PROPYLENE COPOLYMER WITH EXCELLENT OPTICAL PROPERTIES

Abstract

The present invention is directed to a polypropylene composition (P) comprising a first random propylene copolymer (A) and a second random propylene copolymer (B), said first random propylene copolymer (A) and said second random propylene copolymer (B) being copolymers of propylene and 1-hexene. Further, the present invention is directed to a blown film comprising said polypropylene composition (P).

Claims

1-15. (canceled)

16. A polypropylene composition (P), comprising at least 90.0 wt.-%, based on the overall weight of the polypropylene composition (P) of a copolymer (C) of propylene and 1-hexene, comprising i) a first random propylene copolymer (A) of propylene and a 1-hexene having a 1-hexene content in the range of 0.1 to 3.0 wt.-%, and ii) a second random propylene copolymer (B) of propylene and 1-hexene having a higher 1-hexene content than the first random propylene copolymer (A), wherein the copolymer (C) has an overall 1-hexene content in the range of 3.8 to 10.0 wt.-%, and wherein the copolymer (C) has a xylene soluble content (XCS) in the range of 8.0 to 30.0 wt.-%.

17. The polypropylene composition (P) according to claim 16, fulfilling in-equation (1)
MFR(C)/MFR(A)≤1.0  (1), wherein MFR(A) is the melt flow rate MFR.sub.2 (230° C., 2.16 kg) determined according to ISO 1133 in [g/10 min] of the first random propylene copolymer (A) and MFR(C) is the melt flow rate MFR.sub.2 (230° C., 2.16 kg) determined according to ISO 1133 in [g/10 min] of the copolymer (C).

18. The polypropylene composition (P) according to claim 16, wherein the copolymer (C) has a melt flow rate MFR.sub.2 (230° C., 2.16 kg) determined according to ISO 1133 in the range of 0.4 to 12.0 g/10 min.

19. The polypropylene composition (P) according to claim 16, wherein the weight ratio between the first random propylene copolymer (A) and the second random propylene copolymer (B) within the copolymer (C) is in the range of 30:70 to 70:30.

20. The polypropylene composition (P) according to claim 16, wherein the copolymer (C) has an amount of 2,1 erythro regio-defects of at least 0.4 mol.-%.

21. The polypropylene composition (P) according to claim 16, wherein i) the first random propylene copolymer (A) has a melt flow rate MFR.sub.2 (230° C., 2.16 kg) determined according to ISO 1133 in the range of 0.3 to 12.0 g/10 min, and/or ii) the second random propylene copolymer (B) has a melt flow rate MFR.sub.2 (230° C., 2.16 kg) determined according to ISO 1133 in the range of 0.2 to 9.0 g/10 min.

22. The polypropylene composition (P) according to claim 16, wherein the copolymer (C) comprises 35.0 to 65.0 wt.-% of the first random propylene copolymer (A) and 35.0 to 65.0 wt.-% of the second random propylene copolymer (B), based on the overall weight of the copolymer (C).

23. The polypropylene composition (P) according to claim 16, wherein the copolymer (C) fulfills in-equation (2) $\begin{array}{cc}4.5\le \frac{C6\left(C\right)}{C6\left(A\right)*\frac{\left[A\right]}{\left[C\right]}}\le 9.0& \left(2\right)\end{array}$ wherein C6(A) is the 1-hexene content of the first random propylene copolymer (A) based on the total weight of the first random propylene copolymer (A) [in wt.-%]; C6(C) is the 1-hexene content of the copolymer (C) based on the total weight of the copolymer (C) [in wt.-%]; and [A]/[C] is the weight ratio between the first random propylene copolymer (A) and the copolymer (C) [in g/g].

24. The polypropylene composition (P) according to claim 16, wherein the copolymer (C) has an amount of hexane hot solubles (HHS) measured according to FDA 177.1520 equal to or below 1.5 wt.-%.

