JP2014502315A - Bicomponent fibers and methods for making them - Google Patents

Abstract

  The present invention relates to bicomponent polymer fibers and methods for forming these fibers. A bicomponent polymer fiber having a core comprising a core polymer and a sheath comprising a sheath polymer, wherein the sheath polymer is a polyolefin having a Mw of less than about 65,000 g / mol is described. The core polymer has a Mw that is at least about 20,000 g / mol greater than the Mw of the sheath polymer. (I) forming a melt blend of the core polymer and the sheath polymer; and (ii) using an extrusion die having a length to diameter ratio of about 10 or greater, sufficient shear to send the sheath polymer to the die wall. Also described is a method of forming a bicomponent fiber comprising extruding a molten polymer blend under conditions and (iii) forming a meltblown fiber having a core comprising a core polymer and a sheath comprising a sheath polymer. ing.

Description

  Propylene-based polymers and copolymers are well known in the art for their usefulness in the production of meltblown nonwoven fibers. Such fibers are formed into nonwovens in particular and have a wide variety of uses when used in applications such as medical and hygiene products, garments, filter media, and adsorbent products, among others. Meltblown nonwoven fibers are particularly useful in hygiene products such as baby diapers, adult incontinence products, and feminine hygiene products. One consideration for these fibers, particularly in hygiene applications, is the ability to produce aesthetically pleasing fabrics that have good leakage performance at low cost. Good leak performance is achieved by the elasticity of the elastic layer of the fabric, which results in a better fit and fit for the wearer and less leak. A common aesthetic challenge associated with the production of propylene-based nonwovens is their often rubbery, sticky or sticky feel. Furthermore, stickiness or tackiness can lead to processing problems.

  To date, the aesthetic challenges arising from the rubbery and fabric rubber-like or sticky feel have been addressed in two ways. First, nonwoven fabrics formed from propylene-based fibers were coated with an aesthetically pleasing surface layer, resulting in a multilayer composition. The main drawback of such compositions is the increased cost resulting from the need to purchase or manufacture the surface layer and from the added complexity in the supply chain. Second, bicomponent fibers (sometimes referred to as “conjugate” fibers) are separated by a single polymer stream to form a fiber comprising two (or more) polymer compositions. Prepared using a spinning process fed to a die or spinneret. The fiber thus obtained has the properties of both polymer components. Bicomponent fibers are generally classified according to their cross-sectional structure. Such structures include, but are not limited to, cross-sectional structures such as side-by-side, sheath-core, islands-in-the-sea, or segmented pie. obtain. In addition to the processing challenges (such as reduced throughput) that result from flowing two or more chemically and mechanically different polymers, the disadvantages of these conventionally produced bicomponent fibers are two. The cost of the conversion equipment required to allow the polymer to be independently fed to a single die.

  Thus, it would be beneficial to produce fibers with desirable properties for use in elastic nonwovens while reducing the cost and processing challenges encountered so far. The present invention involves blending a low molecular weight polymer component and a high molecular weight polymer component to form a polymer blend. The bicomponent fiber is then formed from the blend under shear conditions sufficient to move the low molecular weight polymer out of the fiber due to molecular weight differences and limited miscibility of the polymers selected for use in the blend. The fiber thus obtained has a core and a sheath structure, the core is formed from a high molecular weight polymer, and the sheath is formed from a low molecular weight polymer.

The present invention relates to bicomponent polymer fibers and methods for forming these fibers. In some embodiments, the invention provides a bicomponent polymer fiber having a core comprising a core polymer and a sheath comprising a sheath polymer, wherein the sheath polymer has a weight average molecular weight (Mw) of less than about 65,000 g / mol. ) And the core polymer has a Mw that is at least about 20,000 g / mol greater than the Mw of the sheath polymer. In certain embodiments, the core polymer comprises about 5 to about 30% by weight ethylene and / or C ₄ -C ₁₂ alpha olefin and has a triad tacticity of greater than about 90% and a heat of fusion of less than about 75 J / g. The sheath polymer is an olefin wax. In other embodiments, the present invention uses (i) forming a melt blend of a core polymer and a sheath polymer, and (ii) using an extrusion die having a length to diameter ratio of about 10 or greater, Extruding the molten polymer blend under shear conditions sufficient to pass the polymer to the die wall; and (iii) forming a meltblown fiber having a core comprising a core polymer and a sheath comprising a sheath polymer. The method of forming component fibers is the subject. In such methods, the sheath polymer is a polyolefin having a Mw of less than about 65,000 g / mol and the core polymer has a Mw that is at least about 20,000 g / mol greater than the Mw of the sheath polymer.

The present invention is directed to bicomponent polymer fibers having a core comprising a core polymer and a sheath comprising a sheath polymer, and methods for forming such fibers. The core polymer and sheath polymer differ in molecular weight between the two polymers so that the core polymer stays in the center of the fiber, while the sheath polymer moves outside the extrusion die to form the outer coating of the fiber, and These limited miscibility are selected so that the polymer can be separated when it is exposed to shear forces during the extrusion process.
While this application refers to “core” and “sheath” and “core polymer” and “sheath polymer”, these terms are used for convenience only. It should be noted that the polymer may not be completely separated during the extrusion process and there may be no defined boundary between the fiber core and sheath described herein. . Rather, the fibers of the present invention also include those fibers having a cross-sectional gradient with the highest concentration of sheath polymer at the surface of the fiber and the highest concentration of core polymer at the center of the fiber.

  As used herein, the term “copolymer” is meant to include polymers having two or more monomers, optionally with other monomers, and can mean interpolymers, terpolymers, and the like. The term “polymer” as used herein includes, but is not limited to, homopolymers, copolymers, terpolymers, etc., and alloys and blends thereof. The term “polymer” as used herein also includes impact, block, graft, random and alternating copolymers. The term “polymer” should further include all possible geometrical configurations, unless otherwise stated. Such conformations can include isotactic, syndiotactic and random symmetries. The term “blend” as used herein means a mixture of two or more polymers.

  The terms “monomer” or “comonomer” as used herein can mean a monomer used to form a polymer, ie, an unreacted compound in a form prior to polymerization, and After incorporation into a polymer (also referred to herein as “units derived from [monomer]” by a polymerization reaction, which typically has fewer hydrogen atoms than it has before the polymerization reaction. Monomer can be meant. Different monomers are discussed herein, including propylene monomers, ethylene monomers, and diene monomers.

  “Polypropylene” as used herein includes propylene homopolymers and copolymers or mixtures thereof. Products comprising one or more propylene monomers polymerized with one or more additional monomers may be more commonly known as random copolymers (RCP) or impact copolymers (ICP). Impact copolymers are also known in the art as heterophasic copolymers. “Propylene-based” as used herein is meant to include any polymer comprising propylene alone or in combination with one or more comonomers, where propylene is the major component (For example, more than 50% by weight of propylene). Similarly, “ethylene-based” as used herein is meant to include any polymer comprising ethylene alone or in combination with one or more comonomers, wherein ethylene is The major component (for example, greater than 50 wt% ethylene).

Core Polymers Polymers intended for use as the core polymer in the fibers described herein include any polymer suitable for use in elastic nonwovens and articles. Such polymers typically include, but are not limited to, propylene-based polymers, ethylene-based polymers, styrene block copolymers, propylene-ethylene block copolymers, acrylates, and combinations of the above. In certain embodiments of the invention, the core polymer has a high molecular weight compared to the molecular weight of the sheath polymer. For example, in some embodiments, the core polymer is at least about 20,000 g / mol greater than the M _{w of} the sheath polymer, or at least about 50,000 g / mol greater, or at least about 75,000 g / mol greater, or at least It has a weight average molecular weight (M _w ) greater than about 100,000 g / mol. In the same or other embodiments, the core polymer has a M _w of greater than about 75,000 g / mol, or greater than about 100,000 g / mol, or greater than about 125,000 g / mol.

Propylene-based polymers In certain embodiments of the invention, the core polymer is propylene and from about 5 to about 30% by weight of one or more comonomers selected from ethylene and / or C ₄ -C ₁₂ α-olefins. One or more propylene-based polymers. In one or more embodiments, the α-olefin comonomer unit may be derived from ethylene, butene, pentene, hexene, 4-methyl-1-pentene, octene, or decene. Although the embodiments described below are discussed with reference to ethylene as the α-olefin comonomer, the embodiments are equally applicable to other copolymers having other α-olefin comonomers. In this regard, the copolymer may simply be referred to as a propylene-based polymer with reference to ethylene as the α-olefin.

  In one or more embodiments, the propylene-based polymer is at least about 5%, or at least about 6%, or at least about 7%, or at least about 8%, or at least about 10%, or at least It may contain units derived from about 12% by weight of ethylene. In these or other embodiments, the copolymer is up to about 30%, or up to about 25%, or up to about 22%, or up to about 20%, or up to about 19%, or up to about 18% by weight. Up to or up to about 17% by weight of units derived from ethylene, the weight percent being based on the total weight of units derived from propylene and units derived from α-olefins. In other words, the propylene-based polymer is at least about 70% by weight, or at least about 75% by weight, or at least about 80% by weight, or at least about 81% by weight units derived from propylene, or at least about 82% by weight. % Of propylene-derived units, or at least about 83% by weight of units derived from propylene, and in these or other embodiments, the copolymer is up to about 95% by weight, or up to about 94% by weight, or Up to about 93 wt%, or up to about 92 wt%, or up to about 90 wt%, or up to about 88 wt% of propylene-derived units may be included, the weight percent being units derived from propylene and alpha-olefins Is based on the total weight of units derived from In certain embodiments, the propylene-based polymer can comprise from about 8 to about 20% by weight of units derived from ethylene, or from about 12 to about 18% by weight of units derived from ethylene.

