MELT BLOWN WEB WITH GOOD WATER BARRIER PROPERTIES

Abstract

Melt-blown fiber comprising two polypropylenes which differ in their molecular weight.

Claims

1. A melt blown fiber comprising a polypropylene composition comprising: (a) a first polypropylene having a melt flow rate MFR.sub.2 (230 C.) measured according to ISO 1133 in the range of 1,500 to 10,000 g/10 min; and (b) a second polypropylene, wherein the first polypropylene has a higher melt flow rate than the second polypropylene, wherein the ratio of the melt flow rate MFR.sub.2 measured according to ISO 1133 of the mixture consisting of the first polypropylene and the second polypropylene to the melt flow rate MFR.sub.2 (230 C.) measured according to ISO 1133 of the first polypropylene is in the range of 0.08 to 0.62, and wherein the amount of the first polypropylene and the second polypropylene together makes up at least 80 wt.-% of the melt blow fiber.

2. The melt blown fiber according to claim 1, wherein the first polypropylene has a weight average molecular weight Mw in the range of 35 to 75 kg/mol and/or a melt flow rate MFR.sub.2 (230 C.) measured according to ISO 1133 of at least 1,000 g/10 min.

3. The melt blown fiber according to claim 1, wherein the mixture has a weight average molecular weight Mw in the range of 50 to 110 kg/mol.

4. The melt blown fiber according to claim 1, wherein the polypropylene composition has: (a) a weight average molecular weight Mw in the range of 50 to 110 kg/mol; and/or (b) a melt flow rate MFR.sub.2 (230 C.) measured according to ISO 1133 of at least 650 g/10 min.

5. The melt blown fiber according to claim 1, wherein the amount of the first polypropylene and the second polypropylene together makes up at least 80 wt.-% of the polypropylene composition.

6. The melt blown fiber according to claim 1, wherein the amount of the polypropylene composition makes up at least 80 wt.-% of the melt blow fiber.

7. The melt blown fiber according to claim 1, wherein the weight ratio between the first polypropylene and the second polypropylene is in the range of 0.05 to 1.90.

8. The melt blown fiber according to claim 1, wherein the ratio of the weight average molecular weight Mw of the mixture to the weight average molecular weight Mw of the first polypropylene is in the range of 0.7 to 3.1.

9. The melt blown fiber according to claim 1, wherein: (a) the mixture and/or the polypropylene composition has/have a molecular weight distribution (Mw/Mn) in the range of 2.0 to 10.0; and/or (b) the first polypropylene has a molecular weight distribution (Mw/Mn) in the range of 2.0 to 8.0.

10. The melt blown fiber according to claim 1, wherein the mixture and/or the polypropylene composition has/have: (a) a comonomer content in the range of 0.1 to 6.0 wt-%; and/or (b) a melting temperature Tm of at least 120 C.

11. The melt blown fiber according to claim 1, wherein the polypropylene composition has a xylene cold soluble fraction in the range of 1.0 to 10.0 wt.-%.

12. The melt blown fiber according to claim 1, the preceding claims, wherein the weight average molecular weight Mw of the second polypropylene is higher than the weight average molecular weight Mw of the first polypropylene, and wherein the weight average molecular weight Mw of the second polypropylene is in the range of 90 to 215 kg/mol.

13. The melt blown fiber according to claim 1, the preceding claims, wherein the second polypropylene has a melt flow rate MFR.sub.2 (230 C.) measured according to ISO 1133 in the range of 50 to 650 g/10 min and/or a comonomer content of more than 2.0 to 8.0 wt.-%.

14. The melt blown fiber according to claim 1, wherein the first polypropylene has: (a) a comonomer content of at most 3.0 wt.-%; and/or (b) a xylene cold soluble fraction in the range of 1.0 to 5.0 wt.-%.

15. The melt blown fiber according to claim 1, wherein the fibers have an average diameter of 0.3 to 5.0 m.

16. A melt-blown web comprising melt blown fibers each comprising: (a) a first polypropylene having a melt flow rate MFR.sub.2 (230 C.) measured according to ISO 1133 in the range of 1,500 to 10,000 g/10 min; and (b) a second polypropylene, wherein the first polypropylene has a higher melt flow rate than the second polypropylene, wherein the ratio of the melt flow rate MFR.sub.2 measured according to ISO 1133 of the mixture consisting of the first polypropylene and the second polypropylene to the melt flow rate MFR.sub.2 (230 C.) measured according to ISO 1133 of the first polypropylene is in the range of 0.08 to 0.62, and wherein the amount of the first polypropylene and the second polypropylene together makes up at least 80 wt.-% of the melt blow fiber.

17. The melt-blown web according to claim 16 having a weight per unit area of at most 120 g/m.sup.2.

18. An article comprising a melt-blown web, the melt blown web comprising melt blown fibers each comprising: (a) a first polypropylene having a melt flow rate MFR.sub.2 (230 C.) measured according to ISO 1133 in the range of 1,500 to 10,000 g/10 min; and (b) a second polypropylene, wherein the first polypropylene has a higher melt flow rate than the second polypropylene, wherein the ratio of the melt flow rate MFR.sub.2 measured according to ISO 1133 of the mixture consisting of the first polypropylene and the second polypropylene to the melt flow rate MFR.sub.2 (230 C.) measured according to ISO 1133 of the first polypropylene is in the range of 0.08 to 0.62, and wherein the amount of the first polypropylene and the second polypropylene together makes up at least 80 wt.-% of the melt blow fiber.

19. The article of claim 18, wherein the article is selected from the group consisting of: filtration medium, diaper, sanitary napkin, panty liner, incontinence product for adults, protective clothing, surgical drape, surgical gown, and surgical wear.

Description

EXAMPLES

1. Definitions/Measuring Methods

[0149] The following definitions of terms and determination methods apply for the above general description of the invention as well as to the below examples unless otherwise defined. Calculation of comonomer content of the second polypropylene (PP2):

[00001]$\begin{array}{cc}\frac{C\left(\mathrm{PP}\right)-w\left(\mathrm{PP}.Math..Math.1\right).Math.C\left(\mathrm{PP}.Math..Math.1\right)}{w\left(\mathrm{PP}.Math..Math.2\right)}=C\left(\mathrm{PP}.Math..Math.2\right)& \left(I\right)\end{array}$

wherein [0150] w(PP1) is the weight fraction [in wt.-%] of the first polypropylene (PP1), [0151] w(PP2) is the weight fraction [in wt.-%] of second polypropylene (PP2), [0152] C(PP1) is the comonomer content [in wt.-%] of the first polypropylene (PP1), [0153] C(PP) is the comonomer content [in wt.-%] of the polypropylene composition (PC)/the mixture (M), [0154] C(PP2) is the calculated comonomer content [in wt.-%] of the second polypropylene (PP2).

[0155] Calculation of the xylene cold soluble (XCS) content of the second polypropylene (PP2):

[00002]$\begin{array}{cc}\frac{\mathrm{XS}.Math..Math.\left(\mathrm{PP}\right)-w\left(\mathrm{PP}.Math..Math.1\right)\mathrm{XS}\left(\mathrm{PP}.Math..Math.1\right)}{w\left(\mathrm{PP}.Math..Math.2\right)}=\mathrm{XS}\left(\mathrm{PP}.Math..Math.2\right)& \left(\mathrm{II}\right)\end{array}$

wherein [0156] w(PP1) is the weight fraction [in wt.-%] of the first polypropylene (PP1), [0157] w(PP2) is the weight fraction [in wt.-%] of second polypropylene (PP2) [0158] XS(PP1) is the xylene cold soluble (XCS) content [in wt.-%] of the first polypropylene (PP1), [0159] XS(PP) is the xylene cold soluble (XCS) content [in wt.-%] of the polypropylene composition (PC)/the mixture (M), [0160] XS(PP2) is the calculated xylene cold soluble (XCS) content [in wt.-%] of the second polypropylene (PP2), respectively.

[0161] Calculation of melt flow rate MFR.sub.2 (230 C./2.16 kg) of the second propylene copolymer fraction (R-PP2):

[00003]$\begin{array}{cc}\mathrm{MFR}.Math..Math.\left(\mathrm{PP}.Math..Math.2\right)=.Math.{10}^{\left[\frac{\log \left(\mathrm{MFR}\left(\mathrm{PP}\right)\right)-w\left(\mathrm{PP}.Math..Math.1\right)\log \left(\mathrm{MFR}\left(\mathrm{PP}.Math..Math.1\right)\right)}{w\left(\mathrm{PP}.Math..Math.2\right)}\right]}& \left(\mathrm{III}\right)\end{array}$

wherein [0162] w(PP1) is the weight fraction [in wt.-%] of the first polypropylene (PP1), [0163] w(PP2) is the weight fraction [in wt.-%] of second polypropylene (PP2), [0164] MFR(PP1) is the melt flow rate MFR.sub.2 (230 C./2.16 kg) [in g/10 min] of first polypropylene (PP1), [0165] MFR(PP) is the melt flow rate MFR.sub.2 (230 C./2.16 kg) [in g/10 min] of the polypropylene composition (PC)/the mixture (M), [0166] MFR(PP2) is the calculated melt flow rate MFR.sub.2 (230 C./2.16 kg) [in g/10 min] of the second polypropylene (PP2).

Quantification of Microstructure by NMR Spectroscopy

[0167] Quantitative nuclear-magnetic resonance (NMR) spectroscopy was used to quantify the comonomer content of the polymers. 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. Approximately 200 mg of material was dissolved in 3 ml of 1,2-tetrachloroethane-d.sub.2 (TCE-d2) along with chromium-(III)-acetylacetonate (Cr(acac).sub.3) resulting in a 65 mM solution of relaxation agent in solvent (Singh, G., Kothari, A., Gupta, V., Polymer Testing 28 5 (2009), 475). 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 and quantitatively needed for accurate ethylene content quantification. Standard single-pulse excitation was employed without NOE, using an optimised tip angle, 1 s recycle delay and a 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, 1128). A total of 6144 (6 k) transients were acquired per spectra.

[0168] Quantitative .sup.13C {.sup.1H} NMR spectra were processed, integrated and relevant quantitative properties determined from the integrals using proprietary computer programs. All chemical shifts were indirectly referenced to the central methylene group of the ethylene block (EEE) at 30.00 ppm using the chemical shift of the solvent. This approach allowed comparable referencing even when this structural unit was not present. Characteristic signals corresponding to the incorporation of ethylene were observed Cheng, H. N., Macromolecules 17 (1984), 1950).

[0169] With characteristic signals corresponding to 2,1 erythro regio defects observed (as described in L. Resconi, L. Cavallo, A. Fait, F. Piemontesi, Chem. Rev. 2000, 100 (4), 1253, in Cheng, H. N., Macromolecules 1984, 17, 1950, and in W-J. Wang and S. Zhu, Macromolecules 2000, 33 1157) the correction for the influence of the regio defects on determined properties was required. Characteristic signals corresponding to other types of regio defects were not observed.

[0170] The comonomer fraction was quantified using the method of Wang et. al. (Wang, W-J., Zhu, S., Macromolecules 33 (2000), 1157) through integration of multiple signals across the whole spectral region in the .sup.13C {.sup.1H} spectra. This method was chosen for its robust nature and ability to account for the presence of regio-defects when needed. Integral regions were slightly adjusted to increase applicability across the whole range of encountered comonomer contents.

[0171] For systems where only isolated ethylene in PPEPP sequences was observed the method of Wang et. al. was modified to reduce the influence of non-zero integrals of sites that are known to not be present. This approach reduced the overestimation of ethylene content for such systems and was achieved by reduction of the number of sites used to determine the absolute ethylene content to:

E=0.5(S+S+S+0.5(S+S))

[0172] Through the use of this set of sites the corresponding integral equation becomes:

E=0.5(I.sub.H+I.sub.G+0.5(I.sub.C+I.sub.D))

using the same notation used in the article of Wang et. al. (Wang, W-J., Zhu, S., Macromolecules 33 (2000), 1157). Equations used for absolute propylene content were not modified.

[0173] The mole percent comonomer incorporation was calculated from the mole fraction:

E[mol %]=100*fE

[0174] The weight percent comonomer incorporation was calculated from the mole fraction:

E[wt %]=100*(fE*28.06)/((fE*28.06)+((1fE)*42.08))

[0175] The comonomer sequence distribution at the triad level was determined using the analysis method of Kakugo et al. (Kakugo, M., Naito, Y., Mizunuma, K., Miyatake, T. Macromolecules 15 (1982) 1150). This method was chosen for its robust nature and integration regions slightly adjusted to increase applicability to a wider range of comonomer contents.

[0176] MFR.sub.2 (230 C./2.16 kg) is measured according to ISO 1133 at 230 C. and 2.16 kg load.

[0177] Zero shear viscosity (.sub.0) Dynamic rheological measurements were carried out with Rheometrics RDA-II QC on compression molded samples under nitrogen atmosphere at 200 C. using 25 mmdiameter plate and plate geometry. The oscillatory shear experiments were done within the linear viscoelastic range of strain at frequencies from 0.01 to 500 rad/s. (1506721-1)

[0178] The values of storage modulus (G), loss modulus (G), complex modulus (G*) and complex viscosity (*) were obtained as a function of frequency ().

[0179] The Zero shear viscosity (.sub.0) was calculated using complex fluidity defined as the reciprocal of complex viscosity. Its real and imaginary part are thus defined by

f()=()/[().sup.2+().sup.2] and

f()=()/[().sup.2+().sup.2]

[0180] From the following equations

=G/ and =G/

f()=G()*/[G().sup.2+G().sup.2]

f()=G()*/[G().sup.2+G().sup.2]

[0181] Number Average Molecular Weight (M.sub.n), Weight Average Molecular Weight (M.sub.w) and Molecular Weight Distribution (MWD)

[0182] 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 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 l. 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.

[0183] Xylene cold soluble fraction (XCS wt.-%): Content of xylene cold solubles (XCS) is determined at 25 C. according ISO 16152; first edition; 2005-07-01.

[0184] 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): 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. The crystallinity is calculated from the melting enthalpy by assuming an Hm-value of 209 J/g for a fully crystalline polypropylene (see Brandrup, J., Immergut, E. H., Eds. Polymer Handbook, 3rd ed. Wiley, New York, 1989; Chapter 3).

[0185] 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.

Grammage of the Web

[0186] The unit weight (grammage) of the webs in g/m.sup.2 was determined in accordance with EN 29073-1 (1992) Test methods for nonwovensDetermination of mass per unit area

Average Fibre Diameter in the Web

[0187] 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.

Hydrohead

[0188] 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.

Air Permeability

[0189] The air permeability was determined in accordance with DIN ISO 9237.

Examples

[0190] A metallocene catalyst as described in example 1 of EP 1741725 A1 was used for the preparation of the propylene polymers of both comparative and inventive examples. The polymerization was carried out as detailed below.

[0191] Comparative example 4 (CE4) used for MB web production likewise is the commercial product HL512FB of Borealis, based on a Ziegler-Natta type catalyst and visbreaking. It has an MFR (230 C./2.16 kg) of 1200 g/10 min, an Mw of 78 kg/mol, an MWD of 3.8 and a Tm of 158 C.

TABLE-US-00001 TABLE 1 Preparation of the Inventive and Comparative Examples IE1 CE1 CE2 CE3 Prepolymerization Temperature [ C.] 30 30 30 30 Catalyst feed [g/h] 2.79 1.90 3.76 3.92 res. time [h] 0.36 0.36 0.36 0.36 Loop (PP1) Temperature [ C.] 70 70 70 70 Pressure [kPa] 5258 5414 5321 5338 Split [%] 52 46 41 42 H2/C3 ratio [mol/kmol] 0.59 0.34 0.31 0.32 C2/C3 ratio [mol/kmol] 4.8 20.0 0.0 0.0 MFR.sub.2 [g/10 min] 5815 1490 1200 1230 XCS [wt.-%] 2.5 3.8 1.6 1.6 C2 content [wt-%] 0.94 3.30 0 0 Mw [kg/mol] 47 73 78 76 MWD [] 2.6 2.7 2.8 2.7 GPR 1 (PP2)* Temperature [ C.] 80 80 80 80 Pressure [kPa] 2050 2663 2370 2063 Split [%] 46.3 54.0 58.8 57.7 H2/C3 ratio [mol/kmol] 9.2 9.1 7.3 13.5 C2/C3 ratio [mol/kmol] 65 43 0 84 MFR.sub.2* [g/10 min] 157 667 1440 1004 Mw* [kg/mol] 150 94 73 83 XCS* [wt.-%] 2.8 2.2 1.9 6.0 C2 content* [wt-%] 4.45 3.00 0 4.31 Final Product C2 content [wt-%] 2.63 3.10 0 2.50 XCS [wt.-%] 2.8 3.9 1.7 4.2 Tm [ C.] 140 134 150 154 Tc [ C.] 106 101 116 110 MFR.sub.2 [g/10 min] 1028 965 1330 1093 .sub.0(200 C.) [Pa .Math. s] 17 17 12.2 15.1 Mw [kg/mol] 65 65 61 63 MWD [] 3.2 2.8 3.0 2.8 *MFR2, Mw, XCS and C2 content are calculated from Loop and Final product!

TABLE-US-00002 TABLE 2 Properties the melt blown web (MBW) at die-to-collector distance (DCD) of 200 mm (n.p.spinning not possible) EX1 CE1 CE4 at melt temperature 250 C. Fiber diameter [m] 1.1 1.4 1.2 Web weight [g/m.sup.2] 9.6 9.1 8.9 Hydrohead [cm 75.2 40.9 68.7 H.sub.2O] Air permeability [mm/s] 762 1656 974 at melt temperature 270 C. Fiber diameter [m] 0.9 1.2 n.p. Web weight [g/m.sup.2] 9.1 9.1 Hydrohead [cm 98.4 65.7 H.sub.2O] Air permeability [mm/s] 664 652 at melt temperature 290 C. Fiber diameter [m] 0.8 1.1 n.p. Web weight [g/m.sup.2] 9.1 9.1 Hydrohead [cm 106.0 79.0 H.sub.2O] Air permeability [mm/s] 657 656 at melt temperature 310 C. Fiber diameter [m] 0.7 0.9 n.p. Web weight [g/m.sup.2] 9.1 9.1 Hydrohead [cm 131.4 98.6 H.sub.2O] Air permeability [mm/s] 478 480