the wax has a number average molecular weight of 200 to 700. The dependent claims indicate preferred embodiments of the invention.

The basic layer of the film contains, in general, at least 85 percent by weight, preferably from 85 to < 100 weight percent, especially 90 to 95 weight percent, of propylene polymer; being '^ all percentages with respect to the basic layer. In general, the propylene polymer contains at least 90 weight percent, preferably 94 to 100 weight percent, especially 98 to 100 weight percent, of propylene. The corresponding comonomer content f, if any, represents a high percentage of 10 per * percent by weight, or from 0 to 6 percent by weight, or from 0 to 2 percent by weight, Wr 10 usually ethylene. The proportions in percentage by weight, in each case, are relative to the propylene homopolymer. The isotactic propylene homopolymer is preferred, with a softening point of 140 to 70 ° C, preferably 155 to 165 ° C, and a melt flow index (measured by DIN 53 735 to 21.6N load and 230 ° C ) from 1.0 to 10 g / 10 minutes, preferably from 1.5 to 6.5 g / 10 minutes. The n-heptanolic portion of the polymer in general corresponds to 1 to 10% by weight, preferably 2 to 5 percent by weight, based on the starting polymer. The molecular weight distribution of the propylene polymers can vary, in each case, within wide limits, according to the intended use. The ratio of weight average molecular weight (Mw) to number average molecular weight (Mn) in general is between 1 and 15. In a preferred embodiment, the film according to the invention has the weight average molecular weight ratio Mw. to average molecular weight of number Mn between 2 and 10, most preferably between 2 and 6. A molecular weight distribution so narrow in the propylene homopolymer of the basic layer, can be obtained, for example, by means of its peroxydic reduction , or by preparing polypropylene by means of of appropriate metallocene catalysts. A measure of the degree of polymer breakdown is the called the disintegration factor A, which gives the relative variation of the index of * melt flow according to DIN 53 735 of polypropylene, in relation to the , starting polymer: • 10 MFI2 A = MF MF = melt flow index of the propylene polymer, before the addition of organic peroxides.

MFI2 = Melt flow index of the propylene polymer, peroxidically disintegrated.

In general, the disintegration factor A of the prepared propylene polymers is in the range from 1 to 15, preferably from 1 to 10. As the organic peroxide, dialkyl peroxides are especially preferred, alkyl radicals being understood as the alkyl radicals lower normal, saturated, straight chain or branched, with up to six carbon atoms. Particularly preferred are 2,5-dimethyl-2,5-di (terbutylperoxy) hexane or diterbutyl peroxide.

In a preferred embodiment, the invention consists of saturated polypropylene, of high isotacticity. As isotactic polypropylenes of this type may be mentioned polypropylenes having at least 95%, preferably 96 to 99% portions not soluble in n-heptane, with an index of chain isotacticity determined by 13 C-NMR spectroscopy. It has been found that the selection of a high isotacticity polypropylene of this type substantially improves in a surprisingly favorable manner with the combination of resin and wax in the basic, concurrent layer, and the water vapor barrier is further improved.

