WO2020139119A1

WO2020139119A1 - A polymer for high-speed production of biaxially oriented film, a film and an article made thereof

Info

Publication number: WO2020139119A1
Application number: PCT/RU2018/000904
Authority: WO
Inventors: Kristina Andreevna SAMAROVA; Ludmila Borisovna SHABALINA; Irina Gennadievna RYZHIKOVA
Original assignee: Sibur Holding PJSC
Current assignee: Sibur Holding PJSC
Priority date: 2018-12-28
Filing date: 2018-12-28
Publication date: 2020-07-02
Anticipated expiration: 2021-06-28
Also published as: CZ2021355A3; EA202191584A1; JP2022515867A; JP7213989B2

Abstract

The invention relates to polypropylene for preparation of films, in particular, biaxially oriented polypropylene (BOPP) films. The structural characteristics of the claimed polypropylene allow to increase the processing speed (450 m/min and more) in the process of producing BOPP films. The invention also provides BOPP films, at least one layer of which comprises polypropylene. Films according to the invention can be used for the packaging manufacture, including packaging for food products, adhesive tapes, labels, etc.

Description

A POLYMER FOR HIGH-SPEED PRODUCTION OF BIAXIALLY ORIENTED FILM, A FILM AND AN ARTICLE MADE THEREOF

Field of the invention

The present invention relates to polypropylene for the preparation of films, in particular biaxially oriented polypropylene (BOPP) films. Structural characteristics of the claimed polypropylene allow to increase the processing speed in the process of preparing BOPP films up to 450 m/min or higher without plate-out formation and the use of gliding additives (for example, metal stearates), which are known to facilitate the process of film production. The invention also relates to BOPP films, at least one layer of which contains polypropylene. Films according to the invention are suitable for producing packaging, including packaging for food products, adhesive tapes, labels, etc.

Background of the invention

Due to the possibility of a wide variation of polypropylene film properties depending on the composition and method of production, polypropylene films are a popular material for the manufacture of high-quality flexible packaging. In particular, biaxially oriented polypropylene (BOPP) films are used for the manufacture of food and non-food products packaging, for individual or multiple-unit packaging, wherein the packaging can be made transparent or metallized, matte, colored (depending on the filler color). Besides, BOPP films are used to make labels, adhesive tapes, etc.

As a rule, the major component of BOPP films is isotactic polypropylene with a degree of isotacticity of 87-89% (isotacticity is determined by the content of isotactic pentads [mmmm] by C¹³ NMR analysis). The presence of a certain number of defects in the structure of isotactic macromolecules contributes to a higher orientation ability of the polymer. The higher orientation ability of polypropylene, in turn, allows increasing the speed of processing and increasing the volume of film production.

It is also known that an increase in the xylene-soluble fraction in the polymer leads to an improvement in the orientation ability of the polymer. However, at the same time, it is noted in the prior art that during the processing of such a polymer, a large number of low molecular weight fractions are released followed by their subsequent combustion and formation of plate-out deposited on the equipment. The latter specifically leads to frequent equipment shutdowns for cleaning, which in turn, contributes to an increase in equipment downtime. From the document EP2143116 a heat-resistant film is known, at least one layer of such film contains polypropylene having a melt flow rate from 0.5 to 15 g/10 min and xylene cold soluble fraction value of less than 3.5 wt.%; the degree of crystallinity determined by X-ray diffraction ranging from 0.5 to 0.85 and xylene and heptane insoluble fractions content of more than 94% by weight. The film additionally contains at least a second layer containing a heterophasic statistical copolymer (impact copolymer), where the heterophasic statistical copolymer has a melt flow rate of from 0.5 to 15.0 g/10 min and a melting point of from 120 to 170°C. The film is characterized by high tensile strength, impact strength, and puncture resistance due to low content of the xylene cold soluble (XCS) fraction. The disadvantage of the solution proposed in EP21431 16 is the slow processing speed of polypropylene due to the low content of xylene cold soluble (XCS) fraction.

From EP0925912 a high metal adhesive film and metallized film are known, the core layer of which is made of isotactic polypropylene having an isotactic pentad [mmmm] content of 88% and higher, preferably 90% or more, Mw/Mn falls within the range from 2 to 6. However, at the same time, other characteristics of isotactic polypropylene (the content of fractions having certain molecular weights and fractions having a certain solubility in xylene and heptane) have not been disclosed. The processing speed is also not specified.