The propylene-based polymer of one or more embodiments is characterized by a melting point (Tm) that can be determined by differential scanning calorimetry (DSC). For purposes herein, the highest temperature peak maximum is considered the melting point of the polymer. In this context, “peak” is defined as the change in the overall slope of the DSC curve from positive to negative (heat flow vs. temperature) that forms a maximum without a shift in baseline, where the DSC curve is Plot so that the endothermic reaction is shown with a positive peak.
In one or more embodiments, the Tm (determined by DSC) of the propylene-based polymer is less than about 115 ° C, or less than about 110 ° C, or less than about 100 ° C, or less than about 90 ° C.
In one or more embodiments, the propylene-based polymer may be characterized by its heat of fusion (Hf) as determined by DSC. In one or more embodiments, the propylene-based polymer is at least about 0.5 J / g, or at least about 1.0 J / g, or at least about 1.5 J / g, or at least about 3.0 J / g, or It may have an Hf that is at least about 4.0 J / g, or at least about 6.0 J / g, or at least about 7.0 J / g. In these or other embodiments, the propylene-based copolymer is characterized by an Hf of less than about 75 J / g, or less than about 70 J / g, or less than about 60 J / g, or less than about 50 J / g, or less than about 30 J / g. May be attached.

  As used herein, the DSC procedure for determining Tm and Hf includes: The polymer is pressed in a heated press at a temperature of about 200 ° C. to about 230 ° C., and the polymer sheet thus obtained is suspended in air under ambient conditions and allowed to cool. About 6-10 mg of polymer sheet is removed with a punching die. The 6-10 mg sample is annealed at room temperature for about 80-100 hours. At the end of this period, the sample is placed in a DSC (Perkin Elmer Pyris One Thermal Analysis System) and cooled to about −50 ° C. to about −70 ° C. The sample is heated at 10 ° C./min to achieve a final temperature of about 200 ° C. The sample is held at 200 ° C. for 5 minutes and a second cooling-heating cycle is performed. Record both cycles of events. Thermal output is recorded as the area under the melting peak of the sample, typically occurring at about 0 ° C to about 200 ° C. This is measured in joules and is a measure of the Hf of the polymer.

Propylene-based polymers have triadactivities of three propylene units as measured by ¹³ C NMR, 75% or more, 80% or more, 85% or more, 90% or more, 92% or more, 95% or more, or 97% or more. You can have a city. In one or more embodiments, triad tacticity is about 75 to about 99%, or about 80 to about 99%, or about 85 to about 99%, or about 90 to about 99%, or about 90 to about It may be 97% or in the range of about 80 to about 97%. Triad tacticity is determined by the method described in US Patent Application Publication No. 2004/0236042.

The propylene-based polymer may have a tacticity index m / r ranging from a lower limit of 4 or 6 to an upper limit of 8 or 10 or 12. The tacticity index, represented herein as “m / r”, is determined by ¹³ C nuclear magnetic resonance (“NMR”). The tacticity index m / r is calculated as defined by HN Cheng in 17 MACROMOLECULES, pp. 1950-1955 (1984), which is incorporated herein by reference. The designation “m” or “r” represents the configuration of adjacent pairs of propylene groups, “m” means meso, and “r” means racemic. An m / r ratio of 1.0 generally represents a syndiotactic polymer and an m / r ratio of 2.0 generally represents an atactic material. Isotactic materials may theoretically have ratios approaching infinity, and many by-product atactic polymers have sufficient isotactic content that results in ratios greater than 50.

In one or more embodiments, the propylene-based polymer comprises about 0.5% to about 40%, or about 1% to about 30%, or about 5% to about 25% crystals, as determined by the DSC procedure. It can have a degree of conversion. Crystallinity may be determined by dividing the Hf of the sample by the Hf of the 100% crystalline polymer, which is assumed to be 189 joules / gram for isotactic polypropylene, or 350 joules / gram for polyethylene. Is done.
In one or more embodiments, the propylene-based polymer, as measured by ASTM D-792 test method at room temperature, about 0.85 g / cm ³ ~ about 0.92 g / cm ³ or from about 0.86 g / cm, ^It may have a density from ³ to about 0.90 g / cm ³ , or from about 0.86 g / cm ³ to about 0.89 g / cm ³ .
In one or more embodiments, the propylene-based polymer is about 100 g / 10 min or less, or about 50 g / 10 min or less, or about 25 g / 10 min or less, or about 10 g / 10 min or less, or Melt index (MI) of about 9.0 g / 10 min or less, or about 8.0 g / 10 min or less, or about 7.0 g / 10 min or less (ASTM D-1238, 2.16 kg, at 190 ° C.) Can have.

In one or more embodiments, the propylene-based polymer is greater than about 1 g / 10 minutes, or greater than about 2 g / 10 minutes, or about as measured by ASTM D-1238 (2.16 kg weight, at 230 ° C.). It may have a melt flow rate (MFR) greater than 5 g / 10 minutes, or greater than about 8 g / 10 minutes, or greater than about 10 g / 10 minutes. In the same or other embodiments, the propylene-based polymer is less than about 500 g / 10 minutes, or less than about 400 g / 10 minutes, or less than about 300 g / 10 minutes, or less than about 200 g / 10 minutes, or about 100 g / 10 minutes. May have an MFR of less than, or less than about 50 g / 10 minutes, or less than about 25 g / 10 minutes. In certain embodiments, the propylene-based polymer can have an MFR of about 1 to about 100 g / 10 minutes, or about 2 to about 50 g / 10 minutes, or about 5 to about 25 g / 10 minutes.
In one or more embodiments, the propylene-based polymer has a Mooney viscosity [ML (1 + 4) @ of less than about 100, or less than about 75, or less than about 50, or less than about 30, as determined by ASTM D-1646. 125 ° C.].

In one or more embodiments, the first and second polymers may have a g ′ index value of 0.95 or greater, or at least 0.97, or at least 0.99, where g ′ is The intrinsic viscosity of isotactic polypropylene is measured as the Mw of the polymer using as a baseline. For use herein, the g ′ index is defined as follows, where η _b is the intrinsic viscosity of the polymer and η _l is the same viscosity average molecular weight (M _v ) as the polymer: It is the intrinsic viscosity of a linear polymer. η _l = KM _v ^α , K and α are the values measured for the linear polymer and should be obtained with the same instrument used for g ′ index measurement.

In one or more embodiments, the propylene-based copolymer has from about 50,000 to about 5,000,000 g / mol, or from about 75,000 to about 1,000,000 g / mol, or from about 100,000 to about It can have a weight average molecular weight (Mw) of 500,000 g / mol, or about 125,000 to about 300,000 g / mol.
In one or more embodiments, the propylene-based copolymer is from about 2,500 to about 2,500,000 g / mol, or from about 5,000 to about 500,000 g / mol, or from about 10,000 to about 250, 000 g / mol, or a number average molecular weight (Mn) of about 25,000 to about 200,000 g / mol.

In one or more embodiments, the propylene-based copolymer has from about 10,000 to about 7,000,000 g / mol, or from about 50,000 to about 1,000,000 g / mol, or from about 80,000 to about It can have a Z-average molecular weight (Mz) of 700,000 g / mol, or from about 100,000 to about 500,000 g / mol.
In one or more embodiments, the molecular weight distribution (equivalent to MWD, Mw / Mn) of the propylene-based copolymer is about 1 to about 40, or about 1 to about 15, or about 1.8 to about 5, or about It may be 1.8 to about 3.

  Techniques for determining molecular weights (Mn, Mw and Mz) and MWD are described in US Pat. No. 4,540,753 (Cosewith, Ju and Verslate), incorporated herein by reference for purposes of US patent practice. And references cited therein, and Macromolecules, 1988, Vol. 21, pp. 3360-3371 (Ver Strate et al.), Which is incorporated herein by reference for purposes of US patent practice. .) And references cited therein. For example, molecular weight can be determined by size exclusion chromatography (SEC) by using a Waters 150 gel permeation chromatograph equipped with a differential refractometer and calibrated using polystyrene standards.

  Optionally, the propylene-based polymer can also include one or more dienes. The term “diene” is defined as a hydrocarbon compound having two sites of unsaturation, ie, a compound having two double bonds connecting carbon atoms. Depending on the context, the term “diene” in this patent broadly means, for example, a diene monomer before polymerization, or a diene monomer after polymerization has been initiated, which forms part of the polymerization medium (diene monomer units or Also referred to as units derived from diene). Exemplary dienes suitable for use in the present invention include, but are not limited to, butadiene, pentadiene, hexadiene (eg, 1,4-hexadiene), heptadiene (eg, 1,6-heptadiene), octadiene (eg, 1,7-octadiene), nonadiene (eg, 1,8-nonadiene), decadiene (eg, 1,9-decadiene), undecadiene (eg, 1,10-undecadiene), dodecadiene (eg, 1,11-dodecadiene) , Tridecadiene (eg, 1,12-tridecadiene), tetradecadiene (eg, 1,13-tetradecadiene), pentadecadiene, hexadecadiene, heptadecadiene, octadecadiene, nonadecadiene, icosadien, heneicosadiene, Docosadien, bird Sajien include Tetorakosajien, Pentakosajien, Hekisakosajien, Heputakosajien, Okutakosajien, Nonakosajien, polybutadiene having a triacontanyl dienes, and the molecular weight of less than 1,000g / mol (Mw). Examples of straight chain acyclic dienes include, but are not limited to, 1,4-hexadiene and 1,6-octadiene. Examples of branched acyclic dienes include, but are not limited to, 5-methyl-1,4-hexadiene, 3,7-dimethyl-1,6-octadiene, and 3,7-dimethyl-1,7- Octadiene is included. Examples of monocyclic alicyclic dienes include, but are not limited to, 1,4-cyclohexadiene, 1,5-cyclooctadiene, and 1,7-cyclododecadiene. Examples of multicyclic alicyclic fused and bridged dienes include, but are not limited to, tetrahydroindene; norbornadiene; methyltetrahydroindene; dicyclopentadiene; bicyclo (2.2.1) hepta-2,5- Dienes; and alkenyl norbornene, alkylidene norbornene, cycloalkenyl norbornene, and cycloalkylidene norbornene [eg, 5-methylene-2-norbornene, 5-ethylidene-2-norbornene, 5-propenyl-2-norbornene, 5-isopropylidene-2 -Norbornene, 5- (4-cyclopentenyl) -2-norbornene, 5-cyclohexylidene-2-norbornene, and 5-vinyl-2-norbornene are included]. Examples of cycloalkenyl-substituted alkenes include, but are not limited to, vinylcyclohexene, allylcyclohexene, vinylcyclooctene, 4-vinylcyclohexene, allylcyclodecene, vinylcyclododecene, and tetracyclododecadiene. In some embodiments of the invention, the diene is 5-ethylidene-2-norbornene (ENB); 1,4-hexadiene; 5-methylene-2-norbornene (MNB); 1,6-octadiene; 1,7-dimethyl-1,6-octadiene; 1,3-cyclopentadiene; 1,4-cyclohexadiene; vinyl norbornene (VNB); dicyclopentadiene (DCPD), and combinations thereof Selected from. In one or more embodiments, the diene is ENB.