• It is essential for the invention that the base layer contain a hydrocarbon resin with a weight average molecular weight (Mw) of 600 to 1500, preferably 700 to 1200, preferably in an amount of 1 to 15% by weight , especially from 5 to 12% by weight, with respect to the weight of the basic layer. 15 It can be pointed out as a hydrocarbon resin mainly synthetic resins or resins of natural origin, which are generally Partially or fully hydrated. The point of softening of the resin, in general, is more than 80 ° C (measured according to DIN 1995-U4 or ASTM E-28), it is preferred that said resin has a softening point from 100 to 180 ° C, especially from 120 to 160 ° C. According to the present invention, the hydrocarbon resins comprise, for example, petroleum resins, styrene resins, cyclopentadiene resins and terpene resins (these resins are described in Ullmanns EncyklopSdie der techn. Chemie, Volume 4 , chapter 12, pages 525 to 555). Petroleum resins are those hydrocarbon resins that can be prepared through the polymerization of petroleum materials of deep decomposition, in the presence of a catalyst. These petroleum materials commonly contain a mixture of resin-forming substances, such as styrene, methylstyrene, vinyltoluene, indene, methylindene, * butadiene, isoprene, piperylene and pentylene. Styrene resins are styrene homopolymers or styrene copolymers with other monomers, as methylstyrene, vinyltoluene and butadiene. The cyclopentadiene resins are cyclopentadiene homopolymers or cyclopentadiene copolymers obtainable from coal tar distillates and decomposed petroleum gas. These resins can be prepared, while keeping the materials containing cyclopentadiene, for a long time, to high temperatures. Depending on the reaction temperature, dimers, trimers or oligomers can be obtained. Terpene resins are terpene polymers, that is, hydrocarbons of the formula C? 0H? 6, which are constituted mostly by ether oils or oil-containing resins, of vegetable origin, and phenol-modified terpene resins . As special examples of terpenes are pinene, alpha-pinene, dipentene, limonene, myrcene, camphor and similar terpenes. The so-called modified hydrocarbon resins can also be cited as hydrocarbon resins. The modification is effected, generally, by the reaction of the starting materials before the polymerization, by the addition of special monomers, or by reaction of the polymerized product, with hydrogenations and partial hydrogenations being particularly noted. As hydrocarbon resins, it is also possible to use styrene homopolymers, styrene copolymers, cyclopentadiene homopolymers, cyclopentadiene copolymers and / or terpene polymers with * a softening point, each above 135 ° C (in polymers) unsaturated, the hydrogenated product is preferred). Especially preferred are cyclopentadiene polymers with a softening point of at least 140 ° C, or copolymers of alpha-methylstyrene and vinyltoluene, with a softening point of 120 to 150 ° C, added in the basic layer. Additionally, it is important for the invention that the basic layer, in addition to the resin, contains a wax with an Mn of 200 to 700, preferably in an amount of less than 10% by weight, especially 1 to 8 percent by weight, especially 1 to 6 percent by weight, relative to the weight of the basic layer. In the context of the present invention, the waxes comprise polyethylene waxes and / or microcrystalline paraffin waxes. Polyethylene waxes are low molecular weight polymers, which are substantially constituted by ethylene units and which are partially or highly crystalline. The polymer chains of the ethylene units are molecules of great length, which may be branched, with short side chains predominating. In general, polyethylene waxes are prepared by direct polymerization of ethylene, optionally with the addition of regulators, or by depolymerization of polyethylenes with high molar masses. According to the invention, the polyethylene waxes have an average molecular weight of number (Mn) of 200 to 700, preferably of 400 to 600 and, preferably, a molecular weight distribution (polydispersity) Mw / Mn of less than 2, preferably from 1 to 1.5. The melting point is generally within the range of 70 to 150 ° C, preferably between 80 and 100 ° C. Paraffins comprise, in their general sense, paraffins • 10 macrocrystallines (paraffin waxes) and microcrystalline paraffins (microwaxes). The macrocrystalline paraffins are obtained from the vacuum distillation fractions, by means of their treatment in lubricating oils. The microcrystalline paraffins are obtained from the recirculation of vacuum distillation and the sediments of paraffinic crude oils (separated paraffins). 15 Macrocrystalline paraffins consist mainly of n-paraffins, each of which, depending on the degree of refining, contains isoparaffin, naphthene and alkylaromatics. Microcrystalline paraffins are obtained from a mixture of hydrocarbons that are predominantly solid at room temperature. They are also macrocrystalline paraffins predominantly isoparaffins and naphthenic paraffins. Microcrystalline paraffins are characterized by the presence of strongly branched isoparaffins and naphthenes and with an impediment to crystallization. For the purposes of the invention, macrocrystalline paraffins with a melting point of 60 to 100 ° C, preferably 60 to 85 ° C, are suitable. It has been discovered that the combination of wax and resin also surprisingly improves the synergistic cooperation and the permeation of the water vapor of the oriented polypropylene films; that is, it reduces it, when the Mn of the wax is on a scale of 200 to 700, and the Mw of the resin is on the scale of 600 to 1500. It has been observed that the wax with Mn of more than 700 does not cooperate with the resin and does not you get substantial elevation of the barrier against water vapor. Similarly, it is important