US20220049389A1

US20220049389A1 - Bi-Component Fibers and Nonwoven Materials Produced Therefrom

Info

Publication number: US20220049389A1
Application number: US17/274,613
Authority: US
Inventors: Srinivasa Syamal S. Tallury; Louis K. Apraku-Boadi; Paul E. Rollin, Jr.; Bin Zhao
Original assignee: ExxonMobil Chemical Patents Inc
Current assignee: ExxonMobil Chemical Patents Inc
Priority date: 2018-09-18
Filing date: 2019-08-30
Publication date: 2022-02-17

Abstract

A method can include (a) extruding a bi-component fiber comprising: a first component comprising a first polypropylene homopolymer; and a second component comprising a blend that comprises a propylene-based elastomer and a second polypropylene homopolymer, wherein the blend has a melt flow rate that is at least 20% greater than or at least 20% less than a melt flow rate of the first polypropylene homopolymer; (b) cooling the bi-component fiber; and (c) thermally and/or mechanically activating the bi-component fiber to cause the bi-component fiber to curl.

Description

PRIORITY

This application claims priority to and the benefit of U.S. Provisional Application No. 62/732,599, filed Sep. 18, 2018, and European Patent Application No. 18199603.4, which was filed Oct. 10, 2018, the disclosures of which are incorporated herein by reference in their entireties.

FIELD

The present disclosure relates to bi-component fibers that when used to produce nonwoven materials enhance the loft of the nonwoven material.

BACKGROUND

Synthetic fibers and nonwoven fabrics often lack a soft feel or “hand” like natural fibers and fabrics. The different aesthetic feeling is due to the lack of “loft” or “bulk” in synthetic materials versus the innate space-filling characteristics of natural fibers. Natural fibers are often not planar materials, and rather they exhibit some crimp or texture in three-dimensions that allow for space between fibers. Natural fibers can often be laid onto a plane and have a surface projecting from that plane, which are “3-dimensional.” By contrast, synthetic fibers are essentially planar. There are a number of methods to impart “bulkiness” or “loft” to synthetic fibers or fabrics, including mechanical treatments such as crimping, air jet texturing, or pleating. These methods are not generally easily applicable to spunbond nonwoven fabrics in cost-effective ways.

SUMMARY

A first embodiment is a method comprising (or consists of, or consists essentially of): (a) extruding a bi-component fiber comprising: a first component comprising a first polypropylene homopolymer; and a second component comprising a blend that comprises a propylene-based elastomer and a second polypropylene homopolymer, wherein the blend has a melt flow rate that is at least 20% greater than or at least 20% less than a melt flow rate of the first polypropylene homopolymer; (b) cooling the bi-component fiber; and (c) thermally and/or mechanically activating the bi-component fiber to cause the bi-component fiber to curl.
A second embodiment is a bi-component fiber comprising: a first component comprising a first polypropylene homopolymer; and a second component comprising a blend that comprises a propylene-based elastomer and a second polypropylene homopolymer, wherein the blend has a melt flow rate that is at least 20% greater than or at least 20% less than a melt flow rate of the first polypropylene homopolymer.
A third embodiment is a nonwoven article comprising the bi-component fiber of the second embodiment.
A fourth embodiment is a laminated article comprising the bi-component fiber of the second embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

The following figures are included to illustrate certain aspects of the embodiments, and should not be viewed as exclusive embodiments. The subject matter disclosed is capable of considerable modifications, alterations, combinations, and equivalents in form and function, as will occur to those skilled in the art and having the benefit of this disclosure.

FIG. 1 is a plot of the shrinkage (ASTM D2259-02(2016)) of example fibers.

FIG. 2A is a scanning electron micrograph of as-produced bi-component fibers before mechanical activation.

FIG. 2B is a scanning electron micrograph of as-produced bi-component fibers after mechanical activation.

FIGS. 3A and 3B are light micrographs of the fibers as-produced before thermal activation.

FIGS. 3C and 3D is that sample after thermal activation at 100° C. for 15 seconds.

