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.

Claims

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.sub.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.sub.2O 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.sup.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.sup.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.sub.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.sub.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.sub.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.sub.4) providing a solution of Group 2 alkoxide of formula M(OR.sub.1).sub.n(OR.sub.2).sub.mX.sub.2-n-m or mixture of Group 2 alkoxides M(OR.sub.1).sub.n′X.sub.2-n′ and M(OR.sub.2).sub.m′X.sub.2-m′, where M is Group 2 metal, X is halogen, R.sub.1 and R.sub.2 are different alkyl groups of C.sub.2 to C.sub.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: ##STR00009##

12. Melt-blown webs according to claim 9, wherein the sulphur compound has the formula R.sub.1—S—H, wherein R.sub.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.sub.4 to C.sub.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.

Description

EXPERIMENTAL PART

A. Measuring Methods

[0223] The following definitions of terms and determination methods apply for the above general description of the invention including the claims as well as to the below examples unless otherwise defined.

Quantification of Microstructure by NMR Spectroscopy

[0224] Quantitative nuclear-magnetic resonance (NMR) spectroscopy was used to quantify the isotacticity and regio-regularity of the propylene homopolymers.

[0225] Quantitative .sup.13C {′H} NMR spectra were recorded in the solution-state using a Bruker Advance III 400 NMR spectrometer operating at 400.15 and 100.62 MHz for .sup.1H and .sup.13C respectively. All spectra were recorded using a .sup.13C optimised 10 mm extended temperature probehead at 125° C. using nitrogen gas for all pneumatics.

[0226] For propylene homopolymers approximately 200 mg of material was dissolved in 1,2-tetrachloroethane-d.sub.2 (TCE-d.sub.2). To ensure a homogenous solution, after initial sample preparation in a heat block, the NMR tube was further heated in a rotary oven for at least 1 hour. Upon insertion into the magnet the tube was spun at 10 Hz. This setup was chosen primarily for the high resolution needed for tacticity distribution quantification (Busico, V., Cipullo, R., Prog. Polym. Sci. 26 (2001) 443; Busico, V.; Cipullo, R., Monaco, G., Vacatello, M., Segre, A. L., Macromolecules 30 (1997) 6251). Standard single-pulse excitation was employed utilising the NOE and bi-level WALTZ16 decoupling scheme (Zhou, Z., Kuemmerle, R., Qiu, X., Redwine, D., Cong, R., Taha, A., Baugh, D. Winniford, B., J. Mag. Reson. 187 (2007) 225; Busico, V., Carbonniere, P., Cipullo, R., Pellecchia, R., Severn, J., Talarico, G., Macromol. Rapid Commun. 2007, 28, 11289). A total of 8192 (8 k) transients were acquired per spectra.

[0227] Quantitative .sup.13C {.sup.1H} NMR spectra were processed, integrated and relevant quantitative properties determined from the integrals using proprietary computer programs.

[0228] For propylene homopolymers all chemical shifts are internally referenced to the methyl isotactic pentad (mmmm) at 21.85 ppm.

[0229] Characteristic signals corresponding to regio defects (Resconi, L., Cavallo, L., Fait, A., Piemontesi, F., Chem. Rev. 2000, 100, 1253; Wang, W-J., Zhu, S., Macromolecules 33 (2000), 1157; Cheng, H. N., Macromolecules 17 (1984), 1950) or comonomer were observed.

[0230] The tacticity distribution was quantified through integration of the methyl region between 23.6-19.7 ppm correcting for any sites not related to the stereo sequences of interest(Busico, V., Cipullo, R., Prog. Polym. Sci. 26 (2001) 443; Busico, V., Cipullo, R., Monaco, G., Vacatello, M., Segre, A. L., Macromolecules 30 (1997) 6251).

[0231] Specifically the influence of regio-defects and comonomer on the quantification of the tacticity distribution was corrected for by subtraction of representative regio-defect and comonomer integrals from the specific integral regions of the stereo sequences.

[0232] The isotacticity was determined at the pentad level and reported as the percentage of isotactic pentad (mmmm) sequences with respect to all pentad sequences:

[mmmm]%=100*(mmmm/sum of all pentads)

[0233] The presence of 2,1 erythro regio-defects was indicated by the presence of the two methyl sites at 17.7 and 17.2 ppm and confirmed by other characteristic sites. Characteristic signals corresponding to other types of regio-defects were not observed (Resconi, L., Cavallo, L., Fait, A., Piemontesi, F., Chem. Rev. 2000, 100, 1253).