that the Mw of the resin is in the # 10 scale from 600 to 1500. When the Mw exceeds 1500, the barrier worsens compared to those films containing the resin and wax combination according to the present invention. In addition to the combination according to the present invention, of resin and wax, the base layer may contain the usual additives, such as neutralizers, stabilizers, antistatic agents and / or lubricants, each in the effective amounts. Preferred antistatic agents are alkali metal alkanesulfonates, polydiorganosiloxanes modified with polyether, ie ethoxylated and / or propoxylated (polydialkylsiloxanes, polyalkylphenylsiloxanes and the like) and / or aliphatic, substantially branched and saturated tertiary amines with an aliphatic residue which has from 10 to 20 carbon atoms; which are substituted with? -hydroxyalkyl groups of 1 to 4 carbon atoms; N, N-bis- (2-hydroxyethyl) alkylamines having from 10 to 20 carbon atoms, preferably from 12 to 18 carbon atoms in the alkyl radical being particularly suitable. The effective amounts of antistatic agent are in the range of 0.05 to 0.5% by weight. In addition, glycerin monostearate is preferably used as antistatic agent in an amount of 0.03% to 0.5%. 5 Lubricating agents are the higher aliphatic acid amides; the higher aliphatic acid esters, the waxes and the metal soaps, as well as polydimethylsiloxane. The effective amount of lubricating agent is in the = scale from 0.01 to 3% by weight, preferably from 0.02 to 1% by weight. The addition of higher aliphatic acid amides in the • 10 scale from 0.01 to 0.25% by weight, in the basic layer. An especially suitable aliphatic acid amide is erucic acid amide. The addition of polydimethylsiloxanes is carried out on a scale from 0.02 to 2.0% by weight, preferably; especially polydimethylsiloxane, with a viscosity of 5,000 to 1,000,000 mm / second. The common stabilizing active compounds for polymers of ethylene, propylene and other alpha-olefins can be used as stabilizers. Its amount is between 0.05 and 2 percent by weight. Phenolic stabilizers are especially suitable, with alkali / alkaline-earth metal stearates and / or metal carbonate being preferred. alkaline / alkaline-earth, in amounts of 0.1 to 0.6 percent by weight, especially 0.15 to 0.3 percent by weight; and with a molar mass of more than 500 g / mol. Particularly advantageous are pentaerythrityl tetracis-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate or 1.Sd-trimethyl ^^ e. trisÍ.d-diterbutil- 4-hydroxybenzyl) benzene. The neutralizers are preferably dihydrotalcite, calcium stearate and / or calcium carbonate, with an average particle size of more than 0.7 μm, an absolute particle size of less than 10 μm and a surface area of specific of at least 40 m2 / g. The amounts mentioned above, given in percentage by weight, refer, in each case, to the weight of the basic layer. "The polypropylene film according to the invention comprises at least one cover layer or sealable coating and, in • A preferred embodiment, sealable coating layers on both sides, of alpha-olefin polymers of 2 to 10 carbon atoms. Examples of sealable alpha-olefin polymers of this type are: a copolymer of: ethylene and propylene; or ethylene and butylene-1, or propylene and butylene-1, or a terpolymer of: ethylene and propylene and butylene-1, or a mixture of two or more of the aforementioned homopolymers, copolymers and terpolymers, or a mixture of two or more of said homopolymers, copolymers and terpolymers, optionally mixed with one or more mentioned homopolymers, copolymers and terpolymers; with particular preference: random copolymers of ethylene-propylene, with: an ethylene content of 1 to 10% by weight, preferably 2.5 to 8% by weight; or 5 random copolymers of propylene-butylene-1, with a butylene content of 2 to 25% by weight, preferably 4 to 20% by weight; in each case in relation to the total weight of the copolymers; or random ethylene-propylene-butylene-1 terpolymers, with an ethylene content of 1 to 10% by weight, preferably 2 to 6% by weight; and a butylene-1 content of 2 to 20% by weight, preferably 4 to 20% by weight; in each case in relation to the total weight of the terpolymer; or a mixture of an ethylene-propylene-butylene-1 terpolymer and a propylene-butylene-1, f copolymer with an ethylene content of 0.1 to 7% by weight; and a propylene content of 50 to 90% by weight; and a butylene-1 content of 10 to 40% by weight; 20 in each case, in relation to the total weight of the polymer mixture. The copolymers and / or terpolymers described above, used in the coating layer or layers generally exhibit a melt flow index of 1.5 to 30 g / 10 minutes, preferably 3 to 15 g / 10 minutes. The melting point is within the range of 120 to 140 ° C. The above-described mixture of copolymers and terpolymers has a melt flow index of 5 to 9 g / 10 minutes, and a melting point of 120 to 150 ° C. All the - f melt flow indexes given above are measured at 230 ° C and with a force of 21.6 N (DIN 53 735). Optionally, all the polymers of the coating layer described above, in the same way as those described for the basic layer, 1 can be peroxidized; basically the same peroxides can be used. The extraction factor for the polymers of the coating layer, in general, is within the range of 3 to 15, preferably 6 to 10. If desired, it can be added to the layer or to the layers of the layer. coating the additives described above for the basic layer, such as antistatic agents, neutralizers, lubricants and / or stabilizers, and, optionally, additional antiblocking agents. The data in percent by weight are correspondingly related to the weight of the coating layer. f 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, as polyamides, polyesters, polycarbonates and the like, preferably benzoguanamine-formaldehyde polymers, silicon dioxide and calcium