Melt-blown webs without shots and with improved barrier properties

1. A method of preparing a melt-blown web which is free of shots, the method comprising blowing a molten polypropylene composition from an extruder die tip onto a conveyer or take-up screen, wherein the polypropylene composition comprises

(A) a propylene polymer and

(B) optionally a polymeric nucleating agent,

wherein the polypropylene composition has

(i) a melt flow rate MFR2 (230° C./2.16 kg) measured according to ISO 1133 of 20 to 5000 g/10min and

(ii) a melting temperature Tm between ≥130° C. and ≤170° C. and

(iii) a molecular weight distribution (MWD)>2

(iv) wherein the propylene polymer has been polymerized in the presence of a) a Ziegler-Natta catalyst (ZN-C) comprising compounds (TC) of a transition metal of Group 4 to 6 of IUPAC, a Group 2 metal compound (MC) and an internal donor (ID), b) optionally a co-catalyst (Co), and c) optionally an external donor (ED), and

(v) wherein the polypropylene composition has been visbroken without the use of peroxides.

2. The method of preparing a melt-blown web according to claim 1 , wherein the propylene polymer is a propylene homopolymer.

3. The method of preparing a melt-blown web according to claim 1 , wherein the polypropylene composition has been visbroken by using a hydroxylamine ester, a sulphur compound, or by purely thermal degradation.

4. The method of preparing a melt-blown web according to claim 3 , wherein the polypropylene composition has been visbroken by using a hydroxylamine ester.

5. The method of preparing a melt-blown web according to claim 1 , wherein the polypropylene composition is free of phthalic compounds as well as their respective decomposition products.

6. The method of preparing a melt-blown web according to claim 1 , wherein the melt-blown web is characterized by the following ratios:

(a) a molecular weight (Mw) ratio of Mw of the web to Mw of the polypropylene composition Mw(web)/Mw(PP)<1 and

(b) a molecular weight distribution (MWD) ratio of MWD of the web to MWD of the polypropylene composition MWD(web)/MWD(PP)<1.

7. The method of preparing a melt-blown web according to claim 6 , wherein the melt-blown web is characterized by the following ratios:

(a) a molecular weight (Mw) ratio of Mw of the web to Mw of the polypropylene composition Mw(web)/Mw(PP) is ≤0.90, and

(b) a molecular weight distribution (MWD) ratio of MWD of the web to MWD of the polypropylene composition MWD(web)/MWD(PP) is ≤0.95.

8. The method of preparing a melt-blown web according to claim 7 , wherein the melt-blown web is characterized by the following ratios:

(a) a molecular weight (Mw) ratio of Mw of the web to Mw of the polypropylene composition Mw(web)/Mw(PP) is ≤0.85, and

(b) a molecular weight distribution (MWD) ratio of MWD of the web to MWD of the polypropylene composition MWD(web)/MWD(PP) is ≤0.90.

9. The method of preparing a melt-blown web according to claim 7 , wherein the melt-blown web is characterized by the following ratios:

(a) a molecular weight (Mw) ratio of Mw of the web to Mw of the polypropylene composition Mw(web)/Mw(PP) is ≤0.80, and

(b) a molecular weight distribution (MWD) ratio of MWD of the web to MWD of the polypropylene composition MWD(web)/MWD(PP) is ≤0.85.

10. The method of preparing a melt-blown web according to claim 1 , wherein the internal donor (ID) is selected from the group consisting of optionally substituted malonates, maleates, succinates, glutarates, cyclohexene-1,2-dicarboxylates, benzoates, derivatives thereof and mixtures thereof; and the molar ratio of co-catalyst (Co) to external donor (ED) [Co/ED] is 5 to 45.

11. The method of preparing a melt-blown web according to claim 1 , wherein the Ziegler-Natta catalyst (ZN-C) is produced by a process comprising the steps of

a)

a 1 ) providing a solution of at least a Group 2 metal alkoxy compound (Ax) being the reaction product of a Group 2 metal compound (MC) and a monohydric alcohol (A) comprising in addition to the hydroxyl moiety at least one ether moiety optionally in an organic liquid reaction medium; or

a 2 ) a solution of at least a Group 2 metal alkoxy compound (Ax′) being the reaction product of a Group 2 metal compound (MC) and an alcohol mixture of the monohydric alcohol (A) and a monohydric alcohol (B) of formula ROH, optionally in an organic liquid reaction medium; or

a 3 ) providing a solution of a mixture of the Group 2 alkoxy compound (Ax) and a Group 2 metal alkoxy compound (Bx) being the reaction product of a Group 2 metal compound (MC) and the monohydric alcohol (B), optionally in an organic liquid reaction medium; or

a 4 ) providing a solution of Group 2 alkoxide of formula M(OR 1 ) m (OR 2 ) m X 2−n−m or mixture of Group 2 alkoxides M(OR 1 ) n′ X 2−n′ and M(OR 2 ) m′ X 2−m′ , where M is Group 2 metal, X is halogen, R 1 and R 2 are different alkyl groups of C 2 to C 16 carbon atoms, and 0≤n<2, 0≤m<2 and n+m+(2−n−m)=2, provided that both n and m≠0, 0<n′≤2 and 0<m′≤2; and

b) adding said solution from step a) to at least one compound (TC) of a transition metal of Group 4 to 6 and

c) obtaining the solid catalyst component particles, and adding an internal electron donor (ID), at any step prior to step c).