Also, from EP0831994, a method of producing a BOPP film is known, where the core layer of the film contains either polypropylene with atacticity of at least 10% or a polymer composition which comprises a mixture of an isotactic polymer with a degree of atacticity of less than 5% and atactic polypropylene, syndiotactic polypropylene, ethylene-propylene copolymers, propylene terpolymer, polybutene or linear low density polyethylene. The use of propylene polymer or polymer composition with a degree of atacticity of 10% or more allows obtaining a BOPP film with high tear resistance. There are no other requirements to the characteristics of isotactic polypropylene. Consequently, the content of fractions having certain molecular weights and fractions having a certain solubility in xylene and heptane is not considered as a criterion for determining suitability of the polypropylene for use in film processing.

Thus, the complete combination of structural characteristics of polypropylene for use in BOPP films preparation, which allows processing at a speed of at least 450 m/min while maintaining the required level of film strength characteristics in accordance with regulatory documents is not known now.

Summary of the Invention

An object of the present invention is to determine the combination of structural characteristics of polypropylene that allows to increase the efficiency of the process of biaxial orientation of polypropylene to obtain a BOPP film.

The technical result of the present invention resides in the increase in the productivity of the process of obtaining BOPP films by using the polypropylene in the film composition, the structural characteristics of the polypropylene making it possible to process the film at the speed of at least 450 m/min.

The technical result also includes a lack of plate-out formation on the die in the process of film preparation, which thereby reduces equipment downtime.

An additional technical result resides in the possibility of obtaining a wide range of films: transparent, matte, filled, general purpose, etc. as well as the possibility of applying layer coatings, for example, a metallized layer, printing, etc.

The object of the present invention is solved and the technical result is achieved by introducing a polypropylene into the film, which polypropylene has the following characteristics:

- the amount of the xylene cold soluble (XCS) fraction in the polymer falls within the range from 4.0 to 6.0 wt.%, wherein the proportion of the fraction with a molecular weight in the range of 50,000 g/mol and greater is at least 40 wt.%, while the proportion of the fraction with a molecular weight in the range from 1,500 to 50,000 g/mol, is not more than 40 wt.%

- the amount of the heptane soluble (HS) fraction in the polymer falls within the range from 2.5 to 3.5 wt.%, wherein the proportion of the fraction with a molecular weight of 50,000 g/mol and greater is at least 60 wt.%, while the proportion of the fraction with a molecular weight in the range of from 1,500 to 50,000 g/mol, is not more than 40 wt.%.

The inventors found out that a certain content of xylene- soluble and heptane- soluble fractions characterized by certain values of molecular weights allows to increase the speed of the process for preparing biaxially oriented films by improving the polypropylene orientation. While not wishing to be bound by any particular theory, the inventors believe that in order to reduce the adverse effect of increased plate-out formation on the forming die and to retain the orientation ability of the polypropylene, said polypropylene must contain a certain amount of XS and HS fractions having a certain content of low molecular weight (from 1,500 to 50,000 g/mol) and high molecular weight (from 50,000 g/mol and above) components.

Description of the Drawings

Fig 1 illustrates a BOPP film prepared from the polypropylene according to the invention.

Fig 2 illustrates the BOPP film prepared in Example 3.

Fig 3 illustrates the BOPP film prepared in Example 4.

Fig 4 illustrates the BOPP film prepared in Example 5.

Detailed Description of the Invention

The following is a detailed description of various aspects and embodiments of the present invention.

The polypropylene to be used in the film preparation is characterized by the following:

- the content of xylene cold soluble (hereinafter referred to as XCS) fraction, is in the range from 4.0 to 6.0 wt.% preferably in the range from 4.5 to 5.8 wt.%;

- the content of heptane soluble (hereinafter referred to as HS) fraction, is in the range from 2.5 to 3.5 wt.%.

A distinctive feature of the claimed polypropylene to be used in the manufacture of BOPP films is the molecular weight of XCS fraction being mainly in the range of from 1,500 to 50,000 g/mol, whereas the proportion of XCS fraction with a molecular weight of more than 50,000 g/mol does not exceed 40 wt.%, preferably does not exceed 30 wt.%, more preferably does not exceed 20 wt.%.