carbonate. The effective amount of antiblocking agent is in the range of 0.1 to 2% by weight, preferably 0.1 to 0.8 percent by weight. The average particle size is between 1 and 6 μm, in particular from 2 to 5 μm, particles with a spherical configuration being particularly suitable, such as those described in EP-A-0 236 945 and DE-A-38 01 535 The films according to the invention comprise at least less the basic layer described above and a sealable coating layer, preferably sealing layers sealable on both sides. The preferred embodiments of polypropylene films are * three layers. The formation, the thickness and the composition of a second coating layer can be selected independently of the coating layer already provided, the second coating layer also being able to contain one of the polymers described above, or mixtures of polymers.; which, however, should not necessarily be identical to those of the first coating layer. The thickness of the layer or layers of sealable coating (s) 15 is more than 0.1 μm and is preferably in the range of 0.3 to 3 μm, especially 0.4 to 1.5 μm, the coating layers being able to be both sides of equal thickness or of different thicknesses. The total thickness of the polypropylene films according to the invention can vary within wide limits, and is adjusted according to the use to which it is intended. Preferably it is between 4 and 60 μm, especially between 5 and 30 μm, preferably from 6 to 25 μm; the basic layer constituting approximately 40 to 100% of the total thickness of the film. The invention further relates to a method for preparing the polypropylene films according to the invention, according to an extrusion process known per se. Within the framework of this procedure, provision is made to extrude • the corresponding fusions for the individual layers of the film through a nozzle, by passing the film thus obtained, for solidification on one or more rollers; and after stretching (orienting) the film, the biaxially stretched film is thermofixed, and the surface is eventually treated by corona or flame surface treatment. The biaxial stretch (orientation) is usually done one • 10 after the other; it is preferred to carry out the biaxial stretching first in the longitudinal direction (in the machine direction) and then in the transverse direction (perpendicular to the machine direction). Next, as in a normal coextrusion process, the polymer or polymer mixture of each individual layer is compressed and fluidized by extrusion, the additives possibly being added in the polymer or in the polymer mixture. The fusion f is then pressed simultaneously through a nozzle (wide groove nozzle) and the multilayer film is extruded under pressure, on one or more receiver rollers, in which it cools and solidifies. The film thus obtained is then stretched longitudinally and transversely with respect to the direction of extrusion, which produces the orientation of the molecular chains. The longitudinal stretching is conveniently carried out with the aid of second rollers which rotate at different speeds to impart a desired stretch ratio, and the transverse stretch is effected with the aid of a corresponding stretch frame. The longitudinal stretch ratios are f within the range of 4 to 8, preferably 5 to 6. The relationships of cross stretch are in the range of 5 to 10, preferably 7 to 9. The biaxial stretch of the films is associated with its thermofixation 8 (heat treatment), maintaining the film for approximately 0.1 to 10 seconds, at a temperature of 100 to 160 ° C. Next, the • 10 film, in the usual way, by means of a winder. It is quite favorable that the roller or the receiving rolls, by which the pressed film is cooled and solidified, are maintained by a heating and cooling circuit at a temperature of 10 to 100 ° C, preferably 20 to 50 ° C. The temperatures at which longitudinal stretching and transverse stretching are effected can vary within a relatively wide range, and are selected according to the properties desired for the film. In general, it is preferred that the longitudinal stretch be carried out at temperatures of 80 to 150 ° C, and that the transverse stretch be carried out, preferably at temperatures of 120 to 170 ° C. It is preferred that, after biaxial stretching, one or both surfaces of the film be (are) treated according to one of the known methods of corona treatment or with flame. The intensity of the treatment, in general, will be within the range of 37 to 50 mN / m, preferably from 39 to 45 mN / m. In the corona treatment, one conveniently proceeds ! so that the film is passed between two carrier elements that serve as electrodes, maintaining between the electrodes such a high current, preferably an alternating current (approximately 5 to 20 kV and from 5 to 30 KHz), that a discharge of sparks or discharge can be established. * of crown. By discharge of sparks or corona discharge, the air that is on the surface of the film is ionized and reacts with the * 10 molecules on the surface of the film, so that polar contributions are established in the polymer matrix substantially not polar. For the treatment with flames, with polarized flames (see US-A-4,622,237), a continuous electric current is established between a burner (negative pole) and a cooling roller. The intensity of the current The selected one is between 400 and 3,000 V, preferably in the range of 500 to 2,000 V. By the current selected, the ionized atoms undergo a high acceleration and strike with increased kinetic energy on the surface of the polymer. The chemical bonds within the polymer molecules break easily and the formation of radicals In that way, the thermal load of the polymer is further reduced with respect to the ordinary flame treatment, and films can be obtained in which the sealing capacity of the treated side is better than that of any untreated side.

