Method for producing polypropylene nonwoven fabric

Abstract

The polypropylene nonwoven fabric produced by the method for producing a polypropylene nonwoven fabric according to the present invention has features that it has excellent stretchability and excellent water pressure resistance.

Claims

1. A method for producing a polypropylene nonwoven fabric comprising the steps of: step 1: spinning a metallocene polypropylene resin to produce filaments; step 2: cooling the spun filaments at a temperature of 10 to 20 C.; and step 3: bonding the cooled filaments together at 150 to 165 C. to form a nonwoven fabric, wherein the metallocene polypropylene resin has: a weight average molecular weight of 100,000 to 150,000, a molecular weight distribution (PDI) of 2.0 to 2.5, a melt index (MI) of 20 to 28 g/10 min measured at 230 C. under a load of 2.16 kg according to ASTM D1238, a melting point of 150 to 155 C., and a xylene soluble (XS) content of 2% by weight or less.

2. The method for producing a polypropylene nonwoven fabric according to claim 1, wherein the metallocene polypropylene resin has a weight average molecular weight of 100,000 to 110,000.

3. The method for producing a polypropylene nonwoven fabric according to claim 1, wherein the metallocene polypropylene resin has a PDI of 2.3 to 2.4.

4. The method for producing a polypropylene nonwoven fabric according to claim 1, wherein the metallocene polypropylene resin has a MI of 22 to 28 g/10 min.

5. The method for producing a polypropylene nonwoven fabric according to claim 1, wherein the metallocene polypropylene resin has a xylene soluble (XS) content of 1.5% by weight or less.

6. The method for producing a polypropylene nonwoven fabric according to claim 1, wherein the metallocene polypropylene resin is prepared by using a compound represented by the following Chemical formula 1 as a catalyst: ##STR00003## in Chemical formula 1, R.sub.1 and R.sub.2 are each independently phenyl, or phenyl substituted with C.sub.1-20 alkyl; R.sub.3 and R.sub.4 are each independently C.sub.1-20 alkyl; A is carbon, silicon, or germanium; M is zirconium, or hafnium, and X is halogen, or C.sub.1-20 alkyl.

7. The method for producing a polypropylene nonwoven fabric according to claim 6, wherein the compound represented by the chemical formula 1 is the following compound: ##STR00004##

8. The method for producing a polypropylene nonwoven fabric according to claim 7, wherein the compound represented by the chemical formula 1 is supported on a support.

9. The method for producing a polypropylene nonwoven fabric according to claim 8, wherein the support is at least one carrier selected from the group consisting of silica, silica-alumina and silica-magnesia.

10. The method for producing a polypropylene nonwoven fabric according to claim 9, wherein the support contains an oxide, a carbonate, a sulfate, or a nitrate.

11. The method for producing a polypropylene nonwoven fabric according to claim 6, wherein in Chemical formula 1, R.sub.1 and R.sub.2 are each independently phenyl substituted with tert-butyl, R.sub.3 and R.sub.4 are ethyl, A is silicon, and X is chloro.

12. The method for producing a polypropylene nonwoven fabric according to claim 6, wherein the catalyst further includes a cocatalyst.

13. The method for producing a polypropylene nonwoven fabric according to claim 12, wherein the cocatalyst is at least one selected from the group consisting of silica, silica-alumina, and an organic aluminum compound.

14. The method for producing a polypropylene nonwoven fabric according to claim 1, wherein step 2 is performed at a temperature of 12 to 20 C.

15. The method for producing a polypropylene nonwoven fabric according to claim 1, wherein the polypropylene nonwoven fabric has a water pressure resistance of 150 mmH.sub.2O or more.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

(1) Hereinafter, preferred examples will be presented to facilitate understanding of the present invention. However, these examples are provided for a better understanding of the present invention only, and are not intended to limit the scope of the invention.

Preparation Example: Preparation of Catalyst

Step 1) Preparation of (diethylsilane-diyl)-bis((2-methyl-4-tert-butyl-phenylindenyl)silane

(2) 2-Methyl-4-tert-butylphenylindene (20.0 g) was dissolved in toluene/THF=10/1 solution (220 mL), and then n-butyllithium solution (2.5 M, hexane solvent, 22.2 g) was slowly added dropwise thereto at 0 C., and the mixture was stirred at room temperature for 1 day. Then, diethyldichlorosilane (6.2 g) was slowly added dropwise to the mixed solution at 78 C., and the mixture was stirred for about 10 minutes and then stirred at room temperature for 1 day. Then, the organic layer was removed by adding water, and the solvent was distilled under reduced pressure to give (diethylsilane-diyl)-bis((2-methyl-4-tert-butyl-phenylindenyl)silane.

