Foam produced from polypropylene with low gel content

1. Process for providing a polypropylene composition that includes:

a branched polypropylene (b-PP), the process comprising:

(A) reacting polypropylene (PP) with a thermally decomposing free radical-forming agent and optionally with bifunctionally unsaturated monomer(s) and/or with multifunctionally unsaturated low molecular weight polymer(s) to obtain the branched polypropylene (b-PP), wherein;

the polypropylene (PP) has a melt flow rate MFR 2 (230° C.) of more than 0.5 g/10 min;

the polypropylene composition and/or the branched polypropylene (b-PP) has/have a F 30 melt strength of more than 20.0 cN and a v 30 melt extensibility of more than 200 mm/s, wherein the F 30 melt strength and the v 30 melt extensibility are measured according to ISO 16790:2005, and

the polypropylene (PP) is used in the form of particles having a particle size distribution d 90 of below 1.500 μm, d 50 of below 1.000 μm, and a d 90 /d 50 ratio of below 1.80.

2. Process according to claim 1 , wherein the polypropylene (PP):

is a propylene homopolymer; and/or

is a linear polypropylene (I-PP) having a F 30 melt strength of more than 1.0 cN and a v 30 melt extensibility of below 200 mm/s, wherein the F 30 melt strength and the v 30 melt extensibility are measured according to ISO 16790:2005.

3. Process according to claim 1 , wherein:

the thermally decomposing free radical-forming agent is a peroxide; and/or

the bifunctionally unsaturated monomer is selected from the group consisting of divinyl compounds, allyl compounds, and dienes.

4. Process according to claim 1 , further comprising subsequent to step (A):

(B) adding to the branched polypropylene (b-PP) a polypropylene (PP′) having a melt flow rate MFR 2 (230° C.) of 0.5 to 18.0 g/10 min.

5. Process according to claim 4 , wherein:

step (b) is initiated when at least 80% of the reaction between the polypropylene (PP) and the thermally decomposing free radical-forming agent and optionally the bifunctionally unsaturated monomer has taken place; and/or

the polypropylene (PP′) is a linear polypropylene (I-PP′), said linear polypropylene (I-PP′) has a F 30 melt strength of more than 1.0 cN and a v 30 melt extensibility of below 200 mm/s, wherein the F 30 melt strength and the v 30 melt extensibility are measured according to ISO 16790:2005.

6. The process according to claim 4 , wherein step (A) and optionally step (B) are accomplished in an extruder, said extruder comprises in operation direction a first mixing zone (MZ 1 ) and a second mixing zone (MZ 2 ), wherein further the step (a) takes place in the first mixing zone (MZ 1 ) whereas optionally step (b) takes place in the second mixing zone (MZ 2 ), the extruder comprises in operation direction a feed-throat (FT), the first mixing zone (MZ 1 ), the second mixing zone (MZ 2 ) and a die (D), wherein between the first mixing zone (MZ 1 ) and the second mixing zone (MZ 2 ) a side feed-throat (SFT) is located, wherein further the polypropylene (PP), the thermally decomposing free radical-forming agent, and optionally the bifunctionally unsaturated monomer are fed via the feed-throat (FT) and optionally the polypropylene (PP′) is fed via the side feed-throat (SFT).

7. The process according to claim 6 , wherein:

the reaction between the polypropylene (PP) and the thermally decomposing free radical-forming agent and optionally the bifunctionally unsaturated monomer takes place in the first mixing zone (MZ 1 ); and/or

not more than 10 wt.-% of the total amount of the branched polypropylene (b-PP) of the polypropylene composition is produced in the second mixing zone (MZ 2 ).

8. The process according to claim 4 , wherein 1 to 6 parts by weight of the polypropylene (PP′) are added to 95 to 99 parts by weight of branched polypropylene (b-PP).

9. The process according to claim 1 , wherein:

the polypropylene (PP′) 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/or

the branched polypropylene (b-PP) is free of additives (A).

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

a F 30 melt strength of 25.0 cN to 50.0 cN and a v 30 melt extensibility of 210 to 300 mm/s; and/or

a gel content of less than 1.00 wt.-%, -of less than 0.80 wt.-%.

11. Polypropylene composition obtained by the process according to claim 1 , comprising:

95 to 99 parts by weight of a branched polypropylene (b-PP);

optionally 1 to 5 parts by weight of a polypropylene (PP′) having a melt flow rate MFR 2 (230 ° C.) measured according to ISO 1133 of more than 0.5 to 18.0 g/10 min; and

optionally 0.005 to 5.0 parts by weight of additives (A), wherein said additives(A) are 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;

wherein the polypropylene composition has;

a melt flow rate MFR 2 (230° C.) measured according to ISO 1133 of 1.0 to below 7.0 g/10 min, and

a gel content of less than 1.00 wt. %, and wherein the polypropylene composition and/or the branched polypropylene (b-PP) has/have a F 30 melt strength of 25.0 cN to 50.0 cN and a v 30 melt extensibility of 210 to 300 mm/s, wherein the F 30 melt strength and the v 30 melt extensibility are measured according to ISO 16790:2005.

12. Process for the manufacture of a foam comprising:

(A) reacting a polypropylene (PP) with a thermally decomposing free radical-forming agent and optionally with bifunctionally unsaturated monomer(s) and/or with multifunctionally unsaturated low molecular weight polymer(s) to obtain a polypropylene composition comprising a branched polypropylene (b-PP), wherein

(i) the polypropylene (PP) has a melt flow rate MFR 2 (230° C.) of more than 0.5 g/10 min;

(ii) the polypropylene composition and/or the branched polypropylene (b-PP) has/have a F 30 melt strength of more than 20.0 cN and a v 30 melt extensibility of more than 200 mm/s, wherein the F 30 melt strength and the v 30 melt extensibility are measured according to ISO 16790:2005, and

(iii) the polypropylene (PP) is used in the form of particles having a particle size distribution d 90 of below 1.500 μm, d 50 of below 1.000 μm, and a d 90 /d 50 ratio of below 1.80;

(B) subjecting the polypropylene composition of step (A) to a foaming process to obtain a foam.

13. Process according to claim 12 , wherein the polypropylene composition comprises:

95 to 99 parts by weight of a branched polypropylene (b-PP); and

optionally 1 to 5 parts by weight of a polypropylene (PP′) having a melt flow rate MFR 2 (230° C.) measured according to ISO 1133 of more than 0.5 to 18.0 g/10 min,

optionally 0.005 to 5.0 parts by weight of additives (A), wherein said additives(A) are 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;

wherein the polypropylene composition has;

a melt flow rate MFR 2 (230 ° C.) measured according to ISO 1133 of 1.0 to below 7.0 g/10 min, and

a gel content of less than 1.00 wt. %, less than 0.80 wt. %;

and wherein the polypropylene composition and/or the branched polypropylene (b-PP) has/have a F 30 melt strength of 25.0 cN to 50.0 cN and a v 30 melt extensibility of 210 to 300 mm/s, wherein the F 30 melt strength and the v 30 melt extensibility are measured according to ISO 16790:2005.

14. Foam comprising a polypropylene composition according to claim 11 .