PHTHALATE-FREE PP HOMOPOLYMERS FOR MELTBLOWN FIBERS

Abstract

The present invention is directed to a new polypropylene composition comprising a propylene homopolymer, to a melt-blown fiber comprising the polypropylene composition, to a melt blown web comprising the melt blown fiber and/or the polypropylene composition, to an article comprising the melt blown fiber 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.

Claims

1-14. (canceled)

15. A polypropylene composition comprising a propylene homopolymer, the polypropylene composition and/or propylene homopolymer having a) a melt flow rate MFR.sub.2 (230 C./2.16 kg) measured according to ISO 1133 of 400 g/10 min, and b) a melting temperature Tm of 150 C., wherein the polypropylene composition and/or propylene homopolymer is free of phthalic acid esters as well as their respective decomposition products, and wherein the polypropylene composition and/or propylene homopolymer has/have been visbroken.

16. The polypropylene composition according to claim 15, wherein the polypropylene composition and/or propylene homopolymer has/have a) a melt flow rate MFR.sub.2 (230 C./2.16 kg) measured according to ISO 1133 in the range from 400 to 3,000 g/10 min, and/or b) a melting temperature Tm in the range from 150 to 200 C.

17. The polypropylene composition according to claim 15, 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.

18. The polypropylene composition according to claim 15, wherein the polypropylene composition and/or propylene homopolymer is/are free of phthalic compounds as well as their respective decomposition products.

19. The polypropylene composition according to claim 15, 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.

20. The polypropylene composition according to claim 15, wherein a) the propylene homopolymer is the only polymer within the polypropylene composition, and/or b) the polypropylene composition comprises at least 95.0 wt.-% of the propylene homopolymer.

21. The polypropylene composition according to claim 15, wherein the propylene homopolymer before visbreaking fulfills inequation (I)
VOC(MFR0.08)+201.0(I) wherein VOC is the volatile organic compound (VOC) value [in ppm] measured according to VDA 278:2002 of the propylene homopolymer before visbreaking; MFR is the melt flow rate MFR.sub.2 (230 C./2.16 kg) measured according to ISO 1133 of the propylene homopolymer before visbreaking.

22. The polypropylene composition according to claim 15, 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; b) optionally a co-catalyst (Co), and further c) optionally an external donor (ED).

23. The polypropylene composition according to claim 22, 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; and b) the molar-ratio of co-catalyst (Co) to external donor (ED) [Co/ED] is 5 to 45.

24. The polypropylene composition according to claim 15, wherein the propylene homopolymer is produced in a sequential polymerization process comprising at least two reactors (R1) and (R2), 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).

25. The polypropylene composition according to claim 16, 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.

26. The polypropylene composition according to claim 16, wherein the polypropylene composition and/or propylene homopolymer is/are free of phthalic compounds as well as their respective decomposition products.

27. The polypropylene composition according to claim 16, 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.

28. The polypropylene composition according to claim 16, wherein a) the propylene homopolymer is the only polymer within the polypropylene composition, and/or b) the polypropylene composition comprises at least 95.0 wt.-% of the propylene homopolymer.

29. A melt-blown fiber having an average diameter of not more than 5.0 m, said fiber comprising a polypropylene composition as defined in claim 15.

30. The melt-blown web comprising the melt blown fiber according to claim 29.

31. An article comprising a melt-blown fiber according to claim 29, wherein said 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.

32. A method 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, the method comprising utilizing the polypropylene composition of claim 15 in the preparation of the web, wherein the improvement is defined by inequation (III)
(PD-web)/(HH-web)0.88(III) 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.rd drop, cm.sup.2 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.

Description

EXAMPLES

A. Measuring Methods

[0162] 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

[0163] Quantitative nuclear-magnetic resonance (NMR) spectroscopy was used to quantify the isotacticity and regio-regularity of the propylene homopolymers.

[0164] 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.

[0165] 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.

[0166] Quantitative .sup.13C {.sup.1H} NMR spectra were processed, integrated and relevant quantitative properties determined from the integrals using proprietary computer programs.

[0167] For propylene homopolymers all chemical shifts are internally referenced to the methyl isotactic pentad (mmmm) at 21.85 ppm.

[0168] 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.

[0169] 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).

[0170] 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.

[0171] 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)

[0172] 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).

[0173] 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

[0174] 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

[0175] 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

[0176] 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)

[0177] MFR.sub.2 (230 C.) is measured according to ISO 1133 (230 C., 2.16 kg load)

[0178] 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.

[0179] 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.a) 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.

[0180] 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

[0181] The unit weight (grammage) of the webs in g/m.sup.2 was determined in accordance with ISO 536:1995.

