Melt-Blown Webs Without Shots and With Improved Barrier Properties

Abstract

Melt-blown webs having no shots and improved barrier properties, whereby the melt-blown webs are made out of a so-called controlled rheology propylene (CR-PP), which was visbroken without any peroxide.

Claims

1. A method of preparing a melt-blown web which is free of shots, the method comprising blowing a molten polypropylene composition from an extruder die tip onto a conveyer or take-up screen, wherein the polypropylene composition comprises (A) a polypropylene polymer and (B) optionally a polymeric nucleating agent, wherein the polypropylene composition has (i) a melt flow rate MFR2 (230 C./2.16 kg) measured according to ISO 1133 of 20 to 5000 g/10 min and (ii) a melting temperature Tm between 130 C. and 170 C. and (iii) a molecular weight distribution (MWD)>2 and (iv) wherein the polypropylene composition has been visbroken without the use of peroxides.

2. The method of preparing a melt-blown web according to claim 1, wherein the polypropylene polymer is a propylene homopolymer.

3. The method of preparing a melt-blown web according to claim 1, wherein the polypropylene composition has been visbroken by using a hydroxylamine ester, a sulphur compound, or by purely thermal degradation.

4. The method of preparing a melt-blown web according to claim 3, wherein the polypropylene composition has been visbroken by using a hydroxylamine ester.

5. The method of preparing a melt-blown web according to claim 1, wherein the polypropylene composition is free of phthalic compounds as well as their respective decomposition products.

6. The method of preparing a melt-blown web according to claim 1, wherein the melt-blown web is characterized by the following ratios: (a) a molecular weight (Mw) ratio of Mw of the web to Mw of the polypropylene composition Mw(web)/Mw(PP)<1 and (b) a molecular weight distribution (MWD) ratio of MWD of the web to MWD of the polypropylene composition MWD(web)/MWD(PP)<1.

7. The method of preparing a melt-blown web according to claim 6, wherein the melt-blown web is characterized by the following ratios: (a) a molecular weight (Mw) ratio of Mw of the web to Mw of the polypropylene composition Mw(web)/Mw(PP) is 0.90, and (b) a molecular weight distribution (MWD) ratio of MWD of the web to MWD of the polypropylene composition MWD(web)/MWD(PP) is 0.95.

8. The method of preparing a melt-blown web according to claim 7, wherein the melt-blown web is characterized by the following ratios: (a) a molecular weight (Mw) ratio of Mw of the web to Mw of the polypropylene composition Mw(web)/Mw(PP) is <0.85, and (b) a molecular weight distribution (MWD) ratio of MWD of the web to MWD of the polypropylene composition MWD(web)/MWD(PP) is 0.90.

9. The method of preparing a melt-blown web according to claim 7, wherein the melt-blown web is characterized by the following ratios: (a) a molecular weight (Mw) ratio of Mw of the web to Mw of the polypropylene composition Mw(web)/Mw(PP) is 0.80, and (b) a molecular weight distribution (MWD) ratio of MWD of the web to MWD of the polypropylene composition MWD(web)/MWD(PP) is 0.85.

10. The method of preparing a melt-blown web according to claim 1, wherein the polypropylene polymer 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), b) optionally a co-catalyst (Co), and c) optionally an external donor (ED).

11. The method of preparing a melt-blown web according to claim 10, wherein the internal donor (ID) is selected from the group consisting of optionally substituted malonates, maleates, succinates, glutarates, cyclohexene-1,2-dicarboxylates, benzoates, derivatives thereof and mixtures thereof; and the molar ratio of co-catalyst (Co) to external donor (ED) [Co/ED] is 5 to 45.

