USE OF POLYMER COMPOSITION ON MAKING SOFT NONWOVEN FABRICS

Abstract

Use of polymer composition comprising a first propylene polymer A and a second propylene polymer B for producing crimped multicomponent fiber having a side by side cross-sectional configuration.

Claims

1. A process for producing crimped multicomponent fibers having a side by side cross-sectional configuration, the process comprising: providing a polymer composition comprising a first propylene polymer A and a second propylene polymer B; and forming the crimped multicomponent fibers having the side by side cross-sectional configuration from the polymer composition, wherein (i) the first propylene polymer A and second propylene polymer B are distributed over the cross section of the fiber in a side-by-side arrangement, (ii) the mass ratio of the first propylene polymer A and the second propylene polymer B [A:B] is in the range of 10:90 to 90:10, (iii) the absolute value of the difference of the crystallization temperature [Tc (A)] of the first propylene polymer A and the crystallization temperature [Tc (B)] of the second propylene polymer B determined according to ISO11357 with a scan rate of 10 C./min is in the range of 6 to 30 C., and the interface line, contained in the radial plane of the fibers, between the two propylene polymers (A) and (B) is curved and its curvature (c) is $c=\frac{h}{b}=0.05\mathrm{to}0.25$ wherein the baseline length (b) is the length of the imaginary straight baseline connecting the two endpoints of the curved interface line, and the bow height (h) is the distance of the crest of the curved interface line from the baseline.

2. (canceled)

3. The process according to claim 1, wherein the interface line, contained in the radial plane of the fibers, between the two propylene polymers (A) and (B) is curved and its curvature (c) is $c=\frac{h}{b}=0.1\mathrm{to}0.2$ wherein the baseline length (b) is the length of the imaginary straight baseline connecting the two endpoints of the curved interface line, and the bow height (h) is the distance of the crest of the curved interface line from the baseline.

4. The process according to claim 1, wherein the first propylene polymer A is a propylene homopolymer or a propylene/-olefin random copolymer, the first propylene polymer A having a melt flow rate (MFR, 230 C., 2.16 kg, ISO 1133) of 15 to 120 g/10 min, and/or having a molecular weight distribution (Mw/Mn) in the range of 2.5 to 10.0 (measured by size exclusion chromatography according to ISO 16014).

5. The process according to any of claims 1 to 4 claim 1, wherein the first propylene polymer A has (i) a melting temperature T.sub.m (DSC, ISO 11357-1 & -2) in the range of 150 C. to 164 C., (ii) a crystallization temperature T.sub.c (DSC, ISO 11357-1 & -2) in the range of 90 C. to 135 C., and (iii) a comonomer content <1.0 wt %.

6. The process according to claim 1, wherein the first propylene polymer A has (i) a melting temperature T.sub.m (DSC, ISO 11357-1 & -2) in the range of 142 C. to 155 C., (ii) a crystallization temperature T.sub.c (DSC, ISO 11357-1 & -2) in the range of 80 C. to 125 C., and (iii) a comonomer content in the range of 1.0-5.5 wt %.

7. The process according to claim 1, wherein the second propylene polymer B is a propylene homopolymer or a propylene/-olefin random copolymer, the second propylene polymer B having a melt flow rate (MFR, 230 C., 2.16 kg, ISO 1133) of 15 to 120 g/10 min, and/or having a molecular weight distribution (Mw/Mn) in the range of 2.5 to 10.0 (measured by size exclusion chromatography according to ISO 16014).

8. The process according to claim 1, wherein the second propylene polymer B has (i) a melting temperature T.sub.m (DSC, ISO 11357-1 & -2) in the range of 150 C. to 164 C., (ii) a crystallization temperature T.sub.c (DSC, ISO 11357-1 & -2) in the range of 90 C. to 135 C., and (iii) comonomer content <1.0 wt %.

9. The process according to claim 1, wherein the second propylene polymer B has (i) a melting temperature T.sub.m (DSC, ISO 11357-1 & -2) in the range of 142 C. to 155 C., (ii) a crystallization temperature T.sub.c (DSC, ISO 11357-1 & -2) in the range of 80 C. to 125 C., and (iii) a comonomer content 1.0-5.5 wt %.

