Polypropylene composition with improved sealing behaviour

1. A polypropylene composition comprising:

(A) a polymer blend comprising:

(A-1) from 55.0 wt % to 75.0 wt %, based on a total amount of the polymer blend, of a propylene polymer including two different comonomer units selected from ethylene and alpha-olefins having from 4 to 12 carbon atoms randomly distributed in a propylene polymer chain comprising,

(i) ethylene-derived comonomer units in an amount of 0.3 wt % to 4.0 wt %, based on a total amount of monomer units in the propylene polymer, and

(ii) comonomer units derived from alpha-olefins having from 4 to 12 carbon atoms in an amount of 4.0 wt % to 16.0 wt %, based on a total amount of monomer units in the propylene polymer,

wherein the propylene polymer has a melt flow rate MFR 2 in a range of 0.5 g/10 min to 20.0 g/10 min, determined according to ISO 1133 at a temperature of 230° C. and a load of 2.16 kg; and

(A-2) from 25.0 wt % to 45.0 wt %, based on a total amount of the polymer blend, of an ethylene-based plastomer having a density of from 0.850 g/cm 3 to 0.915 g/cm 3 , determined according to ISO 1183, and a melt flow rate MFR 2 in a range of 5.0 g/10 min to 50.0 g/10 min, determined according to ISO 1133 at a temperature of 190° C. and a load of 2.16 kg; and

(B) optionally one or more additives in a total amount of from 0.0 to 5.0 wt %, based on a total amount of the polypropylene composition, selected from the group consisting of slip agents, anti-block agents, UV stabilizers, alpha- and/or beta-nucleating agents, antistatic agents and antioxidants,

wherein a MFR 2 ratio of a MFR 2 of the polypropylene composition MFR final to a MFR 2 of the propylene polymer MFR polymer greater than 1.2.

2. The polypropylene composition according to claim 1 , wherein a weight ratio of the propylene polymer and the ethylene-based plastomer in the polymer blend is in a range of 75:25 to 55:45.

3. The polypropylene composition according to claim 1 , wherein the polypropylene composition consists of:

the polymer blend (A) which comprises:

(A-1) from 55.0 wt % to 75.0 wt % of a random terpolymer of propylene with ethylene and 1-butene as comonomer units or a random terpolymer of propylene with ethylene and 1-hexene as comonomer units (A-1-b) comprising,

a) ethylene-derived comonomer units in an amount of 0.3 wt % to 4.0 wt %, based on a total amount of monomer units in the propylene polymer, and

b) 1-butene or 1-hexene derived comonomer units in an amount of 4.0 wt % to 16.0 wt %, based on a total amount of monomer units in the propylene polymer,

wherein the random terpolymer (A-1) has a melt flow rate MFR 2 in a range of 0.5 g/10 min to 20.0 g/10 min, determined according to ISO 1133 at a temperature of 230° C. and a load of 2.16 kg, a melting temperature Tm measured via DSC according to ISO 11357 of 130° C. to 140° C., a xylene cold soluble (XCS) amount in a range of 5.0 wt % to 15.0 wt % (measured according to ISO 16152, 2005, at 25° C.) and a crystallization temperature Tcr measured via DSC according to ISO 11357 of 85° C. to 100° C.; and

(A-2) from 25.0 wt % to 45.0 wt % of a plastomer which is a copolymer of ethylene and 1-octene,

wherein the copolymer of ethylene and 1-octene (A-2) has a density of in a range of from 0.850 g/cm 3 to 0.915 g/cm 3 and a melt flow rate MFR 2 in a range of 5.0 g/10 min to 50.0 g/10 min, determined according to ISO 1133 at a temperature of 190° C. and a load of 2.16 kg; and

(B) optionally one or more additives in a total amount of from 0.0 to 5.0 wt %, based on a total amount of the polypropylene composition, selected from the group consisting of slip agents, anti-block agents, UV stabilizers, alpha- and/or beta-nucleating agents, antistatic agents and antioxidants

wherein the polypropylene composition has a melt flow rate MFR 2 in a range of 1.0 g/10 min to 20.0 g/10 min, determined according to ISO 1133 at a temperature of 230° C. and a load of 2.16 kg, a melting temperature Tm, measured via DSC according to ISO 11357 of 125° C. to 140° C., a xylene cold soluble (XCS) amount in a range of 20 wt % to 50 wt % (measured according to ISO 16152, 2005, at 25° C.).