25. An article, comprising at least 90.0 wt.-% of the polypropylene composition (P) according to claim 16.

26. The article according to claim 25, wherein the article is a film.

27. The article according to claim 26, wherein the film has i) a haze before steam sterilization determined according to ASTM D 1003-00 measured on a 50 μm blown film below 10.0%, and ii) a haze after steam sterilization determined according to ASTM D 1003-00 measured on a 50 μm blown film below 12.0%.

28. The article according to claim 26, wherein the article is a sealing layer in a multi-layer film.

29. A process for the preparation of a copolymer (C) according to claim 16, wherein the process is a sequential polymerization process comprising at least two reactors connected in series, wherein said process comprises the steps of (A) polymerizing in a first reactor (R-1) which is a slurry reactor (SR), propylene and 1-hexene, and obtaining a first random propylene copolymer (A), (B) transferring said first random propylene copolymer (A) and unreacted comonomers of the first reactor (R-1) in a second reactor (R-2) which is a gas phase reactor (GPR-1), (C) feeding to said second reactor (R-2) propylene and 1-hexene, (D) polymerizing in said second reactor (R-2) and in the presence of said first random propylene copolymer (A) propylene and 1-hexene obtaining a second random propylene copolymer (B), said first random propylene copolymer (A) and said second random propylene copolymer (B) form the copolymer (C) of the polypropylene composition (P), wherein further in the first reactor (R-1) and the second reactor (R-2) the polymerization takes place in the presence of a solid catalyst system (SCS), said solid catalyst system (SCS) comprises a transition metal compound of formula (I)
R.sub.n(Cp).sub.2MX.sub.2  (I) wherein each Cp independently is an unsubstituted or substituted and/or fused cyclopentadienyl ligand, substituted or unsubstituted indenyl or substituted or unsubstituted fluorenyl ligand; wherein the optional one or more substituent(s) is independently selected from the group consisting of halogen, hydrocarbyl, C.sub.3-C.sub.12-cycloalkyl which contains 1, 2, 3 or 4 heteroatom(s) in the ring moiety, C.sub.6-C.sub.20-heteroaryl, C.sub.1-C.sub.20-haloalkyl, —SiR″.sub.3, —OSiR″.sub.3, —SR″, —PR″.sub.2, OR″ and —NR″.sub.2, wherein each R″ is independently a hydrogen or hydrocarbyl selected from the group consisting of C.sub.1-C.sub.20-alkyl, C.sub.2-C.sub.20-alkenyl, C.sub.2-C.sub.20-alkynyl, C.sub.3-C.sub.12-cycloalkyl, and C.sub.6-C.sub.20-aryl; or in case of —NR″.sub.2, the two substituents R″ can form a five- or six-membered ring, together with the nitrogen atom to which they are attached; R is a bridge of 1-2 C-atoms and 0-2 heteroatoms, wherein the heteroatom(s) can be Si, Ge and/or O atom(s), wherein each of the bridge atoms may bear independently substituents selected from the group consisting of C.sub.1-C.sub.20-alkyl, tri(C.sub.1-C.sub.20-alkyl)silyl, tri(C.sub.1-C.sub.20-alkyl)siloxy and C.sub.6-C.sub.20-aryl substituents; or a bridge of one or two heteroatoms selected from silicon, germanium and/or oxygen atom(s), M is Zr or Hf, each X is independently a sigma-ligand selected from the group consisting of H, halogen, C.sub.1-C.sub.20-alkyl, C.sub.1-C.sub.20-alkoxy, C.sub.2-C.sub.20-alkenyl, C.sub.2-C.sub.20-alkynyl, C.sub.3-C.sub.12-cycloalkyl, C.sub.6-C.sub.20-aryl, C.sub.6-C.sub.20-aryloxy, C.sub.7-C.sub.20-arylalkyl, C.sub.7-C.sub.20-arylalkenyl, —SR″, —PR″.sub.3, —SiR″.sub.3, —OSiR″.sub.3, —NR″.sub.2 and —CH.sub.2—Y, wherein Y is C.sub.6-C.sub.2M-aryl, C.sub.6-C.sub.20-heteroaryl, C.sub.1-C.sub.20-alkoxy, C.sub.6-C.sub.20-aryloxy, NR″.sub.2, —SR″, —PR″.sub.3, —SiR″.sub.3, or —OSiR″.sub.3; each of the above mentioned ring moieties alone or as a part of another moiety as the substituent for Cp, X, R″ or R can further be substituted with C.sub.1-C.sub.20-alkyl which may contain Si and/or O atoms; and n is 1 or 2.

