C2C3 random copolymer composition with improved balance between sealing initiation temperature and melting point

1. A C 2 C 3 random copolymer composition comprising 3 polymer fractions (A), (B) and (C) with different comonomer content,

(A) 30 to 65 wt % of a C 2 C 3 random copolymer with a C 2 content (C 2 A) of 0.4 to 1.5 wt % based on copolymer (A) as measured with Fourier-transform infrared (FTIR) spectroscopy,

(B) 25 to 50 wt % of a C 2 C 3 random copolymer with a C 2 content (C 2 B) of 3.0 to 10.0 wt % based on copolymer (B) and

(C) 5 to 35 wt % of a C 2 C 3 random copolymer with a C 2 content (C 2 C) of 7.0 to 15.0 wt % based on copolymer (C),

whereby the sum of the amount of the 3 polymer fractions (A), (B) and (C) is 100% and

whereby the comonomer content of the polymer fractions increases from fraction (A) to fraction (C) according to (C 2 A)<(C 2 B)<(C 2 C),

and whereby the composition is characterized by

(i) a total C 2 content in the range of 3.0 wt % up to 7.0 wt %, as measured with Fourier-transform infrared (FTIR) spectroscopy,

(ii) a melt flow rate MFR2 (230° C.) measured according to ISO 1133 in the range of 2.0 to 15.0 g/10 min,

(iii) a melting temperature Tm as determined by DSC according to ISO 11357 of from 128° C. to 145° C.,

(iv) a crystallization temperature T c as determined as determined by DSC according to ISO 11357 of from 85° C. to 110° C. and

(v) a hexane solubles content determined in accordance with FDA section 177.1520 of at most 2.0 wt %.

2. The C 2 C 3 random copolymer composition according to claim 1 being further characterized by only one peak in the temperature range of 25 to −50° C. as determined by dynamic mechanical thermal analysis (DMTA) according to ISO 6721-7, indicating a single phase material and by three peaks in an analytical TREF (temperature rising elution fractionation)-measurement:

one in the temperature range of 0-40° C.,

the second one between 60 and 80° C., and

one peak between 80 and 100° C.

3. The C 2 C 3 random copolymer composition according to claim 1 , whereby the composition is obtained in the presence of a metallocene catalyst.

4. A process for producing a C 2 C 3 random copolymer composition according to claim 1 by a sequential polymerization process comprising at least two reactors connected in series, wherein the process comprises the steps of

a) polymerizing in a first reactor (R-1) being a slurry reactor (SR), propylene and ethylene, obtaining a C 2 C 3 random copolymer (A)

b) transferring said C 2 C 3 random copolymer (A) and unreacted comonomers of the first reactor in a second reactor (R-2) being a first gas phase reactor (GPR-1),

c) feeding to said second reactor (R-2) propylene and ethylene,

d) polymerizing in said second reactor (R-2) and in the presence of said first C 2 C 3 random copolymer (A) propylene and ethylene obtaining a C 2 C 3 random copolymer (B),

e) transferring said mixture of C 2 C 3 random copolymer (A) and C 2 C 3 random copolymer (B), and unreacted comonomers of the second reactor in a third reactor (R-3) being a second gas phase reactor (GPR-2),

c) feeding to said third reactor (R-3) propylene and ethylene,

d) polymerizing in said third reactor (R-3) and in the presence of the mixture of C 2 C 3 random copolymer (A) and C 2 C 3 random copolymer (B) propylene and ethylene obtaining a C 2 C 3 random copolymer (C),

said C 2 C 3 random copolymer (A), C 2 C 3 random copolymer (B) and said C 2 C 3 random copolymer (C) form the C 2 C 3 random copolymer composition according to claim 1 ,

whereby the polymerization takes place in the presence of single site solid particulate catalyst comprising (i) a complex of formula (I):

wherein

M is zirconium or hafnium;

each X is a sigma ligand;

L is a divalent bridge selected from —R′ 2 C—, —R′ 2 C—CR′ 2 —, —R′ 2 Si—, —R′ 2 Si—SiR′ 2 —, —R′ 2 Ge—, wherein each R′ is independently a hydrogen atom, C 1 -C 20 -hydrocarbyl, tri(C 1 -C 20 -alkyl)silyl, C 6 -C 20 -aryl, C 7 -C 20 -arylalkyl or C 7 -C 20 -alkylaryl;

R 2 and R 2 ′ are each independently a C 1 -C 20 hydrocarbyl radical optionally containing one or more heteroatoms from groups 14-16;

R 5′ is a C 1-20 hydrocarbyl group containing one or more heteroatoms from groups 14-16 optionally substituted by one or more halo atoms;

