Nucleated phthalate-free PP homopolymers for melt-blown fibers

Abstract

The present invention is directed to a new polypropylene composition comprising a propylene homopolymer and a polymeric nucleating agent, to melt-blown fibers comprising the polypropylene composition, to a melt-blown web comprising the melt-blown fibers and/or the polypropylene composition, to an article comprising the melt-blown fibers and/or the melt-blown web as well as to the use of the polypropylene composition for improving the relation between pressure drop and hydrohead of a melt-blown web and for improving the thermo-mechanical properties of a melt-blown web in machine direction (MD) and transverse direction (TD).

Claims

1. Polypropylene composition suitable for the production of meltblown PP fibers comprising (A) a propylene homopolymer, produced with a Ziegler-Natta catalyst (ZN-C), and (B) a polymeric nucleating agent, wherein the polypropylene composition has i) a melt flow rate MFR.sub.2 (230 C./2.16 kg) measured according to ISO 1133 of 90 to 5000 g/10 min, and ii) a difference between melting temperature (Tm) and crystallization temperature (Tc) (TmTc) of <45 C.

2. Polypropylene composition according to claim 1, wherein the polypropylene composition is free of phthalic compounds as well as their respective decomposition products.

3. Polypropylene composition according to claim 1 or 2, wherein the polypropylene composition and/or propylene homopolymer has/have been visbroken.

4. Polypropylene composition according to claim 3, wherein the polypropylene composition and/or propylene homopolymer has/have been visbroken with a visbreaking ratio [final MFR.sub.2 (230 C./2.16 kg)/initial MFR.sub.2 (230 C./2.16 kg)] of 5 to 50, wherein final MFR.sub.2 (230 C./2.16 kg) is the MFR.sub.2 (230 C./2.16 kg) of the polypropylene composition and/or propylene homopolymer after visbreaking and initial MFR.sub.2 (230 C./2.16 kg) is the MFR.sub.2 (230 C./2.16 kg) of the polypropylene composition and/or propylene homopolymer before visbreaking.

5. Polypropylene composition according to any one of the preceding claims, wherein the polypropylene composition and/or propylene homopolymer has/have a) 2.1 erythro regio-defects of equal or below 0.4 mol % determined by .sup.13C-NMR spectroscopy, and/or b) a pentad isotacticity (mmmm) of more than 90.0%, and/or c) a xylene cold soluble content (XCS) determined according ISO 16152 (25 C.) of at least 1.8 wt %, and/or d) a crystallization temperature Tc of 110 C.

6. Polypropylene composition according to any one of the preceding claims, wherein the polymeric nucleating agent is a compound of the formula
CH.sub.2CHCHR.sup.1R.sup.2 wherein R.sup.1 and R.sup.2 together form a 5- or 6-membered saturated, unsaturated or aromatic ring, optionally containing substituents, or independently represent an alkyl group comprising 1 to 4 carbon atoms, whereby in case R.sup.1 and R.sup.2 form an aromatic ring, the hydrogen atom of the CHR.sup.1R.sup.2 moiety is not present.

7. Polypropylene composition according to claim 6, wherein the polymeric nucleating agent is selected from vinyl cycloalkane polymer, preferably vinyl cyclohexane (VCH) polymer, vinyl cyclopentane polymer, 3-methyl-1-butene polymer and vinyl-2-methyl cyclohexane polymer.

8. Polypropylene composition according to any one of the preceding claims, wherein the propylene homopolymer 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), wherein said internal donor (ID) is a non-phthalic compound, preferably is a non-phthalic acid ester; b) optionally a co-catalyst (Co), and c) optionally an external donor (ED).

9. Polypropylene composition according to claim 8, wherein a) the internal donor (ID) is selected from optionally substituted malonates, maleates, succinates, glutarates, cyclohexene-1,2-dicarboxylates, benzoates and derivatives and/or mixtures thereof, preferably the internal donor (ID) is a citraconate; b) the molar-ratio of co-catalyst (Co) to external donor (ED) [Co/ED] is 5 to 45.

10. Polypropylene composition according to any one of the preceding claims, wherein the propylene homopolymer is produced in a polymerization process comprising at least one reactor (R1) or at least two reactors (R1) and (R2), whereby in the first reactor (R1) a first propylene homopolymer fraction (H-PP1) is produced and subsequently transferred into the second reactor (R2), in the second reactor (R2) a second propylene homopolymer fraction (H-PP2) is produced in the presence of the first propylene homopolymer fraction (H-PP1).