Step 2) Preparation of [(diethylsilane-diyl)-bis((2-methyl-4-tert-phenylindenyl)]zirconium dichloride

(3) (Diethylsilane-diyl)-bis((2-methyl-4-tert-butyl-phenylindenyl)silane prepared in step 1 was dissolved in toluene/THF=5/1 solution (120 mL), and then n-butyllithium solution (2.5 M, hexane solvent, 22.2 g) was slowly added dropwise thereto at 78 C., and the mixture was stirred at room temperature for 1 day. To the reaction solution, zirconium chloride (8.9 g) was diluted with toluene (20 mL) and then slowly added dropwise at 78 C., and the resulting mixture was stirred at room temperature for 1 day. The solvent of the reaction solution was removed under reduced pressure, dichloromethane was added and filtered, and the filtrate was removed by distillation under reduced pressure. Recrystallization using toluene and hexane gave a high purity rac-[(diethylsilane-diyl)-bis((2-methyl-4-tert-phenylindenyl)]zirconium dichloride (10.1 g, 34%, rac: meso=20:1).

(4) .sup.1H-NMR (400 MHz, CDCl.sub.3) 7.69-7.01 (m, 14H), 6.99 (s, 2H), 2.24 (s, 6H), 1.51-1.41 (m, 4H, 1.32 (s, 18H, 1.07 (t, J=6.9 Hz, 6H)

Step 3) Preparation of the Supported Catalyst

(5) 100 g of silica and 10 wt % of methylaluminoxane (670 g) were added to a 3 L reactor and reacted at 90 C. for 24 hours. After precipitation, the upper layer was eliminated and the rest was washed twice with toluene. The ansa-metallocene compound rac-[(diethylsilane-diyl)-bis((2-methyl-4-tert-phenylindenyl)]zirconium dichloride (5.9 g) prepared in step 2 was diluted in toluene and added to the reactor, and then the solution was reacted at 70 C. for 5 hours. When the precipitation was completed after the reaction, the solution of upper layer was eliminated and the remaining reaction product was washed with toluene and further washed with hexane, and vacuum-dried to give 150 g of a silica-supported metallocene catalyst in the form of solid particles.

Examples 1 to 3

(6) 1) Preparation of Polypropylene Resin

(7) A polypropylene resin was prepared using a continuous two-stage loop reactors. More specifically, triethylaluminum (TEAL) and hydrogen gas were respectively introduced thereto by using separate pumps, and the bulk-slurry copolymerization of propylene was carried out. At this time, a mud catalyst that was prepared by mixing 20 wt % of the catalyst with an oil and grease was used. The reactor was operated under the following conditions: the temperature of the reactor was 70 C., and the output per hour was about 40 kg. At this time, the pressure was maintained at 35 kg/cm.sup.2, and propylene was introduced at 40 kg/h, TEAL at 50 ppm and hydrogen at 700 ppm.

(8) 2) Production of Nonwoven Fabric

(9) Master batch pellets were extruded into microfiber webs to produce a nonwoven fabric, by a process similar to that described in Report No. 4364 of the Naval Research Laboratories, published May 25, 1954 entitled Manufacture of Superfine Organic Fibers by Wente, Van. A. Boone, C. D., and Fluharty, E. L.

(10) In detail, a master batch of the above-prepared polypropylene resin and Exolit OP 950 additive (2.5 wt %) was prepared using a 25 mm twin-screw extruder, and then pelletized. A 31 mm (0.75 in.) Brabender conical twin screw extruder was used to feed the molten masterbatch composition to a melt pump (65 rpm) and then to a 25 cm width meltblowing die having orifices (10 orifices/cm) and orifice diameter of 381 m. The melt temperature was 235 C., the screw speed was 120 rpm, the die was maintained at 235 C., the primary air temperature and pressure were, respectively, 300 C. and 60 kPa (8.7 psi), the polymer throughput rate was 5.44 Kg/hr, and the collector/die distance was 15.2 cm. While the microfibers spun from the orifices fell to the collector, they were cooled by a cooling air using two pumps, and the microfibers collected by the collector were passed through a calendering process using upper and lower rolls to produce a nonwoven fabric. At this time, the temperatures of the cooling air and the temperatures of the upper and lower rolls in the calendaring process are shown in Table 2 below.

Comparative Examples 1 and 2

(11) Polypropylene (product name: H7700) manufactured by LG Chem Ltd. was used as a comparative example, and a nonwoven fabric was produced in the same manner as in Example above except that the conditions shown in Table 2 below were used.

Experimental Example

(12) (1) Evaluation of Physical Properties of Polypropylene

(13) First, the physical properties of the polypropylene prepared in Examples and Comparative Examples were evaluated as follows.

(14) 1) Melt Index (MI): measured at 230 C. under a load of 2.16 kg in accordance with ASTM D1238, and expressed as weight (g) of the polymer obtained by melting for 10 minutes.

(15) 2) Xylene soluble: Xylene was added to the sample, heated at 135 C. for 1 hour, and then cooled for 30 minutes, followed by pre-treatment. Xylene was flowed at a flow rate of 1 mL/min for 4 hours with OminiSec (Viscotek Corporation, FIPA) device. When the base line of RI, DP and IP was stabilized, the concentration and the injection amount of the pre-treated samples were filled and measured, thereby calculating the peak area.

