MULTILAYER NONWOVEN STRUCTURE

Abstract

The present invention is directed to a nonwoven fabric (NF) comprising at least one inner layer (M) surrounded by at least one outer layer (S), said inner layer (M) comprising melt blown fibers and said outer layer (S) comprising spunbonded fibers, wherein said melt blown fibers and said spunbonded fibers comprise propylene polymers. The present invention is further directed to an article comprising said nonwoven fabric (NF).

Claims

1. A nonwoven fabric (NF), comprising a multi-layer structure comprising: i) at least one melt blown layer (M) comprising melt blown fibers (MBF) comprising a first propylene polymer (PP1) having a pentad isotacticity (mmmm) of more than 94.1%, and ii) at least one spunbonded layer (S) comprising spunbonded fibers (SBF) comprising a second propylene polymer (PP2) having a) a pentad isotacticity (mmmm) below 93.7%, b) a melting temperature Tm below 164 C., wherein the second propylene polymer (PP2) is featured by an amount of 2,1 erythro regio-defects equal or below 0.4 mol. %, and wherein the second propylene polymer (PP2) is free of phthalic acid esters as well as their respective decomposition products.

2. The nonwoven fabric (NF) according to claim 1, wherein the first propylene polymer (PP1) and/or the second propylene polymer (PP2) are propylene homopolymers.

3. The nonwoven fabric (NF) according to claim 1, wherein the first propylene polymer (PP1) and/or the second propylene polymer (PP2) are visbroken.

4. The nonwoven fabric (NF) according to claim 1, wherein the first propylene polymer (PP1) and/or the second propylene polymer (PP2) fulfil in equation (I) $\begin{array}{cc}\frac{\mathrm{MFR}\left(\mathrm{final}\right)}{\mathrm{MFR}\left(\mathrm{initial}\right)}>5,& \left(I\right)\end{array}$ wherein MFR(final) is the melt flow rate MFR (230 C.) determined according to ISO 1133 after visbreaking and MFR(initial) is the melt flow rate MFR (230 C.) determined according to ISO 1133 before visbreaking.

5. The nonwoven fabric (NF) according to claim 1, wherein the first propylene polymer (PP1) has a melt flow rate MFR (230 C.) determined according to ISO 1133 after visbreaking of at least 400 g/10 min.

6. The nonwoven fabric (NF) according to claim 1, wherein the second propylene polymer (PP2) has a melt flow rate MFR (230 C.) determined according to ISO 1133 after visbreaking of at least 21 g/10 min.

7. The nonwoven fabric (NF) according to claim 1, wherein the first propylene polymer (PP1) has a xylene soluble content (XCS) below 3.1 wt. %.

8. The nonwoven fabric (NF) according to claim 1, wherein: (i) the first propylene polymer (PP1) has a final molecular weight distribution Mw(final)/Mn(final) after visbreaking of at least 2.7, and/or (ii) the second propylene polymer (PP2) has a final molecular weight distribution Mw(final)/Mn(final) after visbreaking of at least 3.0.

9. The nonwoven fabric (NF) according to claim 1, wherein the second propylene polymer (PP2) has been polymerized in the presence of: a) a Ziegler-Natta catalyst (ZN-C2) 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; b) optionally a co-catalyst (Co), and c) optionally an external donor (ED).

10. The nonwoven fabric (NF) according to claim 9, 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; b) the molar-ratio of co-catalyst (Co) to external donor (ED) [Co/ED] is 5 to 45.

11. A method of producing the nonwoven fabric of claim 1: a) producing the first spunbonded layer (S1) by depositing spunbonded fibers (SBF) through a spinneret, b) optionally producing at least one further spunbonded layer (S) by depositing spunbonded fibers (SBF) on the first spunbonded layer (S1) obtained in step a) through at least one further spinneret, thereby obtaining a multilayered structure comprising two or more, like two or three spunbonded layers (S) in sequence, c) producing the first melt blown layer (M1) by depositing melt blown fibers (MBF) on the first spunbonded layer (S1) obtained in step a) or on the outermost spunbonded layer (S) obtained in step b) through an extruder, thereby obtaining a multilayered structure comprising one or more, like one, two or three spunbonded layer(s) (S) and a melt blown layer (M) in sequence, d) optionally producing at least one further melt blown layer (M) by depositing melt blown fibers (MBF) on the first melt blown layer (M1) obtained in step c) through at least one further extruder, thereby obtaining a multilayered structure comprising one or more, like one, two or three spunbonded layer(s) (S) and two or more, like two or three melt blown layer(s) (M) in sequence, e) producing the second spunbonded layer (S2) by depositing spunbonded fibers (SBF) through a spinneret on the first melt blown layer (M1) obtained in step c) or on the outermost melt blown layer (M) obtained in step d), thereby obtaining a multilayered structure comprising one or more, like one, two or three spunbonded layer(s) (S), one or more, like one, two or three melt blown layer(s) (M), and one spunbonded layer (S) in sequence, and f) optionally producing at least one further spunbonded layer (S) by depositing spunbonded fibers (SBF) on the second spunbonded layer (S2) obtained in step e) through at least one further spinneret, thereby obtaining a multilayered structure comprising one or more, like one, two or three spunbonded layer(s) (S), one or more, like one, two or three melt blown layer(s) (M), and two or more, like one, two or three spunbonded layer(s) (S) in sequence.

12. Article, comprising the nonwoven fabric (NF) according to claim 1.

Description

EXAMPLES

A. Measuring Methods

[0335] 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.

[0336] Quantification of Microstructure by NMR Spectroscopy

[0337] Quantitative nuclear-magnetic resonance (NMR) spectroscopy was used to quantify the isotacticity and regio-regularity of the propylene homopolymers.

[0338] 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.

[0339] 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.

[0340] Quantitative .sup.13C {.sup.1H} NMR spectra were processed, integrated and relevant quantitative properties determined from the integrals using proprietary computer programs. For propylene homopolymers all chemical shifts are internally referenced to the methyl isotactic pentad (mmmm) at 21.85 ppm.

[0341] 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.

[0342] 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).

[0343] 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.

[0344] 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)

[0345] 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).

[0346] 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

[0347] 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

[0348] 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

[0349] 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)

[0350] MFR.sub.2 (230 C.) is measured according to ISO 1133 (230 C., 2.16 kg load)

[0351] Number Average Molecular Weight (M.sub.n), Weight Average Molecular Weight (M.sub.w) and Molecular Weight Distribution (MWD)

[0352] Molecular weight averages (Mw, Mn), and the molecular weight distribution (MWD), i.e. the Mw/Mn (wherein Mn is the number average molecular weight and Mw is the weight average molecular weight), were determined by Gel Permeation

[0353] 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 {umlaut over ({acute over (.Math.)})}. 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 5.0-9.0 mg of polymer in 8 mL (at 160 C.) of stabilized TCB (same as mobile phase) for 2.5 hours for PP or 3 hours for PE at max. 160 C. under continuous gentle shaking in the autosampler of the GPC instrument.

[0354] The Xylene Soluble Fraction at Room Temperature (XS, wt.-%):

[0355] The amount of the polymer soluble in xylene is determined at 25 C. according to ISO 16152; 5.sup.th edition; 2005-07-01.

[0356] DSC Analysis, Melting Temperature (T.sub.m) and Heat of Fusion (H.sub.f), Crystallization Temperature (T.sub.c) and Heat of Crystallization (H.sub.c):

[0357] 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 heat of crystallization (H.sub.c) are determined from the cooling step, while melting temperature (T.sub.m) and heat of fusion (H.sub.f) are determined from the second heating step.

[0358] The glass transition temperature Tg is determined by dynamic mechanical analysis according to ISO 6721-7. The measurements are done in torsion mode on compression moulded samples (40101 mm.sup.3) between 100 C. and +150 C. with a heating rate of 2 C./min and a frequency of 1 Hz.

[0359] The tensile modulus was measured according to ISO 527-2 (cross head speed=1 mm/min; test speed 50 mm/min at 23 C.) using injection molded specimens as described in EN ISO 1873-2 (dog bone shape, 4 mm thickness). The measurement is done after 96 h conditioning time of the specimen.

[0360] Grammage of the Web

[0361] The unit weight (grammage) of the webs in g/m.sup.2 was determined in accordance with ISO 536:1995.

[0362] Average Fibre Diameter in the Web

[0363] 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.

[0364] Hydrohead

[0365] The hydrohead or water resistance as determined by a hydrostatic pressure test is determined according to the WSP (wordwide 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.

[0366] Air Permeability

[0367] The air permeability was determined in accordance with DIN ISO 9237.

B. Examples

[0368] The catalyst used in the polymerization process for the propylene homopolymer (PP2) for the spunbonded layer (S) of the inventive example (IE) was prepared as follows:

[0369] Used Chemicals:

[0370] 20% solution in toluene of butyl ethyl magnesium (Mg(Bu)(Et), BEM), provided by Chemtura

[0371] 2-ethylhexanol, provided by Amphochem

[0372] 3-Butoxy-2-propanol(DOWANOL PnB), provided by Dow

[0373] bis(2-ethylhexyl)citraconate, provided by SynphaBase

[0374] TiCl.sub.4, provided by Millenium Chemicals

[0375] Toluene, provided by Aspokem

[0376] Viscoplex 1-254, provided by Evonik

[0377] Heptane, provided by Chevron

[0378] Preparation of a Mg Alkoxy Compound

[0379] 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).

[0380] Preparation of Solid Catalyst Component

[0381] 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.

[0382] The thus obtained catalyst was used along with triethyl-aluminium (TEAL) as co-catalyst and dicyclopentyl dimethoxy silane (D-Donor) as donor for example IE1 and cyclohexylmethyl dimethoxy silane (C-Donor) as donor for example IE2, respectively.

[0383] The catalyst used in the polymerization process for the propylene homopolymer (PP1) for the melt blown layer (M) of the inventive examples (IE3) is the commercial catalyst ZN180M by Lyondell Basell used along with cyclohexylmethyl dimethoxy silane (C-Donor) as donor.

[0384] The aluminium to donor ratio, the aluminium to titanium ratio and the polymerization conditions are indicated in table 1.

TABLE-US-00001 TABLE 1 Preparation of base polymer PP1 (IE3) and PP2 (IE1, IE2) IE1 IE2 IE3 Prepolymerization TEAL/Ti [mol/mol] 102 100 100 TEAL/donor [mol/mol] 6 8 10 Temperature [ C.] 30 30 20 res.time [h] 0.3 0.3 0.3 Donor [] D C C Loop Temperature [ C.] 80 70 70 Pressure [kPa] 5500 5500 5500 Split [%] 60 100 100 H2/C3 ratio [mol/kmol] 0.5 0.7 4 C2/C3 [mol/kmol] 1.2 0 0 MFR.sub.2 [g/10 min] 2.8 2.7 80 XCS [wt.-%] 0.3 3.4 2.6 GPR 1 Temperature [ C.] 80 Pressure [kPa] 2100 Split [%] 40 H2/C3 ratio [mol/kmol] 8 C2/C3 ratio mol/kmol] 0.4 Properties of final base polymer MFR.sub.2 [g/10 min] 2.3 2.7 81 XCS [wt.-%] 3.1 3.5 2.6 C2 [wt.-%] 0.3 0 0 Mw [kg/mol] 328 310 139,500 MWD [] 8 6.5 6.7 Tm [ C.] 160 162 163 Tg [ C.] 0.5 0 0.1

[0385] As comparative example CE1 for the spunbonded layer (S), HG455FB has been used which is a commercial grade form Borealis having a MFR of 27 g/10 min. The details are listed in Table 2.

[0386] As comparative example CE2 for the melt blown layer (M), HL508FB has been used which is a commercial grade from Borealis having a MFR of 800 g/10 min Basic properties are listed in Table 2.

[0387] The polymers IE1, IE2, IE3, CE1 and CE2 have 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).

[0388] In a second step the propylene homopolymers IE1, IE2, IE3, CE1 and CE2 have 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. The properties of the propylene homopolymers after visbreaking are summarized in table 2.

TABLE-US-00002 TABLE 2 Properties of the inventive and comparative examples after visbreaking Spunbonded (S) Melt blown (M) IE1 IE2 CE1 IE3 CE2 Isotacticity(mmmm) [%] n.a. 92.1 93.7 95.3 94.1 C2 content [wt.-%] 0.3 0 0 0 0 MFR final [g/10 min] 27 27 27 800 800 MWD [] 4.7 4.4 4.3 4 4.2 2,1 regio defects [%] n.d. n.d. n.d. n.d. n.d. Tg [ C.] 0.3 0 0 1 2 Tm [ C.] 162 161 164 162 160 n.d. = not detected n.a. = not applicable

TABLE-US-00003 TABLE 3 Processing conditions for the production and properties of the nonwoven fabrics Example A B C D S-Extruder 1 Material [] IE1 IE1 IE1 CE1 Melt temperature [ C.] 248 248 248 251 Process air temperature [ C.] 20 20 20 20 Pressure [Pa] 4000 4000 4000 4100 Throughput [kg/h] 221 221 221 224 Line speed [m/min] 600 600 600 600 M-Extruder 1 Material [] IE3 IE3 IE3 CE2 DCD [mm] 110 130 130 130 Melt temperature dietip [ C.] 247 247 246 254 Melt temperature [ C.] 292 292 304 308 spinpump Secondary air [ C.] 33 33 33 33 temperature Secondary air blower [rpm] 1800 1800 1800 2000 Process air temperature [ C.] 270 270 270 280 Process air volume [Nm.sup.3/h] 1100 1100 1100 1100 Throughput [kg/h] 43 43 43 44 M-Extruder 2 Material [] IE3 IE3 IE3 CE2 DCD [mm] 110 130 130 130 Melt temperature dietip [ C.] 295 295 265 260 Melt temperature [ C.] 263 263 307 311 spinpump Process air temperature [ C.] 270 270 270 280 Process air volume [Nm.sup.3/h] 1050 1050 1050 1100 Throughput [kg/h] 47 47 47 47 S-Extruder 2 Material [] IE1 IE1 IE1 CE1 Melt temperature [ C.] 250 250 250 249 Process air temperature [ C.] 20 20 20 20 Pressure [Pa] 4000 4000 4000 4000 Throughput [kg/h] 220 220 220 221 Line speed [m/min] 600 600 600 600 Web performance CD elongation [%] 68 nd 75 69 MD elongation [%] 68 nd 75 53 CD tensile strength [N/5 17 nd 15 13 cm] MD tensile strength [N/5 29 nd 29 31 cm] Air permeability [mm/s] 2412 nd 2356 nd Hydrohead [mbar] 20.0 18.1 20.1 16.3 Fabric weight [g/m.sup.2] 11 + 2 11 + 2 11 + 2 11 + 2