In some embodiments, the propylene-based polymer can include 0.05 to about 6% by weight of units derived from diene. In further embodiments, the polymer is from about 0.1 to about 5.0 wt% diene units, or from about 0.25 to about 3.0 wt% diene units, or about 0.5 ˜1.5% by weight units derived from diene.
In one or more embodiments, the propylene-based polymer can be grafted (eg, “functionalized”) using one or more graft monomers. As used herein, the term “graft” refers to the covalent attachment of a graft monomer to the polymer chain of a propylene-based polymer.

  The graft monomer can be or can include at least one ethylenically unsaturated carboxylic acid or acid derivative, such as an acid anhydride, ester, salt, amide, imide, acrylate, and the like. Exemplary monomers include, but are not limited to, acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, mesaconic acid, maleic anhydride, 4-methylcyclohexene-1,2-dicarboxylic anhydride Bicyclo (2.2.2) octene-2,3-dicarboxylic acid anhydride, 1,2,3,4,5,8,9,10-octahydronaphthalene-2,3-dicarboxylic acid anhydride, 2-Oxa-1,3-diketospiro (4.4) nonene, bicyclo (2.2.1) heptene-2,3-dicarboxylic anhydride, maleopimaric acid, tetrahydrophthalic anhydride, norbornene-2,3- Dicarboxylic acid anhydride, nadonic acid anhydride, methyl nadic acid anhydride, hymic acid anhydride, methyl hymic acid anhydride, and 5-methylbicyclo (2.2.1) hep It includes down-2,3-dicarboxylic anhydride. Other suitable grafting monomers include methyl acrylate and higher alkyl acrylate, methyl methacrylate and higher alkyl methacrylate, acrylic acid, methacrylic acid, hydroxymethyl methacrylate, hydroxylethyl methacrylate and higher hydroxyalkyl methacrylate and methacrylic acid. Glycidyl acid is included. Maleic anhydride is a preferred grafting monomer.

  In one or more embodiments, the grafted propylene-based polymer is about 0.5 to about 10% by weight, more preferably about 0.5 to about 6% by weight, more preferably about 0.5 to about 3%. In other embodiments, from about 1 to about 6% by weight, more preferably from about 1 to about 3% by weight of ethylenically unsaturated carboxylic acid or acid derivative. In a preferred embodiment where the grafting monomer is maleic anhydride, the maleic anhydride concentration in the grafted polymer is preferably in the range of about 1 to about 6 wt%, preferably at least about 0.5 wt%, high Is preferably about 1.5% by weight.

Preparation of propylene-based polymer The polymerization of propylene-based polymer is carried out by reacting the monomers in the presence of the catalyst system described herein at a temperature of 0 ° C. to 200 ° C. for a period of 1 second to 10 hours. Is called. Uniform conditions are preferably used, using excess monomer as diluent, such as a continuous solution process or a bulk polymerization process. The continuous process may use some form of agitation to reduce the concentration difference in the reactor and maintain steady state polymerization conditions. The heat of the polymerization reaction is preferably removed by cooling the polymerization feed and heating the polymer until it is polymerized, although an internal cooling system may be used.
A further description of exemplary methods suitable for the preparation of the propylene-based polymers described herein is described in US Pat. No. 6,881, incorporated herein by reference for purposes of US patent practice. It can be found in 800.
The triad tacticity and tacticity index of the propylene-based copolymer is determined by the catalyst (which affects the stereoregularity of the propylene configuration), the polymerization temperature (the stereoregularity can be reduced by increasing the temperature), and the type of comonomer And the amount (which tends to reduce the level of sequences derived from longer propylene).

Too much comonomer can reduce the degree of crystallinity brought about by crystallization of sequences derived from stereoregular propylene before the material lacks strength. If too little comonomer is present, the material can become overly crystalline. The comonomer content and sequence distribution of the polymer can be measured using ¹³ C nuclear magnetic resonance (NMR) by methods well known to those skilled in the art. As described in Wheeler and Willis, Applied Spectroscopy, 1993, Vol. 47, pp. 1128-1130, comonomer content in different molecular weight ranges can be measured by Fourier Transform Infrared Spectroscopy (FTIR) combined with GPC sampling. Can be measured using methods well known to those skilled in the art. For propylene ethylene copolymers containing more than 75% by weight of propylene, the comonomer content (ethylene content) of such polymers can be measured as follows. The uniform film is pressed at a temperature of about 150 ° C. or higher and placed on a Perkin Elmer PE1760 infrared spectrophotometer. Samples of the full spectrum from 600 cm-1 to 4000 cm-1 can be recorded and the monomer weight percent of ethylene can be calculated by the following equation: Ethylene weight% = 82.585−111.987X + 30.045X2 (where X is the ratio of the peak height at 1155 cm −1 to the peak height at 722 cm −1 or 732 cm −1, whichever is higher) is there). For propylene ethylene copolymers having a propylene content of 75% by weight or less, the comonomer (ethylene) content can be measured using the procedure described in Wheeler and Willis.

  Reference is made to US Pat. No. 6,525,157, whose test method is also fully applicable to the various measurements referred to in this specification and claims, for GPC measurements, NMR and DSC measurements. Contains further details about the determination of the ethylene content by.

  The catalyst may also control stereoregularity in combination with comonomer and polymerization temperature. The propylene-based polymers described herein are prepared using one or more catalyst systems. As used herein, a “catalyst system” includes at least one transition metal compound (also referred to as a catalyst precursor) and an activator. Contacting the transition metal compound (catalyst precursor) with the activator in solution upstream of or in the polymerization reactor of the disclosed process produces the catalytically active component (catalyst) of the catalyst system. Any given transition metal compound or catalyst precursor can produce catalytically active components (catalysts) by various activators, providing a wide range of catalysts that can be deployed in the process of the present invention. The catalyst system of the present invention comprises at least one transition metal compound and at least one activator. However, the catalyst system of the present disclosure can also include a plurality of transition metal compounds in combination with one or more activators. Such a catalyst system may optionally include an impurity scavenger. Each of these components is described in further detail below.

In one or more embodiments of the present invention, the catalyst system used to produce the propylene-based polymer comprises a metallocene compound. In some embodiments, the metallocene compound is a bridged bisindenyl metallocene having the general formula (In ¹ ) Y (In ² ) MX ₂ , wherein In ¹ and In ² are bonded to M and Y Are the same substituted or unsubstituted indenyl groups bridged by, Y is a bridging group, the number of atoms in the direct chain connecting In ¹ and In ² is 1 to 8, and the direct chain is C or Si is included, and M is a Group 3, 4, 5, or 6 transition metal. In ¹ and In ² may be substituted or unsubstituted. When In ¹ and In ² are substituted with one or more substituents, the substituents are halogen atoms, C ₁ -C ₁₀ alkyl, C ₅ -C ₁₅ aryl, C ₆ -C ₂₅ alkyl aryl, and Selected from the group consisting of N- or P-containing alkyl or aryl. Exemplary metallocene compounds of this type include, but are not limited to, μ-dimethylsilylbis (indenyl) hafnium dimethyl and μ-dimethylsilylbis (indenyl) zirconium dimethyl.

In other embodiments, the metallocene compound can be a bridged bisindenyl metallocene having the general formula (In ¹ ) Y (In ² ) MX ₂ , wherein In ¹ and In ² are bonded to M and Is the same bridged 2,4-substituted indenyl group, Y is a bridging group, the number of atoms in the direct chain connecting In ¹ and In ² is 1-8, and the direct chain is C or Si is included, and M is a Group 3, 4, 5, or 6 transition metal. In ¹ and In ² are substituted with a methyl group at the 2-position and from the group consisting of C ₅ -C ₁₅ aryl, C ₆ -C ₂₅ alkyl aryl, and N- or P-containing alkyl or aryl at the 4 position Substituted with a selected substituent. Exemplary metallocene compounds of this type include, but are not limited to, (μ-dimethylsilyl) bis (2-methyl-4- (3 ′, 5′-di-tert-butylphenyl) indenyl) zirconium dimethyl, (Μ-dimethylsilyl) bis (2-methyl-4- (3 ′, 5′-di-tert-butylphenyl) indenyl) hafnium dimethyl, (μ-dimethylsilyl) bis (2-methyl-4-naphthylindenyl) ) Zirconium dimethyl, (μ-dimethylsilyl) bis (2-methyl-4-naphthylindenyl) hafnium dimethyl, (μ-dimethylsilyl) bis (2-methyl-4- (N-carbazyl) indenyl) zirconium dimethyl, and (Μ-dimethylsilyl) bis (2-methyl-4- (N-carbazyl) indenyl) hafnium dimethyl Be turned.

