Fiber grade with improved spinning performance and mechanical properties

Abstract

The present invention is directed to a new polypropylene composition, polypropylene fibres comprising said polypropylene composition, a spunbonded fabric comprising said polypropylene fibres and/or polypropylene composition, an article comprising said polypropylene fibres and/or said spunbonded fabric as well as to a process for the preparation of such spunbonded fabric and the use of such polypropylene composition for improving the stability of a fibre spinning line.

Claims

1. A polypropylene composition (PP-C) comprising: a) at least 80 wt. %, based on the total weight of the polypropylene composition (PP-C), of a polypropylene (L-PP) homo- or copolymer having a melt flow rate according to ISO 1133 (230 C./2.16 kg) in the range of 0.6 g/10 min to 5 g/10 min and a comonomer content of up to 5 wt. %, the comonomers are selected from ethylene and/or C.sub.4- to C.sub.10 -olefin, and b) between 2 wt. % and 20 wt. %, based on the total weight of the polypropylene composition (PP-C), of a polypropylene (H-PP) homo- or copolymer having a melt flow rate according to ISO 1133 (230 C./2.16 kg) in the range of 800 g/10 min to 1,600 g/10 min and a comonomer content of up to 5 wt. %, the comonomers are selected from ethylene and/or C.sub.4- to C.sub.10 -olefin, wherein the polypropylene composition (PP-C) comprising polypropylene (L-PP) and polypropylene (H-PP) has been visbroken with a visbreaking ratio [final MFR2 (230 C.)/initial MFR2 (230 C.)] of 9 to 50, wherein final MFR2 (230 C.) is the MFR2 (230 C.) of the polypropylene composition (PP-C) after visbreaking and initial MFR2 (230 C.) is the MFR2 (230 C.) of the polypropylene composition (PP-C) before visbreaking, and wherein the polypropylene composition (PP-C) has a final melt flow rate according to ISO 1133 (230 C./2.16 kg) in the range of 10 g/10 min to 60 g/10 min and a final polydispersity index (PI) of not more than 4.0.

2. The polypropylene composition (PP-C) according to claim 1, wherein the polypropylene (L-PP) has: a) a melt flow rate according to ISO 1133 (230 C./2.16 kg) in the range of 0.7 g/10 min to 3.0 g/10 min, and/or b) a melting temperature Tm measured according to ISO 11357-3 of at least 150 C., and/or c) a xylene cold soluble content (XCS) measured according to ISO 6427 (23 C.) of not more than 3.5 wt. %.

3. The polypropylene composition (PP-C) according to claim 1, wherein the polypropylene (H-PP) has: a xylene cold soluble content (XCS) measured according to ISO 6427 (23 C.) of not more than 3.5 wt. %.

4. The polypropylene composition (PP-C) according to any one of claim 1, wherein: a) the polypropylene (L-PP) is a propylene homopolymer (HL-PP), and/or b) the polypropylene (H-PP) is a propylene homopolymer (HH-PP).

5. The polypropylene composition (PP-C) according to claim 1, wherein the polypropylene composition (PP-C) comprises: a) at least 90 wt. % of polypropylene (L-PP), and b) between 3 wt. % and 10 wt. % of polypropylene (H-PP), based on the total weight of the polypropylene composition (PP-C), optionally based on the total amount of the polypropylene (L-PP) and the polypropylene (H-PP) together.

6. The polypropylene composition (PP-C) according to claim 1, wherein the polypropylene composition (PP-C) has: a) a final melt flow rate according to ISO 1133 (230 C./2.16 kg) in the range of 25 g/10 min to 40 g/10 min, and/or b) a final polydispersity index (PI) in the range of 2.0 to 4.0.

7. The polypropylene composition (PP-C) according to claim 1, wherein the polypropylene composition (PP-C) has a ratio of polydispersity index (PI) [initial PI/final PI] of at least 1.3, wherein final PI is the polydispersity index (PI) of the polypropylene composition (PP-C) after visbreaking and initial PI is the polydispersity index (PI) of the polypropylene composition (PP-C) before visbreaking.

8. Polypropylene fiber (PP-F) having an average filament fineness of not more than 1.50 denier, wherein said fiber (PP-F) comprises at least 95 wt. %, based on the total weight of the polypropylene fiber (PP-F), of a polypropylene composition (PP-C) as defined in claim 1.

9. The polypropylene fibers (PP-F) according to claim 8 being spunbound into a fabric.

10. The polypropylene fibre (PP-F) according to claim 8 being provided in an 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.