30. The process according to claim 29, wherein the transition metal compound of formula (I) is an organo-zirconium compound of formula (II) or (II′) ##STR00004## wherein M is Zr; each X is a sigma ligand selected from the group consisting of a hydrogen atom, a halogen atom, a C.sub.1-C.sub.6 alkoxy group, C.sub.1-C.sub.6 alkyl, phenyl, and a benzyl group; L is a divalent bridge selected from the group consisting of —R′.sub.2C—, —R′.sub.2C—CR′.sub.2, —R′.sub.2Si—, —R′.sub.2Si—SiR′.sub.2—, and —R′.sub.2Ge—, wherein each R′ is independently selected from the group consisting of hydrogen atom, C.sub.1-C.sub.20 alkyl, C.sub.3-C.sub.10 cycloalkyl, tri(C.sub.1-C.sub.20-alkyl)silyl, C.sub.6-C.sub.20-aryl, and C.sub.7-C.sub.20 arylalkyl; each R.sup.2 or R.sup.2′ is a C.sub.1-C.sub.10 alkyl group; R.sup.5′ is a C.sub.1-C.sub.10 alkyl group or a Z′R.sup.3′ group; R.sup.6 is hydrogen or a C.sub.1-C.sub.10 alkyl group; R.sup.6′ is a C.sub.1-C.sub.10 alkyl group or a C.sub.6-C.sub.10 aryl group; R.sup.7 is hydrogen, a C.sub.1-C.sub.6 alkyl group or a ZR.sup.3 group; R.sup.7′ is hydrogen or a C.sub.1-C.sub.10 alkyl group; Z and Z′ are independently O or S; R.sup.3′ is a C.sub.1-C.sub.10 alkyl group, or a C.sub.6-C.sub.10 aryl group optionally substituted by one or more halogen groups; R.sup.3 is a C.sub.1-C.sub.10 alkyl group; each n is independently 0 to 4; and each R.sup.1 is independently a C.sub.1-C.sub.20 hydrocarbyl group.

Description

EXAMPLES

[0270] A. Measuring Methods

[0271] The following definitions of terms and determination methods apply for the above general description of the invention as well as to the below examples unless otherwise defined.

[0272] Comonomer Content of 1-Hexene for a Propylene 1-Hexene Copolymer

[0273] Quantitative .sup.13C{.sup.1H} NMR spectra recorded in the molten-state using a Bruker Avance III 500 NMR spectrometer operating at 500.13 and 125.76 MHz for .sup.1H and .sup.13C respectively. All spectra were recorded using a .sup.13C optimised 7 mm magic-angle spinning (MAS) probehead at 180° C. using nitrogen gas for all pneumatics. Approximately 200 mg of material was packed into a 7 mm outer diameter zirconia MAS rotor and spun at 4 kHz. This setup was chosen primarily for the high sensitivity needed for rapid identification and accurate quantification. (Klimke, K., Parkinson, M., Piel, C., Kaminsky, W., Spiess, H. W., Wilhelm, M., Macromol. Chem. Phys. 2006; 207:382., Parkinson, M., Klimke, K., Spiess, H. W., Wilhelm, M., Macromol. Chem. Phys. 2007; 208:2128., Castignolles, P., Graf, R., Parkinson, M., Wilhelm, M., Gaborieau, M., Polymer 50 (2009) 2373). Standard single-pulse excitation was employed utilising the NOE at short recycle delays of 3s (Klimke, K., Parkinson, M., Piel, C., Kaminsky, W., Spiess, H. W., Wilhelm, M., Macromol. Chem. Phys. 2006; 207:382., Pollard, M., Klimke, K., Graf, R., Spiess, H. W., Wilhelm, M., Sperber, O., Piel, C., Kaminsky, W., Macromolecules 2004; 37:813.). and the RS-HEPT decoupling scheme (Filip, X., Tripon, C., Filip, C., J. Mag. Resn. 2005, 176, 239., Griffin, J. M., Tripon, C., Samoson, A., Filip, C., and Brown, S. P., Mag. Res. in Chem. 200745, S1, S198). A total of 16384 (16k) transients were acquired per spectra.