  Alternatively, in one or more embodiments of the invention, the metallocene compound may correspond to one or more of the formulas disclosed in US Pat. No. 7,601,666. Such metallocene compounds include, but are not limited to, dimethylsilylbis (2- (methyl) -5,5,8,8-tetramethyl-5,6,7,8-tetrahydrobenzo (f) indenyl). Hafnium dimethyl, diphenylsilyl bis (2- (methyl) -5,5,8,8-tetramethyl-5,6,7,8-tetrahydrobenzo (f) indenyl) hafnium dimethyl, diphenylsilyl bis (5,5, 8,8-tetramethyl-5,6,7,8-tetrahydrobenzo (f) indenyl) hafnium dimethyl, diphenylsilylbis (2- (methyl) -5,5,8,8-tetramethyl-5,6 7,8-tetrahydrobenzo (f) indenyl) zirconium dichloride and cyclo-propylsilylbis (2- (methyl) -5,5,8,8 Tetramethyl-5,6,7,8-tetrahydrobenzo (f) indenyl) contains hafnium dimethyl.

In one or more embodiments of the present invention, the activator of the catalyst system used to produce the propylene-based polymer includes a cationic component. In some embodiments, the cationic component has the formula [R ¹ R ² R ³ AH] ⁺ , where A is nitrogen and R ¹ and R ² together are — (CH ₂ ) _a - group (wherein, a is 3, 4, 5 or 6, together with the nitrogen atom, 4-membered, 5-membered to form a non-aromatic ring of 6-membered or 7-membered, which Optionally having one or more aromatic or heteroaromatic rings fused via adjacent ring carbon atoms, and R ³ is C ₁ , C ₂ , C ₃ , C ₄ or C ₅ alkyl, or N-methylpyrrolidinium or N-methylpiperidinium. In other embodiments, the cationic component has the formula [R _n AH] ⁺ , where A is nitrogen, n is 2 or 3, and all R are the same, C ₁ -C ₃ alkyl group, e.g., trimethyl ammonium, trimethyl anilinium, triethyl ammonium, dimethylanilinium or dimethyl ammonium,.

In one or more embodiments of the present invention, the catalyst system activator used to produce the propylene-based polymer comprises an anionic component [Y] ^- . In some embodiments, the anionic component is a non-coordinating anion (NCA) having the formula [B (R ⁴ ) ₄ ] ^— , wherein R ⁴ is an aryl group or a substituted aryl group; The one or more substituents are the same or different and are selected from the group consisting of alkyl, aryl, halogen atoms, aryl halides, and haloalkylaryl groups. In one or more embodiments, the substituent is a perhalogenated aryl group or a perfluorinated aryl group including but not limited to perfluorophenyl, perfluoronaphthyl and perfluorobiphenyl.
Together, the cationic and anionic components of the catalyst system described herein form an activator compound. In one or more embodiments of the invention, the activator is N, N-dimethylanilinium-tetra (perfluorophenyl) borate, N, N-dimethylanilinium-tetra (perfluoronaphthyl) borate, N, N- Dimethylanilinium-tetrakis (perfluorobiphenyl) borate, N, N-dimethylanilinium-tetrakis (3,5-bis (trifluoromethyl) phenyl) borate, triphenylcarbenium-tetra (perfluorophenyl) borate, triphenylcarbe Ni-tetra (perfluoronaphthyl) borate, triphenylcarbenium-tetrakis (perfluorobiphenyl) borate, or triphenylcarbenium-tetrakis (3,5-bis (trifluoromethyl) phenyl) borate Over door may be.

  Any catalyst system resulting from any combination of metallocene compounds, cationic activator components, and anionic activator components referred to in the above paragraph should be considered explicitly disclosed herein. It can be used according to the present invention in the polymerization of one or more olefin monomers. Also, a combination of two different activators can be used with the same or different metallocenes.

Suitable activators for the methods of the present invention also include aluminoxane (or alumoxane) and aluminum alkyl. Without being bound by theory, alumoxanes are typically cyclic compounds of the general formula (R ^x —Al—O) _n , or linear compounds R ^x (R ^x —Al—O). _n It is considered to be an oligomeric aluminum compound represented by AlR ^x ₂ . Most commonly, alumoxanes are considered to be a mixture of cyclic and linear compounds. In the general formula of alumoxane, R ^x is independently a C ₁ -C ₂₀ alkyl group such as methyl, ethyl, propyl, butyl, pentyl, isomers thereof, etc., and n is an integer of 1-50. . In one or more embodiments, R ^x is methyl and n is at least 4. Methylalumoxane (MAO), and modified MAOs that contain some higher alkyl groups to improve solubility, ethylalumoxane, iso-butylalumoxane, and the like for the methods disclosed herein. Useful.
Furthermore, catalyst systems suitable for use in the present invention may contain additional activators (coactivators) and / or scavengers in addition to the transition metal compounds and activators described above. A coactivator is a compound that can react with a transition metal complex such that an active catalyst is formed when used in combination with an activator. Coactivators include alumoxanes and aluminum alkyls.

In some embodiments of the present invention, the scavenger may be used to “purify” the reaction of poisons that react separately from the catalyst to inactivate the catalyst. A typical aluminum alkyl or boron alkyl moiety useful as a scavenger is of the general formula R ^x JZ ₂ , wherein J is aluminum or boron and R ^x is a C ₁ -C ₂₀ alkyl group such as methyl, Ethyl, propyl, butyl, pentyl, and isomers thereof, wherein each Z is independently R ^x or a different monovalent anionic ligand such as halogen (Cl, Br, I), alkoxide (OR ^x ), etc. Is). Exemplary aluminum alkyls include triethyl aluminum, diethyl aluminum chloride, ethyl aluminum dichloride, tri-iso-butyl aluminum, tri-n-octyl aluminum, tri-n-hexyl aluminum, trimethyl aluminum, and combinations thereof. . Exemplary boron alkyl includes triethylboron. The scavenger compounds may also be alumoxanes and modified alumoxanes including methylalumoxane and modified methylalumoxane.

In some embodiments, the catalyst system used to produce the propylene-based polymer includes a transition metal component that is a bridged bisindenyl metallocene having the general formula (In ¹ ) Y (In ² ) MX ₂ ; Where In ¹ and In ² are the same substituted or unsubstituted indenyl group bonded to M and bridged by Y, Y is a bridging group, and in the direct chain connecting In ¹ and In ² The number of atoms is from 1 to 8, the direct chain contains C or Si, and M is a Group 3, 4, 5, or 6 transition metal. In ¹ and In ² may be substituted or unsubstituted. When In ¹ and In ² are substituted with one or more substituents, the substituents are halogen atoms, C ₁ -C ₁₀ alkyl, C ₅ -C ₁₅ aryl, C ₆ -C ₂₅ alkyl aryl, and Selected from the group consisting of N- or P-containing alkyl or aryl. In one or more embodiments, the transition metal component used to produce the propylene-based polymer is μ-dimethylsilylbis (indenyl) hafnium dimethyl.

Ethylene-based polymers In a further embodiment of the present invention, the core polymer may comprise one or more ethylene-based polymers, which may be ethylene homopolymers and / or ethylene copolymers incorporating one or more comonomers. Various types of ethylene-based polymers are known in the art. Exemplary ethylene-based polymers include ethylene-propylene copolymers, low density polyethylene (“LDPE”), linear low density polyethylene (“LLDPE”), and high density polyethylene (“HDPE”).

  In at least one particular embodiment, the core polymer may be or may include one or more ethylene-propylene copolymers (EP). Preferably, the EP is amorphous, eg, atactic or amorphous, but in certain embodiments, the EP may be crystalline (including “semicrystalline”). EP crystallinity is preferably derived from ethylene, and several published methods, procedures and techniques are available to assess whether the crystallinity of a particular material is derived from ethylene. The crystallinity of the EP can be distinguished from the crystallinity of the propylene-based polymer by removing the EP from the composition and then measuring the crystallinity of the remaining propylene-based polymer. Such measured crystallinity is usually calibrated using polyethylene crystallinity and in relation to comonomer content. In such cases, the percent crystallinity is measured as a percentage of the crystallinity of the polyethylene, thus establishing a source of ethylene crystallinity.

  In one or more embodiments, the EP can include one or more optional polyenes, particularly including dienes, and thus the EP is commonly referred to as ethylene-propylene-diene ("EPDM"). Is good). The optional polyene is considered to be any hydrocarbon structure having at least two unsaturated bonds, at least one of the unsaturated bonds being readily incorporated into the polymer. The second bond is partly involved in the polymerization and can form long chain branches, but preferably provides at least some unsaturated bonds suitable for subsequent curing or vulcanization in the post-polymerization step. Examples of EP or EPDM copolymers include V722, V3708P, MDV91-9, V878, available from ExxonMobil Chemical Company under the trade name Vistalon ™ EPDM. In addition, some commercially available EPDM polymers are available from The Dow Chemical Co. Available under the trade names Nordel IP and MG.

