Patent Description:
Polymers, like polypropylene, are increasingly used in different demanding applications. At the same time there is a continuous search for tailored polymers which meet the requirements of these applications. The demands can be challenging, since many polymer properties are directly or indirectly interrelated, i.e. improving a specific property can only be accomplished on the expense of another property.

For example, polypropylene films are quite often used in the packaging industry for consumer related articles with good "see-through" properties on the content of the packed goods. There is an also increasing trend in the medical packaging industry to use such polypropylene films.

Nowadays, due to the higher life standards and more strict requirements, specific properties like high flow (energy saving and long flow length for thinner wall) and a good combination of softness, toughness and transparency, in the sense of low haze, become continuously more important.

It is further important, that the polymers provide good optical properties in the sense of low haze and good transparency despite having undergone mechanical deformation, i.e. there is a strong requirement for polypropylene having a low tendency to stress whitening. Such stress whitening marks are highly disturbing the optical performance and impression of injection moulded final articles and should therefore be avoided.

It is known that heterophasic propylene copolymers (HECOs) are a generally suitable class of soft base polymers applicable for cast and blown film applications. Such heterophasic propylene copolymers comprise a matrix being either a propylene homopolymer or a random propylene copolymer in which an amorphous phase, which contains a propylene copolymer rubber (elastomer), is dispersed. Thus the polypropylene matrix contains (finely) dispersed inclusions not being part of the matrix and said inclusions contain the elastomer. The term inclusion indicates that the matrix and the inclusion form different phases within the heterophasic propylene copolymer, said inclusions are for instance visible by high resolution microscopy, like electron microscopy or scanning force microscopy or atomic force microscopy, or by dynamic mechanical thermal analysis (DMTA). Further the heterophasic polypropylene may contain to some extent a crystalline polyethylene, which is a by-reaction product obtained by the preparation of the heterophasic propylene copolymer. Such crystalline polyethylene is present as inclusion of the amorphous phase due to thermodynamic reasons.

The rubber phase in such heterophasic systems normally scatters the light, which makes the resulting films produced from these systems white. This is due to the fact that the rubber phase has different refractive index than the surrounding matrix and/or forms relatively big spheres. Unfortunately there are very limited ways to tune the optical properties for film compositions.

Generally, for achieving high transparency/low haze in two-phasic systems it is necessary to design a system where no scattering of light occurs at the phase boundaries.

The person skilled however is further well aware, that such heterophasic systems with stiff matrix and elastomeric resin dispersed therein are very sensitive to stress whitening or blushing. This is especially true for heterophasic systems having high rubber content.

Stress whitening results from internal cavitation on the particle/matrix interface or inside the rubber particles of the polymer. As said cavitation is related to energy dissipation in the failure process stress whitening can hardly be avoided when designing materials combining a high level of toughness with high stiffness. While in case of failure, cracks are stopped and energy is dissipated at internal surfaces, this dissipation goes along with craze formation becoming visible in the deformation zone.

One way to improve the optical properties is to reduce the molecular weight of rubber phase, but this may introduce further problems, namely a reduction of the toughening effect and possible problems during production and conversion due to stickiness of the polymer powder.

Stress whitening on the other side can be compensated by either using rubber phases of higher crystallinity or by addition of a high density polyethylene (HDPE) component (<NPL>). Both approaches are, however, also known to reduce transparency or increase haze respectively.

<CIT> discloses a polypropylene composition comprising (a) <NUM>-<NUM> wt. % of a crystalline propylene polymer having an amount of isotactic pentads (mmmm), measured by <NUM>C-NMR on the XCI fraction, higher than <NUM> mol% and a polydispersity index ranging from <NUM> to <NUM>; (b) <NUM>-<NUM> wt% of an elastomeric copolymer of ethylene and propylene having an ethylene content from <NUM> to <NUM> wt% and exhibiting an XCI fraction of less than <NUM> wt%, the XCS fraction having an intrinsic viscosity value ranging from <NUM> to <NUM> dl/g; and (c) <NUM>-<NUM> wt% of an ethylene homopolymer or ethylene-propylene copolymer having a comonomer content lower than <NUM> wt% and an intrinsic viscosity value ranging from <NUM> to <NUM> dl/g; in said composition component (b) plus component (c) being in an amount of at least <NUM> wt%. However the addition of the component (c) affects transparency and haze, as discussed above.

<CIT> is another approach to provide a heterophasic polypropylene composition with good mechanical and optical properties. It discloses a composition comprising (a) <NUM> - <NUM> wt. %, based on the total weight of the composition of a heterophasic propylene/α-olefin copolymer comprising a polymer or copolymer of propylene and an α-olefin with <NUM>-<NUM> mol% of the α-olefin as matrix polymer and a propylene/α-olefin rubber copolymer comprising <NUM>-<NUM> mol% of the α-olefin and (b) <NUM>-<NUM> wt. %, based on the total weight of the composition of an ethylene homopolymer, the ethylene homopolymer having a density lower than <NUM>/cm<NUM> according to ISO1183. However, the composition is not suitable in applications where stress whitening reduction is required. Its mechanical properties are also insufficient due to its long chain branching structure.

<CIT> discloses a polypropylene composition having a melt flow rate MFR<NUM> (<NUM>) of <NUM>-<NUM>/<NUM> and a total ethylene content of <NUM>-<NUM> wt%, the polypropylene composition comprising a polypropylene homopolymer matrix (M) and an ethylene-propylene copolymer (EPC) dispersed in the polypropylene homopolymer matrix (M), wherein the composition comprises: (a) <NUM> to <NUM> wt. -% crystalline fraction (CF) having i) an ethylene content of ≤ <NUM> wt. -% (<NUM>-<NUM> wt. -%), ii) an intrinsic viscosity (IV) of <NUM>-<NUM> dl/g, (b) <NUM> to <NUM> wt. -% soluble fraction (SF) having i) an intrinsic viscosity (IV) of <NUM>- <NUM> dl/g, and ii) an ethylene content of <NUM>-<NUM> wt. -%, wherein said polypropylene composition has a ratio of intrinsic viscosity of the soluble fraction (IV(SF)) to intrinsic viscosity of the crystalline fraction (IV(CF)) [(IV(SF))/ (IV(CF))] in the range from <NUM> to < <NUM> and the flexural modulus may be at least <NUM> MPa. The polypropylene composition provides a good balance between shrinkage and mechanical properties, such as expressed by the brittle-to-ductile transition temperature.

<CIT> discloses a heterophasic propylene copolymer (RAHECO) comprising (i) a matrix (M) being a propylene/ C<NUM> to C<NUM> alpha-olefin copolymer (C-PP), (ii) an elastomeric propylene copolymer (EC) dispersed in said matrix (M). The propylene copolymer has low amount of extractables, is mechanically stable and has good optical properties such as low amount of stress whitening.

<CIT> discloses a soft heterophasic propylene copolymer composition, which comprises: (A) <NUM> to <NUM> wt. % of a heterophasic polypropylene copolymer, said heterophasic propylene copolymer comprises (a-<NUM>) a matrix (M) being a crystalline polypropylene homo- or copolymer and (a-<NUM>) an elastomeric propylene copolymer (E) dispersed in said matrix (M) wherein the heterophasic polypropylene copolymer has (i) a melt flow rate (MFR <NUM>/<NUM>, ISO <NUM>) of <NUM>-<NUM>/<NUM>, (ii) a xylene cold soluble (XCS) content in the range of <NUM>-<NUM> wt. %, (iii) a total ethylene or C<NUM>-C<NUM> comonomer content of <NUM>-<NUM> wt. % ( iv) a comonomer content of the soluble part of <NUM> to <NUM> wt%, (v) an intrinsic viscosity of the soluble part of <NUM> to <NUM> dl/g, and (B) <NUM> to <NUM> wt. % of a styrene-based elastomer. The soft heterophasic propylene copolymer composition may have a flexural modulus measured according to ISO <NUM> on injection moulded specimens of below <NUM> MPa. The heterophasic propylene copolymer compositions have an optimized or improved balance between mechanical and optical properties, especially between softness, haze and resistance to steam sterilization, by which the optical properties are kept on a high level before and after sterilization.

Thus, there is still a need for heterophasic polypropylene compositions, which show improved mechanical and optical properties, especially improved stress whitening performance.