FIG. 4 is a plot of the shrinkage (ASTM D2259-02(2016)) of example fibers.

DETAILED DESCRIPTION

The present disclosure relates to bi-component fibers that when used to produce nonwoven materials enhance the loft of the nonwoven material. More specifically, the bi-component fibers comprise a first component comprising a first polypropylene homopolymer and a second component comprising a blend that comprises a propylene-based elastomer and a second polypropylene homopolymer. The blend has a melt flow rate that is at least 20% greater or at least 20% less than a melt flow rate of the first polypropylene homopolymer. That is, if the melt flow rate of the first polypropylene homopolymer is 36 g/10 min (ASTM D1238-13, 2.16 kg, 230° C.), then the melt flow rate of the blend is greater than 43 g/10 min (ASTM D1238-13, 2.16 kg, 230° C.) or less than 29 g/10 min (ASTM D1238-13, 2.16 kg, 230° C.).

Definitions

As used herein, “extrude” or “extruded” or “extruding” means that a material in its molten or flowable state is forced through a mechanical containment means such as a tube, pre-formed mold, die (preferably of a desired narrowing diameter and/or shape), or extruder, heated or otherwise, such that the material flows from a one point to another, such as a source of unmelted polymer to form a molten stream of such polymer in a stream or formed stream.
As used herein, “spunbond” refers to a meltspinning method of forming a fabric in which a polymeric melt or solution is extruded through spinnerets to form filaments which are cooled then attenuated by suitable means such as by electrostatic charge or high velocity air, such attenuated filaments (“fibers”) then laid down on a moving screen to form the fabric. Fibers resulting from a spunbond process typically have some degree of molecular orientation imparted therein.
As used herein, “meltblown” refers to a method of forming a fabric in which a polymeric melt or solution is extruded through spinnerets to form filaments which are attenuated by suitable means such as by electrostatic charge or high velocity air, such attenuated filaments (“fibers”) are then laid down on a moving screen to form the fabric. The fibers themselves may be referred to as being “spunbond” or “meltblown.”
As used herein, the term “coform” refers to another meltspinning process in which at least one meltspun die head is arranged near a chute through which other materials are added to the fabric while it is forming. Such other materials may be pulp, superabsorbent particles, cellulose or staple fibers, for example. Coform processes are described in U.S. Pat. Nos. 4,818,464 and 4,100,324. For purposes of this disclosure, the coform process is considered a particular embodiment of meltspun processes. In certain embodiments, the propylene-based fabrics described herein are coform fabrics.
As used herein, a “fiber” is a structure whose length is very much greater than its diameter or breadth; the average diameter is on the order of 0.1 μm to 250 μm, and comprises natural and/or synthetic materials. Fibers can be “monocomponent” or “bi-component.” Bi-component fibers comprise two of different chemical and/or physical properties extruded from separate extruders but the same spinnerets with both polymers within the same filament, resulting in fibers having distinct domains. The configuration of such a bi-component fiber may be, for example, sheath/core arrangement wherein one polymer is surrounded by another, side-by-side as described in U.S. Pat. No. 5,108,820, or islands in the sea as described in U.S. Pat. No. 7,413,803.
Any “web” of fibers, regardless of how formed, may be used as it is (unbonded) or bonded such as by heating, for example, by passing the web of fibers over a heated calender or roll.
As used herein, a “laminate” comprises at least two fabrics and/or film layers. Laminates may be formed by any means known in the art. Such a laminate may be made, for example, by sequentially depositing onto a moving forming belt first a meltspun fabric layer, then depositing another meltspun fabric layer or adding a dry-laid fabric on top of the first meltspun fabric layer, then adding a meltspun fabric layer on top of those layers, followed by some bonding of the laminate, such as by thermal point bonding or the inherent tendency of the layers to adhere to one another, hydroentangling, and the like. Alternatively, the fabric layers may be made individually, collected in rolls, and combined in a separate bonding step or steps. Multilayer laminates may also have various numbers of layers in many different configurations and may include other materials like films or coform materials, meltblown and spunbond materials, air-laid materials, and the like.
As used herein, a “film” is a flat unsupported section of a plastic and/or elastomeric material whose thickness is very narrow in relation to its width and length and has a continuous or nearly continuous macroscopic morphology throughout its structure allowing for the passage of air at diffusion-limited rates or lower. The laminates described herein may include one or more film layers and can comprise any material as described herein for the fabrics. In certain embodiments, films are absent from the laminates described herein. Films described herein may contain additives that, upon treatment, promote perforations and allow the passage of air and/or fluids through the film. Additives such as clays, antioxidants, and the like as described herein can also be added.