  Examples of optional polyenes include, but are not limited to, butadiene, pentadiene, hexadiene (eg, 1,4-hexadiene), heptadiene (eg, 1,6-heptadiene), octadiene (eg, 1,7-octadiene). ), Nonadiene (eg, 1,8-nonadiene), decadiene (eg, 1,9-decadiene), undecadiene (eg, 1,10-undecadiene), dodecadiene (eg, 1,11-dodecadiene), tridecadiene (eg, 1,12-tridecadiene), tetradecadiene (for example, 1,13-tetradecadiene), pentadecadiene, hexadecadiene, heptadecadiene, octadecadiene, nonadecadiene, icosadien, heneicosadien, docosadiene, tricosadien, tetra Sajien include Pentakosajien, Hekisakosajien, Heputakosajien, Okutakosajien, Nonakosajien, polybutadiene having a molecular weight of less than triacontanyl dienes, and 1000g / mol (Mw). Examples of straight chain acyclic dienes include, but are not limited to, 1,4-hexadiene and 1,6-octadiene. Examples of branched acyclic dienes include, but are not limited to, 5-methyl-1,4-hexadiene, 3,7-dimethyl-1,6-octadiene, and 3,7-dimethyl-1,7- Octadiene is included. Examples of monocyclic alicyclic dienes include, but are not limited to, 1,4-cyclohexadiene, 1,5-cyclooctadiene, and 1,7-cyclododecadiene. Examples of multicyclic alicyclic fused and bridged dienes include, but are not limited to, tetrahydroindene; norbornadiene; methyltetrahydroindene; dicyclopentadiene; bicyclo (2.2.1) hepta-2,5- Dienes; and alkenyl norbornene, alkylidene norbornene, cycloalkenyl norbornene, and cycloalkylidene norbornene [eg, 5-methylene-2-norbornene, 5-ethylidene-2-norbornene, 5-propenyl-2-norbornene, 5-isopropylidene-2 -Norbornene, 5- (4-cyclopentenyl) -2-norbornene, 5-cyclohexylidene-2-norbornene, and 5-vinyl-2-norbornene are included]. Examples of cycloalkenyl-substituted alkenes include, but are not limited to, vinylcyclohexene, allylcyclohexene, vinylcyclooctene, 4-vinylcyclohexene, allylcyclodecene, vinylcyclododecene, and tetracyclododecadiene.

LLDPE is typically a copolymer of ethylene and one or more other α-olefins. Such α-olefins generally have 3 to 20 carbon atoms. In certain embodiments, the α-olefin is selected from butene-1, pentene-1, 4-methyl-1-pentene, hexene-1, octene-1, decene-1, and combinations thereof. In other embodiments, the α-olefin is selected from butene-1, hexene-1, octene-1, and combinations thereof. LLDPE intended for use herein can be produced from any suitable catalyst system, including conventional Ziegler-Natta type catalyst systems and metallocene based catalyst systems. In certain embodiments, LLDPE polymer may have a density of about 0.89g / cm ³ ~0.94g / cm ³ or from about 0.91 g / cm ³ ~ about 0.94 g / cm ^3,. Exemplary metallocene-catalyzed linear low density polyethylenes include those marketed under the name Exceed ™ mPE resin from ExxonMobil Chemical Company.

HDPE is a semi-crystalline polymer available in a wide range of molecular weights as indicated by MI or HLMI (melt index or high load melt index), and typically has an ethylene content of at least 99 mole percent (total moles of HDPE). Based on). When incorporated into the HDPE, the comonomer may be selected from butene and other C ₃ -C ₂₀ alpha-olefin. In one embodiment, the comonomer is selected from 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene, and mixtures thereof. In certain embodiments, the comonomer can be present in the HDPE up to about 0.68 mole percent, based on the total moles of HDPE. In a further embodiment, the comonomer is present in HDPE up to about 0.28 mole percent. The density of HDPE is typically greater than 0.94 g / cm ³ . In some embodiments, the HDPE can have a density from about 0.94 g / cm ³ to about 0.97 g / cm ³ , or from about 0.95 g / cm ³ to about 0.965 g / cm ³ . In the same or other embodiments, the melting point of HDPE may be from about 120 ° C. to about 150 ° C., or from about 125 ° C. to about 135 ° C. as measured by a differential scanning calorimeter (DSC). Further, the HDPE can be from about 0.1 g / 10 min to about 10.0 g / 10 min, or from about 0.2 g / 10 min to about 5.0 g / 10 min, or from about 0.6 g / 10 min to about 2. It can have a melt index of 0 g / 10 min.

  HDPE includes polymers made using a variety of catalyst systems including Ziegler-Natta, Philips type catalysts, chromium-based catalysts, and metallocene catalyst systems, which are used with alumoxanes and / or ionic activators Can do. Useful methods for preparing such polyethylene include gas phase, slurry, dissolution method and the like. Exemplary HDPEs include, but are not limited to, Marlex TR-130 (manufactured by Phillips Chemical Company), M6211 (manufactured by Equistar Chemical Co.), Dow XU 6151.302 (manufactured by Dow Chemical Co.), and HD7845, HD6733, Commercially available products such as HTA002, HTA108, HYA108, Paxon4700, AD60007, AA45004, BA50100, Nexxstar ™ 0111 and MA001 (from ExxonMobil Chemical Company) are included.

Styrene Block Copolymer In a further embodiment of the invention, the core polymer may comprise one or more styrene block copolymers (SBC). The phrase “block copolymer” is intended to include any aspect of block copolymers including, but not limited to, diblock, triblock, and tetrablock copolymers. “Block copolymer” is further meant to include copolymers having any structure known to those skilled in the art including, but not limited to, linear, radial or multi-arm star, or multi-branched block copolymers. .

  Suitable SBCs include block copolymers of styrene and one or more conjugated dienes such as SI (styrene-isoprene), SIS (styrene-isoprene-styrene), SB (styrene-butadiene), SBS (styrene-butadiene-). Styrene), and styrene-isoprene-butadiene (SIB). Also suitable are styrene block copolymers comprising tetrablock or pentablock copolymers selected from SISI, SISB, SBSB, SBSI, ISISI, ISISB, BSISB, ISBSI, BSBSB, and BSBSI. The block copolymer may be hydrogenated or not hydrogenated.

In one or more embodiments, the SBC comprises a styrene-isoprene-styrene (SIS) block copolymer, a styrene-butadiene-styrene (SBS) block copolymer, a styrene-isoprene-butadiene (SIB) block copolymer, or a combination thereof. May be included.
In one or more embodiments, the SBC can include from about 10 to about 45 weight percent styrene. In the same or other embodiments, the styrene block copolymer component can have a diblock content of from about 0 to about 85 weight percent. The diblock content may be determined by GPC and may be manipulated by the settings of the reactor used to produce the styrene block copolymer component.

  In some embodiments, the SBC may comprise a styrene-isoprene-styrene (SIS) block copolymer. Such SIS block copolymers are thermoplastic elastomers having the structure (SI) nS, where S is a substantially polystyrene block, I is a substantially polyisoprene block, and n is , An integer from about 1 to about 10. The styrene content of the SIS block copolymer is typically about 10 to about 45 wt%, or about 15 to about 35 wt%, or about 20 to 30 wt%. The number average molecular weight (Mn) of the SIS block copolymer may be from about 50,000 to about 500,000. In one or more embodiments, the SIS block copolymer is a triblock copolymer of the above formula and n = 1, ie, a linear polymer of formula S—I—S, where S is It is substantially a polystyrene block and I is substantially a polyisoprene block. These block copolymers are lithium type initiators such as those disclosed in US Pat. Nos. 3,251,905 and 3,239,478, which are incorporated herein by reference in their entirety. Can be prepared by well-known anionic solution polymerization techniques.

  As used herein, the SIS block copolymer is from about 50,000 to 500,000, or from about 70,000 to about 250,000, or from about 90,000 to about 175,000, or from about 90,000 to about 135. May have a number average molecular weight (determined by GPC) in the range of 1,000. The SIS block copolymer may comprise a blend of two or more different SIS copolymers, which may have the same or different styrene content, and may be blended in a ratio ranging from 10: 1 to 1:10 parts by weight. The SIS copolymer may be a pure triblock (having less than 0.1% by weight diblock polymer, preferably having 0% diblock polymer), or from about 0.1 to about 85% by weight, or about. It may contain from 1 to about 75% by weight, or from about 1 to about 65% by weight, or from about 5 to about 50% by weight of a diblock copolymer having structure SI. This material may be present as an impurity in the production of the triblock copolymer or may be blended separately with the triblock as a further technique to achieve the target polystyrene content or to change the adhesive properties of the composition. Also good. In one or more embodiments, the remainder of the SIS copolymer that is not a diblock copolymer may be in radial form. In one or more embodiments, the number average molecular weight of the diblock SI copolymer may range from about 100,000 to about 250,000.

  The SIS copolymer may be linear or radial in structure, or a combination of the two. The radial SIS copolymer may have the same styrene level as the linear copolymer discussed above, for example from about 10 to about 45% by weight polymerized styrene. Radial SIS copolymers useful in the practice of the present invention can have a molecular weight (Mn) of from about 180,000 to about 250,000. Linear and radial SIS block copolymers of the type described herein are commercially available and are prepared by methods known in the art. Examples of SIS copolymers useful in the practice of the present invention are available under the trade names Vector and DPX (from Dexco Polymers LLP), Kraton (from Shell Chemical Company), Europrene (from Enichem), and Quintac (from Nippon Zeon). Is included. Particularly useful SIS block copolymers include, but are not limited to, Vector 4111, Vector 4511 and Vector 4113; DPX552 and DPX556; Kraton D1107, Kraton D1124, Kraton D1160 and Kraton D1161; Quantac 3433 and Quantac 3450 are included.

  In some embodiments, the SBC may comprise a styrene-butadiene-styrene (SBS) block copolymer. Such SBS block copolymers are thermoplastic elastomers having the structure (S-B) nS, where S is substantially a polystyrene block, B is a polybutadiene block, and n is , An integer from about 1 to about 10. The styrene content of the SBS block copolymer is typically about 10 to about 45 wt%, or about 15 to about 35 wt%, or about 20 to 30 wt%. The number average molecular weight (Mn) of the SBS block copolymer may be from about 50,000 to about 500,000. In one or more embodiments, the SBS block copolymer is a triblock copolymer of the above formula, and n = 1, ie, a linear polymer of the formula S—B—S, where S is Substantially a polystyrene block and B is a polybutadiene block substantially. These block copolymers are lithium-type initiators such as those disclosed in US Pat. Nos. 3,251,905 and 3,239,478, which are hereby incorporated by reference in their entirety. Can be prepared by well-known anionic solution polymerization techniques.