11. Polypropylene composition according to any one of the preceding claims, wherein the polymeric nucleating agent is introduced to the propylene homopolymer (A) with the masterbatch technology, whereby the propylene homopolymer (A) is blended mechanically with a carrier polymer containing the polymeric nucleating agent.

12. Polypropylene composition according to claim 11, wherein the carrier polymer containing the polymeric nucleating agent is obtained by preparing a propylene polymer using a polymerization catalyst, obtained by polymerizing a Ziegler-Natta polymerization catalyst according to claim 8 with a vinyl compound of the formula CH.sub.2CHCHR.sup.1R.sup.2 according to claim 6.

13. Melt-blown fibers having an average diameter of not more than 5.0 m, said fibers comprising, preferably comprising at least 95.0 wt % of, a polypropylene composition as defined in any one of the preceding claims 1 to 12.

14. Melt-blown web comprising the melt-blown fibers according to claim 13 and/or a polypropylene composition as defined in any one of the preceding claims 1 to 12.

15. Article comprising melt-blown fibers according to claim 13 and/or a melt-blown web according to claim 14, 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 surgical wear in general.

16. Use of a polypropylene composition as defined in any one of the preceding claims 1 to 12 for improving the relation between pressure drop and hydrohead of a melt-blown web at an air permeability in the range from 500 to 2.000 mm/s, wherein the improvement is defined by inequation (I)
(PD-web)/(HH-web)0.88(I) wherein (PD-web) is the pressure drop (Pa), measured according to DIN ISO 9237, of a melt-blown web having a weight per unit area of 9.51.0 g/m.sup.2, (HH-web) is the hydrohead (3.sup.1d drop, cm H.sub.2O), measured according to standard test WSP 80.6 (09), of a melt-blown web having a weight per unit area of 9.51.0 g/m.sup.2 and for improving the thermo-mechanical properties of a melt-blown web in machine direction (MD) and transverse direction (TD).

Description

EXPERIMENTAL PART

A. Measuring Methods

[0198] 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.

[0199] Quantification of Microstructure by NMR Spectroscopy

[0200] Quantitative nuclear-magnetic resonance (NMR) spectroscopy was used to quantify the isotacticity and regio-regularity of the propylene homopolymers.

[0201] Quantitative .sup.13C{.sup.1H} 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.

[0202] 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 rotatary 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.

[0203] Quantitative .sup.13C{.sup.1H} NMR spectra were processed, integrated and relevant quantitative properties determined from the integrals using proprietary computer programs.

[0204] For propylene homopolymers all chemical shifts are internally referenced to the methyl isotactic pentad (mmmm) at 21.85 ppm.

[0205] 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.

[0206] 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).

[0207] 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. 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)

[0208] 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).

[0209] 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

[0210] 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.CH3+P.sub.12e

[0211] 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

[0212] 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)

[0213] MFR.sub.2 (230 C.) is measured according to ISO 1133 (230 C., 2.16 kg load)

[0214] The xylene soluble fraction at room temperature (XS, 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.

[0215] 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.

[0216] Grammage of the Web

[0217] The unit weight (grammage) of the webs in g/m.sup.2 was determined in accordance with ISO 536:1995.

[0218] Average Fibre Diameter in the Web

[0219] The number average fibre diameter was determined using scanning electron microscopy (SEM). A representative part of the web was selected and an SEM micrograph of suitable magnification was recorded, then the diameter of 20 fibres was measured and the number average calculated.

[0220] Hydrohead

[0221] 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.

[0222] Air Permeability

[0223] 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.

[0224] Filtration Efficiency

[0225] 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 m diameter from a class analysis with 0.1 m 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.

[0226] Pressure Drop

[0227] The pressure drop was measured according to DIN ISO 9237 at an air speed (permeability) of 500 mm/s.

[0228] Tensile Tests on Webs

[0229] The tests were performed in line with the Edana standard WSP 11 110.4 (09) related to ISO/DIS 9073-5 using 10 samples of 500 mm width. The distance of the clamps at the start of test was 100 mm, the test speed was constant for whole test at 100 mm/min. All parameters (in machine and transverse direction) were determined at 23 C., while only the maximum force and related strain at maximum force (both in machine direction) were also determined at 80 C.

B. Examples

[0230] The catalyst used in the polymerization process for the propylene homopolymer of the inventive example (IE) and the Comparative Example (CE) was prepared as follows:

[0231] Used Chemicals:

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

[0232] Preparation of a Mg Alkoxy Compound

[0233] 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 I 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).

[0234] Preparation of Solid Catalyst Component

[0235] 20.3 kg of TiCl.sub.4 and 1.1 kg of toluene were added into a 20 I 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 I 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.