[0234] The amount of 2,1 erythro regio-defects was quantified using the average integral of the two characteristic methyl sites at 17.7 and 17.2 ppm:

P.sub.21e=(I.sub.e6+I.sub.e8)/2

[0235] The amount of 1,2 primary inserted propene was quantified based on the methyl region with correction undertaken for sites included in this region not related to primary insertion and for primary insertion sites excluded from this region:

P.sub.12=I.sub.CH3P.sub.12e

[0236] The total amount of propene was quantified as the sum of primary inserted propene and all other present regio-defects:

P.sub.total=P.sub.12+P.sub.21e

[0237] The mole percent of 2,1 erythro regio-defects was quantified with respect to all propene:

[21e] mol.-%=100*(P.sub.21e/P.sub.total)

[0238] MFR.sub.2 (230° C.) is measured according to ISO 1133 (230° C., 2.16 kg load). The MFR.sub.2 of the polypropylene composition is determined on the granules of the material, while the MFR.sub.2 of the melt-blown web is determined on cut pieces of a compression-molded plaque prepared from the web in a heated press at a temperature of not more than 200° C., said pieces having a dimension which is comparable to the granule dimension.

[0239] The xylene soluble fraction at room temperature (xylene cold soluble XCS, wt %): The amount of the polymer soluble in xylene is determined at 25° C. according to ISO 16152; 5.sup.th edition; 2005-07-01.

[0240] DSC analysis, melting temperature (T.sub.m), melting enthalpy (H.sub.m), crystallization temperature (T.sub.c) and crystallization enthalpy (H.sub.c): measured with a TA Instrument Q200 differential scanning calorimetry (DSC) on 5 to 7 mg samples. DSC is run according to ISO 11357/part 3/method C2 in a heat/cool/heat cycle with a scan rate of 10° C./min in the temperature range of −30 to +225° C. Crystallization temperature (T.sub.c) and crystallization enthalpy (H.sub.c) are determined from the cooling step, while melting temperature (T.sub.m) and melting enthalpy (H.sub.m) are determined from the second heating step respectively from the first heating step in case of the webs.

Number Average Molecular Weight (M.sub.n), Weight Average Molecular Weight (M.sub.w), (M.sub.w/M.sub.n=MWD) of Propylene Homopolymer

[0241] Molecular weight averages Mw, Mn and MWD were determined by Gel Permeation Chromatography (GPC) according to ISO 16014-4:2003 and ASTM D 6474-99. A PolymerChar GPC instrument, equipped with infrared (IR) detector was used with 3×Olexis and 1×Olexis Guard columns from Polymer Laboratories and 1,2,4-trichlorobenzene (TCB, stabilized with 250 mg/L 2,6-Di tert butyl-4-methyl-phenol) as solvent at 160° C. and at a constant flow rate of 1 mL/min. 200 μL of sample solution were injected per analysis. The column set was calibrated using universal calibration (according to ISO 16014-2:2003) with at least 15 narrow MWD polystyrene (PS) standards in the range of 0.5 kg/mol to 11 500 kg/mol. Mark Houwink constants for PS, PE and PP used are as described per ASTM D 6474-99. All samples were prepared by dissolving the polymer sample to achieve concentration of ˜1 mg/ml (at 160° C.) in stabilized TCB (same as mobile phase) for 2.5 hours for PP at max. 160° C. under continuous gently shaking in the autosampler of the GPC instrument. The MWD of the polypropylene composition is determined on the granules of the material, while the MWD of the melt-blown web is determined on a fiber sample from the web, both being dissolved in an analogous way.

Grammage of the Web

[0242] The unit weight (grammage) of the webs in g/m.sup.2 was determined in accordance with ISO 536:1995.

Hydrohead

[0243] The hydrohead or water resistance as determined by a hydrostatic pressure test is determined according to the WSP (worldwide strategic partners) standard test WSP 80.6 (09) as published in December 2009. This industry standard is in turn based on ISO 811:1981 and uses specimens of 100 cm.sup.2 at 23° C. with purified water as test liquid and a rate of increase of the water pressure of 10 cm/min. An H.sub.2O column height of X cm in this test corresponds to a pressure difference of X mbar.