12. The method of preparing a melt-blown web according to claim 10, wherein the Ziegler-Natta catalyst (ZN-C) is produced by a process comprising the steps of a) a.sub.1) providing a solution of at least a Group 2 metal alkoxy compound (Ax) being the reaction product of a Group 2 metal compound (MC) and a monohydric alcohol (A) comprising in addition to the hydroxyl moiety at least one ether moiety optionally in an organic liquid reaction medium; or a.sub.2) a solution of at least a Group 2 metal alkoxy compound (Ax) being the reaction product of a Group 2 metal compound (MC) and an alcohol mixture of the monohydric alcohol (A) and a monohydric alcohol (B) of formula ROH, optionally in an organic liquid reaction medium; or a.sub.3) providing a solution of a mixture of the Group 2 alkoxy compound (Ax) and a Group 2 metal alkoxy compound (Bx) being the reaction product of a Group 2 metal compound (MC) and the monohydric alcohol (B), optionally in an organic liquid reaction medium; or a.sub.4) providing a solution of Group 2 alkoxide of formula M(OR.sub.1).sub.n(OR.sub.2).sub.mX.sub.2-n-m or mixture of Group 2 alkoxides M(OR.sub.1).sub.n.Math.X.sub.2-n and M(OR.sub.2).sub.m.Math.X.sub.2-m, where M is Group 2 metal, X is halogen, R.sub.1 and R.sub.2 are different alkyl groups of C.sub.2 to C.sub.16 carbon atoms, and 0n<2, 0m<2 and n+m+(2nm)=2, provided that both n and m0, 0<n2 and 0<m2; and b) adding said solution from step a) lo at least one compound (TC) of a transition metal of Group 4 to 6 and c) obtaining the solid catalyst component particles, and adding a internal electron donor (ID), at any step prior to step c).

Description

B. EXAMPLES

[0290] The catalyst used in the polymerization process for the propylene homopolymer of the inventive example (IE-1) and the Comparative Example (CE-1) was prepared as follows:

[0291] Used Chemicals:

[0292] 20% solution in toluene of butyl ethyl magnesium (Mg(Bu)(Et), BEM), provided by Chemtura

[0293] 2-ethylhexanol, provided by Amphochem

[0294] 3-Butoxy-2-propanol-(DOWANOL PnB), provided by Dow

[0295] bis(2-ethylhexyl)citraconate, provided by SynphaBase

[0296] TiCl.sub.4, provided by Millenium Chemicals

[0297] Toluene, provided by Aspokem

[0298] Viscoplex 1-254, provided by Evonik

[0299] Heptane, provided by Chevron

[0300] Preparation of a Mg Alkoxy Compound

[0301] 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 ppm).

[0302] Preparation of Solid Catalyst Component

[0303] 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.

[0304] The thus obtained catalyst was used along with triethyl-aluminium (TEAL) as co-catalyst and cyclohexylmethyl dimethoxy silane (C-Donor) as external donor.

[0305] The aluminium to donor ratio, the aluminium to titanium ratio and the polymerization conditions are indicated in tables 1 and 2.

[0306] Polymerization was performed in a polypropylene (PP) pilot plant, comprising only a loop reactor.

TABLE-US-00001 TABLE 1 Preparation of the propylene homopolymer (Component (A)) for IE1 Component (A) TEAL/Ti [mol/mol] 65 TEAL/Donor [mol/mol] 18.8 Catalyst feed [g/h] 1.6 Loop (H-PP1) Time [h] 0.47 Temperature [ C.] 70 Pressure [kPa] 35 MFR.sub.2 [g/10 min] 77 XCS [wt %] 4.9 H.sub.2/C3 ratio [mol/kmol] 3.7 amount [wt.-%] 100 Final MFR.sub.2 [g/10 min] 77 XCS [wt %] 3.4 Tm [ C.] 162 Tc [ C.] 114 Mw [g/mol] 135000 MWD [] 6.5

TABLE-US-00002 TABLE 2 Preparation of the propylene homopolymer (Component (A)) for IE2 and IE3 Component (A) TEAL/Ti [mol/mol] 65 TEAL/Donor [mol/mol] 18.8 Catalyst feed [g/h] 1.6 Loop (H-PP1) Time [h] 0.47 Temperature [ C.] 70 Pressure [kPa] 35 MFR.sub.2 [g/10 min] 3.5 XCS [wt %] 3.5 H.sub.2/C3 ratio [mol/kmol] 0.7 amount [wt %] 100 Final MFR.sub.2 [g/10 min] 3.7 XCS [wt.-%] 3.5 Tm [ C.] 162 Tc [ C.] 113 Mw [g/mol] 320000 MWD 7.2

[0307] 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).

[0308] In a second step the propylene homopolymer has been visbroken by using a co-rotating twin-screw extruder at 200-230 C. and using 1.1 wt % of Irgatec CR76 (hydroxylamine ester in a polymer matrix; sold by BASF) (IE2) to achieve the target MFR.sub.2 of 800 g/10 min.

[0309] For IE-2 0.075 wt % of 1-octadecanthiol and for IE-3 0.12 wt % of 2-octadecanthiol (supplied by Sigma Aldrich) were used.