[0236] The thus obtained catalyst was used along with triethyl-aluminium (TEAL) as co-catalyst and cyclohexylmethyl dimethoxy silane (C-Donor) or di(cyclopentyl) dimethoxy silane (D-donor) as donor.

[0237] The aluminium to donor ratio, the aluminium to titanium ratio and the polymerization conditions are indicated in tables 1 and 2.

[0238] Polymerization was performed in a Borstar pilot plant, comprising a loop reactor and a gas phase reactor.

TABLE-US-00001 TABLE 1 Preparation of the propylene homopolymer (Component (A)) Component (A) Donor type C TEAL/Ti [mol/mol] 150 TEAL/Donor [mol/mol] 18.8 Loop (H-PP1) Time [h] 0.66 Temperature [ C.] 75 Pressure [kPa] 5200 MFR.sub.2 [g/10 min] 77.0 XCS [wt.-%] 4.9 H.sub.2/C3 ratio [mol/kmol] 7.2 amount [wt.-%] 100 1st GPR (H-PP2) Time [h] Temperature [ C.] H.sub.2/C3 ratio [mol/kmol] amount [wt.-%] 0 Final MFR.sub.2 [g/10 min] 79 XCS [wt.-%] 4.9 Tm [ C.] 162.6 Tc [ C.] 122.4 2, 1 [] n.d. mmmm [%] 93.5

[0239] 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).

[0240] In a second step the propylene homopolymer has been visbroken by using a co-rotating twin-screw extruder at 200-230 C. and using an appropriate amount of (tert.-butylperoxy)-2,5-dimethylhexane (Trigonox 101, distributed by Akzo Nobel, Netherlands) to achieve the target MFR.sub.2 of 800 g/10 min.

[0241] The visbroken propylene homopolymer was used as such in the Comparative Examples.

[0242] For the Inventive Examples the visbroken propylene homopolymer was compounded with a masterbatch containing the polymeric nucleating agent and a propylene homopolymer as carrier.

[0243] The masterbatch was obtained by polymerizing propylene in the presence of a catalyst, prepared as described above, with an additional modification step.

[0244] Before the polymerization, the catalyst, prepared as described above, was prepolymerized with vinyl cyclohexane in an amount to achieve a concentration of 120 ppm poly(vinyl cyclohexane) (PVCH) in the final polymer. The respective process is described in EP 1 028 984 and EP 1 183 307.

[0245] The polymerization of the carrier polymer containing the polymeric nucleating agent was performed in a Borstar pilot plant, comprising a loop reactor and a gas phase reactor.

TABLE-US-00002 TABLE 2 Preparation of the carrier polymer containing the polymeric nucleating agent (masterbatch) Prepoly Donor type D TEAL/Ti [mol/mol] 150 TEAL/Donor [mol/mol] 18.8 Time [h] 0.38 Temperature [ C.] 30 Pressure [kPa] 5500 Loop (H-PPI) Time [h] 0.5 Temperature [ C.] 80 Pressure [kPa] 5200 MFR.sub.2 [g/10 min] 0.5 XCS [wt.-%] 1.0 H.sub.2/C3 ratio [mol/kmol] 0.18 split [wt %] 56.0 1st GPR (H-PP2) Time [h] 1.5 Temperature [ C.] 80 Pressure [kPa] 2500 H.sub.2/C3 ratio [mol/kmol] 79.8 split [wt %] 44.0

[0246] The propylene homopolymer has been mixed with 0.15 wt % of Irganox B 215 FF (supplied by BASF) and 0.15 wt % of Calcium stearate (CAS No. 1592-23-0) and pelletised.

[0247] The so obtained pellets had an MFR of 6.5, a Tc of 129 C. and an isotacticity of 97.2 mol % as determined by .sup.13C-NMR spectroscopy.

[0248] For the Inventive Examples 95 wt % of the visbroken propylene homopolymer obtained as described above were compounded with 5 wt % of the masterbatch, prepared as described above. Melt mixing in a co-rotating twin-screw extruder at 200-230 C. was used for this purpose.

[0249] The polypropylene compositions (CE only propylene homopolymer; IE propylene homopolymer+masterbatch) 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.

[0250] The processing conditions for and properties of the melt-blown webs are indicated in tables 3 4, 5 and 6.