  The SBS block copolymer used herein can be from about 50,000 to 500,000, or from about 100,000 to about 180,000, or from about 110,000 to about 160,000, or from about 110,000 to about 140. May have a number average molecular weight (determined by GPC) in the range of 1,000. The SBS copolymer may be a pure triblock (having less than 0.1% by weight diblock polymer, preferably having 0% diblock polymer), or from about 0.1 to about 85% by weight, or about. It may contain from 1 to about 75% by weight, or from about 1 to about 65% by weight, or from about 5 to about 50% by weight of the diblock copolymer having structure SB. This material may be present as an impurity in the production of the triblock copolymer or may be blended separately with the triblock as a further technique to achieve the target polystyrene content or to change the adhesive properties of the composition. Also good. In one or more embodiments, the remainder of the SBS copolymer that is not a diblock copolymer may be in radial form. In one or more embodiments, the number average molecular weight of the diblock SB copolymer may range from about 100,000 to about 250,000.

  SBS copolymers may be linear or radial in structure, or a combination of the two. The radial SBS copolymer can have the same styrene level as the linear copolymer discussed above, for example, from about 10 to about 45 weight percent polymerized styrene. Linear and radial SBS block copolymers of the type described herein are commercially available and are prepared by methods known in the art. Examples of SBS copolymers useful in the practice of this invention include those available under the trade names Vector (from Dexco Polymers LLP), Kraton (from Shell Chemical Company), Europrene (from Enichem), and Finaprene (from Fina Chemicals). Is included. Particularly useful SBS block copolymers include, but are not limited to, Vector8505, Kraton D1102, Kraton D4141, Kraton D4158, Europlane SOL T166, and Finaprene411.

  Radial styrene block copolymers, and other styrene block copolymers suitable for use in the present invention, are those described in US Patent Application No. 2009/0133834, which is hereby incorporated by reference in its entirety. included.

Sheath polymer Polymers intended for use as the sheath polymer in the fibers described herein include an elastic, low molecular weight compared to the core polymer, and limited mixing in the core polymer. Any polymer suitable for use as a feel control agent in nonwovens and articles is included. In one embodiment, such polymers include polypropylene homopolymers such as ExxonMobil Chemical Co. Achieve ™ 6936G1 from Such polymers include, but are not limited to, olefin waxes including propylene wax and ethylene wax and combinations thereof. In certain embodiments of the invention, the sheath polymer has a low molecular weight compared to the molecular weight of the sheath polymer. For example, in some embodiments, the sheath polymer is at least about 20,000 g / mol less than the core polymer M _w , or at least about 50,000 g / mol less, or at least about 75,000 g / mol less, or at least It has a weight average molecular weight (M _w ) of about 100,000 g / mol less. In the same or other embodiments, the sheath polymer is less than about 65,000 g / mol, or less than about 50,000 g / mol, or less than about 45,000 g / mol, or less than about 40,000 g / mol, or about 35 Less than 3,000 g / mol, or less than about 30,000 g / mol, or less than about 25,000 g / mol, or less than about 20,000 g / mol, or less than about 15,000 g / mol, or less than about 10,000 g / mol _Mw .

Olefin waxes suitable for use as a sheath polymer can be polar or nonpolar, branched or unbranched, and include any Ziegler-Natta catalyst, Philips type catalyst, chromium-based catalyst, and metallocene catalyst system. Can be prepared using any suitable catalyst system. The olefin wax, in some embodiments of the present invention, is from about 0.88 g / cm ³ to about 1.0 g / cm ³ , or from about 0.89 g / cm ³ to about 0.99 g / cm ³ , Alternatively, it may be low density, medium density, or high density so that it may have a density in the range of about 0.90 g / cm ³ to about 0.98 g / cm ³ . In the same or other embodiments, the wax may have a viscosity of about 100 to about 2000 mPa · sec, or about 200 to about 1900 mPa · sec, or about 300 to about 1800 mPa · sec.

  In one or more embodiments, the sheath polymer can be grafted or functionalized using one or more graft monomers. The graft monomer can be or can include at least one ethylenically unsaturated carboxylic acid or acid derivative, such as an acid anhydride, ester, salt, amide, imide, acrylate, and the like. Exemplary monomers include, but are not limited to, acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, mesaconic acid, maleic anhydride, 4-methylcyclohexene-1,2-dicarboxylic anhydride Bicyclo (2.2.2) octene-2,3-dicarboxylic acid anhydride, 1,2,3,4,5,8,9,10-octahydronaphthalene-2,3-dicarboxylic acid anhydride, 2-Oxa-1,3-diketospiro (4.4) nonene, bicyclo (2.2.1) heptene-2,3-dicarboxylic anhydride, maleopimaric acid, tetrahydrophthalic anhydride, norbornene-2,3- Dicarboxylic acid anhydride, nadonic acid anhydride, methyl nadic acid anhydride, hymic acid anhydride, methyl hymic acid anhydride, and 5-methylbicyclo (2.2.1) hep It includes down-2,3-dicarboxylic anhydride. Other suitable grafting monomers include methyl acrylate and higher alkyl acrylate, methyl methacrylate and higher alkyl methacrylate, acrylic acid, methacrylic acid, hydroxymethyl methacrylate, hydroxylethyl methacrylate and higher hydroxyalkyl methacrylate and methacrylic acid. Glycidyl acid is included. Maleic anhydride is a preferred grafting monomer. In certain embodiments herein, the sheath polymer may be a grafted polymer having a polyethylene or polypropylene backbone with maleic anhydride grafted to the backbone. In certain other embodiments, the sheath polymer may be a polyethylene or polypropylene wax having at least one functionalized end group that imparts polar character to the polymer, such as vinyltetramethylene (VTM).

  Exemplary olefin waxes suitable for use as the sheath polymer in the present invention include, but are not limited to, the names Licowax and Licocene (especially Licowax PE130, Licowax PE520, Licocene PE5301, and Licocene PP7502) from Clariant Chemicals. Honeywell A-C performance additive (especially A-C9) from Honeywell International, and Achieve ™ (especially Achieve 6936G1) ExxonMobil Chemical Co. That are commercially available.

Preparation of Bicomponent Fibers and Fabrics The present invention is directed to methods of preparing these fibers as well as bicomponent fibers. To form the bicomponent fibers of the present invention, a melt blend is prepared that includes a core polymer and a sheath polymer. The melt blend is then extruded using an extruder having a die having a length to diameter ratio of about 10 or greater under shear conditions sufficient to deliver the sheath polymer to the die wall. The bicomponent fiber thus obtained has a core containing a core polymer and a sheath containing a sheath polymer. While the terms “core” and “sheath” are used herein for ease of reference, the polymer may not be completely separated during the extrusion process and is described herein. It should be appreciated that there may not be a defined boundary between the core and sheath of the bicomponent fiber. Rather, the fibers of the present invention also include those fibers having a cross-sectional gradient in which the concentration of sheath polymer is highest at the surface of the fiber and the concentration of core polymer is highest at the center of the fiber.

  A melt blend comprising a core polymer and a sheath polymer can be prepared by any method that provides an intimate mixture of components. Polymer blending and homogenization is well known in the art and includes single and twin screw mixing extruders, static mixers for mixing low viscosity molten polymer streams, impingement mixers, and first and second polymers Other machines and processes designed to disperse the intimate contact are included. For example, the polymer component and other minor components can be blended by melt blending or dry blending in a continuous or batch process. These processes are well known in the art and include single and twin screw compounding extruders and other machines and processes designed to intimately melt and homogenize the polymer components. Melt blending or compounding extruders are typically equipped with a pelletizing die that converts the homogenized polymer into pellet form. The homogenized pellets can then be fed to an extruder of a fiber or nonwoven processing device to produce a fiber or fabric. Alternatively, the first and second polymers can be dry blended and fed to the extruder of the nonwoven processing equipment. The blend of core and sheath polymer can also be produced by any reactor blending method currently known in the art. A reactor blend is a highly dispersed and mechanically dispersed polymer of in situ produced as a result of sequential polymerization of one or more monomers, with the formation of one polymer in the presence of another polymer. It is a blend that cannot be separated. The polymer can be produced in any of the polymerization methods described above. The reactor blend can be produced in a single reactor or in two or more reactors arranged in sequence. A blend of core and sheath polymer can be further generated by combining a reactor blend and a post reactor blend.

  Blended polymer resins can be used to produce fiber and nonwoven products. As used herein, “nonwoven” means a textile material produced by a method other than weaving. In nonwovens, the fibers are processed directly into a planar sheet-like fabric structure and then chemically or thermally bonded or mechanically interlocked (or some combination thereof) to achieve an adhesive fabric To do.

  The nonwoven fibers and fabrics of the present invention can be formed by any method known in the art. Preferably, the nonwoven fibers are produced by a meltblown or spunbond process.

  In a typical spunbond process, the polymer is fed to a heated extruder to melt and homogenize the polymer. The extruder feeds the molten polymer to the spinneret where it is fiberized as it passes through fine openings arranged in one or more rows in the spinneret, forming a filament curtain. Filaments are typically quenched with air at a low temperature, usually drawn by air pressure, and deposited on a moving mat, belt or “formed wire” to form a nonwoven. For example, U.S. Pat. Nos. 4,340,563; 3,692,618; 3,802,817; 3,338,992; 3,341,394; 3,502,763; and 3,542,615.