Air Permeability

[0244] The air permeability was determined in accordance with DIN ISO 9237 at a pressure difference of 100 Pa. This air permeability is defined as the velocity of an air flow passing perpendicularly through the web specimen.

Filtration Efficiency

[0245] Air filtration efficiency was determined based on EN 1822-3 for flat sheet filter media, using a test filter area of 400 cm.sup.2. The particle retention was tested with a usual aerosol of di-ethyl-hexyl-sebacate (DEHS), calculating efficiency for the fraction with 0.4 μm diameter from a class analysis with 0.1 μm scale. An airflow of 16 m.sup.3 .Math.h.sup.1 was used, corresponding to an airspeed of 0.11 m.Math.s.sup.−1.

Pressure Drop

[0246] The pressure drop was measured according to DIN ISO 9237 at an air speed (permeability) of 500 mm/s.

Shots

[0247] “Shot is a measure of the number of deformations, defects or holes in the formed polymer fabric. A defect can be, for example, an agglomeration of polymer material from 10 to 1000 times greater in diameter than the diameter of the fibers. Qualitative test methods for determining “shot” can be found in U.S. Pat. No. 5,723,217. Fabrics samples are pulled off the MB fabric roll at random and a section several feet long encompassing the full width of the fabric is cut from the roll. The samples are held against a backlit glass plate and visually rated from “1” to “5” according to the level of shot (1=no shot; “5”=very high level of shot). A set of photographs of MB fabrics containing shot levels corresponding to each category from 1 to 5 serve as standards for rating the fabrics. A shot value is then determined by counting the number of defects or holes per unit area. This can be done by, for example, viewing the fabric in a microscope and manually counting the number of shot per unit area. Also, see Yan, Z. and Bresee, R R., Flexible Multifunctional Instrument for Automated Nonwoven Web Structure Analysis, 69 TEXTILE RES. J. 795-804 (1999).”

B. Examples

[0248] The catalyst used in the polymerization process for the propylene homopolymer of the inventive example (IE-1) and the Comparative Example (CE-1) was prepared as follows:

Used Chemicals:

[0249] 20% solution in toluene of butyl ethyl magnesium (Mg(Bu)(Et), BEM), provided by Chemtura
2-ethylhexanol, provided by Amphochem
3-Butoxy-2-propanol—(DOWANOL™ PnB), provided by Dow
bis(2-ethylhexyl)citraconate, provided by SynphaBase
TiCl.sub.4, provided by Millenium Chemicals
Toluene, provided by Aspokem
Viscoplex® 1-254, provided by Evonik
Heptane, provided by Chevron

Preparation of a Mg Alkoxy Compound

[0250] Mg alkoxide solution was prepared by adding, with stirring (70 rpm), into 11 kg of a 20 wt-% solution in toluene of butyl ethyl magnesium (Mg(Bu)(Et)), a mixture of 4.7 kg of 2-ethylhexanol and 1.2 kg of butoxypropanol in a 20 l stainless steel reactor. During the addition the reactor contents were maintained below 45° C. After addition was completed, mixing (70 rpm) of the reaction mixture was continued at 60° C. for 30 minutes. After cooling to room temperature 2.3 kg g of the donor bis(2-ethylhexyl)citraconate was added to the Mg-alkoxide solution keeping temperature below 25° C. Mixing was continued for 15 minutes under stirring (70 rpm).

Preparation of Solid Catalyst Component

[0251] 20.3 kg of TiCl.sub.4 and 1.1 kg of toluene were added into a 20 l stainless steel reactor. Under 350 rpm mixing and keeping the temperature at 0° C., 14.5 kg of the Mg alkoxy compound prepared in example 1 was added during 1.5 hours. 1.7 l of Viscoplex® 1-254 and 7.5 kg of heptane were added and after 1 hour mixing at 0° C. the temperature of the formed emulsion was raised to 90° C. within 1 hour. After 30 minutes mixing was stopped catalyst droplets were solidified and the formed catalyst particles were allowed to settle. After settling (1 hour), the supernatant liquid was siphoned away. Then the catalyst particles were washed with 45 kg of toluene at 90° C. for 20 minutes followed by two heptane washes (30 kg, 15 min). During the first heptane wash the temperature was decreased to 50° C. and during the second wash to room temperature.