Polypropylene Homopolymer

The bi-component fibers of the present invention comprise a first component comprising a first polypropylene homopolymer and a second component comprising a blend that comprises a propylene-based elastomer and a second polypropylene homopolymer. The first and second polypropylene homopolymers can be the same or different. As used herein, the term “propylene homopolymer” refers to polymers with only propylene monomer units and is used to generally describe the first and second propylene homopolymers. That is, the propylene homopolymer compositions and properties are suitable for the first propylene homopolymer and/or the second propylene homopolymer.
In certain embodiments, the polypropylene homopolymer is predominately crystalline, as evidenced by having a melting point generally greater than 110° C., alternatively greater than 115° C., and most preferably greater than 130° C., or within a range from 110° C., or 115° C., or 130° C. to 150° C., or 160° C., or 170° C. The term “crystalline,” as used herein, characterizes those polymers which possess high degrees of inter- and intra-molecular order. The polypropylene preferably has a heat of fusion greater than 60 J/g, alternatively at least 70 J/g, alternatively at least 80 J/g, as determined by DSC analysis. The heat of fusion is dependent on the composition of the polypropylene.
The weight average molecular weight (Mw) of the polypropylene homopolymer can be within a range from 40,000 g/mole or 50,000 g/mole, or 80,000 g/mole to 200,000 g/mole, or 400,000 g/mole, or 500,000 g/mole, or 1,000,000 g/mole. The number average molecular weight (Mn) is within a range from 20,000 g/mole, or 30,000 g/mole, or 40,000 g/mole to 50,000 g/mole, or 55,000 g/mole, or 60,000 g/mole, or 70,000 g/mole. The z-average molecular weight (Mz) is at least 300,000 g/mole, or 350,000 g/mole, or within a range from 300,000, or 350,000 g/mole to 500,000 g/mole. The molecular weight distribution, Mw/Mn, in any embodiment is less than 5.5, or 5, or 4.5, or 4, or within a range from 1.5, or 2, or 2.5, or 3 to 4, or 4.5 or 5 or 5.5.
The melt flow rate (MFR) of the polypropylene homopolymer can be within a range from 1 g/10 min to 500 g/10 min, alternatively within a range from 1 g/10 min, or 5 g/10 min, or 10 g/10 min, or 15 g/10 min, or 20 g/10 min, or 25 g/10 min to 45 g/10 min, or 55 g/10 min, or 100 g/10 min, or 300 g/10 min, or 350 g/10 min, or 400 g/10 min, or 450 g/10 min, or 500 g/10 min, as measured per ASTM D1238-13 with a 2.16 kg load at 230° C. (ASTM D1238-13, 2.16 kg, 230° C.).
There is no particular limitation on the method for preparing the polypropylene homopolymer of the invention. For example, the polymer may be a propylene homopolymer obtained by homopolymerization of propylene in a single stage or multiple stage reactor. Polymerization methods include high pressure, slurry, gas, bulk, or solution phase, or a combination thereof, using a traditional Ziegler-Natta catalyst or a single-site, metallocene catalyst system, or combinations thereof including bimetallic supported catalyst systems. Polymerization may be carried out by a continuous or batch process and may include use of chain transfer agents, scavengers, or other such additives as deemed applicable. Most preferably however a Ziegler-Natta catalyst is used to form the polypropylene homopolymer.
The polypropylene homopolymer may be reactor grade, meaning that it has not undergone any post-reactor modification by reaction with peroxides, cross-linking agents, e-beam, gamma-radiation, or other types of controlled rheology modification. In any embodiment, the polypropylene homopolymer may have been visbroken by peroxides as is known in the art. In any case, the polyolefins used in the examples set forth here, and described above, have the stated properties as used, visbroken or not.
Exemplary commercial products of the polypropylene polymers in polypropylene homopolymer ExxonMobil™ PP3155 (a 36 g/10 min MFR (ASTM D1238-13, 2.16 kg, 230° C.) homopolymer, available from ExxonMobil Chemical Company), ExxonMobil™ PP3155E5 (a 36 g/10 min MFR (ASTM D1238-13, 2.16 kg, 230° C.) homopolymer, available from ExxonMobil Chemical Company), ExxonMobil™ PP1264E1 (a 20 g/10 min MFR (ASTM D1238-13, 2.16 kg, 230° C.) homopolymer, available from ExxonMobil Chemical Company), ExxonMobil™ PP1105E1 (a 35 g/10 min MFR (ASTM D1238-13, 2.16 kg, 230° C.) homopolymer, available from ExxonMobil Chemical Company), ExxonMobil™ PP1074KNE1 (a 20 g/10 min MFR (ASTM D1238-13, 2.16 kg, 230° C.) homopolymer, available from ExxonMobil Chemical Company), Achieve™ Advanced PP1605 (a 32 g/10 min MFR (ASTM D1238-13, 2.16 kg, 230° C.) homopolymer, available from ExxonMobil Chemical Company), and Achieve™ Advanced PP3854 (a 24 g/10 min MFR (ASTM D1238-13, 2.16 kg, 230° C.) homopolymer, available from ExxonMobil Chemical Company).
The bi-component fibers comprise a first component comprising a first polypropylene homopolymer and a second component comprising a blend that comprises a propylene-based elastomer and a second polypropylene homopolymer.
The amount of polypropylene homopolymer or blend of propylene homopolymers in the first component can be 80 wt % to 100 wt % based on the weight of the first component, or 90 wt % to 99 wt %, or 95 wt % to 98 wt %. The first component can optionally further comprise additives described herein.
The amount of polypropylene homopolymer or blend of propylene homopolymers in the second component can be 10 wt % to 90 wt % based on the weight of the second component, or 20 wt % to 50 wt %, or 50 wt % to 80 wt %. The second component can optionally further comprise additives described herein.