Another essential feature of the claimed polypropylene for use in the preparation of BOPP films is that the proportion of HS fraction with a molecular weight of 50,000 g/mol and greater is at least 60 wt.%, preferably at least 65 wt.%, most preferably at least 70 wt.%, and the proportion of HS fraction with a molecular weight ranging from 1,500 to 50,000 g/mol is not more than 40 wt.%, preferably not more than 25 wt.%, most preferably not more than 15 wt.%.

An increase of the proportion of low molecular weight components (with a molecular weight of not more than 50,000 g/mol) in the heptane soluble and xylene soluble fractions leads to deterioration of the physico-mechanical properties of the film, as well as to an increased plate-out formation on the die/spinneret during film processing.

Preferably, the molecular weight distribution of the polypropylene is of from 4 to 7, more preferably is in the range from 5 to 7.

Preferably the content of the isotacticity pentad of polypropylene [mmmm] is of from 87 to 89%.

The present invention provides a polymer for the preparation of BOPP films at high processing speed (at least 450 m/min), which can be obtained using supported Ziegler-Natta titanium-magnesium catalysts of the general formula MgCb/TiCU/Di/Di/TEA, where titanium tetrahalides are supported on magnesium halides, D1 is an internal electron donor, D2 is an external electron donor, triethylaluminum (TEA) is a co-catalyst.

As Dl, any compound known from the prior art as a donor of the Ziegler-Natta catalyst is used, wherein the compound comprises at least one of the following functional groups: alcohol, amino, amide or ester group. Specific examples of internal donors include, but are not limited to: methanol, ethanol, isopropanol and butanol, diethylamine, diisopropylamine and triethylamine, formamide and acetamide, C1-C20 benzoic acid alkyl esters, Ci-Cs alkyl esters of aliphatic monocarboxylic acids, 1,8- naphthyl diesters, malonates, succinates and glutarates. However, in the present invention it is not recommended to use fourth-generation Ziegler-Natta catalysts (comprising phthalate compounds as donors) and internal electron donors represented by fluorene compounds.

As D2, the organosilicon compound represented by the following formula R_nSi(OR)4-_n can be used, where R is a hydrocarbon radical, OR is an alkoxy group, R is a hydrocarbon group, and n is an integer 0 < n < 4. Examples of the organosilicon compounds represented by this formula which may be used in the present invention include the following: diisopropyldimethoxysilane, tert-butylmethyldimethoxysilane, tert-butylmethyldiethoxysilane, tert-amylmethyldiethoxysilane, dicyclohexyl dimethoxysilane, cyclohexylmethyldimethoxysilane, cyclohexylmethyldiethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, tert-butyltriethoxysilane, phenyltriethoxysilane, cyclohexyltrimethoxysilane, cyclopentyltrimethoxysilane, 2 - methylcyclopentyl trimethoxysilane, cyclopentiltrietoksisilan, n- propyltrimethoxysilane, dicyclopentyl dimethoxysilane, dicyclopentyldiethoxysilane, tricyclopentylmethoxysilane, dicyclopentylmethyl methoxysilane, dicyclopentylethylmethoxysilane and cyclopentyldimetiletoksisilan.

It is known to a person skilled in the art that the characteristics of polypropylene (the proportion of xylene-soluble and heptane-soluble fractions and molecular weight distribution thereof) depend both on the nature and on the amount of external electron donor used in the catalyst system. Preferably, the external donor is added at a molar ratio of co-catalyst (Co) to external donor (ED) [Co/ED ratio] in the range of from 2 to 180.

More specific examples of the described catalysts and methods for preparation thereof are catalysts and methods for preparation thereof disclosed in EP2221320, EP2638080, EP2951215 documents.

The polypropylene of the present invention can be obtained by gas phase or suspension polymerization of propylene in the presence of the above catalysts. In any of the polymerization processes used, the components of the catalytic system (catalyst, cocatalyst and optionally an external electron donor) can be brought into contact with each other before adding them to the polymerization reactor. As the co-catalyst, an alkyl-Al compound can be used, for example, triethyl aluminum, diethyl aluminum chloride, triisobutyl aluminum, tri-n-butyl aluminum, tri-n-hexylamine aluminum, tri-n-octyl aluminum.