The films according to the invention are characterized by a clearly improved barrier against water vapor. Surprisingly it was discovered that the good barrier values that are obtained by the • f addition of resin, can be further reduced by the addition of wax with a selected molecular weight of 200 to 700. In this way it is possible to offer films with extraordinary barrier values or to reduce the usual amounts of resin, according to the state of the art, to * obtain comparable barrier values. The following measurement methods are used for the characterization of the raw materials and of the 10 films. The melt flow index The melt flow index is measured according to DIN 53 735, at 21.6 N load and at 230 ° C. The melting point 15 Measurement by differential scanning calorimetry (DSC), maximum of the melting curve, heating rate 20 ° C / min. f The passage of water vapor and oxygen The water vapor capacity is determined in accordance with DIN 53 122 part 2. 20 Surface tension The surface tension is determined by means of the so-called ink method (DIN 53 364 ).

The determination of molecular weight The average molecular weight and average number of molar masses and the average molecular weight ratio of • weight / average dispersion number of molar masses, following the stipulation of DIN 55672, part 1, by means of gel permeation chromatography. Instead of THF, orthodichlorobenzene is used as the eluent. In those cases in which the olefinic polymers investigated are not soluble at room temperature, the corresponding measurement is carried out at elevated temperature (around 135 ° C). The isotactic portion The isotactic portion of the homopolymers can be characterized in approximation by the insoluble fraction of the raw material in n-heptane. Typically, an extraction is carried out in Soxiet with boiling n-heptane, it being convenient that the capacity of the Soxiet apparatus for granulates be filled with tablets. The thickness of the tablets should not exceed 500 micrometers. For the quantitative formation of phases of the n-heptane insoluble portion of the homopolymer, it is decisive that a sufficient extraction time is ensured, from 8 to 24 hours. The operative definition of the isotactic portions PP, So. in 20 percent, it is given by the ratio of the weights of the fraction insoluble in n-heptane, dried, for balance: PPiso = 100 x (insoluble fraction in n-heptane / balance) An analysis of dried n-heptane extracts indicates that as a rule these are not obtained from crude atactic propylene homopolymers. In the extraction, aliphatic oligomers are also included and olefins, especially isotactic oligomers, as well as possible additives, such as hydrated hydrocarbon resins and wax. The chain isotacticity index The PPIS0 isotactic portion defined above, taken as the portion Insoluble in n-heptane is not sufficient for the characterization of the chain isotacticity of homopolymers. It is significant that the index of The chain isotacticity II of the homopolymers was determined by means of highly soluble 13 C-NMR spectroscopy, with the NMR probe not being selected as the original raw material, but rather as its insoluble fraction in n-heptane. For the characterization of the sotacticity of the polymer chains, the index II isotacticity index of triad is used in practice spectroscopic by 13 C-NMR (Triada). Determination of the chain isotacticity index II with f with respect to the triad (Triada). The determination of the chain sotacticity index (Triad) of the n-heptane insoluble portion of the homopolymers is carried out, as well as as of the film, from its 13C-NMR spectrum. It compares the intensities of the Triada signals that result from the methyl groups, with different local environments. Next, two cases of the use of the 13 C-NMR spectrum are differentiated: A) The raw material examined is a propylene homopolymer without statistical content of G2. f B) The raw material examined is a propylene homopolymer with a statistically small content of C2; in the following, C2-C3 copolymer means: CASE A: The chain isotacticity index of the homopolymer is determined from its 13 C-NMR spectrum. The f 10 intensities of the signals obtained as a result of the methyl groups with different environments are compared. In the 13 C-NMR spectrum, a homopolymer exhibits essentially three signal groups, termed triads. 1. By a chemical shift of approximately 21 to 22 ppm, the "mm-Triad" appears, which adds the methyl groups with groups methyl left and right neighbors, directly. 2. By means of a chemical displacement of approximately 20.2 to 21 f ppm, the "mr-Triad" appears which adds the methyl groups to left or right neighboring methyl groups, directly. 3. By a chemical shift of approximately 19.3 to 20 20 ppm, the "rr-Triad" appears, which adds the methyl groups without neighboring methyl groups directly. The intensities of the added signal groups are determined as the integral of the signal. The isotacticity index of the chain is defined as follows: Jmm "*" O. Or Jmr Triadas II =. 100 • Jmnrt "•" Jmr "*" Jrr where Jmm, Jmr and Jrr mean the integral of the added signal groups. Case B: In the 13 C-NMR spectrum an ethylene-propylene copolymer 10 has the chemical displacement of the methyl groups of interest, in the • scale from 19 to 22 ppm. The spectrum of the methyl groups can be divided into three blocks. In these blocks CH3 groups are present in sequences of triads, whose incorporation into local environments is clarified in more detail in the following: Block 1: Groups CH3 in the sequence PPP (mm-Triad) • C C C I I I 20 C - C - C - C - C - C Block 2: CH3 groups in the PPP sequence (Triads mr or rm) C C I I C-C-C-C-C-C- • and CH3 groups in the EPP sequence (m string): C C 10 C-C-C-C-C-C- • Block 3: CH3 groups in the PPP sequence (triads rr) C -C-C-C-C-C-C- 20 C C CH3 groups in an EPP sequence (r chain): -C-C-C-C-C-C C CH3 groups in an EPE sequence: • -CCCCCC- 5 During the determination of the index II (Triads) of chain isotacticity referred to the triads, of the insoluble portions in heptane of an ethylene-propylene copolymer, only the PPP triads, that is, only those propylene units that are between • 10 two neighboring propylene units (see also EP-B-0 115 940, page 3, lines 48 and 49). The definition of the isotacticity index of the triad of an ethylene-propylene copolymer is as follows: II (Triad) = 100x (Jmm / Jppp) Calculation of the isotacticity index of an ethylene-propylene copolymer: 1. Jmm is given by means of the peak integral of block 1. 20 2. The integral (Jtotai) of the peaks of all the methyl groups of the blocks is calculated. 1, 2 and 3. 3. By means of simple considerations, it can be pointed out that Jppp = Jtotai - EPP "JEPE- Test and Measurement Preparations: 60 to 100 mg of polypropylene is introduced into a 10 mm tube for NMR and add hexachlorobutadiene and tetrachloroethane in a mixing ratio of 1.5: 1, until a filling height of about 45 mm is reached.The suspension is maintained (usually about one hour) at about 140 ° C, until form a homogeneous solution In order to accelerate the dissolution, it is shaken from time to time with a glass bar.The emission of the 13C-NMR spectrum at high temperature is obtained • 10 (usually at 365 ° K) under normal measurement conditions (semiquantitative).