[0252] The thus obtained catalyst was used along with triethyl-aluminium (TEAL) as co-catalyst and cyclohexylmethyl dimethoxy silane (C-Donor) as external donor.

[0253] The aluminium to donor ratio, the aluminium to titanium ratio and the polymerization conditions are indicated in tables 1 and 2.

[0254] Polymerization was performed in a polypropylene (PP) pilot plant, comprising only a loop reactor.

TABLE-US-00001 TABLE 1 Preparation of the propylene homopolymer (Component (A)) for IE1 Component (A) TEAL/Ti [mol/mol] 65 TEAL/Donor [mol/mol] 18.8 Catalyst feed [g/h] 1.6 Loop (H-PP1) Time [h] 0.47 Temperature [° C.] 70 Pressure [kPa] 35 MFR.sub.2 [g/10 min] 77 XCS [wt %] 4.9 H.sub.2/C3 ratio [mol/kmol] 3.7 amount [wt.-%] 100 Final MFR.sub.2 [g/10 min] 77 XCS [wt %] 3.4 Tm [° C.] 162 Tc [° C.] 114 Mw [g/mol] 135000 MWD [—] 6.5

TABLE-US-00002 TABLE 2 Preparation of the propylene homopolymer (Component (A)) for IE2 and IE3 Component (A) TEAL/Ti [mol/mol] 65 TEAL/Donor [mol/mol] 18.8 Catalyst feed [g/h] 1.6 Loop (H-PP1) Time [h] 0.47 Temperature [° C.] 70 Pressure [kPa] 35 MFR.sub.2 [g/10 min] 3.5 XCS [wt %] 3.5 H.sub.2/C3 ratio [mol/kmol] 0.7 amount [wt %] 100 Final MFR.sub.2 [g/10 min] 3.7 XCS [wt.-%] 3.5 Tm [° C.] 162 Tc [° C.] 113 Mw [g/mol] 320000 MWD 7.2

[0255] The propylene homopolymer has been mixed with 400 ppm calcium Stearate (CAS No. 1592-23-0) and 1,000 ppm Irganox 1010 supplied by BASF AG, Germany (Pentaerythrityl-tetrakis(3-(3′,5′-di-tert. butyl-4-hydroxyphenyl)-propionate, CAS No. 6683-19-8). In a second step the propylene homopolymer has been visbroken by using a co-rotating twinscrew extruder at 200-230° C. and using 1.1 wt % of Irgatec® CR76 (hydroxylamine ester in a polymer matrix; sold by BASF) (IE1) to achieve the target MFR.sub.2 of 800 g/10 min. For IE-2 0.075 wt % of 1-octadecanthiol and for IE-3 0.12 wt % of 1-octadecanthiol (supplied by Sigma Aldrich) were used.

TABLE-US-00003 TABLE 3 Properties of visbroken PP of IE2 and IE3 (reference is without visbreaking) Example unit reference IE2 IE3 1-octadecanthiol [wt %] 0 0.075 0.12 MFR.sub.2 [g/10 min] 3.7 27.2 38.2 Mw [g/mol] 320000 177500 156000 MWD [—] 7.2 4.8 4.5

[0256] For Comparative Example CE1 the above produced propylene homopolymer including the additives as described above has been visbroken by using a co-rotating twinscrew extruder at 200-230° C. and using an appropriate amount (1750 ppm) of (tert.-butylperoxy)-2,5-dimethylhexane (Trigonox 101, distributed by Akzo Nobel, Netherlands) to achieve the target MFR2 of 800 g/10 min.

[0257] For Comparative Example CE2 polymerization was performed with catalyst Avant ZN L1, commercially available from Basell. The catalyst contains a phthalate based internal donor. The catalyst was used along with triethyl-aluminium (TEAL) as co-catalyst and cyclohexylmethyl dimethoxy silane (C-Donor) as external donor. Polymerization was performed in a PP pilot plant, comprising only a loop reactor.