11. Process for the preparation of a spunbonded fabric comprising: spunbonding a polypropylene composition (PP-C) by using a fibre spinning line at a maximum cabin air pressure of at least 3,000 Pa, wherein the polypropylene composition (PP-C) includes: a) at least 80 wt. %, based on the total weight of the polypropylene composition (PP-C), of a polypropylene (L-PP) homo- or copolymer having a melt flow rate according to ISO 1133 (230 C/2.16 kg) in the range of 0.6 g/10 min to 5 g/10 min and a comonomer content of up to 5 wt. %, the comonomers are selected from ethylene and/or C.sub.4- to C.sub.10 -olefin, and b) between 2 wt. % and 20 wt. %, based on the total weight of the polypropylene composition (PP-C), of a polypropylene (H-PP) homo- or copolymer having a melt flow rate according to ISO 1133 (230 C/2.16 kg) in the range of 800 g/10 min to 1,600 g/10 min and a comonomer content of up to 5 wt. %, the comonomers are selected from ethylene and/or C.sub.4- to C.sub.10 -olefin, visbreaking the polypropylene composition (PP-C) comprising polypropylene (L-PP) and polypropylene (H-PP) with a visbreaking ratio [final MFR2 (230 C.)/initial MFR2 (230 C.)] of 9 to 50, wherein final MFR2 (230 C.) is the MFR2 (230 C.) of the polypropylene composition (PP-C) after visbreaking and initial MFR2 (230 C.) is the MFR2 (230 C.) of the polypropylene composition (PP-C) before visbreaking, and wherein the polypropylene composition (PP-C) has a final melt flow rate according to ISO 1133 (230 C/2.16 kg) in the range of 10 g/10 min to 60 g/10 min and a final polydispersity index (PI) of not more than 4.0.

12. The process according to claim 11, wherein the fibre spinning line comprises the following steps of: a) feeding the polypropylene composition (PP-C) into an extruder to melt the polypropylene composition (PP-C), b) forcing the molten polypropylene composition (PP-C) through a spinneret having holes of 0.4 mm to 0.7 mm diameter and 65 to 75 holes per cm at a rate of 0.3 g to 1 g per hole per meter to form polypropylene fibres (PP-F), and c) quenching and drawing the polypropylene fibers (PP-F) at filament speeds of at least 3800 m/min.

Description

EXAMPLES

(1) 1. Definitions/Measuring Methods

(2) 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.

(3) Quantification of Isotacticity in Polypropylene by .sup.13C NMR Spectroscopy

(4) The isotacticity is determined by quantitative .sup.13C nuclear magnetic resonance (NMR) spectroscopy after basic assignment as e.g. in: V. Busico and R. Cipullo, Progress in Polymer Science, 2001, 26, 443-533. Experimental parameters are adjusted to ensure measurement of quantitative spectra for this specific task as e.g. in: S. Berger and S. Braun, 200 and More NMR Experiments: A Practical Course, 2004, Wiley-VCH, Weinheim. Quantities are calculated using simple corrected ratios of the signal integrals of representative sites in a manner known in the art. The isotacticity is determined at the pentad level i.e. mmmm fraction of the pentad distribution.

(5) Randomness

(6) In the FTIR measurements, films of 250-mm thickness were compression moulded at 225 C. and investigated on a Perkin-Elmer System 2000 FTIR instrument. The ethylene peak area (760-700 cm.sup.1) was used as a measure of total ethylene content. The absorption band for the structure P-E-P (one ethylene unit between propylene units), occurs at 733 cm.sup.1 This band characterizes the random ethylene content. For longer ethylene sequences (more than two units), an absorption band occurs at 720 cm.sup.1. Generally, a shoulder corresponding to longer ethylene runs is observed for the random copolymers. The calibration for total ethylene content based on the area and random ethylene (PEP) content based on peak height at 733 cm.sup.1 was made by .sup.13C.sup.NMR. (Thermochimica Acta, 66 (1990) 53-68).
Randomness=random ethylene (P-E-P) content/the total ethylene content100%.

(7) Rheology: 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. (ISO 6721-10)

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

(9) 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]

(10) From the following equations
=G/ and =G/
f()=G()*/[G().sup.2+G().sup.2]
f()=G()*/[G().sup.2+G().sup.2]
The Polydispersity Index, PI,

(11) PI=10.sup.5/Gc (Cross-over Modulus), is calculated from the cross-over point of G() and G(), for which G(c)=G(c)=Gc (calculated in SI unit Pa) holds.

(12) Density is measured according to ISO 1183-187. Sample preparation is done by compression molding in accordance with ISO 1872-2:2007

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

(14) Quantification of Comonomer Content by FTIR Spectroscopy

(15) The comonomer content is determined by quantitative Fourier transform infrared spectroscopy (FTIR) after basic assignment calibrated via quantitative .sup.13C nuclear magnetic resonance (NMR) spectroscopy in a manner well known in the art. Thin films are pressed to a thickness of 250 m and spectra recorded in transmission mode.

(16) Specifically, the ethylene content of a polypropylene-co-ethylene copolymer is determined using the baseline corrected peak area of the quantitative bands found at 720-722 and 730-733 cm.sup.1. Propylene-1-butene-copolymers were evaluated at 767 cm.sup.1.Quantitative results are obtained based upon reference to the film thickness.