10. The process according to claim 1, wherein the first propylene polymer A and second propylene polymer B are different, and at least one of the propylene polymers (A and B) is visbroken.

11. The process according to claim 1, wherein only one of the propylene polymers (A and B) is visbroken, and the absolute value of the difference of Mz/Mw between propylene polymer A and propylene polymer B is from 0.3 to 10.0.

12. The process according to claim 1, wherein both of the propylene polymers (A and B) are visbroken, and the absolute value of the difference of Mz/Mw between propylene polymer A and propylene polymer B is from 0.0 to 0.3.

13. The process according to claim 1, wherein at least one of the propylene polymers A and B is nucleated, and the amount of nucleating agent is between 0.01-5000 ppm based on the total amount of the nucleated propylene polymer.

14. The process according to claim 1, wherein the first propylene polymer A is a propylene homopolymer and the second propylene polymer B is a propylene/-olefin random copolymer.

15. The process according to claim 13, wherein the amount of first propylene polymer A is less than the amount of second propylene polymer B.

Description

[0100] Further details and advantages of the invention will become apparent from the figures and examples described in the following. The figures show:

[0101] FIG. 1: a schematic cross-section of a generic side-by-side bicomponent fiber without curvature;

[0102] FIG. 2: a schematic illustration of a crimped fiber;

[0103] FIG. 3: a schematic illustration of a spinning machine suitable for producing spunbonded nonwoven fabric sheets according to the invention;

[0104] FIG. 4: a schematic illustration of a production line suitable for producing multilayer sheets according to the invention;

[0105] FIG. 5: a SEM (Scanning Electron Microscope) picture of a cross-section of a side-by-side bicomponent fiber having a curved interface line;

[0106] FIG. 1 shows schematic illustration of a cross-section of a side-by-side bicomponent fiber. The fiber F comprise first and second propylene polymer A and B arranged side-by-side. The arrangement extends over the entire length of the fiber.

[0107] FIG. 2 is a schematic illustration of a section of a crimped fiber F as comprised in a nonwoven fabric sheet of the invention. The fiber is curved and comprises a certain crimp radius and a certain crimp count.

[0108] FIG. 3 shows a spinning machine 100 that is suitable for producing spunbonded nonwovens according to the invention. Spunbonded nonwovens NW are produced from continuous fibers F of thermoplastic material, which are spun in a spinnerette 101 and subsequently passed through a cooling device 102. A monomer suctioning device 104 to remove gases in the form of decomposition products, monomers, oligomers and the like generated during the spinning of the fibers F is arranged between the spinnerette 101 and the cooling device 102. The monomer extraction device 4 comprises suction openings or suction gaps.

[0109] In the cooling device 102, process air is applied to the fiber curtain from the spinnerette 101 from opposite sides. The cooling device 102 is divided into two sections 102a and 102b, which are arranged in series along the flow direction of the fibers. Thus, process air of a relatively higher temperature (for example 60 C.) can be applied to the fibers at an earlier stage in chamber section 102a and process air of a relatively lower temperature (for example 30 C.) can be applied to the fibers at a later stage in chamber section 102b. The supply of process air takes place via air supply chambers 105a and 105b, respectively. The cabin pressure within chambers 105a and 105b can be the same and can, for example, be about 3000 Pascal above ambient pressure, for example.

[0110] A drawing device 106 to draw and stretch the fibers 103 is arranged below the cooling device 102. The drawing device includes an intermediate channel 107, which preferably converges and gets narrower with increasing distance from the spinnerette 101. It one embodiment the converging angle of the intermediate channel 107 can be adjusted. After the intermediate channel 107 the fiber curtain enters the lower channel 108.

[0111] The cooling device 102 and the drawing device 106, including intermediate channel 107 and lower channel 108, are together formed as a closed aggregate, meaning that over the entire length of the aggregate, no major air flow can enter from the outside and no major process air supplied in the cooling device 102 can escape to the out-side. Some fume extraction devices directly under the spinneret extracting a minor air volume can be incorporated.