REFERENCES W. O. Crain, Jr., A. Zambelli and J. D. Roberts, Macromolecuies, 4, 330 (1971). A. Zambelli, G. Gatti, C. Sacchi, W. O. Crain, Jr., and J. D. Roberts, Macromolecules, 4, 471 (1971). C. J. Carman and C. E. Wilkes, Rubber Chem. Technol., 44, 781-20 (1971).

EXAMPLE 1 It is prepared by coextrusion and then stepwise orientation in the longitudinal direction and in the transverse direction, a film transparent, of three layers, with symmetrical construction, and with a total thickness of 20 μm. The coating layers had a thickness of 0.6 μm each. A.- The basic layer: 86.85% by weight of highly isotactic propylene homopolymer, with a melting point of 166 ° C and a melt flow index of 3.4 g / 10 minutes, the insoluble portion in n-heptane having a chain isotacticity index of 98%. 10.0% by weight of hydrocarbon resin, with softening point of 120 ° C, and with weight average molecular weight (Mw) of 1000. 15 3.0% by weight of polyethylene wax, with number average molecular weight (Mn) of 500 and a molecular weight ratio Mw / Mn of 1.08 flft 0.15% by weight of N, N-bis-ethoxyalkylamine (antistatic). B. The coating layers: Approximately 75% by weight of ethylene-propylene random copolymer, with C2 content of 4.5% by weight. 25% by weight, approximately, of ethylene-propylene-butylene random terpolymer, having an ethylene content of 3% by weight and a butylene content of 7% by weight (the remainder, propylene). 0. 33% by weight of SiO 2 as antiblocking agent with an average particle size of 2 μm. 0.90% by weight of polydimethylsiloxane, with a viscosity of 30,000 mm2 / s. • The preparation conditions in the individual stages of the procedure were: Extrusion: Temperatures: Basic layer 260 ° C Coating layers 240 ° C ^ Receiver roller temperature 20 ° C. Longitudinal stretching: Temperature 110 ° C. 10 Longitudinal stretch ratio: 5.5 Transverse stretch: Temperature 160 ° C Transverse stretch ratio 9 Fixation: Temperature: 140 ° C. Convergence: 20%. 15 By means of the transversal stretch ratio? O = 9 we want to indicate an effective value. This effective value is calculated from the final width B of the film, less twice the width b of the hem band, divided by the width C of the longitudinally stretched film, optionally less than twice the width b of the film. hem band. EXAMPLE 2 A film is prepared as described in Example 1. In place of the highly isotactic propylene homopolymer, a common raw material was added, with a melting point of 165 ° C and a melt flow rate of 3.5 g / 10 minutes. . The chain isotacticity index of the portion • insoluble in n-heptane, of this polypropylene, was 94%. The remaining composition and the preparation conditions were not different from those of Example 1.