Propylene-Based Elastomer

The propylene-based elastomer as described herein is a copolymer of propylene-derived units and units derived from at least one of ethylene or a C₄to C₁₀α-olefin. The propylene-based elastomer may contain at least 50 wt % propylene-derived units. The propylene-based elastomer may have limited crystallinity due to adjacent isotactic propylene units and a melting point as described herein. The crystallinity and the melting point of the propylene-based elastomer can be reduced compared to highly isotactic polypropylene by the introduction of errors in the insertion of propylene. The propylene-based elastomer is generally devoid of any substantial intermolecular heterogeneity in tacticity and comonomer composition, and also generally devoid of any substantial heterogeneity in intramolecular composition distribution.
The amount of propylene-derived units present in the propylene-based elastomer may range from an upper limit of 95 wt %, 94 wt %, 92 wt %, 90 wt %, or 85 wt %, to a lower limit of 60 wt %, 65 wt %, 70 wt %, 75 wt %, 80 wt %, 84 wt %, or 85 wt % of the propylene-based elastomer. The comonomer-derived units include at least one of ethylene or a C₄to C₁₀α-olefin may be present in an amount of 1 wt % to 35 wt %, or 5 wt % to 35 wt %, or 7 wt % to 32 wt %, or 8 wt % to 25 wt %, or 8 wt % to 20 wt %, or 8 wt % to 18 wt %, of the propylene-based elastomer. The comonomer content may be adjusted so that the propylene-based elastomer has a heat of fusion of less than 80 J/g, a melting point of 105° C. or less, and a crystallinity of 2% to 65% of the crystallinity of isotactic polypropylene, and a MFR within a range from 2 g/10 min to 50 g/min (ASTM D1238-13, 2.16 kg, 230° C.).
In preferred embodiments, the comonomer is ethylene, 1-hexene, or 1-octene, with ethylene being most preferred. In embodiments where the propylene-based elastomer comprises ethylene-derived units, the propylene-based elastomer may comprise 5 wt % to 25 wt %, or 8 wt % to 20 wt %, or 9 wt % to 16 wt %, ethylene-derived units. In some embodiments, the propylene-based elastomer consists essentially of units derived from propylene and ethylene, that is, the propylene-based elastomer does not contain any other comonomer in an amount other than that typically present as impurities in the ethylene and/or propylene feedstreams used during polymerization, or in an amount that would materially affect the heat of fusion, melting point, crystallinity, or melt flow rate of the propylene-based elastomer, or in an amount such that any other comonomer is intentionally added to the polymerization process.
In some embodiments, the propylene-based elastomer may comprise more than one comonomer. Preferred embodiments of a propylene-based elastomer having more than one comonomer include propylene-ethylene-octene, propylene-ethylene-hexene, and propylene-ethylene-butene polymers. In embodiments where more than one comonomer derived from at least one of ethylene or a C₄to C₁₀α-olefin is present, the amount of one comonomer may be less than 5 wt % of the propylene-based elastomer, but the combined amount of comonomers of the propylene-based elastomer is 5 wt % or greater.
The propylene-based elastomer may have a triad tacticity of three propylene units, as measured by ¹³C NMR, of at least 75%, at least 80%, at least 82%, at least 85%, or at least 90%. Preferably, the propylene-based elastomer has a triad tacticity of 50% to 99%, or 60% to 99%, or 75% to 99%, or 80% to 99%. In some embodiments, the propylene-based elastomer may have a triad tacticity of 60% to 97%.