(16) 3) Melting point (Tm) and recrystallization temperature (Trc): The melting point of polypropylene was measured using Differential Scanning Calorimeter (DSC, device name: DSC 2920, manufacturer: TA Instrument). Specifically, the polymer was heated up to 220 C. and then maintained at that temperature for 5 minutes. After lowering to 20 C., the temperature was again increased. At this time, the increasing speed and the lowering speed of the temperature was adjusted to 10 C./min, respectively.

(17) 4) Weight average molecular weight, number average molecular weight, molecular weight distribution: A sample was dissolved in 1,2,4-trichlorobenzene containing 0.0125% using BHT PL-SP260 at 160 C. for 10 hours and subjected to pretreatment. The number average molecular weight and the weight average molecular weight were measured at a temperature of 160 C. using PL-GPC220. The molecular weight distribution was expressed by a ratio between the weight average molecular weight and the number average molecular weight.

(18) 5) Tensile strength: measured at a rate of 50 mm/min according to ASTM D790.

(19) 6) Flexural strength and flexural modulus: In accordance with ASTM D790, when a sample was laid and fixed to a support and then loaded at a rate of 28 mm/min by a loading nose, the strength (kg/cm.sup.2) applied was measured. The flexural strength, which is the maximum value where the load does not increase any more, and the flexural modulus, which is a measure of the stiffness during the initial step of the bending process and is represented by the slope of the initial straight line part of the flexural stress-strain curve, were measured.

(20) 7) Izod impact strength: Izod impact strength was measured at normal temperature (23 C.) according to ASTM D256.

(21) 8) TVOC (total volatile organic compound emissions): In accordance with the method of VDA 277, the gas generated after heating at 120 C. for 5 hours was evaluated using Headspace Sampler-GC/FID.

(22) The results are shown in Table 1 below.

(23) TABLE-US-00001 TABLE 1 Comparative Unit Examples 1 to 3 Examples 1 and 2 MI g/10 min 26.2 33.3 Xylene content wt % 0.8 1.8 Tm C. 152.7 160.3 Trc C. 110.9 113.0 Number average g/mol 44,521 37,624 molecular weight Weight average g/mol 105,860 106,862 molecular weight Molecular weight 2.37 2.84 distribution Tensile strength kg/cm.sup.2 371 338 Flexural strength kg/cm.sup.2 513 451 Flexural modulus kg/cm.sup.2 16444 15049 Izod impact strength kg-cm/cm 2.2 2.2 TVOC Ppm 15 260

(24) (2) Evaluation of Physical Properties of Nonwoven Fabric

(25) The physical properties of the nonwoven fabric prepared in Examples and Comparative Examples were evaluated as follows.

(26) 1) Tensile strength and elongation: The film test sample whose thickness was measured was fixed to UTM equipment (ZWICK Roell Inc.) to fill the cross-sectional area. MD and TD directions of the test sample were measured at a speed of 200 mm/min, respectively. The tensile strength (kg/cm.sup.2) was confirmed by dividing the elongation (%), the yield load (Kgf) and load at break (kg) of the respective samples into the cross-sectional area (cm.sup.2).

(27) 2) Water pressure resistance: The pressure was measured at the time when 3 drops were transmitted to the top of the nonwoven fabric while increasing water pressure using a water pressure resistance testing machine.

(28) 3) Filament thickness: The thickness of the filament was measured using SEM.

(29) The results are shown in Table 2 below.

(30) TABLE-US-00002 TABLE 2 Comparative Comparative Example 1 Example 2 Example 3 Example 1 Example 2.sup.5) Cooling Temperature 16/16 18/17 12/12 11/12 16/16 Air.sup.1) ( C.) Calendering temperature.sup.2) 160/155 160/155 160/155 165/155 165/155 ( C.) Tensile MD.sup.3) 114 119 107 101 98 strength CD.sup.4) 49 52 48 44 44 Elongation MD 69 64 70 56 53 CD 65 66 65 65 60 Water pressure resistance 150 165 138 97 92 (mmH.sub.2O) Filament thickness (m) 16.3 14.7 18.7 20.4 18.8 .sup.1)Temperature of two cooling airs .sup.2)Temperature of upper and lower rolls .sup.3)MD: machine direction .sup.4)CD: cross machine direction .sup.5)In Comparative Example 2, partial fiber cutting (breakage) was observed

(31) As described above, it was confirmed that in the case of the nonwoven fabric of Examples according to the present invention, the tensile strength was improved as compared with that of the nonwoven fabric of Comparative Examples, and the elongation was similar but the water pressure resistance was remarkably improved. In addition, it was confirmed that the thickness of the filament was smaller than that of Comparative Examples. Further, when comparing Examples 1 and 2, Example 2 showed more excellent tensile strength, water pressure resistance and thinner filament thickness depending on the cooling conditions.