Hence, it is an object of the present invention to provide such a heterophasic polypropylene composition, a process for its production, improved articles and uses involving such a heterophasic polypropylene composition.

The present invention is based on the finding that the above objects can be achieved by a heterophasic polyolefin composition comprising specific matrix and rubber design.

Thus, the present invention concerns a polypropylene composition and articles produced thereof which fulfil low stress whitening requirements.

The present invention also deals with a polymerization method, suitable for the production of such a heterophasic polypropylene composition.

The present invention is based on the finding that the above mentioned objects can be achieved by a particular heterophasic propylene copolymer composition, comprising.

The heterophasic propylene copolymer composition preferably further comprises an ethylene copolymer (EC), and/or an alpha-nucleating agent (NU), preferably a polymeric alpha-nucleating agent.

The ethylene copolymer (EC) may preferably be contained in the heterophasic propylene copolymer composition in an amount of from <NUM> to <NUM> wt. %, more preferably from <NUM> to <NUM> wt. %, even more preferably from <NUM> to <NUM> wt. %, still more preferably from <NUM> to <NUM> wt. The heterophasic propylene copolymer (HECO) may preferably have a hexane soluble content, determined in accordance with FDA section <NUM> of <NUM> to lower than <NUM> wt. %, more preferably <NUM> to <NUM> wt. %, even more preferably <NUM> to <NUM> wt. % or <NUM> to <NUM> wt.

It has surprisingly been found out that such a heterophasic propylene copolymer composition has not only improved mechanical properties but also improved optical properties, especially an improved stress whitening performance. The inventive heterophasic propylene copolymer compositions are applicable for the preparation of films for packaging of consumer goods, as well as for medical packaging.

The present invention further relates to a process for the production of the above heterophasic propylene copolymer composition, comprising polymerizing propylene in at least two subsequent polymerization steps in the presence of a Ziegler-Natta catalyst (ZN-C), as described in more detail below.

In one further embodiment of the present invention, the heterophasic propylene copolymer composition preferably has a stress whitening intensity, determined as described in more detail below, of not more than <NUM>, more preferably <NUM> to <NUM>, even more preferably from <NUM> to <NUM>. The stress whitening intensity may even be <NUM> which can be combined with any upper limit. The stress whitening intensity is determined as described in the method section below.

In the following the individual components of the inventive heterophasic propylene copolymer composition are defined in more detail.

The particular heterophasic polypropylene composition of the present invention comprises at least a heterophasic propylene copolymer (HECO) comprising.

Optionally the heterophasic polypropylene composition further comprises a component (c) being an ethylene copolymer (EC), and/or a component (d) being a nucleating agent, preferably an alpha-nucleating agent. In a more preferred embodiment, the component (d) is a polymeric alpha-nucleating agent.

The term "heterophasic propylene copolymer composition" used herein denotes compositions comprising a heterophasic propylene copolymer (HECO) as specified in detail below containing a matrix resin (M), being a propylene homopolymer (H-PP) and an elastomeric propylene copolymer (EPC) dispersed in said matrix resin (M) and said composition optionally further comprising an ethylene copolymer (EC) and/or an alpha-nucleating agent.

In the present invention, the term "matrix" is to be interpreted in its commonly accepted meaning, i.e. it refers to a continuous phase (in the present invention a continuous polymer phase) in which isolated or discrete particles such as rubber particles may be dispersed. The propylene homopolymer, preferably crystalline propylene homopolymer is present in such an amount that it forms a continuous phase which can act as a matrix. In the present invention polypropylene content and ethylene content of the matrix phase is measured by the crystalline fraction (CF) determined by TREF fractionation on CRYSTEX QC, Polymer Char (Valencia, Spain) as described in the method section below.

Furthermore the terms "elastomeric propylene copolymer (EPC)", "dispersed phase" and "ethylene-propylene rubber" denote the same, i.e. are interchangeable. In the present invention polymer content and ethylene content of the disperse phase is measured by the soluble fraction (SF) determined by TREF fractionation on CRYSTEX QC, Polymer Char (Valencia, Spain) as described in the method section below.

A propylene homopolymer (H-PP), which may be a crystalline, more preferably crystalline isotactic propylene homopolymer forms the matrix of the heterophasic propylene copolymer (HECO).

The expression "homopolymer" used in the present invention relates to a polypropylene that consists substantially, i.e. of at least <NUM> wt%, preferably of at least <NUM> wt%, more preferably of at least <NUM> wt%, still more preferably of at least <NUM> wt% of propylene units. In a preferred embodiment only propylene units in the propylene homopolymer are detectable.

The propylene homopolymer matrix may preferably be isotactic having a high pentad concentration, i.e. higher than <NUM> mol%, like a pentad concentration of at least <NUM> mol%. The pentad concentration is preferably <NUM> mol% up to <NUM>% and more preferably <NUM> mol% to <NUM>%.

The propylene homopolymer matrix preferably has a melt flow rate MFR<NUM> (ISO <NUM>; <NUM>; <NUM>) in the range of <NUM> - <NUM>/<NUM>, more preferably in the range of <NUM> - <NUM>/<NUM> and even more preferably in the range of <NUM> - <NUM>/<NUM>.

The propylene homopolymer matrix can be unimodal or multimodal, e.g. bimodal.

When the propylene homopolymer matrix phase is unimodal with respect to the molecular weight distribution, it may be prepared in a single stage process e.g. a slurry or gas phase process in a slurry or gas phase reactor. Preferably, a unimodal matrix phase is polymerized as a slurry polymerization. Alternatively, the unimodal matrix may be produced in a multistage process using at each stage process conditions which result in similar polymer properties.

Where the propylene homopolymer matrix comprises two or more different propylene polymers, like propylene homopolymer fractions (H-PP-<NUM>) and (H-PP-<NUM>) these may be polymers with different monomer make up and/or with different molecular weight distributions. These components may have identical or differing monomer compositions and tacticities.

Thus in one embodiment or the present invention the matrix (M) is unimodal, whereas in another embodiment the matrix (M) is bimodal and consists of two propylene homopolymer fractions (H-PP-<NUM>) and (H-PP-<NUM>).

An elastomeric propylene copolymer (EPC), which is a copolymer of propylene and an alpha-olefin comonomer is dispersed in said matrix (M) (i.e. dispersed phase). The alpha-olefin comonomer is preferably ethylene.

Preferably, the elastomeric propylene copolymer (EPC) of the heterophasic propylene copolymer (HECO) is a predominantly amorphous propylene copolymer.

The elastomeric propylene copolymer (EPC) is characterized by its soluble fraction content (SF) determined by TREF fractionation on CRYSTEX QC, Polymer Char (Valencia, Spain) as described in the method section below. The amount of the soluble fraction (SF) in the heterophasic propylene copolymer (HECO) may be in the range of <NUM> to <NUM> wt. %, preferably <NUM> to <NUM> wt. %, more preferably <NUM> to <NUM> wt.

The soluble fraction (SF) is preferably composed of propylene and ethylene monomer units, wherein the ethylene content of the soluble fraction content (SF) may be in the range of from <NUM> wt. % to less than <NUM> wt. %, preferably in the range of <NUM> - <NUM> wt. -%, more preferably in the range of <NUM> - <NUM> wt. -%, such as <NUM> - <NUM> wt.

The intrinsic viscosity (IV) of the soluble fraction (SF), determined according to DIN ISO <NUM>/<NUM> (in decalin at <NUM>), is in the range of from <NUM> to <NUM> dl/g, preferably in the range of from <NUM> to <NUM> dl/g, more preferably in the range of from <NUM> to <NUM> dl/g.

The dispersed phase can be unimodal or multimodal, like bimodal.

In one embodiment, the dispersed phase is unimodal. More particularly, the dispersed phase is preferably unimodal in view of the intrinsic viscosity and/or the comonomer distribution.

Preferably the unimodal dispersed phase is made in one reaction stage, more preferably in a gas phase reactor and comprises, respectively consists of one propylene copolymer fraction (EPC).

The elastomeric propylene copolymer (EPC) can either be synthesized in the later step(s) of a multistage process, after the propylene homopolymer (H-PP) has been synthesized. Alternatively, the elastomeric propylene copolymer (EPC) can be polymerised separately and mixed with the propylene homopolymer (H-PP) in a separate melt blending step. It is preferred, that the incorporation of the EPC into the H-PP is done during a multistage polymerisation process.

The heterophasic propylene copolymer composition of the present invention may contain the heterophasic propylene copolymer (HECO) as a major but also as the only resin component.

The heterophasic propylene copolymer (HECO) has an ethylene content, determined from the soluble fraction (SF) obtained by TREF fractionation on CRYSTEX QC, Polymer Char (Valencia, Spain), as described in the method section below, in the range of from <NUM> to less than <NUM> wt. %, preferably in the range of <NUM> - <NUM> wt. -%, more preferably in the range of <NUM> - <NUM> wt. -%, such as <NUM> - <NUM> wt.

The heterophasic propylene copolymer (HECO) has an soluble fraction content (SF), determined by TREF fractionation on CRYSTEX QC, Polymer Char (Valencia, Spain), as described in the method section below, in the range of from <NUM> to <NUM> wt. %, preferably <NUM> to <NUM> wt. %, more preferably <NUM> to <NUM> wt.

The intrinsic viscosity (IV) measured according to ISO <NUM>-<NUM> (at <NUM> in decalin) of the soluble fraction (SF) is in the range of from <NUM> to <NUM> dl/g, preferably in the range of <NUM> to <NUM> dl/g, more preferably in the range of <NUM> to <NUM> dl/g. A low intrinsic viscosity (IV) value reflects a low average molecular weight.

The heterophasic propylene copolymer (HECO) has a crystalline fraction content (CF), determined by TREF fractionation on CRYSTEX QC, Polymer Char (Valencia, Spain), as described in the method section below, in the range of from <NUM> to <NUM> wt. %, preferably in the range of from <NUM> to <NUM> wt. %, more preferably in the range of from <NUM> to <NUM> wt. The crystalline fraction content (CF) is mainly determined by the presence of the propylene homopolymer matrix.

The heterophasic propylene copolymer (HECO) has an ethylene content, determined from the crystalline fraction (CF) obtained by TREF fractionation on CRYSTEX QC, Polymer Char (Valencia, Spain), as described in the method section below, in the range of from <NUM> to <NUM> wt. %, preferably in the range of from <NUM> to <NUM> wt. % and more preferably in the range of from <NUM> to <NUM> wt. Any lower limit may be combined with any upper limit. In preferred embodiments, the intrinsic viscosity (IV) measured according to ISO <NUM>-<NUM> (at <NUM> in decalin) of the crystalline fraction (CF) may be in the range of from <NUM> to <NUM> dl/g, preferably in the range of <NUM> to <NUM> dl/g. Any lower limit may be combined with any upper limit in the above ranges.

It is further preferred that the heterophasic propylene copolymer (HECO) has a limited amount of hexane soluble content, determined in accordance with FDA section <NUM> (C6FDA). This is especially advantageous for food applications which should comply with strict government regulations. Thus, the amount of hexane soluble content (C6FDA) is preferably lower than <NUM> wt. %, more preferably not more than <NUM> wt. %, even more preferably not more than <NUM> wt.

The heterophasic polypropylene composition of the present invention may further comprise an optionally crystalline ethylene copolymer (EC) with an α-olefin comonomer with <NUM>-<NUM> carbon atoms, preferably <NUM>-<NUM> carbon atoms, more preferably <NUM> to <NUM> carbon atoms, like <NUM> or <NUM> carbon atoms.

Alpha-olefins with <NUM>-<NUM> carbon atoms are for example propylene, <NUM>-butene, <NUM>-pentene, <NUM>-hexene, <NUM>-heptene and <NUM>-octene.

The ethylene copolymer (EC) may also be added/compounded as external component to the heterophasic propylene copolymer (HECO) In these cases, the EC may have a density of from <NUM> to <NUM>/m<NUM>, preferably from <NUM> to <NUM>/m<NUM>, more preferably from <NUM> to <NUM>/m<NUM>.

The ethylene copolymer (EC) may have a melt flow rate MFR<NUM> (ISO <NUM>; <NUM>; <NUM>) in the range of from <NUM> to <NUM>/<NUM>, preferably from <NUM> to <NUM>/<NUM>, more preferably from <NUM> to <NUM>/<NUM>.

The EC may be a unimodal or multimodal, e.g. bimodal polymer.

The ethylene copolymer (EC) may preferably be contained in the heterophasic propylene copolymer composition of the present invention in an amount of from <NUM> to <NUM> wt. %, more preferably in the range of from <NUM> to <NUM> wt. %, even more preferably in the range of from <NUM> to <NUM> wt.

The crystalline ethylene copolymer has a melting temperature Tm2 as determined by DSC analysis according to ISO <NUM>.

Preferably, Tm2 of the crystalline ethylene copolymer is within the range of <NUM> to <NUM>, more preferably within the range of <NUM> to <NUM> and most preferably within the range of <NUM> to <NUM>.

The heterophasic polypropylene composition of the present invention may further comprise an alpha-nucleating agent (NA) for promoting the α-phase of polypropylene. Preferably the alpha-nucleating agent is a polymeric alpha-nucleating agent, more preferably a vinylcycloalkane polymer and/or a vinylalkane polymer.

Said polymeric alpha-nucleating agent may be introduced into the composition by blending with a masterbatch (MB) together with e.g. a carrier polymer or during polymerization of the heterophasic propylene copolymer (HECO), preferably, the polymeric alpha-nucleating agent is introduced into the composition by pre-polymerizing the catalyst used to prepare a part or all of the heterophasic propylene copolymer (HECO).

Any known polymeric alpha-nucleating agent may be employed including polymers of vinyl alkanes and vinyl cycloalkanes.

A preferred example of such a polymeric alpha-nucleating agent is a vinyl polymer, such as a vinyl polymer derived from monomers of the formula.

wherein R<NUM> and R<NUM>, together with the carbon atom they are attached to, form an optionally substituted saturated or unsaturated or aromatic ring or a fused ring system, wherein the ring or fused ring moiety contains four to <NUM> carbon atoms, preferably <NUM> to <NUM>-membered saturated or unsaturated or aromatic ring or a fused ring system or independently represent a linear or branched C<NUM>-C<NUM> alkane, C<NUM>- C<NUM> cycloalkane or C<NUM>-C<NUM> aromatic ring. Preferably R<NUM> and R<NUM>, together with the C-atom wherein they are attached to, form a five- or six-membered saturated or unsaturated or aromatic ring or independently represent a lower alkyl group comprising from <NUM> to <NUM> carbon atoms. Preferred vinyl compounds for the preparation of a polymeric alpha-nucleating agent to be used in accordance with the present invention are in particular vinyl cycloalkanes, in particular vinyl cyclohexane (VCH), vinyl cyclopentane, and vinyl-<NUM>-methyl cyclohexane, <NUM>-methyl-<NUM>-butene, <NUM>-ethyl-<NUM>-hexene, <NUM>-methyl-<NUM>-pentene, <NUM>-methyl-<NUM>-pentene or mixtures thereof. VCH is a particularly preferred monomer.

Polymeric nucleating agents can either be incorporated by in-reactor nucleation (also called BNT technology) or by the so called masterbatch technology (compounding technology). In a preferred embodiment of the present invention, the polymeric alpha-nucleating agent is introduced into the propylene copolymer by means of a suitably modified catalyst, into the reactor (i.e. in-reactor nucleation) i.e. the catalyst to be used in catalyzing the polymerisation of any of the polypropylene homopolymer (H-PP) or the ethylene-propylene rubber (EPC), is subjected to a polymerisation of a suitable monomer for the polymeric alpha-nucleating agent to produce first said polymeric alpha-nucleating agent. The catalyst is then introduced together with the obtained polymeric alpha-nucleating agent to the actual polymerisation step of the heterophasic polypropylene composition. In a particularly preferred embodiment of the present invention, the heterophasic propylene copolymer (HECO) is prepared in the presence of such a modified catalyst.

Another embodiment, different to the above mentioned in-reactor blend, is a mechanical blend of a polymer with an alpha-nucleating agent, wherein the polymer is first produced in the absence of a polymeric alpha-nucleating agent and is then blended mechanically with the polymeric alpha-nucleating agent or with a small amount of nucleated polymer or with polymers, which already contain the polymeric alpha-nucleating agent (so-called master batch technology) in order to introduce the polymeric nucleating agent into the polymer mixture. The preparation of a reactor made polymer composition ensures the preparation of a homogenous mixture of the components, for example a homogenously distributed polymeric alpha-nucleating agent in the heterophasic polypropylene copolymer, even at high concentrations of polymer alpha-nucleating agent. As outlined above, the reactor made polymer composition is a preferred embodiment of the present invention, although also mechanical blends prepared, for example, by using master batch technology are envisaged by the present invention.

In case the alpha-nucleating agent is incorporated to the polypropylene composition in the form of a masterbatch (MB) said polymeric alpha-nucleating agent, most preferably a vinylcycloalkane, like vinylcyclohexane (VCH), polymer and/or vinylalkane polymer, preferably vinylcyclohexane (VCH), as defined above or below, is preferably present in an amount of not more than <NUM> ppm, more preferably of <NUM> to <NUM> ppm, and still more preferably of <NUM> to <NUM> ppm, based on the weight of the master batch (<NUM> wt%). In this embodiment, more preferably, said masterbatch (MB) is present in an amount of not more than <NUM> wt%, more preferably not more than <NUM> wt% and most preferably not more than <NUM> wt%, with the preferred amount of masterbatch (MB) being from <NUM> to <NUM> wt%, based on the total amount of the heterophasic propylene copolymer (HECO). Most preferably, the masterbatch (MB) comprises, preferably consists of a homopolymer or copolymer, preferably homopolymer, of propylene which has been nucleated according to BNT-technology as described below.

It is preferred that the alpha-nucleating agent is introduced into the polypropylene composition during the polymerization process of the heterophasic propylene copolymer (HECO). The alpha-nucleating agent is preferably introduced into the heterophasic propylene copolymer (HECO) by first polymerizing the above defined vinyl compound, preferably vinylcycloalkane, in the presence of a catalyst system comprising a solid catalyst component, preferably a solid Ziegler Natta catalyst component comprising an internal donor (ID), a co-catalyst and optional external donor (ED), and the obtained reaction mixture of the polymer of the vinyl compound, and the catalyst system is then used for producing the heterophasic propylene copolymer (HECO). The above incorporation of the polymeric alpha-nucleating agent to the heterophasic propylene copolymer (HECO) during the polymerization of said heterophasic propylene copolymer (HECO) is called herein BNT-technology as described below.

Said obtained reaction mixture is herein below referred interchangeably as modified catalyst system.

Preferably the polymeric alpha-nucleating agent is vinylcyclohexane (VCH) polymer which is introduced into the heterophasic propylene copolymer (HECO) by the BNT technology.

More preferably in this preferred embodiment, the amount of polymeric alpha-nucleating agent, like vinylcyclohexane (VCH), polymer and/or vinylalkane polymer, more preferably of vinylcyclohexane (VCH) polymer, in the heterophasic propylene copolymer (HECO) is not more than <NUM> ppm, more preferably of <NUM> to <NUM> ppm, most preferably <NUM> to <NUM> ppm.

With regard to the BNT-technology reference is made to the international applications <CIT>, <CIT> and particularly <CIT>. According to this technology a catalyst system, preferably a Ziegler-Natta pro-catalyst, can be modified by polymerizing a vinyl compound in the presence of the catalyst system, comprising in particular the Ziegler-Natta procatalyst, an external donor and a co-catalyst, which vinyl compound has the formula: CH<NUM>=CH-CHR<NUM>R<NUM> as defined above.

The polymerized vinyl compound acts as an alpha-nucleating agent. The weight ratio of vinyl compound to solid catalyst component in the modification step of the catalyst is preferably of up to <NUM> (<NUM>:<NUM>), preferably up to <NUM> (<NUM>:<NUM>) most preferably from <NUM> (<NUM>:<NUM>) to <NUM> (<NUM>:<NUM>). The most preferred vinyl compound is vinylcyclohexane (VCH).

When an alpha-nucleating agent is introduced to the heterophasic propylene copolymer (HECO) during the polymerization process, the amount of alpha-nucleating agent present in the heterophasic propylene copolymer (HECO) is preferably not more than <NUM> ppm, more preferably is <NUM> to <NUM> ppm, still more preferably is <NUM> to <NUM> ppm, and most preferably is <NUM> to <NUM> ppm, based on the heterophasic propylene copolymer (HECO) and the alpha-nucleating agent, preferably based on the total weight of the heterophasic propylene copolymer (HECO) including all additives.

The use of the polymeric alpha-nucleating agent in accordance with the present invention enables the preparation of heterophasic propylene copolymer (HECO) having highly satisfactory mechanical properties, i.e. for improved stiffness / impact balance, so that it is not required for the compositions in accordance with the present invention to contain low molecular weight nucleating agents, in particular costly particulate nucleating agents like organo-phosphates or soluble nucleants like sorbitol- or nonitol-derived nucleating agents.

The heterophasic propylene copolymer composition of the present invention is further characterized by a total melt flow rate (MFR<NUM>) (ISO <NUM>; <NUM>; <NUM>) in the range of <NUM> - <NUM>/<NUM>, preferably in the range of <NUM> - <NUM>/<NUM>, more preferably in the range of <NUM> - <NUM>/<NUM>.

According to one embodiment the final melt flow rate of the heterophasic propylene copolymer composition is adjusted during the polymerization process. Accordingly the reactor-made heterophasic propylene copolymer (HECO) has the melt flow rate as defined above. "Reactor-made heterophasic propylene copolymer (HECO)" denotes herein that the melt flow rate of the heterophasic propylene copolymer (HECO) has not been modified on purpose by post-treatment. Thus it is preferred that the heterophasic propylene copolymer (HECO) does not contain any peroxide and/or decomposition product thereof.

The final melt flow rate of the heterophasic propylene copolymer composition may be modified by the introduction of additional components like the optional crystalline ethylene copolymer (EC) defined above. Thus, the melt flow rate of the heterophasic propylene copolymer (HECO) and the melt flow rate of the heterophasic propylene copolymer composition may differ.

It is also appreciated that the total content of the ethylene comonomers in the total heterophasic propylene copolymer composition is at least <NUM> wt. %, preferably at least <NUM> wt. The total ethylene comonomer content in the heterophasic propylene copolymer composition may be up to <NUM> wt. %, preferably up to <NUM> wt. %, even more preferably up to <NUM> wt. Any of the above lower ranges may be combined with any of the above upper ranges. The ethylene content is determined by quantitative NMR spectroscopy as described in the method section below.

The heterophasic propylene composition of the present invention may have improved optical properties, in particular advanced stress whitening properties. Thus, the heterophasic propylene composition may preferably have a stress whitening intensity, determined as described in the method section below, of not more than <NUM>, more preferably of not more than <NUM>, even more preferably not more than <NUM>.

The heterophasic propylene copolymer composition of the present invention may have improved mechanical properties, in particular advanced stiffness properties. Thus, the heterophasic propylene composition may preferably have a flexural modulus of not less than <NUM> MPa, more preferably not less than <NUM> MPa, even more preferably not less than <NUM> MPa, or <NUM> MPa, determined in a <NUM>-point-bending test according to ISO <NUM> as described in the method section below. The heterophasic propylene copolymer (HECO) may preferably have a flexural modulus of up to <NUM> MPa, more preferably up to <NUM> MPa, even more preferably up to <NUM> MPa.

The heterophasic propylene composition of the present invention may preferably have a Charpy notched impact strength (NIS), determined according to ISO <NUM>1eA at <NUM> of at least <NUM> kJ/m<NUM>, more preferably of at least <NUM>. 0kJ/m<NUM>.

The heterophasic propylene copolymer composition according to the present invention apart from the polymeric components and the alpha-nucleating agent, optionally in the form of a masterbatch (MB), may comprise further non-polymeric components, e.g. additives for different purposes.

The following are optional additives: process and heat stabilisers, pigments and other colouring agents allowing retaining transparency, antioxidants, antistatic agents, slip agents, antiblocking agent, UV stabilisers and acid scavengers.

Depending on the type of additive, these may be added in an amount of <NUM> to <NUM> wt%, based on the weight of the heterophasic propylene copolymer composition.

As used herein the term "molded article" is intended to encompass articles that are produced by any conventional molding technique, e.g. injection molding, stretch molding, compression molding, rotomolding or injection stretch blow molding. The term is not intended to encompass articles that are produced by casting or extrusion, such as extrusion blow molding. Thus, the term is not intended to include films or sheets. Articles produced by injection molding, stretch molding, or injection stretch blow molding are preferred. Articles produced by injection molding are especially preferred. The articles preferably are thin-walled articles having a wall thickness of <NUM> to <NUM>. More preferably, the thin-walled articles have a wall thickness of <NUM> to <NUM>, and even more preferably the thin-walled articles have a wall thickness of <NUM> to <NUM>. The articles of the current invention can be containers, such as cups, buckets, beakers, trays or parts of such articles, such as see-through-windows, lids, or the like. The articles of the current invention are especially suitable for containing food, especially frozen food, such as ice-cream, frozen liquids, sauces, pre-cooked convenience products, and the like. Articles of the current invention are also suitable for medical or diagnostic purposes, such as syringes, beaker, pipettes, etc..

The heterophasic propylene copolymer composition in accordance with the present invention may be prepared by any suitable process, including in particular blending processes such as mechanical blending including mixing and melt blending processes and any combinations thereof as well as in-situ blending during the polymerization process. These can be carried out by methods known to the skilled person, including batch processes and continuous processes.

The heterophasic propylene copolymer composition according to the invention is preferably prepared by a sequential polymerization process, as described below, in the presence of a catalyst system comprising a Ziegler-Natta catalyst (ZN-C) comprising an internal donor (ID), a co-catalyst (Co) and optionally an external donor (ED), as described below.

The term "sequential polymerization system" according to this invention indicates that the heterophasic propylene copolymer composition is produced in at least two polymerization reactors connected in series. Accordingly, the present polymerization system comprises at least a first polymerization reactor (R1), a second polymerization reactor (R2), optionally a third polymerization reactor (R3), and further optionally a fourth polymerization reactor (R4). The term "polymerization reactor" shall indicate that the main polymerization takes place.

Preferably, at least one of the two polymerization reactors (R1) and (R2) is a gas phase reactor (GPR). More preferably the second polymerization reactor (R2), the optional third polymerization reactor (R3) and the optional fourth polymerization reactor (R4) are gas phase reactors (GPRs), i.e. a first gas phase reactor (GPR1) and a second gas phase reactor (GPR2) and a third gas phase reactor (GPR3). A gas phase reactor (GPR) according to this invention is preferably a fluidized bed reactor, a fast fluidized bed reactor or a settled bed reactor or any combination thereof.

Accordingly, the first polymerization reactor (R1) is preferably a slurry reactor (SR) and can be any continuous or simple stirred batch tank reactor or loop reactor operating in bulk or slurry. Bulk means a polymerization in a reaction medium that comprises of at least <NUM> % (w/w) monomer. According to the present invention the slurry reactor (SR) is preferably a (bulk) loop reactor (LR).

In this first polymerization reactor (R1) the matrix polypropylene (H-PP) or part of it, i.e. a first propylene homopolymer fraction (H-PP-<NUM>), is produced.

Preferably this propylene homopolymer of the first polymerization reactor (R1), more preferably the polymer slurry of the loop reactor (LR) containing the matrix (M) or part of it, i.e. a first propylene homopolymer fraction (H-PP-<NUM>), is directly fed into the second polymerization reactor (R2), i.e. into the (first) gas phase reactor (GPR1), without a flash step between the stages.

This kind of direct feed is described in <CIT>, <CIT>, <CIT> and <CIT>.

By "direct feed" is meant a process wherein the content of the first polymerization reactor (R1), i.e. of the loop reactor (LR), the polymer slurry comprising the propylene homopolymer matrix (H-PP) or part of it, i.e. a first propylene homopolymer fraction (H-PP-<NUM>), is led directly to the next stage gas phase reactor.

Alternatively, the propylene homopolymer of the first polymerization reactor (R1), preferably polymer slurry of the loop reactor (LR) containing the propylene homopolymer matrix, may be also directed into a flash step or through a further concentration step before fed into the second polymerization reactor (R2), i.e. into the <NUM>st gas phase reactor (GPR1). Accordingly, this "indirect feed" refers to a process wherein the content of the first polymerization reactor (R1), of the loop reactor (LR), i.e. the polymer slurry, is fed into the second polymerization reactor (R2), into the (first) gas phase reactor (GPR1), via a reaction medium separation unit and the reaction medium as a gas from the separation unit.

More specifically, the second polymerization reactor (R2) and any subsequent reactor, for instance, the third (R3) or fourth polymerization reactor (R4) are preferably gas phase reactors (GPRs). Such gas phase reactors (GPR) can be any mechanically mixed or fluid bed reactors. Preferably the gas phase reactors (GPRs) comprise a mechanically agitated fluid bed reactor with gas velocities of at least <NUM>/sec. Thus it is appreciated that the gas phase reactor is a fluidized bed type reactor preferably with a mechanical stirrer.

Thus, in a preferred embodiment the first polymerization reactor (R1) is a slurry reactor (SR), like loop reactor (LR), whereas the second polymerization reactor (R2) and the optional third polymerization reactor (R3), and the optional fourth polymerization reactor (R4) are gas phase reactors (GPRs).

Accordingly for the present process at least two, preferably two polymerization reactors (R1), and (R2) or three polymerization reactors (R1), (R2) and (R3), or even four polymerization reactors (R1), (R2), (R3) and (R4), namely a slurry reactor (SR), like loop reactor (LR) and a (first) gas phase reactor (GPR1), an optional second gas phase reactor (GPR2), and optionally a third gas phase reactor (GPR3) connected in series are used.

Prior to the slurry reactor (SR) a pre-polymerization reactor may be placed.

As the process covers also a pre-polymerization step, all of the Ziegler-Natta catalyst (ZN-C) is fed in the pre-polymerization reactor. Subsequently the pre-polymerization product containing the Ziegler-Natta catalyst (ZN-C) is transferred into the first polymerization reactor (R1).

Especially good results are achieved in case the temperature in the reactors is carefully chosen.

Accordingly it is preferred that the operating temperature in the first polymerization reactor (R1) is in the range of <NUM> to <NUM>, more preferably in the range of <NUM> to <NUM>, still more preferably in the range of <NUM> to <NUM>.

Alternatively or additionally to the previous paragraph it is preferred that the operating temperature in the second polymerization reactor (R2) and in the optional third reactor (R3) and the optional the fourth reactor (R4) is in the range of <NUM> to <NUM>, more preferably in the range of <NUM> to <NUM>.

Preferably the operating temperature in the second polymerization reactor (R2) is equal to or higher than the operating temperature in the first polymerization reactor (R1). Accordingly it is preferred that the operating temperature in the first polymerization reactor (R1) is in the range of <NUM> to <NUM>, more preferably in the range of <NUM> to <NUM>, still more preferably in the range of <NUM> to <NUM>, like <NUM> to <NUM>.

It is further preferred that the operating temperature in the second polymerization reactor (R2) is in the range of <NUM> to <NUM>, more preferably in the range of <NUM> to <NUM>, still more preferably in the range of <NUM> to <NUM>, with the proviso that the operating temperature in the in the second polymerization reactor (R2) is equal or higher to the operating temperature in the first polymerization reactor (R1).

Typically the pressure in the first polymerization reactor (R1), preferably in the loop reactor (LR), is in the range from <NUM> to <NUM> bar, preferably <NUM> to <NUM> bar, like <NUM> to <NUM> bar, whereas the pressure in the second polymerization reactor (R2), i.e. in the (first) gas phase reactor (GPR1), and in any subsequent reactor, like in the third polymerization reactor (R3), e.g. in the second gas phase reactor (GPR2), or in a fourth polymerization reactor (R4), e.g. in the third gas phase reactor (GPR3) is in the range from <NUM> to <NUM> bar, preferably <NUM> to <NUM> bar.

Preferably hydrogen is added in each polymerization reactor in order to control the molecular weight, i.e. the melt flow rate MFR<NUM>.

In the pre-polymerization reactor (PR) a polypropylene (Pre-PP) is produced. The pre-polymerization is conducted in the presence of the Ziegler-Natta catalyst (ZN-C). According to this embodiment the Ziegler-Natta catalyst (ZN-C), the co-catalyst (Co), and the external donor (ED) are all introduced to the pre-polymerization step. However, this shall not exclude the option that at a later stage for instance further co-catalyst (Co) and/or external donor (ED) is added in the polymerization process, for instance in the first reactor (R1). In one embodiment the Ziegler-Natta catalyst (ZN-C), the co-catalyst (Co), and the external donor (ED) are only added in the pre-polymerization reactor (PR).

The pre-polymerization reaction is typically conducted at a temperature of <NUM> to <NUM>, preferably from <NUM> to <NUM>, and more preferably from <NUM> to <NUM>.

The pressure in the pre-polymerization reactor is not critical but must be sufficiently high to maintain the reaction mixture in liquid phase. Thus, the pressure may be from <NUM> to <NUM> bar, for example <NUM> to <NUM> bar.

In a preferred embodiment, the pre-polymerization is conducted as bulk slurry polymerization in liquid propylene, i.e. the liquid phase mainly comprises propylene, with optionally inert components dissolved therein. Furthermore, according to the present invention, an ethylene feed can be employed during pre-polymerization as mentioned above.

It is possible to add other components also to the pre-polymerization stage. Thus, hydrogen may be added into the pre-polymerization stage to control the molecular weight of the polypropylene (Pre-PP) as is known in the art. Further, antistatic additive may be used to prevent the particles from adhering to each other or to the walls of the reactor.

The precise control of the pre-polymerization conditions and reaction parameters is within the skill of the art.

Due to the above defined process conditions in the pre-polymerization, a mixture (MI) of the Ziegler-Natta catalyst (ZN-C) and the polypropylene (Pre-PP) produced in the pre-polymerization reactor (PR) is obtained. Preferably the Ziegler-Natta catalyst (ZN-C) is (finely) dispersed in the polypropylene (Pre-PP). In other words, the Ziegler-Natta catalyst (ZN-C) particles introduced in the pre-polymerization reactor (PR) split into smaller fragments which are evenly distributed within the growing polypropylene (Pre-PP). The sizes of the introduced Ziegler-Natta catalyst (ZN-C) particles as well as of the obtained fragments are not of essential relevance for the instant invention and within the skilled knowledge.

A preferred multistage process is a "loop-gas phase"-process, as developed by Borealis (known as BORSTAR® technology) and is described e.g. in patent literature, such as in <CIT>, <CIT> <CIT>, <CIT>, <CIT>, <CIT> or in <CIT>.

A further suitable slurry-gas phase process is the Spheripol® process of Basell.

In the process described above a Ziegler-Natta catalyst (ZN-C) for the preparation of the heterophasic polypropylene composition is applied. This Ziegler-Natta catalyst (ZN-C) can be any stereo-specific Ziegler-Natta catalyst (ZN-C) for propylene polymerization, which preferably is capable of catalysing the polymerization and copolymerization of propylene and comonomers at a pressure of <NUM> to <NUM> kPa, in particular <NUM> to <NUM> kPa, and at a temperature of <NUM> to <NUM>, in particular of <NUM> to <NUM>.

Preferably, the Ziegler-Natta catalyst (ZN-C) comprises a high-yield Ziegler-Natta type catalyst including an internal donor component, which can be used at high polymerization temperatures of <NUM> or more.

Such high-yield Ziegler-Natta catalyst (ZN-C) comprises a non-phthalate donor as internal donor (ID). The internal donor (ID) used in the preparation of the catalyst used in the present invention is preferably selected from (di)esters of non-phthalic carboxylic (di)acids, <NUM>,<NUM>-diethers, derivatives and mixtures thereof. Especially preferred donors are diesters of mono-unsaturated dicarboxylic acids, in particular esters belonging to a group comprising malonates, maleates, succinates, citraconates, glutarates, cyclohexene-<NUM>,<NUM>-dicarboxylates and benzoates, and any derivatives and/or mixtures thereof. Preferred examples are e.g. substituted maleates and citraconates, most preferably citraconates.

Accordingly, the internal donor preferably is free of phthalic acid esters as well as decomposition products thereof. "Free of phthalic acid esters as well as decomposition products thereof" indicates absence of such components within the well accepted understanding in the art. "Free of phthalic acid esters as well as decomposition products thereof" indicates a maximum of <NUM>µg/kg, i.e. <NUM> ppb by weight (<NPL>). Phthalates and decomposition products thereof may be detected by gas chromatography coupled with one- or twodimensional mass spectrometry (GC-MS respectively GC-MS/MS) optionally preceded by enrichment on a suitable adsorption material.

The Ziegler-Natta catalyst (ZN-C) is preferably used in association with an alkyl aluminum co-catalyst (Co) and optionally external donors (ED).

As further component in the present polymerization process an external donor (ED) is preferably present. Suitable external donors include certain silanes, ethers, esters, amines, ketones, heterocyclic compounds and blends of these. It is especially preferred to use a silane. It is most preferred to use silanes of the general formula.

wherein Ra, Rb and Rc denote a hydrocarbon radical, in particular an alkyl or cycloalkyl group, and wherein p and q are numbers ranging from <NUM> to <NUM> with their sum p + q being equal to or less than <NUM>. Ra, Rb and Rc can be chosen independently from one another and can be the same or different. Specific examples of such silanes are (tert-butyl)<NUM>Si(OCH<NUM>)<NUM>, (cyclohexyl)(methyl)Si(OCH<NUM>)<NUM>, (phenyl)<NUM>Si(OCH<NUM>)<NUM> and (cyclopentyl)<NUM>Si(OCH<NUM>)<NUM>, or of general formula.

wherein R<NUM> and R<NUM> can be the same or different a represent a hydrocarbon group having <NUM> to <NUM> carbon atoms.

R<NUM> and R<NUM> are independently selected from the group consisting of linear aliphatic hydrocarbon group having <NUM> to <NUM> carbon atoms, branched aliphatic hydrocarbon group having <NUM> to <NUM> carbon atoms and cyclic aliphatic hydrocarbon group having <NUM> to <NUM> carbon atoms. It is in particular preferred that R<NUM> and R<NUM> are independently selected from the group consisting of methyl, ethyl, n-propyl, n-butyl, octyl, decanyl, iso-propyl, iso-butyl, iso-pentyl, tert. -butyl, tert. -amyl, neopentyl, cyclopentyl, cyclohexyl, methylcyclopentyl and cycloheptyl.

More preferably, both R<NUM> and R<NUM> are the same, yet more preferably both R<NUM> and R<NUM> are an ethyl group.

Especially preferred external donors (ED) are the dicyclopentyl dimethoxy silane donor (D-donor) or the cyclohexylmethyl dimethoxy silane donor (C-Donor).

In addition to the Ziegler-Natta catalyst (ZN-C) and the optional external donor (ED), a co-catalyst (Co) can be used. The co-catalyst (Co) is preferably a compound of group <NUM> of the periodic table (IUPAC), e.g. organo aluminum, such as an aluminum compound, like aluminum alkyl, aluminum halide or aluminum alkyl halide compound. Accordingly, in one specific embodiment the co-catalyst (Co) is a trialkylaluminum, like triethylaluminum (TEAL), dialkyl aluminum chloride or alkyl aluminum dichloride or mixtures thereof. In one specific embodiment the co-catalyst (Co) is triethylaluminum (TEAL).

Preferably the ratio between the co-catalyst (Co) and the external donor (ED) [Co/ED] and/or the ratio between the co-catalyst (Co) and the transition metal (TM) [Co/TM] should be carefully chosen.

Accordingly, the mol-ratio of co-catalyst (Co) to external donor (ED) [Co/ED] must be in the range of <NUM> to <NUM>, preferably is in the range of <NUM> to <NUM>, more preferably is in the range of <NUM> to <NUM>; and optionally
(b) the mol-ratio of co-catalyst (Co) to titanium compound (TC) [Co/TC] must be in the range of above <NUM> to <NUM>, preferably is in the range of <NUM> to <NUM>, still more preferably is in the range of <NUM> to <NUM>.

The heterophasic polypropylene composition (HECO) according to this invention is preferably produced in the presence of.

As mentioned above the Ziegler-Natta catalyst (ZN-C) is optionally modified by the so called BNT-technology during the above described pre-polymerization step in order to introduce the polymeric nucleating agent.

The following definitions of terms and determination methods apply for the above general description of the invention including the claims as well as to the below examples unless otherwise defined.

The melt flow rate (MFR) is determined according to ISO <NUM> and is indicated in g/<NUM>. The MFR is an indication of the flowability, and hence the processability, of the polymer. The higher the melt flow rate, the lower the viscosity of the polymer. The MFR<NUM> of polypropylene is determined at a temperature of <NUM> and a load of <NUM>.

Quantitative nuclear-magnetic resonance (NMR) spectroscopy was used to quantify the isotacticity and regio-regularity of the propylene homopolymers.

Quantitative <NUM>C{<NUM>H} NMR spectra were recorded in the solution-state using a Bruker Advance III <NUM> NMR spectrometer operating at <NUM> and <NUM> for <NUM>H and <NUM>C respectively. All spectra were recorded using a <NUM>C optimised <NUM> extended temperature probehead at <NUM> using nitrogen gas for all pneumatics.

For propylene homopolymers approximately <NUM> of material was dissolved in <NUM>,<NUM>-tetrachloroethane-d<NUM> (TCE-d<NUM>). To ensure a homogenous solution, after initial sample preparation in a heat block, the NMR tube was further heated in a rotatary oven for at least <NUM> hour. Upon insertion into the magnet the tube was spun at <NUM>. This setup was chosen primarily for the high resolution needed for tacticity distribution quantification (<NPL>; <NPL>). Standard single-pulse excitation was employed utilising the NOE and bi-level WALTZ16 decoupling scheme (<NPL><NPL>). A total of <NUM> (<NUM>) transients were acquired per spectra.

Quantitative <NUM>C{<NUM>H} NMR spectra were processed, integrated and relevant quantitative properties determined from the integrals using proprietary computer programs.

For propylene homopolymers all chemical shifts are internally referenced to the methyl isotactic pentad (mmmm) at <NUM> ppm.

Characteristic signals corresponding to regio defects (Resconi, L. , Cavallo, L. , Piemontesi, F. <NUM>, <NUM>, <NUM>;; Wang, W-J. , Macromolecules <NUM> (<NUM>), <NUM>; Cheng, H. , Macromolecules <NUM> (<NUM>), <NUM>) or comonomer were observed.

The tacticity distribution was quantified through integration of the methyl region between <NUM>-<NUM> ppm correcting for any sites not related to the stereo sequences of interest(Busico, V. , Cipullo, R. <NUM> (<NUM>) <NUM>; Busico, V. , Cipullo, R. , Monaco, G. , Vacatello, M. , Segre, A. , Macromolecules <NUM> (<NUM>) <NUM>).

Specifically the influence of regio-defects and comonomer on the quantification of the tacticity distribution was corrected for by subtraction of representative regio-defect and comonomer integrals from the specific integral regions of the stereo sequences.

The isotacticity was determined at the pentad level and reported as the percentage of isotactic pentad (mmmm) sequences with respect to all pentad sequences: <MAT>.

The presence of <NUM>,<NUM> erythro regio-defects was indicated by the presence of the two methyl sites at <NUM> and <NUM> ppm and confirmed by other characteristic sites. Characteristic signals corresponding to other types of regio-defects were not observed (Resconi, L. , Cavallo, L. , Piemontesi, F. <NUM>, <NUM>, <NUM>).

The amount of <NUM>,<NUM> erythro regio-defects was quantified using the average integral of the two characteristic methyl sites at <NUM> and <NUM> ppm: <MAT>.

The total amount of propene was quantified as the sum of primary inserted propene and all other present regio-defects: <MAT>.

The mole percent of <NUM>,<NUM> erythro regio-defects was quantified with respect to all propene: <MAT>.

The crystalline (CF) and soluble fractions (SF) of the polypropylene (PP) compositions as well as the comonomer content and intrinsic viscosities of the respective fractions were analysed by the CRYSTEX QC, Polymer Char (Valencia, Spain).

The crystalline and amorphous fractions are separated through temperature cycles of dissolution at <NUM>, crystallization at <NUM> and re-dissolution in a <NUM>,<NUM>,<NUM>-trichlorobenzene (<NUM>,<NUM>,<NUM>-TCB) at <NUM>. Quantification of SF and CF and determination of ethylene content (C2) are achieved by means of an infrared detector (IR4) and an online <NUM>-capillary viscometer which is used for the determination of the intrinsic viscosity (IV).

The IR4 detector is a multiple wavelength detector detecting IR absorbance at two different bands (CH3 and CH2) for the determination of the concentration and the Ethylene content in Ethylene-Propylene copolymers. IR4 detector is calibrated with series of <NUM> EP copolymers with known Ethylene content in the range of <NUM> wt. -% to <NUM> wt. -% (determined by 13C-NMR) and various concentration between <NUM> and <NUM>/ml for each used EP copolymer used for calibration.

The amount of soluble fraction (SF) and crystalline fraction (CF) are correlated through the XS calibration to the "Xylene Cold Soluble" (XCS) fraction and "Xylene Cold Insoluble" (XCI) fraction, respectively, determined according to standard gravimetric method as per ISO16152. XS calibration is achieved by testing various ethylene propylene copolymers with XS content in the range <NUM>-<NUM> wt.

The intrinsic viscosity (IV) of the parent ethylene propylene copolymer and its soluble and crystalline fractions are determined with a use of an online <NUM>-capillary viscometer and are correlated to corresponding intrinsic viscosities, determined by standard method in decalin according to ISO <NUM>/<NUM> at <NUM>. Calibration is achieved with various ethylene propylene and polypropylene copolymers with IV = <NUM>-<NUM> dl/g.

A sample of the polypropylene composition to be analysed is weighed out in concentrations of <NUM>/ml to <NUM>/ml. After automated filling of the vial with <NUM>,<NUM>,<NUM>-TCB containing <NUM>/l <NUM>,<NUM>-tert-butyl-<NUM>-methylphenol (BHT) as antioxidant, the sample is dissolved at <NUM> until complete dissolution is achieved, usually for <NUM>, with constant stirring of <NUM> rpm.

A defined volume of the sample solution is injected into the column filled with inert support where the crystallization of the sample and separation of the soluble fraction from the crystalline part is taking place. This process is repeated two times. During the first injection the whole sample is measured at high temperature, determining the IV[dl/g] and the C2[wt. %] of the polypropylene composition. During the second injection the soluble fraction (at low temperature) and the crystalline fraction (at high temperature) with the crystallization cycle are measured (wt.

Stress whitening is determined by a modified three point bending test, namely the reversed three point bending test, (cf.

The reversed three point bending test is carried out on a universal testing machine (Zwick Z010) at <NUM>/min. The samples are <NUM> thick injection moulded UL94 specimens (125x12.5x2mm).

The experimental set-up consists of the reversed three point bending test coupled with an optical detection system.

The mechanical set up consists of:
a fix part (<NUM>), with a span (<NUM>) of <NUM>, a moving part including a loading edge (<NUM>) with a light source (<NUM>) and an optical sensor (<NUM>) fixed on the moving part closely above and beneath the specimen (<NUM>) by a vertical rod. This ensures that the distance between light source and optical sensor remains constant during the test, which is a prerequisite for a good reproducibility of the measurements.

The force-deflection and the optical signal-deflection curves are recorded. At the beginning of the test, the optical signal (<NUM>) is calibrated to <NUM> % (7a), regardless of the initial transparency/haziness of the inserted sample.

Occurrence of stress whitening is correlated with a sharp drop in the optical signal-deflection curve (cf. <FIG>, reference <NUM> and further below).

Three different parameters are determined:.

The onset angle for stress whitening is determined according to formula (VI): <MAT> wherein
"s" denominates the deflection of the loading edge, at which the light transmission curve drops and is determined as illustrated in <FIG>:
At the beginning of the test, the optical signal (<NUM>) is calibrated to <NUM> % (7a), regardless of the initial transparency/haziness of the inserted sample. The deflection of the loading edge (s), at which the in the light transmission curve drops is determined by the abscissa-value (<NUM>) of the intersection between the tangent of the slope of the optical signal (7b) and the <NUM> % line of the initial optical signal (7a).

b) Residual size (width) of the blushing zones immediately after a bending of <NUM>°, measured in [mm], also denominated as "Res-SW <NUM>°" or "residual stress whitening";
The width of a blushing zone (b) is determined as follows:
Tests are conducted to a deflection corresponding to an angle of <NUM>° according to the formula (VI) above. Then the specimen is abruptly unloaded with a crosshead speed of <NUM>/min. The width of the blushing area is measured immediately after testing using a slide gage.

c) Stress whitening intensity: this is the residual intensity of the blushing zone immediately after a bending of <NUM> deg. C (visual appreciation from <NUM> to <NUM>, with <NUM>: no remaining blush, <NUM>: intensive whitening), also denominated as "SW-intensity".

A mark of <NUM> is attributed when there is no residual blushing; a note of <NUM> when the whitening of the deformed zone is extremely pronounced. The obtained value is entered manually in a result sheet; average calculations are automated. The determination of these parameters is somewhat subjective and dependent on an operator. Although the obtained values are somewhat subjective they give essential information on the elastic recovery potential of the material.

The following degrees of intensity are noted:.

Hexane solubles (wt. -%): determined in accordance with FDA section <NUM><NUM> of a polymer cast film of <NUM> thickness (produced on a PM30 cast film line using chill-roll temperature of <NUM>) is extracted by <NUM> hexane at <NUM> for <NUM> hours while stirring with a reflux cooler. After <NUM> hours the mixture is immediately filtered on a filter paper N°<NUM>. The precipitate is collected in an aluminum recipient and the residual hexane is evaporated on a steam bath under nitrogen flow. The precipitate was weighted again and hexane solubles were calculated.

These properties were measured with a TA Instrument Q200 differential scanning calorimetry (DSC) on <NUM> to <NUM> samples. Crystallization temperature (Tc) and crystallization enthalpy (Hc) are determined from the cooling step, while melting temperature (Tm) and melting enthalpy (Hm) are determined from the second heating step, respectively, from the first heating step in case of the webs.

The Charpy notched impact strength (NIS) was measured according to ISO <NUM>1eA at +<NUM>, using injection molded bar test specimens of 80x10x4 mm<NUM> prepared in accordance with EN ISO <NUM>-<NUM>.

Flexural Modulus was determined in three-point bending according to ISO <NUM> using 80x10x4 mm<NUM> test bars injection molded in line with EN ISO <NUM>-<NUM>.

<NUM> litre of <NUM>-ethylhexanol and <NUM> of propylene glycol butyl monoether (in a molar ratio <NUM>/<NUM>) were added to a <NUM> reactor. Then <NUM> of a <NUM> % solution in toluene of BEM (butyl ethyl magnesium) provided by Crompton GmbH, were slowly added to the well stirred alcohol mixture. During the addition the temperature was kept at <NUM>. After addition the temperature of the reaction mixture was raised to <NUM> and mixing was continued at this temperature for 30minutes. Finally after cooling to room temperature the obtained Mg-alkoxide was transferred to a storage vessel. <NUM> of Mg alkoxide prepared above was mixed with <NUM> bis-(<NUM>-ethylhexyl) citraconate for <NUM>. After mixing the obtained Mg complex was used immediately in the preparation of the catalyst component. <NUM> of titanium tetrachloride was placed in a <NUM> reactor equipped with a mechanical stirrer at <NUM>. Mixing speed was adjusted to <NUM> rpm. <NUM> of Mg-complex prepared above was added within <NUM> minutes keeping the temperature at <NUM>. <NUM> of ViscoplexR <NUM>-<NUM> and <NUM> of a toluene solution with <NUM> Necadd <NUM>™ was added. Then <NUM> of heptane was added to form an emulsion. Mixing was continued for <NUM> minutes at <NUM>, after which the reactor temperature was raised to <NUM> within <NUM> minutes. The reaction mixture was stirred for a further <NUM> minutes at <NUM>. Afterwards stirring was stopped and the reaction mixture was allowed to settle for <NUM> minutes at <NUM>. The solid material was washed <NUM> times: Washings were made at <NUM> under stirring for <NUM> with <NUM> rpm. After stirring was stopped the reaction mixture was allowed to settle for <NUM>-<NUM> minutes and followed by siphoning. Wash <NUM>: Washing was made with a mixture of <NUM> of toluene and <NUM> donor Wash <NUM>: Washing was made with a mixture of <NUM> of TiCl<NUM> and <NUM> of donor.

Wash <NUM>: Washing was made with <NUM> of toluene. Wash <NUM>: Washing was made with <NUM> of heptane. Wash <NUM>: Washing was made with <NUM> of heptane under <NUM> minutes stirring. Afterwards stirring was stopped and the reaction mixture was allowed to settle for <NUM> minutes while decreasing the temperature to <NUM> with subsequent siphoning, followed by N<NUM> sparging for <NUM> minutes to yield an air sensitive powder. Ti content was <NUM> wt-% External Donor:
In the Examples, the external donor D (Dicyclopentyl dimethoxy silane <NPL>) was used. The co-catalyst component used was triethyl aluminum (TEAL).

The polymerization conditions for Polymer <NUM> and Polymer <NUM> are listed in the Table below.

The materials used in the inventive examples are produced in a Borstar® pilot plant, equipped with a loop, a first gas phase reactor and a second gas phase reactor configuration. The loop and first gas phase reactor are used to produce the matrix and second gas phase reactor for rubber phase. The chemical composition of the reactants in each reactor were adjusted by man skilled in the art to reach the desired polymer design. The typical values are listed in Table <NUM> below.

Examples IE1 and IE5 were stabilized with:.

IE2, IE3, and IE4 were compounded with HE9621-PH as modifier in the amounts indicated in Table <NUM>.

HE9621-PH is a high density polyethylene with narrow molecular weight distribution. It has a density (according to ISO <NUM>) of <NUM>/m<NUM> , a melt flow rate (<NUM>/<NUM>,<NUM>) according to ISO <NUM> of <NUM>/<NUM> and a flexural modulus (ISO <NUM>) of <NUM> MPa.

The compounding was done using a ZSK <NUM> twin screw extruder. The melt temperature was <NUM>, throughput was <NUM>/h.

For IE4 <NUM> wt. % of a nucleating masterbatch were additionally added to introduce a polymeric nucleating agent. The nucleating masterbatch comprises a propylene homopolymer having MFR<NUM> of <NUM>/<NUM> and <NUM> ppm of a polymeric nucleating agent and has a flexural modulus of <NUM> MPa.

CE1 is BE170CF which is a heterophasic propylene copolymer having a MFR<NUM> of <NUM>/<NUM>, commercially available from Borealis AG.

CE2 is BC545MO, which is a low-blush polypropylene heterophasic copolymer produced by Borealis AG. It has a MFR<NUM> of <NUM>/<NUM> and a flexural modulus of <NUM> MPa.

The above result show that a heterophasic propylene copolymer composition as defined in the present invention shows improved optical properties, expressed by stress whitening intensity and stress whitening angle, but also improved mechanical properties, expressed by increased flexural modulus (FM) and notched Charpy impact strength (NIS). The composition further has low hexane soluble content which makes them highly attractive for food and medical applications.

Claim 1:
Heterophasic propylene copolymer composition, comprising
a heterophasic propylene copolymer (HECO) comprising a matrix (M) being a propylene homopolymer (H-PP) and an elastomeric propylene copolymer (EPC) dispersed in said matrix (M),
wherein the heterophasic propylene copolymer (HECO) has
a) a melt flow rate MFR<NUM> (<NUM>, <NUM>) measured according to ISO <NUM> in the range of <NUM> to <NUM>/<NUM>,
(b) a soluble fraction content (SF) determined by TREF fractionation on CRYSTEX QC, Polymer Char (Valencia, Spain) as described in the experimental part of the description, in the range of <NUM> to <NUM> wt.%,
(c) an ethylene content of the soluble fraction content (SF) determined under (b) in the range of from <NUM> wt.% to less than <NUM> wt.%,
(d) an intrinsic viscosity (IV) determined according to DIN ISO <NUM>/<NUM> (in decalin at <NUM>) of the soluble fraction (SF) in the range of from <NUM> to <NUM> dl/g,
(e) a crystalline fraction content (CF) determined by TREF fractionation on CRYSTEX QC, Polymer Char (Valencia, Spain) as described in the experimental part of the description, in the range of <NUM> to <NUM> wt.%,
(f) an ethylene content of the crystalline fraction content (CF) determined under (e) of from <NUM> wt.% to <NUM> wt.%,
(g) a flexural modulus of not less than <NUM> MPa, determined in a <NUM>-point-bending according to ISO <NUM> on injection molded specimens of <NUM> × <NUM> × <NUM>, prepared in accordance with EN ISO <NUM>-<NUM>, and
the heterophasic propylene copolymer composition has a total ethylene content in the range of from <NUM> wt.% to <NUM> wt.%, determined by quantitative NMR spectroscopy as described in the experimental part of the description.