The propylene-based elastomer has a heat of fusion (“H_f”), as determined by DSC, of 80 J/g or less, or 70 J/g or less, or 50 J/g or less, or 40 J/g or less. The propylene-based elastomer may have a lower limit H_fof 0.5 J/g, or 1 J/g, or 5 J/g. For example, the H_fvalue may range from 1.0 J/g, 1.5 J/g, 3.0 J/g, 4.0 J/g, 6.0 J/g, or 7.0 J/g, to 30 J/g, 35 J/g, 40 J/g, 50 J/g, 60 J/g, 70 J/g, 75 J/g, or 80 J/g.
The propylene-based elastomer may have a percent crystallinity, as determined according to the DSC procedure described herein, of 2% to 65%, or 0.5% to 40%, or 1% to 30%, or 5% to 35%, of the crystallinity of isotactic polypropylene. The thermal energy for the propylene of 100% crystallinity is estimated at 189 J/g. In some embodiments, the copolymer has crystallinity less than 40%, or within a range from 0.25% to 25%, or within a range from 0.5% to 22% of the crystallinity of isotactic polypropylene.
In some embodiments, the propylene-based elastomer may further comprise diene-derived units (as used herein, “diene”). The optional diene may be any hydrocarbon structure having at least two unsaturated bonds wherein at least one of the unsaturated bonds is readily incorporated into a polymer. For example, the optional diene may be selected from straight chain acyclic olefins, such as 1,4-hexadiene and 1,6-octadiene; branched chain acyclic olefins, such as 5-methyl-1,4-hexadiene, 3,7-dimethyl-1,6-octadiene, and 3,7-dimethyl-1,7-octadiene; single ring alicyclic olefins, such as 1,4-cyclohexadiene, 1,5-cyclooctadiene, and 1,7-cyclododecadiene; multi-ring alicyclic fused and bridged ring olefins, such as tetrahydroindene, norbornadiene, methyl-tetrahydroindene, dicyclopentadiene, bicyclo-(2.2.1)-hepta-2,5-diene, norbornadiene, alkenyl norbornenes, alkylidene norbornenes, for example, ethylidiene norbornene (“ENB”), cycloalkenyl norbornenes, and cycloalkyliene norbornenes (such as 5-methylene-2-norbornene, 5-ethylidene-2-norbornene, 5-propenyl-2-norbornene, 5-isopropylene-2-norbornene, 5-(4-cyclopentenyl)-2-norbornene, 5-cyclohexylidene-2-norbornene, 5-vinyl-2-norbornene); and cycloalkenyl-substituted alkenes, such as vinyl cyclohexene, allyl cyclohexene, vinyl cyclooctene, 4-vinyl cyclohexene, allyl cyclodecene, vinyl cyclododecene, and tetracyclo-(A-11,12)-5,8-dodecene. The amount of diene-derived units present in the propylene-based elastomer may range from an upper limit of 15%, 10%, 7%, 5%, 4.5%, 3%, 2.5%, or 1.5%, to a lower limit of 0%, 0.1%, 0.2%, 0.3%, 0.5%, 1%, 3%, or 5%, based on the weight of the propylene-based elastomer.
The propylene-based elastomer may have a single peak melting transition as determined by DSC. In some embodiments, the copolymer has a primary peak transition of 90° C. or less, with a broad end-of-melt transition of 110° C. or greater. The peak “melting point” (“T_m”) is defined as the temperature of the greatest heat absorption in melting of the sample. However, the copolymer may show secondary melting peaks adjacent to the principal peak, and/or at the end-of-melt transition. For the purposes of this disclosure, such secondary melting peaks are considered together as a single melting point, with the highest of these peaks being considered the T_mof the propylene-based elastomer. The propylene-based elastomer may have a T_mof 110° C. or less, 105° C. or less, 100° C. or less, 90° C. or less, 80° C. or less, or 70° C. or less. In some embodiments, the propylene-based elastomer has a T_mof 25° C. to 105° C., or 60° C. to 105° C., or 70° C. to 105° C., or 90° C. to 105° C.