TABLE-US-00004 TABLE 4 Preparation of the propylene homopolymer (Component (A)) for CE2 Component (A) TEAL/Ti [mol/mol] 65 TEAL/Donor [mol/mol] 18.8 Catalyst feed [g/h] 1.3 Loop (H-PP1) Time [h] 0.5 Temperature [° C.] 70 Pressure [kPa] 35 MFR.sub.2 [g/10 min] 76 XCS [wt.-%] 3.2 H.sub.2/C3 ratio [mol/kmol] 4.3 amount [wt.-%] 100 Final Tm [° C.] 162 Tc [° C.] 116 Mw [g/mol] 133500 MWD 7.6

[0258] The propylene homopolymer for CE2 has been mixed with 400 ppm calcium Stearate (CAS No. 1592-23-0) and 1,000 ppm Irganox 1010 supplied by BASF AG, Germany (Pentaerythrityl-tetrakis(3-(3′,5′-di-tert. butyl-4-hydroxyphenyl)-propionate, CAS No. 6683-19-8).

[0259] In a second step the propylene homopolymer has been visbroken by using a co-rotating twinscrew extruder at 200-230° C. and using 1.1 wt % of Irgatec® CR76 (hydroxylamine ester in a polymer matrix; sold by BASF) yielding Mw of 131000 and MWD 6.0.

[0260] The polypropylene compositions of IE1, CE1 and CE2 have been converted into melt-blown webs on a Reicofil MB250 line using a spinneret having 470 holes of 0.4 mm exit diameter and 35 holes per inch. Webs were produced at different melt temperatures, throughputs, DCD (die to collector distance) and air volumes.

[0261] The processing conditions for and properties of the melt-blown webs are indicated in tables 5 6, 7 and 8.

TABLE-US-00005 TABLE 5 Processing conditions for the production of the melt-blown webs Melt Web Temperature DCD Air volume Throughput weight Example ° C. mm m.sup.3/h kg/h .Math. m g/m.sup.2 IE1-1 270 200 360 10 9.4 IE1-2 290 200 210 10 9.4 CE1-1 250 200 410 10 9.5 CE1-2 270 200 300 10 9.3 CE2-1 270 200 520 10 10.0 CE2-2 290 200 310 10 10.0

TABLE-US-00006 TABLE 6 Properties of the melt-blown webs Air Pressure Filtration Quality Hydrohead permeability drop Efficiency factor (3.sup.rd drop) Example mm/s Pa % 100/Pa cm H.sub.2O* IE1-1 823 57.4 25.08 0.504 88 IE1-2 485 122.1 48.67 0.547 136.2 CE1-1 952 44.3 25.47 0.664 74.7 CE1-2 752 60.4 30.56 0.605 50.5 CE2-1 1100 36.5 29.0 0.635 70.1 CE2-2 1215 32 19.88 0.593 20.5 *also mbar

TABLE-US-00007 TABLE 7 MFR, Mw, MWD and shots for IE1 and CE1 on web MFR Mw Mw Mw(web)/ MWD MWD MWD(web)/ (web) (web) (PP)* Mw(PP) (web) (PP)** MWD(PP) Shots .sup.a) IE1-1 860 62300 137000 0.45 3.9 6.0 0.65 No (1) IE2-1 1806 50400 137000 0.37 3.5 6.0 0.58 No (1) CE1-1 850 64000 67350 0.95 4.1 4.2 0.98 yes (2).sup.  CE1-2 1044 60000 67350 0.89 4 4.2 0.95 Yes (4)  *Mw measured on the visbroken PP granules **MWD for the visbroken PP .sup.a) rating 1 = no shots; rating 2 = low level of shots; rating 4 = high level of shots

[0262] As can be seen from Table 3, 4 and 5 that at the same throughput, the polymer of the Inventive Example (visbroken with Irgatec®; IE1-1 and IE1-2) can go to higher melt temperature without producing shots in the web than the polymer of the Comparative Example (visbroken with peroxide; CE1-1 and CE1-2). (Polymers of IE1 and CE1 produced with the same catalyst, but different visbreaking agents used).

[0263] Furthermore it can be seen that the use of the polymer of the Inventive Example (visbroken with Irgatec®; IE1-1 and IE1-2) yields webs with improved water barrier properties, as can be seen in the higher hydrohead values compared to the comparative examples CE1 and CE2.