Polymerization using a Ziegler-Natta catalyst is generally carried out at a temperature in the range of 50-80°C, preferably in the range of 65-75°C and an operating pressure in the range from 0.1 to 5.0 MPa, preferably in the range of from 0.5 to 3.5 MPa.

Preferably, in order to preserve the physico-mechanical properties of the produced film, the melt flow index (MFl230_°c_/2.i6 _kg) of the used polymers determined according to ASTM D 1238, should be at least 3 g/10 min.

In particular, polypropylene can be prepared according to the processes described, for example, in the documents US8178633, EP2726517, etc.

These methods for producing polypropylene, given as examples, allow to achieve the above characteristics, however, these methods are not exclusive. Polypropylene with the specified properties can be obtained in other ways, known from the prior art.

Preferably, the polypropylene contains stabilizers, which comprise at least a mixture of antioxidants and acid absorbers. Any antioxidants known from the prior art can be used as antioxidants, preferably a mixture of phosphite and phenol antioxidants is used. As an acid absorber, any acid absorber known from prior art other than the metal stearate class compounds can be used. Besides, other known additives can be additionally used to allow polypropylene to retain its properties during processing and operation. The amount of stabilizers added to the polypropylene is from 1 to 3 kg per ton of polypropylene, preferably from 1.2 to 2.5 kg per ton of polypropylene, more preferably from 1.2 to 1.5 kg per ton of polypropylene.

The polypropylene according to the invention is substantially free from calcium stearate. Calcium stearate transforms into stearic acid when interacting with acids, which readily migrates to the surface making it impossible to produce a metallized film. The term“substantially free” means a content of less than 0.010% by weight, preferably less than 0.005 wt.%, most preferably less than 0.001 wt.%.

The specified polypropylene can be used both as a primary and as an additional component of any film layer of any formulations known from the prior art. The exact structure of the film (the number and order of layers) and the content of the layers depend on the requirements for the film and articles made from the film.

In addition to the polypropylene of the invention, the film may contain other polyolefins as well as functional polymers. Copolymers and terpolymers of a-olefins are used as polyolefins, specifically, copolymers of propylene and ethylene, propylene and butene, terpolymers of propylene, ethylene and butene, etc. The following compounds are used as functional polymers: copolymers of ethylene with vinyl alcohol, polyvinylidene chloride, copolymers of vinylidene chloride, polyesters, polyamides (to impart gas and/or aroma-proof properties to the film), interpolymers of ethylene and a- olefin (for adhesive-free paper-to-film lamination), maleic anhydride homopolypropylene (adhesive layer in coextrusion films), etc.

In the first embodiment of the present invention, the film is intended for the preparation of wrapping paper, as the base for adhesive tapes, etc. and is a multi-layer polypropylene film, each layer of which consists of polypropylene that has the above characteristics as well as of antistatic substances and/or anti-caking substances and/or antioxidant. The antiblocking agents are silicon dioxide (S1O2), polymethyl methacrylate (PMMA), and the like, and the antioxidant is a phenolic antioxidant.

In the second embodiment of the invention, the film is intended for adhesive- free film-to-paper lamination and includes at least the following: a core layer containing polypropylene having the above characteristics, and a functional layer comprising: ethylene-butene copolymer, ethylene-octene copolymer, ethylene-butene-octene terpolymer, ethylene-butene copolymer modified with grafted maleic anhydride, ethylene-octene copolymer modified with grafted maleic anhydride, ethylene-butene- octene terpolymer, modified by grafted maleic anhydride or mixtures thereof, or mixtures formed from any of the above copolymer and/or terpolymer, modified copolymers and/or terpolymers, and blends with hydrogenated petroleum resin.

In the third embodiment of the invention, the film has barrier properties and contains at least the following layers: one layer of propylene polymer that has the above characteristics, and a layer of gas barrier material represented by polyamide, a copolymer of ethylene and vinyl alcohol, etc. A layer of modified polyolefin, for example, a layer of propylene polymer modified with maleic anhydride may optionally be used to improve the adhesion between the layer of propylene polymer meeting the above characteristics and the layer of gas barrier material.

Other embodiments of the present invention are clear to a person skilled in the art and are not disclosed in detail in the description of the invention. For example, additives can be included in the formulation in effective amounts, i.e. in quantities that provide the desired functional properties or improve the parameters and/or functionality of the finished film. In particular, examples of additives include, but are not limited to the following: additives that offer anti-block, anti-static and slip effects as well as antioxidants and neutralizers, technological additives, nucleating agents, additives that reduce the effect of UV radiation, and UV-absorbers, dyes, fillers, thickeners, modifiers based on hydrocarbon resins, etc.