The propylene-based elastomer may have a density of 0.850 g/cm³to 0.900 g/cm³, or 0.860 g/cm³to 0.880 g/cm³, at 22° C. as measured per ASTM D1505-18.
The propylene-based elastomer may have a melt flow rate (“MFR”), as measured per ASTM D1238-13, 2.16 kg at 230° C., of at least 2 g/10 min. In some embodiments, the propylene-based elastomer may have an MFR of 2 g/10 min to 50 g/10 min, or 2 g/10 min to 20 g/10 min, or 30 g/10 min to 50 g/10 min, or 40 g/10 min to 50 g/10 min.
The propylene-based elastomer may have an elongation at break of less than 2000%, less than 1800%, less than 1500%, less than 1000%, or less than 800%, as measured per ASTM D412-16.
The propylene-based elastomer may have a weight average molecular weight (Mw) of 5,000 g/mole to 5,000,000 g/mole, or 10,000 g/mole to 1,000,000 g/mole, or 50,000 g/mole to 400,000 g/mole. The propylene-based elastomer may have a number average molecular weight (Mn) of 2,500 g/mole to 250,000 g/mole, or 10,000 g/mole to 250,000 g/mole, or 25,000 g/mole to 250,000 g/mole. The propylene-based elastomer may have a z-average molecular weight (Mz) of 10,000 g/mole to 7,000,000 g/mole, or 80,000 g/mole to 700,000 g/mole, or 100,000 g/mole to 500,000 g/mole. Finally, the propylene-based elastomer may have a molecular weight distribution MWD of 1.5 to 20, or 1.5 to 15, or 1.5 to 5, or 1.8 to 3, or 1.8 to 2.5.
The first component and/or second component of the bi-component fibers disclosed herein may include one or more different propylene-based elastomers, such as distinct propylene-based elastomers each having one or more different properties such as, for example, different comonomer or comonomer content. Such combinations of various propylene-based elastomers are all within the scope of the invention.
The propylene-based elastomer may comprise copolymers prepared according to the procedures described in WO/2002/036651, U.S. Pat. No. 6,992,158, and/or WO/2000/001745. Preferred methods for producing the propylene-based elastomer may be found in U.S. Pat. Nos. 7,232,871 and 6,881,800. The invention is not limited by any particular polymerization method for preparing the propylene-based elastomer, and the polymerization processes are not limited by any particular type of reaction vessel.
Suitable propylene-based elastomers may be available commercially under the trade names Vistamaxx™ (available from ExxonMobil Chemical Company), VERSIFY™ (available from The Dow Chemical Company), certain grades of TAFMER™ XM or NOTIO™ (available from Mitsui Company), and certain grades of SOFTEL™ (available from Basell Polyolefins). The particular grade(s) of commercially available propylene-based elastomer suitable for use in the invention can be readily determined using methods commonly known in the art.
The amount of propylene-based elastomer or blend of propylene-based elastomers in the second component can be 10 wt % to 90 wt % based on the weight of the second component, or 20 wt % to 50 wt %, or 50 wt % to 80 wt %. The second component can optionally further comprise additives described herein.