EXAMPLE 3 • 10 A film is prepared as described in Example 2. Unlike Example 2, in this case the film contains in the basic layer 8% by weight of the same hydrocarbon resin. The remaining composition and the preparation conditions were not different from those of Example 2.

EXAMPLE 4 f A film was prepared as described in example 1. In contrast to example 1, in this case the film contained in the basic layer 8% by weight of the same hydrocarbon resin. The remaining composition and the preparation conditions were not different from those of Example 1.

EXAMPLE 5 A film was prepared as described in example 4. A different from example 4, in this case the film contained in the basic layer 5 percent by weight of the same polyethylene wax. The remaining composition and the preparation conditions were not different from those of Example 4.

EXAMPLE 6 • 10 A film was prepared as described in example 3. In contrast to example 3, the film in this case contained in the basic layer 10% by weight of the same hydrocarbon resin and 5 percent by weight of the same wax which was described in Example 3. The remaining composition and the preparation conditions were not different from those of Example 3. 15 EXAMPLE 7 • A film was prepared as described in example 3. In contrast to example 3, the film in this case contained in the basic layer 5 weight percent of the same wax as described in Example 3. The remaining composition and the preparation conditions were not different from those of Example 3.

EXAMPLE 8 A film was prepared as described in example 1. A ^ difference from example 1, in this case the film contained in the basic layer 5% by weight of the same wax as described in example 1. The remaining composition and the preparation conditions were not different from those of example 1.

EXAMPLE 9 • 10 A film was prepared as described in Example 3. In contrast to Example 3, the film in this case contained in the basic layer 3 weight percent of a macrocrystalline paraffin wax. The remaining composition and the preparation conditions were not different from those of the example 3.

• EXAMPLE 10 A film was prepared as described in example 2. A Unlike the example 2, the film in this case contained in the basic layer 5 weight percent of a macrocrystalline paraffin wax. The remaining composition and the preparation conditions were not different from those of Example 2.

COMPARATIVE EXAMPLE 1 A film was prepared as described in example 3. A f1 difference from example 3, in this case the film did not contain in the basic layer no polyethylene wax. The remaining composition and the preparation conditions were not different from those of Example 3.

COMPARATIVE EXAMPLE 2 • 10 A film was prepared as described in example 3. Unlike in example 3, the film in this case did not contain any hydrocarbon resin in the basic layer. The remaining composition and the preparation conditions did not vary with respect to those of Example 3.

COMPARATIVE EXAMPLE 3 f A film was prepared as described in example 3. In contrast to example 3, in this case the film contained in the basic layer a polyethylene wax with number average molecular weight (Mn) of 1000, 20 and a ratio of Mw / Mn molecular weight of approximately 1.08. The remaining composition and the preparation conditions did not vary with respect to those of Example 3.

COMPARATIVE EXAMPLE 4 A film was prepared as described in example 3. A f difference from example 3, in this case the film contained in the basic layer a hydrocarbon resin with a weight average molecular weight (Mw) of 2000. The rest of the composition and the preparation conditions did not vary with respect to those of example 3.

COMPARATIVE EXAMPLE 5 • 10 A film was prepared as described in comparative example 1. Unlike comparative example 1, the film in this case contains in the basic layer the highly isotactic propylene homopolymer described in example 1. The remaining composition and the conditions of The preparation did not vary with respect to those of comparative example 1.

COMPARATIVE EXAMPLE 6 A film was prepared as described in the example Comparative 3. Unlike comparative example 3, the film in this case contains in the basic layer the highly isotactic propylene homopolymer described in example 1. The remaining composition and the preparation conditions did not vary with respect to those of the comparative example 3.

COMPARATIVE EXAMPLE 7 A film was prepared as described in example 2. Unlike in example 2, the film does not contain, in this case, in the basic layer 5, polyethylene wax. The remaining composition and the preparation conditions did not vary with respect to those of Example 2.

COMPARATIVE EXAMPLE 8 # 10 A film was prepared as described in comparative example 2. Unlike comparative example 2, in this case the film does not contain polyethylene wax in the basic layer either. The remaining composition and the preparation conditions did not vary with respect to those of Comparative Example 2. COMPARATIVE EXAMPLE 9 • A film was prepared as described in Example 9. In contrast to Example 9, in this case the film does not contain the basic layer 20 no resin. The remaining composition and the preparation conditions did not vary with respect to those of Example 9.