The total thickness of the films varies over wide ranges depending on the intended purpose of use. In the preferred embodiments, the film has a total thickness of from 2 to 100 pm, preferably from 5 to 50 pm, more preferably from 10 to 30 pm. The film of the present invention is obtained by coextrusion of polypropylene with other polymers followed by biaxial orientation. The orientation value of the film in the Machine Direction is from 4.5 to 5.5, in the Transverse Direction - up to 10.

Films prepared according to the present invention after the drawing can be subjected to processing by the following procedures:

1. embossing on the surface of the film;

2. film surface activation/modification to make it suitable for printing (for example, by plasma treatment, corona treatment, and flame treating),·

3. laminating the prepared film on a woven or non- woven material, in particular, laminating on a paper, foil or other films;

4. depositing a metallic layer (for example, depositing aluminum layer by vacuum technology that uses the condensation of a metal vapor)·,

5. applying an adhesive layer on one or both surfaces of the film, thus obtaining an adhesive film.

Optionally, the treated film is used to make the final article such as packaging, metallized packaging, label, bag, adhesive tape and other articles using the BOPP films according to the invention. Specific examples include, but are not limited to: making a label as specified in EP2197669, WO2017077184 documents, making a bag as disclosed in particular in US9108391 document, preparing food packaging as indicated, for example, in WO2016205381 document, producing a metallized film as described in EP0925912 document.

Embodiments of the invention

Test methods

1. The melt flow index (MFI) was determined in accordance with ASTM D1238

2. The mass fraction of the soluble fraction in boiling heptane/isotactic fraction was determined according to National State Standard 26996-86.

3. The mass fraction of the fraction soluble in p-xylene was determined according to ISO 16152.

4. Determination of molecular weight distribution (MWD) of polypropylene samples and statistical copolymer of propylene and ethylene was performed by Gel Permeation Chromatography (GPC) on the Agilent PL-GPC 220 system, according to ISO 16014-4-2012: High-temperature method. The dissolution temperature was 150 °C, the solvent was 1,2,4-trichlorobenzene.

5. Determination of molecular weight properties of xylene-soluble (XCS) and heptane-soluble (HS) substances from the samples was carried out by the method of low-temperature GPC on an Agilent 1200 liquid chromatograph (Agilent), according to ISO 16014-4-2012: Low-temperature method. The measured dissolution temperature was 40 °C, the solvent was tetrahydrofuran.

6. The microstructure, the degree of isotacticity, and the pentad ratio of polypropylene samples were determined by the method of high resolution nuclear magnetic resonance spectroscopy on carbon nuclei (¹³C NMR) on Bruker Avance III 400 MHz NMR spectrometer. For research purposes, a sample weighing 250 mg was dissolved in 2.5 ml of trichlorobenzene with heating to 140°C. The number of scans on ¹³C nuclei is 16,000. The experiment temperature was 140°C.

The invention is described in more detail by the examples below. Examples are provided to illustrate the present invention only and do not limit the scope thereof.

Example 1:

Propylene polymer having MFI 3.0 g/10 min (at 230°C and 2.16 kg) was obtained by gas-phase technology at a temperature of 65-75°C and a working pressure of 2.2 MPa. A catalyst prepared in a similar way as in example 6 of EP0361493 was used as a catalyst, except that diisobutyl dimethoxysilane was used as an external electron donor.

The BOPP film was a five-layer film, with each layer thereof consisting of the above polypropylene and antioxidants, such as the hindered phenolic antioxidant, pentaerythritol tetraoxy (3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate) (Irganox 1010), and phosphorus-containing antioxidant, tris (2,4-di-tert-butylphenyl) phosphite (Irgafos 168), and also hydrotalcite as an acid absorber, in the amount of 1.35 kg of stabilizers per ton of polypropylene. The film was prepared by continuous extrusion of polypropylene with a stepwise orientation, heat setting and cooling of the film slab: molten materials plasticized in each of the extruders (five extruders corresponding to the number of layers); were combined in a die (head) and flowed confluent from a slot die onto a cooling drum (shaft) in the form of a slab, then the slab was cooled down by passing through a water bath. Next, the film slab was reheated to 100-115°C on heating cylinders and stretched up to 6 times its original length in the machine direction on the rollers. The film stretched in the machine direction went into an oven, where it was heated once again by air up to 170-180°C and stretched up in the transverse direction 10 times its original width. The total film thickness was 20 pm, while the outer layers were 0.9 pm thick, the intermediate layers were 2.5 pm, the core layer was 13.2 pm. The characteristics of the used polypropylene and the processing speed of the film are shown in Table 1.