  Fibers produced in the spunbond process typically range in diameter from about 10 to about 50 microns, depending on the process conditions and the desired end use for fabrics produced from such fibers. For example, increasing the polymer molecular weight or decreasing the processing temperature results in larger diameter fibers. Changes in pressure drawn by quench air temperature and air pressure also have an effect on fiber diameter.

  In a typical meltblown process, the extruder delivers the molten polymer to a metered melt pump. The melt pump delivers the molten polymer to a special meltblowing die at a stable output rate, which may include a plurality of fine, usually annular, die capillaries (also referred to as spinnerets). As the molten polymer filaments exit the die, they come into contact with high temperature, high velocity wind (referred to as processing air or primary air). This air is rapidly drawn and in combination with quench air solidifies the filament. The meltblown fibers are then carried by the high velocity gas stream and are deposited on the collection surface to form a randomly dispersed meltblown fiber web or nonwoven. Such a process is generally described, for example, in US Pat. Nos. 3,849,241 and 6,268,203. Meltblown fibers are ultrafine fibers that are continuous or discontinuous, and may be less than about 10 μm depending on the resin (eg, high MFR isotactic polypropylene resins such as PP3746G or Achieve ™ 6936G1, ExxonMobil Chemical). On the other hand, for certain high throughput processes such as certain resins (eg, Vistamaxx ™ propylene-based elastomer, available from ExxonMobil Chemical Company) or those described herein. The fibers can have a diameter greater than 10 μm, such as from about 10 to about 30 μm, or from about 10 to about 15 μm. The term melt blow, as used herein, is meant to encompass a melt spray process.

  It is known that polymer flow under high shear conditions can induce molecular sequestration. The degree of sequestration and the time required for sequestration depends on the amount of shear produced. And then, the level of shear depends on the process conditions and the level of immiscibility of the polymer components. The immiscibility of the polymer blend components is the result of differences in composition and differences in the molecular weight of the blend components, with larger differences resulting in a higher likelihood of sequestration. Process conditions that cause shear and thus affect sequestration include flow rate (related to pressure through the die), and die size and / or cross-sectional area. Sequestration is also affected by the temperature and duration that the polymer blend is exposed to a high shear environment. Residence time is particularly important because the residence time must be long enough to ensure that the molecules of the low molecular weight sheath polymer have sufficient time to migrate to the polymer / die wall interface. . Capillaries with longer length to diameter (L / D) ratios typically result in longer residence times and thus better separation of the polymer components. Conventional meltblown dies typically have an L / D ratio of less than 10, usually less than 5. In order to form the bicomponent fibers described herein, the blend of core and sheath polymer may have a greater L / D ratio, eg, at least 10, or greater than 10, greater than 15, greater than 20, greater than 25, Melt blow through a die having an L / D ratio of greater than 30, greater than 50, greater than 75, or greater than 100. Under proper processing conditions, such as those described herein, sufficient shear is generated using a meltblown die having a high L / D ratio to deliver the sheath polymer to the die wall. The bicomponent fiber thus obtained has a sheath containing a sheath polymer and a core containing a core polymer. Such fibers have ideal properties for use in non-woven applications because they continue to achieve superior elasticity with the core layer while having a desirable feel over the previous fibers with the sheath layer.

  The fabric formed from the bicomponent fibers described herein may be a single layer or a multilayer laminate. One application is to laminate (or “composite”) from a meltblown fabric (“M”) and a spunbond fabric (“S”) that combines the strength of the spunbond fabric and the greater barrier properties of the meltblown fabric. It is to make. A typical laminate or composite has three or more layers, with a meltblown layer sandwiched between two or more spunbond layers, or an “SMS” fabric composite. Examples of other combinations are SSMMSS, SMMS, and SMMSS complexes. The composite is also made of the meltblown fabrics of the present invention, along with other synthetic or natural materials, to produce useful articles.

  In some embodiments of the invention, the fibers or fabrics described herein can be annealed. Annealing partially relieves internal stress in the stretched fiber and restores the elastic recovery properties of the core polymer in the fiber. Annealing has been shown to result in significant changes in the internal structure of the crystal structure, as well as relative ordering of the semi-amorphous and semi-crystalline phases. This provides a recovery of elasticity. For example, annealing the fiber at a temperature of at least 40 ° C. above room temperature but slightly below the crystalline melting point of the blend is suitable for restoring elasticity in the fiber. Thermal annealing of the polymer blend may cause the polymer blend or an article made from such a blend to have a duration of from a few seconds to about 1 hour, such as from about 25 ° C to about 160 ° C, or alternatively from about 60 ° C to about 130 ° C. This is done by maintaining the temperature. A typical annealing period is 1-5 minutes at 100 ° C. In non-woven processing, the fabric web is usually passed through a calendar and the web is point bonded (fixed). Passing the unsecured nonwoven web through a calendar heated at a relatively high temperature is sufficient to anneal the fibers and increase the elasticity of the nonwoven web. The nonwoven web should be under low tension to allow web shrinkage in both the flow direction (MD) and the transverse direction (TD) to enhance the elasticity of the nonwoven web. In some embodiments, the bonded calender roll temperature may range from about 60 ° C to about 130 ° C. In another embodiment, the temperature is about 100 ° C. Annealing time and temperature can be adjusted by the composition of the particular polymer blend.

  Depending on the intended purpose, various additives may be incorporated into the polymers used to make the fibers and fabrics described herein. Such additives include, but are not limited to, stabilizers, antioxidants, fillers, colorants, nucleating agents, dispersants, mold release agents, slip agents, flame retardants, plasticizers, pigments, Vulcanizing agents or curing agents, vulcanization accelerators or curing accelerators, curing retarders, processing aids, tackifying resins, and the like may be included. Other additives may include fillers and / or reinforcing materials such as carbon black, clay, talc, calcium carbonate, mica, silica, silicates, combinations thereof, and the like. Primary and secondary antioxidants include, for example, hindered phenols, hindered amines, and phosphates. Nucleating agents include, for example, sodium benzoate and talc. Other nucleating agents such as Ziegler-Natta olefin products or other highly crystalline polymers may also be used to improve the crystallization rate. Other additives such as dispersants such as Arowax C can also be included. Slip agents include, for example, oleamide and erucic acid amide. Catalyst deactivators, such as calcium stearate, hydrotalcite, and calcium oxide, and / or other acid neutralizing agents known in the art are also commonly used.

  The nonwoven products described above may be used in many articles, such as hygiene products, including but not limited to diapers, feminine care products, and adult incontinence products. Nonwoven products may also be used in medical articles such as sterile wraps, isolation gowns, operating room gowns, surgical gowns, surgical drapes, first aid dressings, and other disposable items.

The following notation is used herein to refer to the core (C) and sheath (S) polymers used in the examples below.
Polymer C1 is a propylene-based polymer comprising propylene and ethylene having an ethylene content of about 15% by weight, an MFR of about 18 g / 10 min (230 ° C., 2.16 kg), and an Mw of about 130,000 g / mol. .
Polymer C2 is an ethylene-propylene copolymer rubber having an ethylene content of about 72 wt%, a melt index of about 1.0 g / 10 min (190 ° C., 2.16 kg), and an Mw of about 250,000 g / mol. is there.
Polymer C3 is a SEBS linear triblock block copolymer having a styrene content of about 20% by weight and a Mw of about 130,000 g / mol.
Polymer C4 is an ethylene-based olefin block copolymer having a melt index (190 ° C., 2.16 kg) of about 5.0 g / 10 min and Mw of about 130,000 g / mol.
Polymer C5 is a propylene-based polymer comprising propylene and ethylene having an ethylene content of about 13 wt%, an MFR of about 79 g / 10 min (230 ° C., 2.16 kg), and an Mw of about 142,000 g / mol. .
Polymer S1 is a polyethylene wax having a viscosity of about 300 mPa · s, a density of about 0.96 to 0.98 g / cm ³ , and a Mw of about 14,850 g / mol.
Polymer S2 is a polyethylene wax having a viscosity of about 650 mPa · s, a density of about 0.92 to 0.94 g / cm ³ , and a Mw of about 6,800 g / mol.
Polymer S3 is a polyethylene homopolymer wax having a viscosity of about 450 mPa · s and a Mw of about 7,000 g / mol.
Polymer S4 is a metallocene catalyzed polyethylene wax having a viscosity of about 350 mPa · s, a density of about 0.96 to 0.98 g / cm ³ , and a Mw of about 4,300 g / mol.
Polymer S5 is a polypropylene wax having a viscosity of about 1800 mPa · s, a density of about 0.90 g / cm ³ , and a Mw of about 27,300 g / mol.
Polymer S6 is a high melt flow rate homopolypropylene having an MFR of about 1550 g / 10 min (230 ° C., 2.16 kg) and an Mw of about 63,000 g / mol.

  Various polymer blends were formed as described in Table 1.