(17) Melting temperature T.sub.m, crystallization temperature T.sub.c, is measured with Mettler TA820 differential scanning calorimetry (DSC) on 5-10 mg samples. Both crystallization and melting curves were obtained during 10 C./min cooling and heating scans between 30 C. and 225 C. Melting and crystallization temperatures were taken as the peaks of endotherms and exotherms.

(18) Also the melt- and crystallization enthalpy (Hm and Hc) were measured by the DSC method according to ISO 11357-3.

(19) The content of xylene cold solubles (XCS, wt.-%) was determined at 25 C. according ISO 16152; first edition; 2005-07-01.

(20) Grammage of the Web

(21) 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

(22) Average Fiber Diameter in the Fabric

(23) The average fibre diameter has been determined by using an optical microscope and measuring the diameter of 20 random selected fibres.

(24) Filament Fineness

(25) The filament fineness in denier has been calculated from the average fibre diameter by using the following correlation:
Fibre diameter(in cm)=(4.44410.sup.6denier/0.91)
Mechanical Properties of the Web

(26) The mechanical properties of the webs were determined in accordance with EN 29073-3 (1989), Test methods for nonwovensDetermination of tensile strength and elongation

(27) 2. Preparation of the Examples

(28) 2.1 Preparation of the Polymers

Inventive Examples

(29) L-PP polymers with different MFRs and a XCS content of about 3 wt.-% have been polymerized in a Spheripol process by using the Ziegler-Natta M1 catalyst, a commercial 4.sup.th generation Ziegler-Natta catalyst from Lyondell-Basell. The typical melting point of these polymers is 161 C. These polymers have been mixed with 400 ppm Calcium Stearate, 1000 ppm Irgafos 168 and 400 ppm Irganox 3114 and an amount of H-PP as mentioned in the table. As H-PP, HL512 FB has been used. HL512FB is a commercial grade form Borealis having a MFR of 1,200 g/10 min and a melting temperature of 158 C.

(30) In a second step these mixtures 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 as mentioned in the table 1. By using a dynamic rheometer the polydispersity index has been determined at a temperature of 200 C. for all samples produced.

Comparative Example (CE1)

(31) The commercial polypropylene homopolymer HG455FB (Borealis) having an MFR.sub.2 of 27 g/10 min produced in a visbreaking process was used as comparative example. This polymer is characterized by a melting temperature of 161 C. and a polydispersity index of 2.7, determined at a temperature of 200 C. by using a dynamic rheometer.

(32) The details for inventive examples IE1, IE2 and IE3 and comparative example CE1 are summarized in Table 1.

(33) TABLE-US-00001 TABLE 1 L-PP L-PP H-PP Final MFR.sub.2 Final PI Sample MFR [wt.-%] [wt.-%] [g/10 min] [] IE1 2 95 5 34 2.7 IE2 0.8 95 5 25 2.7 IE3 2 95 5 25 3.5 CE1 27 100 0 27 2.7
2.2 Preparation of Polypropylene Fibers and Spunbonded Fabrics

(34) The polypropylene compositions have been converted into spunbonded fabrics on a Reicofil 4 line using a spinneret having 7377 holes of 0.6 mm exit diameter and 6827 holes per meter. The gap of the pre-diffuser exit has a diameter of 23 mm, while the SAS gap exit has a diameter of 20 mm. The temperature of the outlet roll was set to 100 C. and the die temperature to 260 C. The throughput per hole has been kept constant at 0.49 g/(min*hole), at a throughput per meter of 200.5 kg/(h*m) and a total throughput of 216.7 kg/h. The line speed was set to 330 m/min and the fabrics produced had a weight of 10 g/m.sup.2.

(35) Table 2 summarizes data regarding filament fineness, processability and mechanical properties with respect to inventive examples IE1, IE2, IE3 and CE1.

(36) TABLE-US-00002 TABLE 2 Properties Max Cabin Spinning Filament Filament Max MD tensile Max CD tensile Elongation Elongation Remark spinning Grade pressure (Pa) stability fineness (den) speed (m/min) strength (N) strength (N) MD (%) CD (%) stability IE1 10000 ++++ 1.1 4006 34.0 15.8 68.1 75.4 stable IE2 10000 +++ 1.1 4006 35.4 16.5 59.8 71.2 Some drops IE3 9000 ++ 1.15 3832 31.6 16.3 69.2 87.2 Some drops CE1 8000 + 1.2 3670 30.1 14.1 66.9 72.7 stable

(37) From the results obtained, it can be gathered that CE1 can be run at a maximum cabin pressure of 8000 Pa. At this condition the filament titre is 1.2 denier. IE2 is clearly better regarding the filament fineness of 1.1 denier which can be obtained at a maximum cabin air pressure of 10,000. The best spinning stability, however, is observed for IE1. It can be run at a maximum cabin air pressure of 10,000 Pa at stable conditions. In addition thereto, it should be noted that IE1, IE2 and IE3 show improved mechanical properties compared to the standard CE1.