R 6 and R 6′ are each independently hydrogen or a C 1-20 hydrocarbyl group optionally containing one or more heteroatoms from groups 14-16;

R 7 is hydrogen or C 1-20 hydrocarbyl group optionally containing one or more heteroatoms from groups 14-16;

R 7 ′ is hydrogen;

Ar is independently an aryl or heteroaryl group having up to 20 carbon atoms optionally substituted by one or more groups R 1 ;

Ar′ is independently an aryl or heteroaryl group having up to 20 carbon atoms optionally substituted by one or more groups R 1 ;

each R 1 is a C 1-20 hydrocarbyl group or two R 1 groups on adjacent carbon atoms taken together can form a fused 5 or 6 membered non aromatic ring with the Ar group, said ring being itself optionally substituted with one or more groups R 4 ;

each R 4 is a C 1-20 hydrocarbyl group;

and (ii) a cocatalyst comprising a compound of a group 13 metal.

5. The process according to claim 4 , wherein the a catalyst comprises a complex of formula (III) or (III′)

wherein

M is zirconium or hafnium;

each X is a sigma ligand;

L is a divalent bridge selected from —R′ 2 C— or —R′ 2 Si— wherein each R′ is independently a hydrogen atom, C 1-20 alkyl or C 3-10 cycloalkyl;

R 6 is hydrogen or a C 1-10 alkyl group;

R 6′ is a C 1-10 alkyl group or C 6-10 aryl group;

R 7 is hydrogen, C 1-6 alkyl or OC 1-6 alkyl;

Z′ is O or S;

R 3′ is a C 1-10 alkyl group, or C 6-10 aryl group optionally substituted by one or more halo groups;

n is independently 0 to 4; and

each R 1 is independently a C 1-10 alkyl group.

6. A process for producing water or air quench blown films, comprising

i) blowing up a tube of a molten C 2 C 3 random copolymer composition according to claim 1 with air perpendicularly to the upwards direction from a side-fed blown film die;

ii) cooling the composition down with a water contact cooling ring or air quench; and

iii) folding and guiding the composition over deflector rolls onto a winder.

7. A sterilizable or sterilized article, comprising a C 2 C 3 random copolymer composition according to claim 1 .

8. A sterilizable or sterilized film comprising a C 2 C 3 random copolymer composition according to claim 1 .

9. The sterilizable or sterilized film according to claim 8 , whereby the films are characterized by

(i) a seal initiation temperature (SIT) of below 110° C.,

(ii) satisfying the equation T m -SIT≥25, wherein Tm is the melting point of the C 2 C 3 random copolymer composition,

(iii) a haze (determined according to ASTM D1003-00 on cast films with a thickness of 50 μm) of at most 2.5%,

(iv) a transparency (determined according to ASTM D1003-00 on cast films with a thickness of 50 μm) of at least 90.0%,

(v) a relative tear resistance in machine direction [N/mm] according to Elmendorf method (ISO 6383-2) for a cast film thickness of 50 μm of at least 28.0 N/mm and

(vi) a relative tear resistance in transverse direction [N/mm] according to Elmendorf method (ISO 6383-2) for a cast film thickness of 50 μm of at least 200.0 N/mm.

10. A film according to claim 9 prepared by cast film technology.

11. The film according to claim 8 having a haze value (determined according to ASTM D1003-00 on cast films with a thickness of 50 μm) after steam sterilization at 121° C. for 30 min of at most 25% and a transparency (determined according to ASTM D1003-00 on cast films with a thickness of 50 μm) after steam sterilization at 121° C. for 30 min of at least 90.0%.

12. The film according to claim 9 having a haze value (determined according to ASTM D1003-00 on cast films with a thickness of 50 μm) after steam sterilization at 121° C. for 30 min of at most 25% and a transparency (determined according to ASTM D1003-00 on cast films with a thickness of 50 μm) after steam sterilization at 121° C. for 30 min of at least 90.0%.

13. The process according to claim 4 , comprising

a) polymerizing in a first reactor (R-1) being a loop reactor (LR), propylene and ethylene, obtaining a C 2 C 3 random copolymer (A).

14. The process according to claim 4 , wherein R 6′ is a tertiary alkyl group.

15. The process according to claim 5 , wherein

each X is independently a hydrogen atom, a halogen atom, C 1-6 alkoxy group, C 1-6 alkyl, phenyl or benzyl group.

16. The process according to claim 15 , wherein

R 6′ is a tertiary alkyl group.

17. The process according to claim 16 , wherein

n is independently 0, 1 or 2.