[0274] Quantitative .sup.13C{.sup.1H} NMR spectra were processed, integrated and relevant quantitative properties determined from the integrals. All chemical shifts are internally referenced to the methyl isotactic pentad (mmmm) at 21.85 ppm.

[0275] Characteristic signals corresponding to the incorporation of 1-hexene were observed and the comonomer content quantified in the following way.

[0276] The amount of 1-hexene incorporated in PHP isolated sequences was quantified using the integral of the αB4 sites at 44.2 ppm accounting for the number of reporting sites per comonomer:

H=IαB4/2

[0277] The amount of 1-hexene incorporated in PHHP double consecutive sequences was quantified using the integral of the ααB4 site at 41.7 ppm accounting for the number of reporting sites per comonomer:

HH=2*IααB4

[0278] When double consecutive incorporation was observed the amount of 1-hexene incorporated in PHP isolated sequences needed to be compensated due to the overlap of the signals αB4 and αB4B4 at 44.4 ppm:

H=(IαB4−2*IααB4)/2

[0279] The total 1-hexene content was calculated based on the sum of isolated and consecutively incorporated 1-hexene:

Htotal=H+HH

[0280] When no sites indicative of consecutive incorporation observed the total 1-hexeen comonomer content was calculated solely on this quantity:

Htotal=H

[0281] Characteristic signals indicative of regio 2,1-erythro defects were observed (Resconi, L., Cavallo, L., Fait, A., Piemontesi, F., Chem. Rev. 2000, 100, 1253).

[0282] The presence of 2,1-erythro regio defects was indicated by the presence of the Pαβ (21e8) and Pay (21e6) methyl sites at 17.7 and 17.2 ppm and confirmed by other characteristic signals.

[0283] The total amount of secondary (2,1-erythro) inserted propene was quantified based on the αα21e9 methylene site at 42.4 ppm:

P21=Iαα21e9

[0284] The total amount of primary (1,2) inserted propene was quantified based on the main Sαα methylene sites at 46.7 ppm and compensating for the relative amount of 2,1-erythro, αB4 and ααB4B4 methylene unit of propene not accounted for (note H and HH count number of hexene monomers per sequence not the number of sequences):

P12=I.sub.Sαα+2*P21+H+HH/2

[0285] The total amount of propene was quantified as the sum of primary (1,2) and secondary (2,1-erythro) inserted propene:

Ptotal=P12+P21=I.sub.Sαα+3*Iαα21e9+(IαB4−2*IααB4)/2+IααB4

[0286] This simplifies to:

Ptotal=I.sub.Sαα+3*Iαα21e9+0.5*IαB4

[0287] The total mole fraction of 1-hexene in the polymer was then calculated as:

fH=Htotal/(Htotal+Ptotal)

[0288] The full integral equation for the mole fraction of 1-hexene in the polymer was:

fH=(((IαB4−2*IααB4)/2)+(2*IααB4))/((I.sub.Sαα+3*Iαα21e9+0.5*IαB4)+((IαB4−2*IααB4)/2)+(2*IααB4))

[0289] This simplifies to:

fH=(IαB4/2+IααB4)/(I.sub.Sαα+3*Iαα21e9+IαB4+IααB4)

[0290] The total comonomer incorporation of 1-hexene in mole percent was calculated from the mole fraction in the usual manner:

H[mol %]=100*fH

[0291] The total comonomer incorporation of 1-hexene in weight percent was calculated from the mole fraction in the standard manner:

H[wt %]=100*(fH*84.16)/((fH*84.16)+((1−fH)*42.08))

[0292] Calculation of comonomer content of the second random propylene copolymer (B):

[00003]$\frac{C\left(\mathrm{CPP}\right)-w\left(A\right)\times C\left(A\right)}{w\left(B\right)}=C\left(B\right)$ [0293] wherein [0294] w(A) is the weight fraction of the first random propylene copolymer (A), [0295] w(B) is the weight fraction of the second random propylene copolymer (B), [0296] C(A) is the comonomer content [in wt.-%] measured by .sup.13C NMR spectroscopy of the first random propylene copolymer (A), i.e. of the product of the first reactor (R.sup.1), [0297] C(CPP) is the comonomer content [in wt.-%] measured by .sup.13C NMR spectroscopy of the product obtained in the second reactor (R.sup.2), i.e. the mixture of the first random propylene copolymer (A) and the second random propylene copolymer (B) [of the propylene copolymer (C-PP)], [0298] C(B) is the calculated comonomer content [in wt.-%] of the second random propylene copolymer (B).

[0299] Melt Flow Rate (MFR)

[0300] The melt flow rates are measured with a load of 2.16 kg (MFR.sub.2) at 230° C. The melt flow rate is that quantity of polymer in grams which the test apparatus standardised to ISO 1133 extrudes within 10 minutes at a temperature of 230° C. under a load of 2.16 kg.

[0301] Calculation of melt flow rate MFR.sub.2 (230° C., 2.16 kg) of the second random propylene copolymer (B):

[00004]$\mathrm{MFR}\left(B\right)={10}^{\left[\frac{\log \left(\mathrm{MFR}\left(C\right)\right)-w\left(A\right)\times \log \left(\mathrm{MFR}\left(A\right)\right)}{w\left(B\right)}\right]}$ [0302] wherein [0303] w(A) is the weight fraction of the first random propylene copolymer (A), [0304] w(B) is the weight fraction of the second random propylene copolymer (B), [0305] MFR(A) is the melt flow rate MFR.sub.2 (230° C., 2.16 kg) [in g/10 min] measured according ISO 1133 of the first random propylene copolymer (A), [0306] MFR(C) is the melt flow rate MFR.sub.2 (230° C., 2.16 kg) [in g/10 min] measured according ISO 1133 of the Polypropylene composition (P), [0307] MFR(B) is the calculated melt flow rate MFR.sub.2 (230° C., 2.16 kg) [in g/10 min] of the second random propylene copolymer (B).

[0308] The xylene cold solubles (XCS, wt.-%): Content of xylene cold solubles (XCS) is determined at 25° C. according ISO 16152; first edition; 2005-07-01.

[0309] Hexane hot solubles (HHS, wt.-%)

[0310] FDA section 177.1520

[0311] 1 g of a polymer film of 100 μm thickness is added to 400 ml hexane at 50° C. for 2 hours while stirring with a reflux cooler.

[0312] After 2 hours the mixture is immediately filtered on a filter paper No 41.

[0313] The precipitate is collected in an aluminium recipient and the residual hexane is evaporated on a steam bath under N.sub.2 flow.

[0314] The amount of hexane solubles is determined by the formula

((wt.sample+wt.crucible)−(wt crucible))/(wt.sample)−100.

[0315] Melting temperature T.sub.m, crystallization temperature T.sub.c, is measured with Mettler TA820 differential scanning calorimetry (DSC) on 5-10 mg samples. Both crystallization and melting curves were obtained during 10° C./min cooling and heating scans between 30° C. and 225° C. Melting and crystallization temperatures were taken as the peaks of endotherms and exotherms.

[0316] Haze was determined according to ASTM D1003-00 on blown films of 50 μm thickness.