While various aspects of the composition have been described herein, further specific embodiments of the invention include those described in the following lettered paragraphs.
A. A core comprising a core polymer, wherein the sheath polymer is a polyolefin having a weight average molecular weight (Mw) of less than about 65,000 g / mol, wherein the Mw of the core polymer is at least about 20,000 g / mol greater than the Mw of the sheath polymer; A bicomponent polymer fiber having a sheath comprising a sheath polymer.
B. The polymer fiber of paragraph A, wherein the core polymer is selected from a propylene-based polymer, an ethylene-based polymer, a propylene-ethylene block copolymer, a styrene block copolymer, an acrylate, or a combination of the above.
C. A core polymer comprising from about 5 to about 30% by weight ethylene and / or C ₄ -C ₁₂ alpha olefins and having a triad tacticity of greater than about 90% and a heat of fusion of less than about 75 J / g A polymer fiber of any of paragraphs A-B.
D. The polymer fiber of any of paragraphs B-C, wherein the propylene-based polymer comprises about 8 to about 20 weight percent ethylene.
E. The polymer fiber of any of paragraphs BD, wherein the propylene-based polymer comprises from about 12 to about 18 weight percent ethylene.
F. The polymer fiber of any of paragraphs AE, wherein the core polymer Mw is at least about 50,000 g / mol, or at least about 75,000 g / mol greater than the Mw of the sheath polymer.
G. The polymer fiber of any of paragraphs AF, wherein the Mw of the core polymer is at least about 100,000 g / mol greater than the Mw of the sheath polymer.
H. The Mw of the sheath polymer is less than about 50,000 g / mol and the Mw of the core polymer is greater than about 100,000 g / mol, or the Mw of the sheath polymer is less than about 30,000 g / mol; And the polymer fiber of any of paragraphs AG, wherein the core polymer Mw is greater than about 125,000 g / mol.
I. The polymer fiber of any of paragraphs A-H, wherein the sheath polymer is selected from polypropylene wax, polyethylene wax, and combinations thereof.
J. et al. The polymer fiber of any of paragraphs A-I, wherein the sheath polymer comprises a propylene or ethylene backbone having maleic anhydride grafted to the backbone.
K. The polymer fiber of any of paragraphs A-J, wherein the sheath polymer is a polyethylene or polypropylene wax containing at least one functionalized end group that imparts polar character to the polymer.
L. A nonwoven fabric comprising polymer fibers according to any of paragraphs A to K.
M.M. i. Forming a melt blend of a core polymer and a sheath polymer;
ii. Extruding the molten polymer blend under shear conditions sufficient to send the sheath polymer to the die wall using an extruder having a die having a length to diameter ratio of about 10 or greater;
iii. Forming a meltblown fiber having a core comprising a core polymer and a sheath comprising a sheath polymer, wherein the sheath polymer is a polyolefin having a weight average molecular weight (Mw) of less than about 65,000 g / mol; A bicomponent polymer fiber having a Mw of at least about 20,000 g / mol greater than the Mw of the sheath polymer.
N. The method of paragraph M, wherein the core polymer is selected from a propylene-based polymer, an ethylene-based polymer, a propylene-ethylene block copolymer, a styrene block copolymer, an acrylate, or a combination of the above.
O. A core polymer comprising from about 5 to about 30% by weight ethylene and / or C ₄ -C ₁₂ alpha olefins and having a triad tacticity of greater than about 90% and a heat of fusion of less than about 75 J / g A method according to any of paragraphs M to N.
P. Process according to any of paragraphs N-O, wherein the propylene-based polymer comprises about 8 to about 20 wt% ethylene.
Q. Process according to any of paragraphs N-P, wherein the propylene-based polymer comprises from about 12 to about 18% by weight ethylene.
R. The method of any of paragraphs M-Q, wherein the Mw of the core polymer is at least about 50,000 g / mol, or at least about 75,000 g / mol greater than the Mw of the sheath polymer.
S. The method of any of paragraphs MR, wherein the Mw of the core polymer is at least about 100,000 g / mol greater than the Mw of the sheath polymer.
T. T. et al. The Mw of the sheath polymer is less than about 50,000 g / mol and the Mw of the core polymer is greater than about 100,000 g / mol, or the Mw of the sheath polymer is less than about 30,000 g / mol; And the method according to any of paragraphs MS, wherein the core polymer Mw is greater than about 125,000 g / mol.
U. The method of any of paragraphs MT, wherein the sheath polymer is selected from polypropylene wax, polyethylene wax, and combinations thereof.
V. The method according to any of paragraphs MU, wherein the sheath polymer comprises a propylene or ethylene backbone having maleic anhydride grafted to the backbone.
W. Process according to any of paragraphs M to V, wherein the sheath polymer is a polyethylene or polypropylene wax comprising at least one functionalized end group that imparts polar character to the polymer.
X. A nonwoven fabric comprising polymer fibers made according to any of paragraphs M-W.
Y. An article comprising a nonwoven fabric according to any of paragraphs M-X.
Z. A fiber according to any of paragraphs A-Y, further comprising at least one of carbon black, clay, talc, calcium carbonate, mica, silica, and silicate.
AA. At least one of carbon black, clay, talc, calcium carbonate, mica, silica, silicate, hindered phenol, hindered amine, phosphate, sodium benzoate, oleamide, erucamide, calcium stearate, hydrotalcite, and calcium oxide A fiber according to any of paragraphs A to Z, comprising:

  Certain embodiments and features have been described using a set of numerical upper limits and a set of numerical lower limits. It should be appreciated that ranges from any lower limit to any upper limit are intended unless otherwise indicated. Certain lower limits, upper limits and ranges appear in one or more of the following claims. All numerical values are “about” or “approximately” the indicated value and take into account experimental errors and variations expected by those skilled in the art.

  The broadest term given to a term by a person skilled in the relevant art, as reflected in at least one publication or issued patent, unless the term used in the claims is defined above. A definition should be given. In addition, all patents, test procedures, and other documents cited in this application are to the extent that such disclosure is consistent with this application and for all jurisdictions where such incorporation is permissible. , Fully incorporated by reference.

  While the foregoing is directed to embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, which is determined by the following claims.

Claims (25)

  A bicomponent polymer fiber having a core comprising a core polymer and a sheath comprising a sheath polymer, wherein the sheath polymer is a polyolefin having a weight average molecular weight (Mw) of less than about 65,000 g / mole; Polymer fibers having a Mw of at least about 20,000 g / mole greater than the Mw of the sheath polymer.   The polymer fiber of claim 1, wherein the core polymer is selected from propylene-based polymers, ethylene-based polymers, propylene-ethylene block copolymers, styrene block copolymers, acrylates, or combinations thereof. It said core polymer is a propylene-based polymer having from about 5 to comprise of about 30% by weight of ethylene and / or C ₄ -C ₁₂ alpha-olefin, and about 90% of the triad tacticity and heat of fusion of less than about 75 J / g The polymer fiber according to claim 1 or 2, wherein   The polymer fiber of any of claims 1 to 3, wherein the propylene-based polymer comprises about 8 to about 20 wt% ethylene.   The polymer fiber of any of claims 1 to 4, wherein the propylene-based polymer comprises about 12 to about 18 wt% ethylene.   6. The polymer fiber of any of claims 1-5, wherein the core polymer Mw is at least about 75,000 g / mole greater than the sheath polymer Mw.   7. A polymer fiber according to any preceding claim, wherein the Mw of the core polymer is at least about 100,000 g / mol greater than the Mw of the sheath polymer.   8. The polymer fiber of claim 1, wherein the sheath polymer has an Mw of less than about 50,000 g / mol and the core polymer has an Mw of greater than about 100,000 g / mol.   The polymer fiber according to any one of claims 1 to 8, wherein the sheath polymer is selected from polypropylene wax, polyethylene wax, and combinations thereof.   The polymer fiber according to any one of claims 1 to 9, wherein the sheath polymer comprises a propylene or ethylene skeleton having maleic anhydride grafted to the skeleton.   11. A polymer fiber according to any preceding claim, wherein the sheath polymer is a polyethylene or polypropylene wax comprising at least one functionalized end group that imparts polar characteristics to the polymer.   A nonwoven fabric comprising the polymer fiber according to claim 1. a. Forming a melt blend of a core polymer and a sheath polymer;
b. Extruding the molten polymer blend under shear conditions sufficient to deliver the sheath polymer to the die wall using an extruder having a die having a length to diameter ratio of about 10 or greater;
c. Forming a meltblown fiber having a core comprising the core polymer and a sheath comprising the sheath polymer, wherein the sheath polymer is a polyolefin having a weight average molecular weight (Mw) of less than about 65,000 g / mol. , Forming a bicomponent polymer fiber wherein the Mw of the core polymer is at least about 20,000 g / mol greater than the Mw of the sheath polymer.   14. The method of claim 13, wherein the core polymer is selected from a propylene-based polymer, an ethylene-based polymer, a propylene-ethylene block copolymer, a styrene block copolymer, an acrylate, or a combination of the above. It said core polymer is a propylene-based polymer having from about 5 to comprise of about 30% by weight of ethylene and / or C ₄ -C ₁₂ alpha-olefin, and about 90% of the triad tacticity and heat of fusion of less than about 75 J / g The method according to claim 13 or 14, wherein:   The process according to any of claims 13 to 15, wherein the propylene-based polymer comprises from about 8 to about 20% by weight of ethylene.   17. A method according to any of claims 13 to 16, wherein the Mw of the core polymer is at least about 75,000 g / mol greater than the Mw of the sheath polymer.   18. A method according to any of claims 13 to 17, wherein the Mw of the core polymer is at least about 100,000 g / mol greater than the Mw of the sheath polymer.   19. The method of any of claims 13-18, wherein the sheath polymer Mw is less than about 50,000 g / mole and the core polymer Mw is greater than about 100,000 g / mole.   20. A method according to any one of claims 13 to 19 wherein the sheath polymer is selected from polypropylene wax, polyethylene wax, and combinations thereof.   21. A method according to any of claims 13 to 20, wherein the sheath polymer comprises a propylene or ethylene backbone with maleic anhydride grafted to the backbone.   22. A method according to any of claims 13 to 21 wherein the sheath polymer is a polyethylene or polypropylene wax containing at least one functionalized end group that imparts polar character to the polymer.   A nonwoven fabric comprising polymer fibers made according to claim 13.   An article comprising the nonwoven fabric of claim 23.   At least one of carbon black, clay, talc, calcium carbonate, mica, silica, silicate, hindered phenol, hindered amine, phosphate, sodium benzoate, oleamide, erucic acid amide, calcium stearate, hydrotalcite, and calcium oxide The fiber according to any one of claims 1 to 12, comprising: