One-step production of a polypropylene composition

1. A process for providing a polypropylene composition comprising a branched polypropylene (b-PP), the process comprising the steps of:

a) providing a linear polypropylene (I-PP') having a melt flow rate MFR 2 (230° C.) in the range of 3.0 to 18 g/10min, a F 30 melt strength in the range of 6.5 to 65 cN, and a v 30 melt extensibility in the range of 125 to 190 mm/s, wherein the F 30 melt strength and the v 30 melt extensibility are measured according to ISO 16790:2005;

b) providing a thermally decomposing free radical-forming agent,

c) providing bifunctionally unsaturated monomer(s) and/or multifunctionally unsaturated low molecular weight polymer(s),

d) providing a linear polypropylene homopolymer (I-PP) having a melt flow rate MFR 2 (230° C.) of 20.0 to 40.0 g/10min,

e) reacting the linear polypropylene (I-PP') of step a) with the thermally decomposing free radical-forming agent of step b) and the bifunctionally unsaturated monomer(s) and/or multifunctionally unsaturated low molecular weight polymer(s) of step c) obtaining thereby the branched polypropylene (b-PP), and

f) reacting the branched polypropylene (b-PP) obtained in the step e) with the linear polypropylene homopolymer (I-PP) of the step d),

wherein the polypropylene composition has

i) a melt flow rate MFR 2 (230° C.) measured according to ISO 1133 of 18.0 to 35.0 g/10min, and

ii) a F 30 melt strength of more than 4-20 cN and a v 30 melt extensibility of 240-300 mm/s, wherein the F 30 melt strength and the v 30 melt extensibility are measured according to ISO 16790:2005,

wherein the branched polypropylene (b-PP) is present in the polypropylene composition in an amount of 80.0 to 99.0 parts by weight, based on the total weight of the polypropylene composition, and

wherein the steps e) and f) of the process are conducted in one extruder without a subsequent vis-breaking step.

2. The process according to claim 1 , wherein

(a) the thermally decomposing free radical-forming agent of saki step b) is a peroxide,

and/or

(b) the bifunctionally unsaturated monomer(s) and/or multifunctionally unsaturated low molecular weight polymer(s) of said step c) is/are selected from the group consisting of divinyl compounds, allyl compounds and dienes.

3. The process according to claim 1 , wherein

(a) the linear polypropylene homopolymer (l-PP) of said step d) comprises at least one additive (A) selected from the group consisting of antioxidants, metal deactivators, UV-stabilizers, antistatic agents, antifogging agents, acid scavengers, blowing agents, cling agents, lubricants, nucleating agents, slip agents, antiblocking agents and mixtures thereof, and

(b) the branched polypropylene (b-PP) obtained in said step e) is free of additives (A).

4. The process according to claim 1 , wherein said extruder comprises in operation direction a first mixing zone (MZ1) and a second mixing zone (MZ2), wherein further said step e) takes place in the first mixing zone (MZ1), whereas said step f) takes place in the second mixing zone (MZ2).

5. The process according to claim 4 , wherein the extruder comprises in operation direction a feed-throat (FT), the first mixing zone (MZ1), the second mixing zone (MZ2) and a die (D), wherein between the first mixing zone (MZ1) and the second mixing zone (MZ2) a side feed-throat (SFT) is located, wherein further the linear polypropylene (l-PP') of said step a), the thermally decomposing free radical-forming agent of said step b), and the bifunctionally unsaturated monomer(s) and/or multifunctionally unsaturated low molecular weight polymer(s) of said step c) are fed via the feed-throat (FT) and the linear polypropylene homopolymer (I-PP) of said step d) is fed via the side feed-throat (SFT).

6. The process according to claim 4 , wherein not more than 10.0 wt.-% of the total amount of the branched polypropylene (b-PP) of the polypropylene composition is produced in the second mixing zone (MZ2).

7. The process according to claim 1 , wherein 1.0 to 6.0 parts by weight of the linear polypropylene homopolymer (I-PP) are added to 94.0 to 99.0 parts by weight of said branched polypropylene (b-PP).

8. The process according to claim 1 , wherein the resulting polypropylene composition

(a) has said melt flow rate MFR 2 (230° C.) measured according to ISO 1133 of 19.0 to 30.0 g/10min, and

(b) has an OCS gel index of less than 2,500.

9. The process according to claim 1 , wherein the resulting polypropylene composition has

(a) 95.0 to 99.0 parts by weight of the branched polypropylene (b-PP); and

(b) 1.0 to 5.0 parts by weight of the linear polypropylene homopolymer (I-PP);

wherein the polypropylene composition has

an OCS gel index of less than 2,500.

10. The process according to claim 1 , wherein the linear polypropylene (I-PP') has a melt flow rate MFR 2 (230° C.) measured according to ISO in the range from 3.0 to 15.0 g/10min.

11. The process according to claim 1 , wherein

(a) the linear polypropylene homopolymer (I-PP) of said step d) has a melt flow rate MFR 2 (230° C.) measured according to ISO 1133 from 25.0 to 38.0 g/10min, and

(b) the linear polypropylene homopolymer (I-PP) of said step d) comprises two additives (A) selected from the group consisting of antioxidants, metal deactivators, UV-stabilizers, antistatic agents, antifogging agents, acid scavengers, blowing agents, cling agents, lubricants, nucleating agents, slip agents, antiblocking agents and mixtures thereof, and

(c) the branched polypropylene (b-PP) obtained in said step e) is free of the additives (A).

12. The process according to claim 1 , wherein 1.0 to 3.0 parts by weight of the linear polypropylene homopolymer (I-PP) are added to 97.0 to 99.0 parts by weight of said branched polypropylene (b-PP).

13. The process according to claim 1 , wherein the resulting polypropylene composition

(a) has said melt flow rate MFR 2 (230° C.) measured according to ISO 1133 of 19.0 to 30.0 g/10min, and

(b) has an OCS gel index of less than 2,000.

14. The process according to claim 1 , wherein the resulting polypropylene composition has

(a) 95.0 to 99.0 parts by weight of the branched polypropylene (b-PP); and

(b) 1.0 to 5.0 parts by weight of the linear polypropylene homopolymer (I-PP);

wherein the polypropylene composition has

a melt flow rate MFR 2 (230 ° C.) measured according to ISO 1133 from 19.0 to 30.0 g/10min, and

an OCS gel index of less than 2,500.

15. The polypropylene composition produced in accordance with claim 1 comprising:

(a) 95.0 to 99.0 parts by weight of the branched polypropylene (b-PP); and

(b) 1.0 to 5.0 parts by weight of the linear polypropylene homopolymer (I-PP) having a melt flow rate MFR 2 (230 ° C.) measured according to ISO 1133 of 20.0 to 40.0 g/10min;

wherein the polypropylene composition has

an OCS gel index of less than 2,500.

16. The polypropylene composition according to claim 15 , comprising

(a) 95.0 to 99.0 parts by weight of said branched polypropylene homopolymer (b-PP); and

(b) 1.0 to 5.0 parts by weight of said linear polypropylene (I-PP) having a melt flow rate MFR 2 (230 ° C.) measured according to ISO 1133 from 25.0 to 38.0 g/10min;

wherein the polypropylene composition has

said melt flow rate MFR 2 (230 ° C.) measured according to ISO 1133 is from 19.0 to 25.0 g/10min, and

said OCS gel index is less than 2,000.

17. The polypropylene composition according to claim 15 , wherein the polypropylene composition comprises at least one additive (A) selected from the group consisting of antioxidants, metal deactivators, UV-stabilizers, antistatic agents, antifogging agents, acid scavengers, blowing agents, cling agents, lubricants, nucleating agents, slip agents, antiblocking agents and mixtures thereof.

18. A film comprising the polypropylene composition according to claim 15 .