Polypropylene composition with low shrinkage at wide application temperature range

1. A polypropylene composition having a melt flow rate MFR 2 (230° C.) measured according to ISO 1133 in the range of 5 to 50 g/10 min, the polypropylene composition comprising:

(a) 55 to 75 wt. %, based on the total weight of the polypropylene composition, of a crystalline fraction (CF) as determined in the CRYSTEX QC method, the crystalline fraction (CF) having

i) a melting temperature (Tm) measured by differential scanning calorimetry (DSC) between 147° C. and 162° C., and

ii) an ethylene content of 1 wt. %, based on the total weight of the crystalline fraction (CF); and

(b) 25 to 45 wt. %, based on the total weight of the polypropylene composition, of a soluble fraction (SF) as determined in a CRYSTEX QC method, the soluble fraction (SF) having

i) an intrinsic viscosity (IV) in the range of 1.0 to 2.0 dl/g, and

ii) an ethylene content in the range of 18 to 30 wt. %, based on the total weight of the soluble fraction (SF),

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 0.8 to 1.1, and

wherein the polypropylene composition is polymerized in the presence of a single-site catalyst consisting of racemic anti-dimethylsilanediyl[2-methyl-4-(4-tert-butylphenyl)-inden-1-yl] [2-methyl-4-(4-tert-butylphenyl)-5-methoxy-6-tert-butyl-inden-1-yl]zirconium dichloride and methylaluminoxane (MAO) as cocatalyst.

2. The polypropylene composition according to claim 1 , wherein the polypropylene composition comprises a polypropylene homopolymer matrix (M) and an ethylene-propylene copolymer (EPC) dispersed in the polypropylene homopolymer matrix (M).

3. The polypropylene composition according to claim 1 , wherein the polypropylene composition comprises 60 to 72 wt. %, based on the total weight of the polypropylene composition, of the crystalline fraction (CF), and 28 to 40 wt. %, based on the total weight of the polypropylene composition, of the soluble fraction (SF).

4. The polypropylene composition according to claim 1 , wherein the polypropylene composition has:

i) an ethylene content in the range of 4.0 to 15.0 wt. %, based on the total weight of the polypropylene composition, and/or

ii) a melt flow rate MFR 2 (230° C.) measured according to ISO 1133 in the range of 8 to 40 g/10 min.

5. The polypropylene composition according to claim 1 , wherein the polypropylene composition has:

i) a melting temperature (T m ) measured by differential scanning calorimetry (DSC) between 147° C. and 162° C., and/or

ii) a crystallization temperature (T c ) measured by differential scanning calorimetry (DSC) between 105° C. and 135° C.

6. The polypropylene composition according to claim 1 , wherein the polypropylene composition has been produced in a multi-stage process.

7. The polypropylene composition according to claim 1 , wherein the crystalline fraction (CF) has:

i) a melting temperature (T m ) measured by differential scanning calorimetry (DSC) between 148° C. and 156° C., and/or

ii) an ethylene content in the range from 0.1 to 0.8 wt. %, based on the total weight of the crystalline fraction, and/or

iii) an intrinsic viscosity (IV) in the range of 0.9 to 2.2 dl/g, and/or

iv) an isotacticity determined as pentad regularity from 13C-NMR spectroscopy of at least 98%, and/or

v) a content of <2,1>erythro regiodefects as determined from 13C-NMR spectroscopy of equal or less than 0.2 mol.-%.

8. The polypropylene composition according to claim 1 , wherein the soluble fraction (SF) has:

an intrinsic viscosity (IV) in the range of 1.1 to 1.9 dl/g.

9. The polypropylene composition according to claim 1 , wherein the relative content of isolated to block ethylene sequences (I(E)):

i) of the polypropylene composition is at most 30%, and/or

ii) of the xylene cold soluble fraction (XCS) is at least 30%,

wherein the I(E) content is defined by equation (I)

I

⁡

(

E

)

=

fPEP

(

fEEE

+

fEEP

+

fPEP

)

×

100

(

I

)

wherein I(E) is the relative content of isolated to block ethylene sequences [in %];

fPEP is the mol fraction of propylene/ethylene/propylene sequences (PEP) in the sample;

fEEP is the mol fraction of ethylene/ethylene/propylene sequences (EEP) and of propylene/ethylene/ethylene sequences (PEE) in the sample;

fEEE is the mol fraction of ethylene/ethylene/ethylene sequences (EEE) in the sample wherein all sequence concentrations being based on a statistical triad analysis of 13 C-NMR data.

10. A process for the preparation of a polypropylene composition according to claim 1 , wherein a polypropylene homopolymer matrix (M) is prepared in a first stage and an ethylene-propylene copolymer (EPC) is prepared in a second stage in the presence of the polypropylene homopolymer matrix (M).

11. A composition comprising the polypropylene composition according to claim 1 and one or more additive(s) in an amount of up to 4 wt.-%, based on the total weight of the composition.

12. An article comprising the polypropylene composition according to claim 1 .

13. The process according to claim 10 , wherein the polymer composition has a brittle-to-ductile transition temperature (BDTT) as measured in an instrumented Charpy notched impact strength test in line with ISO 179 1 eA in the range from −10 to +5° C.