4. A process for preparing a polypropylene composition according to claim 1 , wherein the process comprises the steps of:

(i) preparing the propylene polymer by polymerizing propylene and two different comonomer units selected from ethylene and alpha-olefins having from 4 to 12 carbon atoms in the presence of a Ziegler-Natta catalyst,

(ii) mixing said propylene polymer with the ethylene-based plastomer, optionally in the presence of one or more additives, to obtain a mixture of said propylene polymer and ethylene-based plastomer, and

(iii) extruding said mixture to obtain said polypropylene composition.

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

6. The article according to claim 5 , wherein the article is an unoriented mono-layered or multi-layered film.

7. The article according to claim 6 , wherein the unoriented mono-layered or multi-layered film is a cast film or a blown film.

8. The article according to claim 6 , wherein the film has a sealing initiation temperature SIT of from 50° C. to 85° C.

9. The article according to claim 6 , wherein the film has a hot-tack force, determined on a 50 μm blown film, of from 2.8 N to 7.0 N.

10. The article according to claim 6 , wherein the film has a hot-tack temperature, determined on a 50 μm blown film, of 50° C. to 95° C.

11. The article according to claim 6 , wherein the film has a dart drop strength, determined on a 50 μm blown film, of from 100 g to 900 g.

12. The article according to claim 6 , wherein the film has a tensile modulus, determined in machine direction on a 50 μm blown film, of from 100 MPa to 385 MPa.

13. The article according to claim 6 , wherein the article is a multi-layered film comprising a sealing layer, which comprises the polypropylene composition.

14. A polypropylene composition consisting of:

(A) a polymer blend comprising:

(A-1) from 55.0 wt % to 75.0 wt % of a random terpolymer of propylene with ethylene and 1-butene as comonomer units or a random terpolymer of propylene with ethylene and 1-hexene as comonomer units (A-1-b) comprising:

a) ethylene-derived comonomer units in an amount of 0.3 wt % to 4.0 wt %, based on a total amount of monomer units in the propylene polymer, and

b) 1-butene or 1-hexene derived comonomer units in an amount of 4.0 to 16.0 wt %, based on a total amount of monomer units in the propylene polymer,

wherein the random terpolymer (A-1) has a melt flow rate MFR 2 in a range of 0.5 g/10 min to 20.0 g/10 min, determined according to ISO 1133 at a temperature of 230° C. and a load of 2.16 kg, a melting temperature Tm measured via DSC according to ISO 11357 of 130° C. to 140° C., a xylene cold soluble (XCS) amount in a range of 5.0 wt % to 15.0 wt % (measured according to ISO 16152, 2005, at 25° C.) and a crystallization temperature Tcr measured via DSC according to ISO 11357 of 85° C. to 100° C.; and

(A-2) from 25.0 wt % to 45.0 wt % of a plastomer which is a copolymer of ethylene and 1-octene,

wherein the copolymer of ethylene and 1-octene (A-2) has a density in a range of from 0.850 g/cm 3 to 0.915 g/cm 3 and a melt flow rate MFR 2 in a range of 5.0 g/10 min to 50.0 g/10 min, determined according to ISO 1133 at a temperature of 190° C. and a load of 2.16 kg; and

(B) optionally one or more additives in a total amount of from 0.0 to 5.0 wt %, based on a total amount of the polypropylene composition, selected from the group consisting of slip agents, anti-block agents, UV stabilizers, alpha- and/or beta-nucleating agents, antistatic agents and antioxidants,

wherein the polypropylene composition has a melt flow rate MFR 2 in a range of 1.0 g/10 min to 20.0 g/10 min, determined according to ISO 1133 at a temperature of 230° C. and a load of 2.16 kg, a melting temperature Tm, measured via DSC according to ISO 11357 of 125° C. to 140° C., a xylene cold soluble (XCS) amount in a range of 20 wt % to 50 wt % (measured according to ISO 16152, 2005, at 25° C.).