Melt-Blown Webs Without Shots and With Improved Barrier Properties

Abstract

Melt-blown webs having no shots and improved barrier properties, whereby the melt-blown webs are made out of a so-called “controlled rheology” propylene (CR-PP), which was visbroken without any peroxide.

1 . Melt-blown webs comprising melt-blown fibers made of at least 80% of a polypropylene composition comprising
 (A) a polypropylene 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/10 min or a molecular weight M w  (measured with GPC) of below 180 000 g/mol, and   (ii) a melting temperature Tm between ≧130° C. and ≦170° C. and   (iii) a molecular weight distribution (MWD)>2 and   (iv) wherein the polypropylene composition has been visbroken without the use of peroxide and wherein the melt-blown web is free of shots and has a hydrohead (3rd drop, cm H 2 O resp. mbar), measured according to standard test WSP 80.6 (09), of a melt-blown web (produced with 270° C. melt temperature) having a weight per unit area of 9.5±1.0 g/m 2 , of at least 80 mbar and of a melt-blown web (produced with 290° C. melt temperature) having a weight per unit area of 9.5±1.0 g/m 2 , of at least 130 mbar.   
     
     
         2 . Melt-blown webs according to  claim 1 , wherein the polypropylene composition has been visbroken with a visbreaking ratio [final MFR2 (230° C./2.16 kg)/initial MFR2 (230° C./2.16 kg)] of 5 to 50, wherein “final MFR2 (230° C./2.16 kg)” is the MFR2 (230° C./2.16 kg) of the polypropylene composition after visbreaking and “initial MFR2 (230° C./2.16 kg)” is the MFR2 (230° C./2.16 kg) of the polypropylene composition before visbreaking. 
     
     
         3 . Melt-blown webs according to  claim 1  or  2 , being 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. 
 
     
     
         4 . Melt-blown webs according to  claim 3 , wherein
 (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.   
     
     
         5 . Melt-blown webs according to  claim 1 , whereby the polypropylene 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). 
     
     
         6 . Melt-blown webs according to  claim 5  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. 
     
     
         7 . Melt-blown webs according to  claim 5 , 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 ) n (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 a internal electron donor (ID), at any step prior to step c).   
     
     
         8 . Melt-blown webs according to  claim 1 , whereby the polypropylene composition is free of phthalic compounds and their respective decomposition products. 
     
     
         9 . Melt-blown webs according to  claim 1 , whereby the polypropylene polymer is visbroken with a hydroxylamine ester or a sulphur compound or by purely thermal degradation. 
     
     
         10 . Melt-blown webs according to  claim 9 , wherein the polypropylene polymer is visbroken with a hydroxylamine ester or a sulphur compound. 
     
     
         11 . Melt-blown webs according to  claim 9 , wherein the hydroxylamine ester is selected from the group consisting of sterically hindered amine derivatives of formula: 
       
         
           
           
               
               
           
         
       
     
     
         12 . Melt-blown webs according to  claim 9 , wherein the sulphur compound has the formula R 1 —S—H, wherein R 1  represents C8-C18alkyl. 
     
     
         13 . Melt-blown web according to  claim 1 , wherein the polypropylene polymer is a propylene homopolymer or a random propylene copolymer comprising propylene and ethylene and/or C 4  to C 12  α-olefins with a comonomer content in the range of 1.0 to below 20.0 wt %, preferably is a propylene homopolymer. 
     
     
         14 . Article comprising the melt-blown web according to  claim 1 , wherein said article is selected from the group consisting of filtration media, diapers, sanitary napkins, panty liners, incontinence products for adults, protective clothing, breathing protection masks, surgical drapes, surgical gowns, and other surgical wear. 
     
     
         15 . 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 polypropylene polymer, preferably a propylene homopolymer 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/10 min and   (ii) a melting temperature Tm between ≧130° C. and ≦170° C. and   (iii) a molecular weight distribution (MWD)>2 and   (iv) wherein the polypropylene composition has been visbroken by using a hydroxylamine ester or a sulphur compound.   
     
     
         16 . Melt-blown webs according to  claim 4 , wherein
 (a) Mw(web)/Mw(PP) is ≦0.85, and   (b) MWD(web)/MWD(PP) is ≦0.90.   
     
     
         17 . Melt-blown webs according to  claim 4 , wherein
 (a) Mw(web)/Mw(PP) is ≦0.80 and   (b) MWD(web)/MWD(PP) is ≦0.85.   
     
     
         18 . Melt-blown webs according to  claim 5  wherein the internal donor (ID) is a non-phthalic compound. 
     
     
         19 . Melt-blown webs according to  claim 5  wherein the internal donor (ID) is a non-phthalic acid ester. 
     
     
         20 . Melt-blown webs according to  claim 6  wherein the internal donor (ID) is a citraconate. 
     
     
         21 . Melt-blown webs according to  claim 10 , wherein the polypropylene polymer is visbroken with a hydroxylamine ester.