[0317] Steam sterilization was performed in a Systec D series machine (Systec Inc., USA). The samples were heated up at a heating rate of 5° C./min starting from 23° C. After having been kept for 30 min at 121° C., they were removed immediately from the steam sterilizer and stored at room temperature till processed further.

[0318] Sealing Initiation Temperature (SIT); Sealing End Temperature (SET), Sealing Range:

[0319] The method determines the sealing temperature range (sealing range) of polypropylene films, in particular blown films or cast films. The sealing temperature range is the temperature range, in which the films can be sealed according to conditions given below.

[0320] The lower limit (heat sealing initiation temperature (SIT)) is the sealing temperature at which a sealing strength of >3 N is achieved. The upper limit (sealing end temperature (SET)) is reached, when the films stick to the sealing device.

[0321] The sealing range is determined on a J&B Universal Sealing Machine Type 3000 with a film of 50 μm thickness with the following further parameters:

[0322] Specimen width: 25.4 mm

[0323] Seal Pressure: 0.1 N/mm.sup.2

[0324] Seal Time: 0.1 sec

[0325] Cool time: 99 sec

[0326] Peel Speed: 10 mm/sec

[0327] Start temperature: 80° C.

[0328] End temperature: 150° C.

[0329] Increments: 10° C.

[0330] specimen is sealed A to A at each sealbar temperature and seal strength (force) is determined at each step.

[0331] The temperature is determined at which the seal strength reaches 3 N.

[0332] Hot Tack Force:

[0333] The hot tack force is determined on a J&B Hot Tack Tester with a blown film of 50 μm thickness with the following further parameters:

[0334] Specimen width: 25.4 mm

[0335] Seal Pressure: 0.3 N/mm.sup.2

[0336] Seal Time: 0.5 sec

[0337] Cool time: 99 sec

[0338] Peel Speed: 200 mm/sec

[0339] Start temperature: 90° C.

[0340] End temperature: 140° C.

[0341] Increments: 10° C.

[0342] The maximum hot tack force, i.e the maximum of a force/temperature diagram is determined and reported.

[0343] Tensile modulus in machine and transverse direction were determined according to ISO 527-3 on 50 m blown films at a cross head speed of 1 mm/min.

[0344] Dart-drop strength (DDI) is measured using ASTM D1709, method A (Alternative Testing Technique) from the film samples. A dart with a 38 mm diameter hemispherical head is dropped from a height of 0.66 m onto a film clamped over a hole. Successive sets of twenty specimens are tested. One weight is used for each set and the weight is increased (or decreased) from set to set by uniform increments. The weight resulting in failure of 50% of the specimens is calculated and reported.

[0345] Tear resistance (determined as Elmendorf tear (N)): Applies both for the measurement in machine direction (MD) and transverse direction (TD). The tear strength is measured using the ISO 6383/2 method. The force required to propagate tearing across a film sample is measured using a pendulum device. The pendulum swings under gravity through an arc, tearing the specimen from pre-cut slit. The film sample is fixed on one side by the pendulum and on the other side by a stationary clamp. The tear resistance is the force required to tear the specimen. The relative tear resistance (N/mm) is then calculated by dividing the tear resistance by the thickness of the film.

2. Examples

[0346] Preparation of the Catalyst

[0347] The catalyst used in the inventive examples is prepared as described in detail in WO 2015/011135 A1 (metallocene complex MCi with methylaluminoxane (MAO) and borate resulting in Catalyst 3 described in WO 2015/011135 A1) with the proviso that the surfactant is 2,3,3,3-tetrafluoro-2-(1,1,2,2,3,3,3-heptafluoropropoxy)-1-propanol. The metallocene complex (MCi in WO 2015/011135 A1) is prepared as described in WO 2013/007650 A1 (metallocene E2 in WO 2013/007650 A1).

[0348] Preparation of the Polypropylene Composition (P)

[0349] The Polypropylene compositions (P) were prepared in a sequential process comprising a loop reactor and a gas phase reactor. The reaction conditions are summarized in Table 1. Table 2 contains the properties of the comparative and inventive examples.