Example 2:

The BOPP film was prepared as in Example 1, except for using the polypropylene having the characteristics shown for Example 2 in Table 1, and the film consisting of five layers, each layer comprising of polypropylene. The processing speed of the film is shown in Table 1.

Example 3 (Comparative).

A BOPP film was prepared as in Example 1, except that polypropylene was prepared using a Ziegler-Natta catalyst with dibutyl phthalate as internal electron donor and wherein the polypropylene had the characteristics shown in Table 1 for the comparative Example 3. The processing speed of the film is shown in Table 1.

Example 4 (Comparative).

The BOPP film was prepared as in Example 1 , except for using polypropylene prepared using a Ziegler-Natta catalyst with 9,9-bis-methoxymethylfluorene as internal electron donor and wherein the polypropylene had the characteristics shown in Table 1 for the comparative Example 4. The processing speed of the film is shown in Table 1.

Example 5 (Comparative).

The BOPP film was prepared as in Example 1, except for using polypropylene prepared using a Ziegler-Natta catalyst with a molar ratio of co-catalyst (Co) to an external donor (ED) [Co/ED ratio] of 40 (to achieve a low XCS), said polypropylene having characteristics listed in Table 1 for comparative Example 5. The processing speed of the film is shown in Table 1.

Example 6 (Comparative).

A BOPP film was prepared as in Example 1, except that polypropylene was prepared using a Ziegler-Natta catalyst with isobutyl phthalate as internal electron donor and wherein the polypropylene had the characteristics shown in Table 1 for the comparative Example 6. The processing speed of the film is shown in Table 1.

Table 1. Characteristics of polypropylene used in the preparation of films, the speed of processing and time to plate-out formation

quite high (450 m/min) if the content of xylene cold soluble fractions is in the range from 4 to 6 wt.%. However, it should be noted that non-compliance with the requirements of maintaining a certain established content of low molecular weight (from 1,500 to 50,000 g/mol) and high molecular weight (from 50,000 g/mol and higher) fractions leads to a significant deterioration of the physico-mechanical characteristics, as well as to rapid accumulation of low molecular weight fractions on die surface, followed by combustion thereof which leads to the need for frequent equipment shutdowns for cleaning maintenance. At the same time, compliance with requirement of the content of low molecular weight fractions (Example 6) permits to increase the time to plate-out formation (amorphous carbon deposits); however, the processing speed in this case is limited to 380 m/min.

Thus, to achieve a high processing speed of 450 m/min or more, to ensure high physico-mechanical characteristics of the film and to reduce the degree of plate-out formation, the following combination of features has to be observed:

- the amount of the xylene cold soluble fraction (XCS) in the polymer is within the range from 4.0 to 6.0 wt.%;

Claims

1. A polypropylene for producing a biaxially oriented film, wherein said polypropylene has the following characteristics:

- the amount of the xylene cold soluble fractions (XCS) in the polymer falls within the range of from 4.0 to 6.0 wt.%, wherein the proportion of the fraction having a molecular weight of 50,000 g/mol and greater is at least 60 wt.%, whereas the proportion of the fraction having a molecular weight in the range from 1,500 to 50,000 g/mol, is not more than 40 wt.%

- the amount of the heptane soluble fractions (HS) in the polymer falls within the range of from 2.5 to 3.5 wt.%, wherein the proportion of the fraction having a molecular weight of 50,000 g/mol and greater is at least 60 wt.%, whereas the proportion of the fraction having a molecular weight in the range from 1,500 to 50,000 g/mol is not more than 40 wt.%.

2. The polypropylene according to claim 1 having the molecular weight distribution from 4 to 7.

3. The polypropylene according to claim 2 having the molecular weight distribution from 5 to 7.

4. The polypropylene according to claim 1, wherein said polypropylene has a content of iso tacti city pentad (mmmm) of from 87 to 89%;

5. The polypropylene according to claim 1, wherein said polypropylene contains stabilizers comprising at least one antioxidant and at least one acid absorber.