Average Fibre Diameter in the Web

[0182] 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

[0183] 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

[0184] The air permeability was determined in accordance with DIN ISO 9237.

Filtration Efficiency

[0185] 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 an 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.

Total Volatiles

VOC

[0186] VOC was determined according to VDA 278:2002 from pellets or plates of 60602 mm.sup.3 prepared by injection molding in accordance with ISO 294-1:1996.

[0187] VOC according to VDA 278 is the sum of all high and medium volatile compounds. It is calculated as toluene equivalent (TE). VOC according to VDA 278 represents all organic compounds in the boiling point and elution range of up to C.sub.20 (n-eicosane).

B. Examples

[0188] The catalyst used in the polymerization process for the propylene homopolymer of the inventive example (IE) was prepared as follows:

Used Chemicals:

[0189] 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

[0190] 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

[0191] 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.

[0192] The thus obtained catalyst was used along with triethyl-aluminium (TEAL) as co-catalyst and cyclohexylmethyl dimethoxy silane (C-Donor) as donor.

[0193] 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 the inventive example IE IE Donor type C TEAL/Ti [mol/mol] 150 TEAL/Donor [mol/mol] 18.8 Loop (H-PP1) Time [h] 0.66 Temperature [ C.] 75 MFR.sub.2 [g/10 min] 77.0 XCS [wt.-%] 4.9 H.sub.2/C3 ratio [mol/kmol] 7.2 amount [wt.-%] 100 1 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

[0194] As comparative example CE, HL508 FB has been used. HL508FB is a commercial grade form Borealis having a MFR of 1 200 g/10 min and a melting temperature of 158 C. The catalyst used in the polymerization processes of CE was the catalyst Avant ZN L1 along with triethyl-aluminium (TEAL) as co-catalyst and cyclohexyl dimethoxy silane (C-donor) as donor.

[0195] The polymers IE and CE 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).

[0196] In a second step the propylene homopolymers IE and CE 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 as mentioned in table 2.

TABLE-US-00002 TABLE 2 Properties of the Examples H-PP MFR.sub.2 H-PP Final MFR.sub.2 Sample [g/10 min] [wt.-%] [g/10 min] IE 77 100 800 CE 80 100 800

[0197] The polypropylene compositions 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. The processing conditions for and properties of the melt-blown webs are indicated in tables 3 and 4.

TABLE-US-00003 TABLE 3 Processing conditions for the production of the melt-blown webs Melt Air Web Exam- Temperature DCD volume Throughput weight ple Polymer C. mm m.sup.3/h kg/h .Math. m g/m.sup.2 IE1 IE 250 500 470 10 8.8 IE2 IE 250 200 470 10 9.1 IE3 IE 250 200 550 30 9.8 IE4 IE 270 500 380 10 8.9 IE5 IE 270 200 310 10 9.1 IE6 IE 270 200 490 30 9.8 IE7 IE 290 500 280 10 8.3 IE8 IE 290 200 230 10 8.5 IE9 IE 290 200 380 30 9.8 CE1 CE 260 200 550 10 10 CE2 CE 260 500 500 10 10 CE3 CE 270 200 450 30 9.6 CE4 CE 280 500 420 30 9.6 CE5 CE 290 500 400 30 9.6 CE6 CE 290 200 350 30 9.6

TABLE-US-00004 TABLE 4 Properties of the melt-blown webs Air Pressure Quality Hydrohead Hydrohead permeability drop factor (1.sup.st drop) (3.sup.rd drop) Example Polymer mm/s Pa Efficiency % 100/Pa mbar mbar IE1 IE 1680 20.2 18.54 1.016 36.1 37.9 IE2 IE 1033 40.5 21.72 0.606 42.6 56.5 IE3 IE 1505 22.7 16.38 0.647 38.2 41.5 IE4 IE 1144 32.7 20.21 0.691 47.3 50.8 IE5 IE 811 51.8 25.18 0.561 74.4 81.5 IE6 IE 950 40.9 21.77 0.536 30.8 55.6 IE7 IE 799 52.2 30.47 0.639 52.7 69.6 IE8 IE 624 77.7 37.8 0.612 96.7 104.1 IE9 IE 675 67 26.22 0.455 61.7 85.2 CE1 CE 1060 37.5 20.54 0.612 43.4 52.2 CE2 CE 1850 16.6 13.04 0.84 25.5 29.9 CE3 CE 986 55 26.61 0.739 58.8 69.8 CE4 CE 1435 29.7 19.43 0.805 41.3 44.7 CE5 CE 1649 35.2 21.65 0.754 48.3 50.9 CE6 CE 718 69.2 34.09 0.695 72.5 87.6

[0198] 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.

[0199] 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.