COMPARATIVE EXAMPLE 10 A film was prepared as described in example 10. A • difference of example 10, in this case the film does not contain any resin in the basic layer. The remaining composition and the preparation conditions did not vary with respect to those of Example 10. The water vapor barriers of the films according to the examples and the comparative examples are summarized in the following tables. • 10 • ro o O n n TABLE 2 -4 VB comparative example • • ro o O n n TABLE 1 OR? B = example

Claims (19)

1. NOVELTY OF THE INVENTION CLAIMS • 5 1. Biaxially oriented multilayer polypropylene film comprising a base layer and at least one sealable coating layer, which contains in its basic layer a combination of A resin and wax; characterized in that the base layer contains a resin with a weight average molecular weight (Mw) of 600 to 1500; and a wax with an average number molecular weight (Mn) of 200 to 700.
2. 2. Polypropylene film according to claim 1, further characterized in that the insoluble portion in n-heptane of the polypropylene of the base layer it has an index of chain sotacticity, measured by means of 13 C-NMR spectroscopy, of at least 95%.
3. 3. Polypropylene film according to claim 1 and / or claim 2, further characterized in that the base layer contains a polypropylene whose Mw / Mn is from 1 to 10.
4. 4.- Polypropylene film in accordance with a or more of claims 1 to 3, further characterized in that the propylene polymer 20 of the base layer is disintegrated with peroxide, or is prepared by means of metallocene catalyst.
5. 5. Polypropylene film according to one or more of claims 1 to 4, characterized in that it contains as resin a non-hydrogenated styrene polymer, a methyl styrene-styrene copolymer, a pentadiene or cyclopentadiene copolymer, an alpha- or beta-pinene polymer, rosin or a rosin derivative, or a terpene polymer, and hydrogenated compounds thereof, or an alpha- • 5-methylstyrene-vinyltoluene copolymer or mixtures thereof.
6. 6. Polypropylene film according to one or more of claims 1 to 5, further characterized in that the hydrocarbon resin is contained in an amount of 1 to 15 weight percent, based on the J weight of the base layer.
7. 7. The polypropylene film according to one or more of claims 1 to 6, further characterized in that the wax is contained in an amount of 1 to 10 weight percent relative to the weight of the base layer.
8. 8. Polypropylene film according to one or more of claims 1 to 7, further characterized in that the wax is a polyethylene wax with Mw / Mn from 1 to 2.
9. 9.- Polypropylene film in accordance with one or more than Claims 1 to 8, further characterized in that the wax is a wax of macrocrystalline paraffin.
10. 10. Polypropylene film according to one or more of claims 1 to 9, further characterized in that it has on both sides a sealable coating layer of alpha-olefinic polymers.
11. 11.- Polypropylene film in accordance with one or more of ^^ g ggfjgHj ^^ claims 1 to 10, further characterized in that the polymer of the coating layer or layers is disintegrated with peroxide and the disintegration factor is in the range of 3 to 15, preferably 6 to 10.
12. 12 .- Polypropylene film in accordance with one or more of • 5 claims 1 to 11, further characterized in that an intermediate layer of alpha-olefin polymers is included, on one or both sides, between the base layer and the coating layer (s).
13. 13. Polypropylene film according to one or more of claims 1 to 12, further characterized in that the thickness of the film is from 4 to 60 μm; especially from 5 to 30 μ and, preferably from 6 to 25 μm; the base layer constituting approximately 40 to 60% of the total thickness.
14. 14. Polypropylene film according to one or more of claims 1 to 13, further characterized in that the base layer 15 contains an antistatic agent, preferably a tertiary aliphatic amine.
15. 15. Polypropylene film according to one or more of claims 1 to 14, further characterized in that the layer or layers • coating contains (n) lubricating agents, preferably polydimethylsiloxane, and antiblocking agent, preferably Si02.
16. 16. Polypropylene film according to one or more of claims 1 to 15, further characterized in that all the layers of the film contain neutralizing and stabilizing agents. 17.- Procedure to prepare a polypropylene film according to claim 1, characterized in that the orientation is carried out in the longitudinal direction, with a longitudinal stretch ratio of 5: 1 to 9: 1, and in the transverse direction with a transverse stretch ratio of 5: 1 to 10: 1. • The use of polypropylene films according to one or more of claims 1 to 16, as packaging films, preferably as films for cigar packs. 19.- The use of a mixture of polypropylene and resin with a weight 4 molecular weight average (Mw) of 600 to 1500, and wax with a number average molecular weight (Mn) of 200 to 700, in the preparation of oriented polypropylene films, to improve the water vapor barrier.