[0112] The fibers 103 leaving the drawing device 106 are then passed through a laying unit 109, which comprises two successively arranged diffusers 110 and 111 are provided, with diffuser 110 having a divergent section and diffuser 111 having a convergent section and an adjoining divergent section. The diffuser angles, in particular the diffuser angles in the divergent regions of the diffusers 110 and 111, are adjustable. Between the diffusers 110 and 111 is a gap 115 through which ambient air is sucked into the fiber flow space.

[0113] After passing through the laying unit 109, the fibers F are deposited as nonwoven web NW on a spinbelt 113, formed from an air-permeable web. A suctioning device 116 is arranged below the laydown area of the spinbelt 113 so suck off process air, which is illustrated in FIG. 3 by the arrow 117.

[0114] Once deposited the nonwoven web NW is first guided through the gap between a pair of pre-consolidation rollers 114 for pre-consolidating the nonwoven web NW.

[0115] FIG. 4 illustrates a production line 200 for producing SMS-type nonwoven laminate fabric sheets NWLS of the present invention.

[0116] Specifically, the machine is configured for producing an SMS-type nonwoven laminate fabric sheet NWLS in the form of, specifically, an SMMSH sheet, where S stands for a regular spunbonded layer, i.e. a layer formed from uncrimped fibers, M stands for a meltblown layer, and SH stands for a high loft spunbonded layer formed from crimped bicomponent fibers. The layer SH within this fabric is the layer that is according to the invention. An SMS-type sheet where the spunbonded structure on one side of the internal meltblown structure is high loft and the spunbonded structure on one side of the internal meltblown structure is a regular spunbonded sheet are known as semi-high-loft structures. The regular S layer provides mechanical stability, the M layer improves liquid barrier properties, and the loft S layer enhances softness and flexibility of the fabric.

[0117] The production line 200 comprises a spinning machine 100 for producing the SH-layer, which is configured as illustrated in FIG. 3. The two reservoirs 118a and 118b contain the two different polymer components A and B used for spinning the bicomponent fibers. An annex reservoir 119 may contain a masterbatch with an additive such as a nucleating agent or a visbreaking additive.

[0118] Further, the production line 200 comprises a spinbelt 213, a first spinning machine 220, comprising only one polymer reservoir 218 and configured for spinning monocomponent fibers, for forming the regular S layer, two meltblowing machines 230 for forming the MM double layer meltblown structure. The machines 220, 230 and 100 are serially arranged along the spinbelt 213.

[0119] Downstream each spinning machine 220 and 100 a pair of pre-consolidation rollers 214 and 114 is arranged. A calender/embossing roll 240 for firmly bonding the layers of the laminate sheet NWLS is arranged downstream the last spinning machine.

[0120] FIG. 5 shows an SEM picture (Scanning Electron Microscope) of a cross-section of a bicomponent fiber having a curved interface line between the polymer components.

[0121] The picture of FIG. 5 was taken by the method explained in the following, which is generally a good method to measure the curvature that defines the present invention. The curvature, in principle, is an absolute geometrical property of the fibers and not dependent on how it is measured. There are naturally some variations of curvature within a single fiber over its length, and not every fiber in the fabric sheet is the same. For practical purposes, it is most preferred that at least ten fibers are picked from a nonwoven sheet, the curvature of each of the picked fiber measured at a randomly selected length position, and the average number used.

[0122] When measured from a nonwoven sheet, firstly the machine direction is identified and the sheet encapsulated and demobilized in a polyester or epoxy resin. The resulting polymer block is then cut in a cross-machine directional plane that is perpendicular to the plane of the encapsulated nonwoven sheet. The cut surface is polished to have a visible interface after etching. The cross-sectional surface of the fibers exposed at the polished cut surface are etched to etch away the more amorphous of the polymer components. Fiber ends having the most circular cross sections and hence being oriented in machine direction as strictly as possible at the cut surface are selected for measurement. Small direction deviations can be corrected for distortion. In practical terms, a useful fiber-cross-section is an ellipse with a ratio between the major and minor axis below 1.2. Preferred is that the fibers show up as circle. After the SEM pictures are taken in a manner generally known to practitioners, picture based measurement systems like DatInf measure from DatInf GmbH can be used to determine curvature.

[0123] It can be seen that the interface between the two polymers is curved. In this example of FIG. 5, the polymer on the left hand side was a propylene--olefin copolymer with a relatively lower crystallization temperature and the polymer on the right hand side was a propylene homopolymer with a relatively higher crystallization temperature. The curved interface is arched toward the left side, i.e. arched toward the propylene--olefin copolymer with a relatively lower crystallization temperature. The polymer component with the higher crystallization temperature has the more compact cross-section.

[0124] The curvature c is measured and calculated according to the following description. First the distance b between the polymer surface intersections is measured with a line drawn between the polymer intersections of the fiber surfaces. This line is the imaginary baseline. It is 540 pixels in the given example. Next the bow height h is measured by drawing a line orthogonally from the baseline (usually the middle of the baseline) to the crest of the curved interface line. The length of the line corresponds to the bow height h and, in the given example, is 111 pixels.

[0125] The curvature is then given by 111/540=0.206. FIG. 5 hence shows a fiber having a curvature within the range required by the invention.

[0126] The invention will now be described with reference to the following non-limiting examples.

Experimental Part A) Methods

[0127] 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. MFR.sub.2 (230 C.) was 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.

[0128] 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 Jul. 1.

[0129] DSC analysis, melting temperature (T.sub.m), melting enthalpy (H.sub.m), crystallization temperature (T.sub.c) and crystallization enthalpy (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 11357-1, -2 and -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.c) 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.

[0130] Number average molecular weight (Mn), weight average molecular weight (Mw), Z-average molecular weight (Mz), and MWD (Mw/Mn) of polypropylene 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.

Grammage and Thickness of the Web

[0131] The unit weight (grammage) of the webs in g/m.sup.2 was determined in accordance with ISO 536:1995. The Thickness of the webs was measured in webs with a grammage of 20 g/m.sup.2.

Curvature (c) of the Crimped Fibers

[0132] Curvature (c) of the fibers was determined by the method as specified above in connection with FIG. 5

Filament Fineness

[0133] The filament fineness in denier has been calculated from the average fibre diameter by using the following correlation:

Fibre diameter (in cm)=(4.44410-6denier/0.91)

B) Examples

[0134] The preparation of propylene polymers (PP1-PP4) used in inventive examples (IE1-6) and the comparative Examples (CE1-2) were described in details below.

[0135] Base polymers: the base polymers were produced as follows: [0136] PP1: The production of base polymer of PP1 is described in WO2017118612 as the polypropylene homopolymer used for inventive examples. [0137] PP2: base polymer of PP2 was prepared by compounding 95 wt % of PP1 base polymer with 5 wt % of PP-MB (described as IE2 in EP3184587B1). [0138] PP3: The catalyst used in the polymerization process of base polymer of PP3 was prepared as follows:

Used Chemicals:

[0139] 20% solution in toluene of butyl ethyl magnesium (Mg(Bu)(Et), BEM), provided by Chemtura 2-ethylhexanol, provided by Amphochem [0140] 3-Butoxy-2-propanol-(DOWANOL PnB), provided by Dow [0141] bis(2-ethylhexyl) citraconate, provided by SynphaBase [0142] TiCl.sub.4, provided by Millenium Chemicals [0143] Toluene, provided by Aspokem [0144] Viscoplex 1-254, provided by Evonik [0145] Heptane, provided by Chevron

Preparation of a Mg Alkoxy Compound

[0146] 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

[0147] 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.

[0148] The thus obtained catalyst was used along with triethyl-aluminium (TEAL) as co-catalyst and dicyclopentyl dimethoxy silane donor (D-donor) as external donor.

[0149] Polymerizations were performed in a Borstar PP-type polypropylene (PP) pilot plant, comprising one loop reactor and one gas phase reactor.

[0150] polymerization conditions for PP3 base polymer are described in Table 1.

TABLE-US-00001 TABLE 1 Preparation of the base propylene polymers PP3 PP3 base Prepolymerization TEAL [g/tC3] 150 Donor [g/tC3] 40 Temperature [ C.] 30 res. time [h] 0.3 Donor [] D Loop Temperature [ C.] 70 Split [%] 44 H2/C3 ratio [mol/kmol] 0.5 C2/C3 ratio [mol/kmol] 4.8 MFR.sub.2 [g/10 min] 2.7 XCS [wt.-%] 5 GPR 1 Temperature [ C.] 80 Pressure [kPa] 2000 Split [%] 56 H2/C3 ratio [mol/kmol] 6.4 C2/C3 ratio [mol/kmol] 11.6

[0151] The base polymer of PP3 has been visbroken together with 5 wt % of PP-MB, 500 ppm of Irganox 3114 (BASF), 500 ppm of Irgafos 168 (BASF), 500 ppm of Ceasit FI (Baerlocher) by a co-rotating twin-screw extruder at 200-230 C. using an appropriate amount of (tert.butylperoxy)-2,5-dimethylhexane (Trigonox 101, distributed by Akzo Nobel, Netherlands).

[0152] PP4: The production of base polymer of PP4 is described in EP2999721B2 as inventive example IE3.

TABLE-US-00002 TABLE 2 properties of polypropylene polymers for inventive and comparative examples measured after visbreaking on pellets PP1 PP2 PP3 PP4 C2 content [wt.-%] 0.4 0.4 2.1 3.6 MFR final [g/10 min] 27 27 27 33 Mw/Mn [] 4.7 4.7 4.6 6.4 Mz/Mw [] 2.07 2.08 2.06 2.7 XCS [wt.-%] 4.5 4.4 3.4 8.1 Tg [ C.] 0.5 0.5 2.1 4.7 Tm [ C.] 158 163 154 149 Tc [ C.] 111 124 119 120

Preparation of Crimped Multicomponent Fiber Having a Side by Side Cross-Sectional Configuration

[0153] A series of options with two polymers in a side-by-side configuration was processed on a machine as illustrated in FIG. 3.

[0154] For all options, a basis weight of 20 g/m.sup.2 for the spunbonded nonwoven material sheet was used. Specific polymer throughput in the spinnerette 101 was approximately 0.52 g polymer per hole per minute. The cabin pressure was kept mostly constant at 4000 Pascal. Other process settings were kept in a normal range for the production of crimped fibers. For instance, the ceramic pre-consolidation rollers 114 on the spinbelt at the outlet side of the beam were run with a temperature of 50-70 C. The calender (not shown in FIG. 3, but positioned downstream the pre-consolidation rollers 114) was a standard open dot calender with 12% bonding area and 25 circular bonding points per cm.sup.2. The temperature of the calender was in the range of 135-145 C.

[0155] Table 3 summarizes data regarding polymer composition used in the fiber preparation process, bow height of the cross-section of the fiber and thickness of the fabric made from the fibers with respect to inventive examples IE1, IE2, IE3, IE4, IE5 and IE6 and CE1 to CE2.

TABLE-US-00003 TABLE 3 Thickness of web@ Exam- Polymer Polymer T.sub.c Mz/ Curvature 20 gsm ples A B [A:B] [ C.] Mw (c) [mm] CE1 PP2 PP4 40:60 4 0.62 0.031 0.33 CE2 PP2 PP3 40:60 5 0.02 0.278 0.36 IE1 PP1 PP2 60:40 13 0.01 0.114 0.46 IE2 PP1 PP2 30:70 13 0.01 0.129 0.54 IE3 PP1 PP3 50:50 8 0.01 0.116 0.57 IE4 PP1 PP2 40:60 13 0.01 0.171 0.58 IE5 PP1 PP4 40:60 9 0.63 0.134 0.63 IE6 PP1 PP2 30:70 13 0.01 0.120 0.70

[0156] As can be seen, in order to get higher thickness of webs, the polymers in both sides need to have the right combination. As can be seen from table 3 webs of IE1 to IE6 have much higher thickness than the webs of CE1 and 2, while the grammage of the webs are the same (20 g/m2).