HIGH QUALITY MELT-BLOWN WEBS WITH IMPROVED BARRIER PROPERTIES

Abstract

High quality melt-blown webs having improved barrier properties (3rd drop, cm H2O resp. mbar) and a widened process window. The melt-blown webs show a specific chain structure.

Claims

1: Melt-blown webs comprising melt-blown fibers made of at least 80 wt % of a polypropylene composition comprising: (A) a polypropylene homo- or copolymer with a comonomer content of up to 12.0 wt %, (B) optionally a polymeric nucleating agent, wherein the melt-blown webs show an integral ratio [Rv], being defined as ratio of the integral value specifying the area under the peak with the chemical shift at 4.77 ppm of a .sup.1H NMR spectrum to the integral value specifying the area under the peak with the chemical shift at 4.70 ppm .sup.1H NMR spectrum, of 0.95 to 1.40, whereby the .sup.1H NMR spectrum was determined by solution-state .sup.1H-NMR spectroscopy.

2: Melt-blown webs according to claim 1, having a total unsaturation, being defined as sum of terminal vinylidene and internal vinylidene, of more than 28/100000 C atoms determined by liquid-state proton-NMR spectroscopy.

3: Melt-blown webs according to claim 1, wherein the polypropylene composition has been prepared by a controlled radical polymerization process or by visbreaking using a carbon based radical generator, a bis azo compound, a stable nitroxyl compound or a sterically hindered NO-acyl compound as radical initiator.

4: Melt-blown webs according to claim 3, wherein the polypropylene composition has been visbroken with at least one compound (C) being capable of thermally decomposing into carbon-based free radicals of formula (I) or (II) by breaking at least one single bond: ##STR00005## wherein in these formulas each of R.sub.1, R.sub.2 and R.sub.3, respectively R.sub.4, R.sub.5 and R.sub.6 can be independently selected from hydrogen, substituted or unsubstituted straight chain, branched or cyclic saturated or mono-unsaturated hydrocarbons with 1 to 12 C-atoms, substituted or unsubstituted aromatic hydrocarbons with 5 to 12 C-atoms or carboxylate groups COOX, with X being a C.sub.1-C.sub.6-alkyl group, whereby at least one of R.sub.1, R.sub.2 and R.sub.3, respectively R.sub.4, R.sub.5 and R.sub.6 is a substituted or unsubstituted aromatic hydrocarbon with 5 to 12 C-atoms, wherein the amount of compound(s) (C) being added to the polypropylene composition for visbreaking is in the range of 0.01 to 10 wt % based on the polypropylene composition.

5: Melt-blown webs according to claim 3, wherein the carbon-based free radicals of formula (I) or (II) being generated from one or more compounds (C) of the formula (III): ##STR00006## wherein each of R.sub.1, R.sub.3, R.sub.4 and R.sub.6 independently is selected from the group consisting of hydrogen, substituted and unsubstituted straight, branched, and cyclic, hydrocarbons with 1 to 12 C-atoms and substituted and unsubstituted aromatic hydrocarbons with 5 to 12 C-atoms, and each of R.sub.2 and R.sub.5 independently is selected from the group consisting of substituted and unsubstituted straight, branched, and cyclic hydrocarbons with 1 to 12 C-atoms and substituted and unsubstituted aromatic hydrocarbons with 5 to 12 C-atoms and wherein at least one of R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5 and R.sub.6 is a substituted or unsubstituted aromatic hydrocarbon with 5 to 12 C-atoms.

6: Melt-blown webs according to claim 1, wherein the melt-blown webs have 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 290 C. melt temperature) having a weight per unit area of 9.51.0 g/m2, of at least 60 mbar, and of a melt-blown web (produced with 300 C. melt temperature) having a weight per unit area of 9.51.0 g/m2, of at least 65 mbar.

7: 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 surgical wear in general.

Description

EXPERIMENTAL PART

A. Measuring Methods

[0195] 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.

[0196] Quantification of Microstructure by NMR Spectroscopy

[0197] Quantitative nuclear-magnetic resonance (NMR) spectroscopy was used to quantify the content of unsaturated groups present in the polymers.

[0198] Quantitative .sup.1H NMR spectra recorded in the solution-state using a Bruker Advance III 400 NMR spectrometer operating at 400.15 MHz. All spectra were recorded using a .sup.13C optimised 10 mm selective excitation probehead at 125 C. using nitrogen gas for all pneumatics. Approximately 250 mg of material was dissolved in 1,2-tetrachloroethane-d.sub.2 (TCE-d.sub.2) using approximately 3 mg of Hostanox 03 (CAS 32509-66-3) as stabiliser. Standard single-pulse excitation was employed utilising a 30 degree pulse, a relaxation delay of 5 s and 10 Hz sample rotation. A total of 512 transients were acquired per spectra using 4 dummy scans. This setup was chosen primarily for the high resolution needed for unsaturation quantification and stability of the unsaturated groups {re98, ka04, re00}. All chemical shifts were indirectly referenced to TMS at 0.00 ppm using the signal resulting from the residual protonated solvent at 5.95 ppm.

[0199] Characteristic signals corresponding to the presence of terminal vinylidene groups (CH.sub.2C(CH.sub.3)R) were observed and the amount quantified using the integral of one of the equivalent two terminal CH.sub.2 protons (H.sub.t1 and H.sub.t2) H.sub.t2 at 4.70 ppm accounting for the number of reporting sites per functional group:

Ntermv=IH.sub.t2

[0200] When characteristic signals corresponding to the presence of internal vinylidene groups (RC(CH.sub.2)R) were observed, then the amount quantified using the integral of the two equivalent internal CH.sub.2 protons H.sub.i at 4.77 ppm and subtract the integral of H.sub.t2 at 4.70 ppm (the second equivalent proton from terminal vinylidene H.sub.t1 resonates as well at 4.77 ppm; compensation performed by subtracting IH.sub.t2) accounting for the number of reporting sites per functional group:

Nintv=(IH.sub.iIH.sub.t2)/2

[0201] When characteristic signals corresponding to the presence of internal vinylidene groups (RC(CH.sub.2)R), were not visually observed, then these groups were not counted and the parameter Nintv was not used.

[0202] The Hostanox 03 stabliser was quantified using the integral of multiplet from the aromatic protons (A) at 6.92, 6.91, 6.69 and at 6.89 ppm and accounting for the number of reporting sites per molecule:

H=IA/4

[0203] As is typical for unsaturation quantification in polyolefins the amount of unsaturation was determined with respect to total carbon atoms, even though quantified by .sup.1H NMR spectroscopy. This allows direct comparison to other microstructure quantities derived directly from .sup.13C NMR spectroscopy.

[0204] The total amount of carbon atoms was calculated from integral of the bulk aliphatic signal between 2.60 and 0.00 ppm with compensation for the methyl signals from the stabiliser and carbon atoms relating to unsaturated functionality not included by this region:

NCtotal=(Ibulk42*H)/2+2*Ntermv+2*Nintv

[0205] The content of unsaturated groups (U) was calculated as the number of unsaturated groups in the polymer per hundred thousand total carbons (100 kCHn):

U=100000*N/NCtotal

[0206] The total amount of unsaturated group was calculated as the sum of the individual observed unsaturated groups and thus also reported with respect per hundred thousand total carbons:

Utotal=Utermv+Uintv

[0207] The ratio of both H.sub.t1 from terminal vinylidene and H.sub.i from internal vinylidene resonating at 4.77 ppm to H.sub.t2 from terminal vinylidene at 4.70 ppm groups (Rv) is reported as the ratio of the given signals:

[Rv]=IH.sub.t1H.sub.i/IH.sub.t2

REFERENCES

[0208] re98 [0209] L. Resconi, F. Piemontesi, I. Camurati, O. Sudmeijer, J. Am. Chem. Soc. 1998, 120, 2308-2321

[0210] ka04 [0211] N. Kawahara, S. Kojoh, Y. Toda, A. Mizuno, N. Kashiwa, Polymer 45 (2004), 2883-2888

[0212] re00 [0213] L. Resconi, L. Cavallo, A. Fait, F. Piemontesi, Chem. Rev. 2000, 100, 1253-1345

[0214] 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.

[0215] 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.

[0216] DSC analysis, melting temperature (T.sub.m), melting enthalpy (H.sub.m), crystallization temperature (T) and crystallization enthalpy (H): 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 C.sub.2 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 (Tc) 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.

[0217] Number Average Molecular Weight (M.sub.n), Weight Average Molecular Weight (M.sub.w), (M.sub.w/M.sub.n=MWD) of Propylene Homopolymer

[0218] 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 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 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.

[0219] Grammage of the Web

[0220] The unit weight (grammage) of the webs in g/m.sup.2 was determined in accordance with ISO 536:1995.

[0221] Hydrohead

[0222] 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.

[0223] Air Permeability

[0224] 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.

B. Examples

[0225] The catalyst used in the polymerization process for the propylene homopolymer of the inventive example (IE-1) and (IE-2) was the commercial Avant ZN180M of LyondellBasell.

[0226] The catalyst was used together with donor C.

[0227] The aluminium to donor ratio, the aluminium to titanium ratio and the polymerization conditions are indicated in tables 1 and 2.

[0228] Polymerization was performed in a polypropylene (PP) pilot plant.

TABLE-US-00001 TABLE 1 Preparation of the propylene homopolymer IE-1 IE-1 TEAL/Ti [mol/mol] 170 TEAL/Donor [mol/mol] 10 Catalyst feed [g/h] 1.4 Loop (H-PP1) Time [h] 0.7 Temperature [ C.] 70 Pressure [kPa] 5500 MFR.sub.2 [g/10 min] 86 XCS [wt %] 2.5 H.sub.2/C3 ratio [mol/kmol] 3.8 amount [wt %] 62 GPR1 Time [h] 2.4 Temperature [ C.] 75 Pressure [kPa] 2131 MFR.sub.2 [g/10 min] 90 XCS [wt.-%] 2.4 H.sub.2/C3 ratio [mol/kmol] 58 amount [wt.-%] 38

[0229] The propylene homopolymer was compounded by using a co-rotating twin-screw extruder at 200-230 C. with 1700 ppm of 2,3-Dimethyl-2,3-diphenylbutane (Pergasafe, sold by Pergan GmbH), 400 ppm calcium Stearate (CAS No. 1592-23-0) and 1000 ppm Irganox 1010 supplied by BASF AG, Germany (Pentaerythrityl-tetrakis(3-(3,5-di-tert.butyl-4-hydroxyphenyl)-propionate, CAS No. 6683-19-8).

TABLE-US-00002 TABLE 2 Preparation of the propylene homopolymer IE2: IE-2 TEAL/Ti [mol/mol] 170 TEAL/Donor [mol/mol] 10 Catalyst feed [g/h] 1.4 Loop (H-PP1) Time [h] 0.7 Temperature [ C.] 70 Pressure [kPa] 5500 MFR.sub.2 [g/10 min] 25 XCS [wt %] 2.3 H.sub.2/C3 ratio [mol/kmol] 2.2 amount [wt %] 60 GPR1 Time [h] 2.6 Temperature [ C.] 75 Pressure [kPa] 2131 MFR.sub.2 [g/10 min] 21 XCS [wt %] 2.1 H.sub.2/C3 ratio [mol/kmol] 18.5 amount [wt %] 40

[0230] The propylene homopolymer was compounded by using a co-rotating twin-screw extruder at 200-230 C. with 2200 ppm of 2,3-Dimethyl-2,3-diphenylbutane (Pergasafe, sold by Pergan GmbH), 400 ppm calcium Stearate (CAS No. 1592-23-0) and 1000 ppm Irganox 1010 supplied by BASF AG, Germany (Pentaerythrityl-tetrakis(3-(3,5-di-tert.butyl-4-hydroxyphenyl)-propionate, CAS No. 6683-19-8).

[0231] For Comparative Example (CE-1) the commercial propylene homopolymer Borflow HL512FB (sold by Borealis) based on a Ziegler-Natta type catalyst having a MFR2 of 1200 g/10 min and being produced in a visbreaking process was used.

[0232] The polypropylene compositions of IE1, IE2 and CE1 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.

[0233] 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 Temperature DCD volume Throughput weight Example C. mm m.sup.3/h kg/h .Math. m g/m.sup.2 IE1-1 290 200 250 10 10.1 IE1-2 300 200 200 10 9.7 IE1-3 300 500 230 10 10.0 IE1-4 310 200 120 10 8.4 IE1-5 310 200 220 30 10.6 IE2-1 290 200 320 10 9.7 IE2-2 300 200 230 10 10.4 IE2-3 320 200 160 10 8.2 CE1-1 250 200 360 10 9.5 CE1-2 260 200 320 10 9.5 CE1-3 260 200 400 30 9.8

TABLE-US-00004 TABLE 4 Properties of the melt-blown webs Air perme- Hydrohead Shift 1 Shift 2 Exam- ability (3.sup.rd drop) 4.77 4.70 Ratio Utotal ple mm/s cm H.sub.2O* ppm ppm Rv /100000 C. IE1-1 785 92 100 99.0 1.01 31 IE1-2 680 102 100 103.7 0.96 38 IE1-3 805 79 100 103.1 0.97 40 IE1-4 370 131 100 103.3 0.97 46 IE1-5 1050 58 100 104.2 0.96 37 IE2-1 810 72 100 97.3 1.03 38 IE2-2 740 89 100 101.3 0.99 51 IE2-3 490 130 100 99.1 1.01 64 CE1-2 1060 71 100 70.5 1.42 25 CE1-1 905 21 100 56.1 1.78 26 CE1-3 1045 65 100 55.3 1.81 28

[0234] It can be seen from above that the higher the unsaturation level is, the better the barrier properties are. (see also FIG. 1)

[0235] It can be further seen that the higher the unsaturation level is, the higher melt temperature can be used for preparing the webs. (see FIG. 2)

[0236] FIG. 3 shows the NMR spectra of IE1-1 and CE1-1.