TABLE-US-00003 TABLE 3 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 IE1-1 250 500 550 30 9.1 IE1-2 250 200 350 30 9.6 IE1-3 250 200 450 10 9.8 IE2-1 270 500 520 30 9.3 IE2-2 270 200 480 30 9.7 IE2-3 270 200 350 15 9.4 IE2-4 270 200 310 10 9.5 IE3-1 290 200 300 25 9.6 IE3-2 290 200 320 30 9.6 CE1-1 250 500 450 10 8.3 CE1-2 250 200 410 10 9.5 CE2-1 270 500 470 30 10.0 CE2-2 270 200 430 30 10.0 CE2-3 270 200 350 15 9.9 CE3-1 290 500 380 40 9.9 CE3-2 290 200 240 35 10.0 CE3-3 290 200 250 40 10.0 CE3-4 290 200 230 30 10.0

TABLE-US-00004 TABLE 4 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 2340 12.9 19.04 1.644 26.4 IE1-2 1342 30.5 17.64 0.639 48.6 IE1-3 1102 42.3 18.16 0.474 64.7 IE2-1 1947 22.3 15.2 0.742 38.3 IE2-2 1029 46.2 19.92 0.481 62.7 IE2-3 874 42.7 18.37 0.477 67.1 IE2-4 795 51.7 22.52 0.494 76.3 IE3-1 761 58.1 28.06 0.567 83.4 IE3-2 701 57.7 24.76 0.495 96.5 CE1-1 1646 22.1 21.68 1.106 40.3 CE1-2 952 44.3 25.47 0.664 74.7 CE2-1 1069 27.1 14.47 0.709 44.8 CE2-2 792 50.3 25.2 0.58 78.7 CE2-3 753 55.3 21.83 0.445 82.1 CE3-1 1184 35.3 24.07 0.78 56.2 CE3-2 875 43.9 21.47 0.552 58.8 CE3-3 879 48.0 18.45 0.425 60.1 CE3-4 931 43.2 19.71 0.511 66.8 *also mbar

[0251] FIG. 1 summarizes the melt-blown web performance with regard to the relation between pressure drop and hydrohead at a weight per unit area of 9.51.0 g/m.sup.2 by adapting process conditions with respect to inventive example IE and CE.

[0252] From FIG. 1, it can be concluded that the melt-blown webs obtained from inventive Example IE show an improved or optimized relation between pressure drop and hydrohead. It clearly shows that the hydrohead can go higher for the inventive composition than for the comparative composition.

TABLE-US-00005 TABLE 5 DSC of IE and CE on web Tm(web, 1.sup.st Hm (web, 1.sup.st Melt Temp./ C. heat)/J/g heat)/J/g Tc/ C. IE1-1 250 164 87 125 IE2-1 270 163 105 126 CE1-1 250 164 87 115 CE2-2 270 162 80 116

[0253] Table 5 shows the DSC results of inventive and comparative examples on webs. The Tc is 125 C. with BNT and 115 C. without BNT. Thus, the PVCH addition increases Tc by 10 C., a clear indication of good dispersion and high nucleation efficiency of BNT, even at extremely lower concentration (ca. 1 ppm). Under the process condition, the webs also have a higher Hm, especially at higher melting temperature, meaning the crystallinity is higher.

TABLE-US-00006 TABLE 6 Mechanical properties 1E1-3 1E2-2 1E3-1 CE1-2 CE2-2 Tensile MD Force at N 7.1 7.7 8.1 6.6 5.7 (23 C.) break Max. force N 8.0 9.0 8.3 8.0 7.6 Rel. force N/cm 1.4 1.5 1.6 1.3 1.1 at break Rel. max. N/cm 1.6 1.8 1.7 1.6 1.5 force Strain at % 28.8 22.7 11.1 24.6 29.5 break Strain at % 26.3 20.8 10.6 22.4 26.8 max. force Tensile TD Force at N 5.6 4.5 3.2 3.7 3.8 (23 C.) break Max. force N 6.1 5.5 3.9 5.3 5.6 Rel. force N/cm 1.1 0.9 0.6 0.7 0.8 at break Rel. max. N/cm 1.2 1.1 0.8 1.1 1.1 force Strain at % 39.8 37.2 27.6 43.5 48.9 break Strain at % 36.5 34.3 24.4 39.4 42.5 max. force Tensile MD Max. force N 2.9 3.3 3.0 3.3 3.0 (80 C.) Strain at % 32.2 27.3 13.2 26.6 31.0 force

[0254] FIG. 2 shows the mechanical properties of the webs. At the same melt temperature and web weight, BNT improves the mechanical properties in both TD and MD direction, and the effect is even more pronounced at the higher application (testing) temperature of 80 C., in line with the DSC results discussed above (see Table 6).