Blend of the Second Component

The second component of the bi-component fiber comprises a blend that comprises a propylene-based elastomer and a second polypropylene homopolymer.
The blend may have a MFR (ASTM D1238-13, 2.16 kg, 230° C.) of at least 2 g/10 min. In some embodiments, the propylene-based elastomer may have an MFR of 2 g/10 min to 50 g/10 min, or 2 g/10 min to 20 g/10 min, or 30 g/10 min to 50 g/10 min, or 40 g/10 min to 50 g/10 min. The blend has a melt flow rate that is at least 20% greater or at least 20% less than a melt flow rate of the first polypropylene homopolymer.
The weight ratio of propylene homopolymer(s) to propylene-based elastomer(s) in the second component can be 10:90 to 90:10, or 20:80 to 80:20, or 15:85 to 50:50, or 30:70 to 40:60, or 50:50 to 85:15, or 60:40 to 70:30.

Additives

A variety of additives may be incorporated into the propylene homopolymer and/or blend of the second component described above used to make the fibers and fabric. Such additives include, for example, stabilizers, antioxidants, fillers, colorants, nucleating agents, and slip additives. Primary and secondary antioxidants include, for example, hindered phenols, hindered amines, and phosphates. Nucleating agents include, for example, sodium benzoate and talc. Also, other nucleating agents may also be employed such as Ziegler-Natta olefin product or other highly crystalline polymer. Other additives such as dispersing agents, for example, ACROWAX™ C (available from Lonza), can also be included. Slip agents include, for example, oleamide and erucamide. Catalyst deactivators are also commonly used, for example, calcium stearate, hydrotalcite, and calcium oxide, and/or other acid neutralizers known in the art.
Other additives include, for example, fire/flame retardants, plasticizers, vulcanizing or curative agents, vulcanizing or curative accelerators, cure retarders, processing aids, tackifying resins, and the like. The aforementioned additives of may also include fillers and/or reinforcing materials, either added independently or incorporated into an additive. Examples include carbon black, clay, talc, calcium carbonate, mica, silica, silicate, combinations thereof, and the like. Other additives which may be employed to enhance properties include antiblocking agents, lubricants, and nucleating agents. The lists described herein are not intended to be inclusive of all types of additives which may be employed with the present invention. Upon reading this disclosure, those of skill in the art will appreciate other additives may be employed to enhance properties. As is understood by those skilled in the art, the blends of the present invention may be modified to adjust the characteristics of the blends as desired.
In any embodiment, the blend of the second component described herein can comprise (or consist of) the propylene-based elastomer, the second polypropylene homopolymer, and within a range from 0.1 wt % to 3 wt %, or 4 wt %, or 5 wt % of additives by weight of the blend. Most preferably, those additives include primary and secondary antioxidants, acid scavenger, nucleating agent, and pigment or other colorant.