TABLE-US-00003 TABLE 3 Properties of visbroken PP of IE2 and IE3 (reference is without visbreaking) Example unit reference IE2 IE3 1-octadecanthiol [wt %] 0 0.075 0.12 MFR.sub.2 [g/10 min] 3.7 27.2 38.2 Mw [g/mol] 320000 177500 156000 MWD [] 7.2 4.8 4.5

[0310] For Comparative Example CE1 the above produced propylene homopolymer including the additives as described above has been visbroken by using a co-rotating twinscrew extruder at 200-230 C. and using an appropriate amount (1750 ppm) of (tert.-butylperoxy)-2,5-dimethylhexane (Trigonox 101, distributed by Akzo Nobel, Netherlands) to achieve the target MFR2 of 800 g/10 min.

[0311] For Comparative Example CE2 polymerization was performed with catalyst Avant ZN L1, commercially available from Basell. The catalyst contains a phthalate based internal donor. The catalyst was used along with triethyl-aluminium (TEAL) as co-catalyst and cyclohexylmethyl dimethoxy silane (C-Donor) as external donor. Polymerization was performed in a PP pilot plant, comprising only a loop reactor.

TABLE-US-00004 TABLE 4 Preparation of the propylene homopolymer (Component (A)) for CE2 Component (A) TEAL/Ti [mol/mol] 65 TEAL/Donor [mol/mol] 18.8 Catalyst feed [g/h] 1.3 Loop (H-PP1) Time [h] 0.5 Temperature [ C.] 70 Pressure [kPa] 35 MFR.sub.2 [g/10 min] 76 XCS [wt.-%] 3.2 H.sub.2/C3 ratio [mol/kmol] 4.3 amount [wt.-%] 100 Final Tm [ C.] 162 Tc [ C.] 116 Mw [g/mol] 133500 MWD 7.6

[0312] The propylene homopolymer for CE2 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).

[0313] In a second step the propylene homopolymer has been visbroken by using a co-rotating twin-screw extruder at 200-230 C. and using 1.1 wt % of Irgatec CR76 (hydroxylamine ester in a polymer matrix; sold by BASF) yielding Mw of 131000 and MWD 6.0.

[0314] The polypropylene compositions of IE1, CE1 and CE2 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.

[0315] The processing conditions for and properties of the melt-blown webs are indicated in tables 5 6, 7 and 8.

TABLE-US-00005 TABLE 5 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 IE1-1 270 200 360 10 9.4 IE1-2 290 200 210 10 9.4 CE1-1 250 200 410 10 9.5 CE1-2 270 200 300 10 9.3 CE2-1 270 200 520 10 10.0 CE2-2 290 200 310 10 10.0

TABLE-US-00006 TABLE 6 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* IE1-1 823 57.4 25.08 0.504 88 IE1-2 485 122.1 48.67 0.547 136.2 CE1-1 952 44.3 25.47 0.664 74.7 CE1-2 752 60.4 30.56 0.605 50.5 CE2-1 1100 36.5 29.0 0.635 70.1 CE2-2 1215 32 19.88 0.593 20.5 *also mbar

TABLE-US-00007 TABLE 7 MFR, Mw, MWD and shots for IE1 and CE1 on web MFR Mw Mw Mw(web)/ MWD MWD MWD(web)/ (web) (web) (PP)* Mw(PP) (web) (PP)** MWD(PP) Shots .sup.a) IE1-1 860 62300 137000 0.45 3.9 6.0 0.65 No (1) IE2-1 1806 50400 137000 0.37 3.5 6.0 0.58 No (1) CE1-1 850 64000 67350 0.95 4.1 4.2 0.98 yes (2) CE1-2 1044 60000 67350 0.89 4 4.2 0.95 Yes (4) *Mw measured on the visbroken PP granules **MWD for the visbroken PP .sup.a) rating 1 = no shots; rating 2 = low level of shots; rating 4 = high level of shots

[0316] As can be seen from Table 3, 4 and 5 that at the same throughput, the polymer of the Inventive Example (visbroken with Irgatec; IE1-1 and IE1-2) can go to higher melt temperature without producing shots in the web than the polymer of the Comparative Example (visbroken with peroxide; CE1-1 and CE1-2). (Polymers of IE1 and CE1 produced with the same catalyst, but different visbreaking agents used).

[0317] Furthermore it can be seen that the use of the polymer of the Inventive Example (visbroken with Irgatec; IE1-1 and IE1-2) yields webs with improved water barrier properties, as can be seen in the higher hydrohead values compared to the comparative examples CE1 and CE2.