6. The polypropylene according to claim 5, wherein said polypropylene comprises at least one phenolic antioxidant and at least one phosphite antioxidant as stabilizers.

7. The polypropylene according to claims 5 or 6, wherein said polypropylene comprises hydrotalcite as an acid absorber.

8. The polypropylene according to claim 5, wherein said polypropylene comprises from 1 to 3 kg of stabilizers per ton of polypropylene, preferably from 1.2 to 2.5 kg of stabilizers per ton of polypropylene, more preferably from 1.2 to 1.5 kg of stabilizers per ton of polypropylene.

9. The polypropylene according to claim 1, wherein said polypropylene is substantially free from calcium stearate.

10. The polypropylene according to claim 1, wherein the amount of xylene cold soluble fraction (XCS) is from 4.5 to 5.5% by weight.

11. The polypropylene according to claim 1 , wherein the proportion of xylene cold soluble fraction (XCS) with a molecular weight greater than 50,000 g/mol is at least 65 wt.%, preferably at least 70 wt.%.

12. The polypropylene according to claim 1, wherein the proportion of heptane soluble fraction (HS) with a molecular weight from 1,500 to 50,000 g/mol is not more than 25 wt.%, preferably not more than 15 wt.%

13. The polypropylene according to claim 1, wherein the amount of heptane soluble fraction (HS) with a molecular weight of 50000 g/mol and greater is at least 65 wt.%, preferably at least 70 wt.%.

14. A film comprising at least one layer comprising polypropylene wherein said polypropylene has the following characteristics:

- the amount of the xylene cold soluble fractions (XCS) in the polymer falls within the range from 4.0 to 6.0 wt.%, wherein the proportion amount of the fraction having a molecular weight of 50000 g/mol and greater is at least 60 wt.%, whereas the proportion of the fraction having a molecular weight in the range of from 1,500 to 50,000 g/mol is not more than 40 wt.%

- the amount of the heptane soluble fractions (HS) in the polymer falls within the range from 2.5 to 3.5 wt.%, wherein the proportion amount of the fraction having a molecular weight of 50000 g/mol and greater is at least 60 wt.%, whereas the proportion of the fraction having a molecular weight in the range of from 1,500 to 50,000 g/mol is not more than 40 wt.%.

15. The film according to claim 14, wherein the polypropylene has a molecular weight distribution in the range of from 4 to 7.

16. The film according to claim 15, wherein the polypropylene has a molecular weight distribution in the range of from 5 to 7.

17. The film according to claim 14, wherein said polypropylene has a content of isotacticity pentad (mmmm) of from 87 to 89%.

18. The film according to claim 14, wherein said polypropylene which the polypropylene contains stabilizers comprising at least one antioxidant and at least one acid absorber.

19. The film according to claim 18, wherein said film comprises at least one phenolic antioxidant and at least one phosphite antioxidant as stabilizers.

20. The film according to claim 18 or 19, wherein polypropylene comprises hydrotalcite as an acid absorber.

21. The film according to claim 17, wherein polypropylene comprises from 1 to

3 kg of stabilizers per ton of polypropylene, preferably from 1.2 to 2.5 kg per ton of polypropylene, more preferably from 1.2 to 1.5 kg per ton of polypropylene.

22. The film according to claim 14, wherein the polypropylene is substantially free of calcium stearate.

23. The film according to claim 14, wherein the amount of xylene cold soluble fractions in the polypropylene is from 4.5 to 5.5 wt.%.

24. The film according to claim 14, wherein the amount of xylene cold soluble fractions with a molecular weight of 50,000 g/mol and greater is at least 65 wt.%, preferably at least 70 wt.%.

25. The film according to claim 14, in which the amount of heptane soluble fractions with a molecular weight from 1,500 to 50,000 g/mol is not more than 25 wt.%, preferably no more 15 wt.%.

26. The film according to claim 14, wherein the said film is prepared by coextrusion.

27. The film according to claim 14, wherein the said film is a biaxially oriented film.

28. The use of the film according to any one of claims 14 to 27 for the preparation of an article.

29. An article comprising the film according to any one of claims 14 to 27.