TABLE-US-00001 TABLE 1 Preparation of the Polypropylene composition (P) IE1 IE2 Prepolymerization Temperature [° C.] 20 20 Catalyst feed [g/h] 2.5 2.5 TEAL/C3 [g/t] 0 0 C3 feed [kg/h] 60.9 60.7 H2 feed [g/h] 0.5 0.5 Residence time [h] 0.2 0.2 Loop (R1) Temperature [° C.] 70 70 Pressure [kPa] 5297 5292 H2/C3 ratio [mol/kmol] 0.08 0.08 C6/C3 ratio [mol/kmol] 15.5 14.1 MFR.sub.2 [g/10 min] 1.9 1.8 XCS [wt.-%] 1.9 1.9 C6 [wt.-%] 1.7 1.7 Residence time [h] 0.5 0.5 Split [wt.-%] 42.5 42.0 GPR (R2) Temperature [° C.] 80 80 Pressure [kPa] 2406 2406 H2/C3 ratio [mol/kmol] 0.3 0.8 C6/C3 ratio [mol/kmol] 8.7 9.2 C6 (GPR) [wt.-%] 6.9 8.2 MFR.sub.2 (GPR) [g/10 min] 1.1 1.2 Residence time [h] 2.6 2.6 Split [wt.-%] 57.5 58.0 MFR.sub.2 (copolymer) [g/10 min] 1.4 1.4 MFR(C)/MFR(A) [—] 0.74 0.74

TABLE-US-00002 TABLE 2 Properties of the comparative and inventive examples IE1 IE2 CE1 CE2 C2 [wt.-%] 0 0 1.6 5.5 C6 [wt.-%] 4.7 5.5 0 0 C4 [wt.-%] 0 0 7.1 0 Tm [° C.] 139 135 135 141 XCS [wt.-%] 11.1 26.9 10.7 15.0 C6 FDA [wt.-%] 0.51 0.67 2.0 2.1 1,2 erythro regio-defects [mol-%] 0.46 0.47 0.0 0.0 50 μm blown film Tm [° C.] 139 135 135 141 SIT [° C.] 113 107 114 114 Tm − SIT [° C.] 26 28 21 27 HTF [N] 3.3 2.8 2.5 2.0 TM/MD [MPa] 768 633 598 707 TM/TD [MPa] 778 652 599 700 Elmendorf MD [N/mm] 7.9 8.4 nd 4.8 Elmendorf TD [N/mm] 31.6 203 nd 10.3 DDI [g] 131 301 71 70 Haze b.s. [%] 4.3 3.8 20 12 Haze a.s. [%] 3.9 2.6 15 14 CE1 is a C2/C3/C4-terpolymer prepared in the presence of a Ziegler-Natta having a melt flow rate (230° C., 2.16 kg) of 1.6 g/10 min, a melting temperature Tm of 135° C., a xylene soluble content of 10.7 wt.-%, a 1-butene content of 7.1 wt.-% and an ethylene content of 1.6 wt.-%. It is identical with comparative example CE1 of EP 17186987. CE2 is the commercial nucleated C2/C3 copolymer RB709CF of Borealis having a melt flow rate of 1.5 g/10 min, a melting temperature Tm of 141° C., a xylene soluble content of 15.0 wt.-% and an ethylene content of 5.5 wt.-%.

[0350] All film properties were determined on monolayer blown films of 50 μm thickness produced on a Collin blown film line. This line has a screw diameter of 30 millimeters (mm), L/D of 30, a die diameter of 60 mm, a die gap of 1.5 mm and a duo-lip cooling ring. The film samples were produced at 190° C. with an average thickness of 50 m, with a 2.5 blow-up-ratio and an output rate of about 8 kilograms per hour (kg/h).

[0351] As can be gathered from Table 2, the haze values of inventive examples before and after steam sterilization are significantly lower than the haze values of the comparative examples. Further, the balance between stiffness and impact behavior is also improved as shown by the tensile modulus and dart-drop strength (DDI) values.