Blending

The blend of the second component described herein may be prepared by any procedure that produces a mixture of the components, for example, dry blending, melt blending, and the like. In certain embodiments, a complete mixture of the polymeric components is indicated by the uniformity of the morphology of the dispersion of the polymer components.
Melt blend: Continuous melt mixing equipment are generally used. These processes are well known in the art and include single and twin screw compounding extruders as well as other machines and processes, designed to homogenize the polymer components intimately.
Dry blend: The propylene-based elastomer, the second polypropylene homopolymer, and other optional components may be dry blended and fed directly into the fiber or nonwoven process extruders. Dry blending is accomplished by combining the propylene-based elastomer, the second polypropylene homopolymer, and other optional components in a dry blending equipment. Such equipment and processes are well known in the art and include a drum tumbler, a double cone blender, and the like. In this case, the propylene-based elastomer, the second polypropylene homopolymer, and other optional components are melted (where applicable) and homogenized in the process extruder similar to the melt blend process. Instead of making the pellets, the homogenized molten polymer is delivered to the die or spinneret to form the fiber and fabric.

Process for Producing Nonwoven Fabric of Fibers

The invention further discloses a process for producing a nonwoven fabric of bi-component fibers, the process comprising: (a) forming a first component polymer melt comprising: a first polypropylene homopolymer, (b) forming a second component polymer melt comprising: a propylene-based elastomer and a second polypropylene homopolymer, (c) extruding (e.g., via a melt spun process or a spunbonding process) the first component polymer melt and the second component polymer melt through a die configured for a desired bi-component fiber compositional cross-section, and (d) cooling the bi-component fibers. In such methods, the vast majority as-produced bi-component fibers are not crimped or curled. That is, a crimp or curled portion of the bi-component fibers is less than 5 wt % of the total weight of the bi-component fibers.
Desired bi-component fiber compositional cross-sections include, but are not limited to, side-by-side, segmented, sheath/core, island-in-the-sea structures (“matrix fibril”), and others as is known in the art. The first component described herein can compose 10 wt % to 90 wt % of the bi-component fiber, or 20 wt % to 80 wt % of the bi-component fiber, or 25 wt % to 60 wt % of the bi-component fiber, or 40 wt % to 75 wt % of the bi-component fiber. The second component can compose the balance of the bi-component fiber.
The method can further include (e) thermally and/or mechanically activating the bi-component fiber to cause the bi-component fiber to crimp or curl. Activation preferably occurs after the bi-component fibers are cooled and before thermal bonding (e.g., via calendering). For example, activation can occur immediately after the fibers are laid on a forming belt. In another example, activation can occur after the compaction roller but before calendering.
Activation can be achieved with, for example, a hot air knife, a heated roller (e.g., using heated oil or heating coils), mechanical crimping rollers, fabric tensioning rollers, and the like, and any combination thereof. Thermal activation can include heating the bi-component fibers to 50° C. or greater (e.g., 50° C. to 150° C., or 75° C. to 125° C., or 90° C. to 115° C.) for 1 second or greater (e.g., 1 second to 5 minutes, or 1 second to 1 minute, or 5 seconds to 15 seconds). Mechanical activation can include applying a force of at least 0.01 N (e.g., 0.01 N to 10 N, or 0.1 N to 5 N, or 0.5 N to 2 N) to the bi-component fibers. Thermal and/or mechanical activation can cause the fibers to have a shrinkage of at least 5% (e.g., 5% to 80%, or 20% to 75%, or 40% to 65%), as determined in accordance with ASTM D2259-02(2016).
The spunbonding process in certain embodiments involves the process of melt-extruding (or “extruding”) the desired material through one or more dies, the stream of molten material then being attenuated (drawn) by pressurized air, creating a venturi effect. The material may be added to their respective melt-extruder as pellets having desirable additives, or additives may be combined in this step.
In particular, the formation of bi-component fibers is accomplished by extruding the molten material through an appropriate die as known in the art to produce the desired bi-component fiber compositional cross-section, followed by quenching the molten material (having a desirable melt temperature within the die) with a quench air system the temperature of which may be controlled. Common quench air systems include those that deliver temperature controlled air in a cross-flow direction. Filaments are then pulled away from the one or more spinnerets and thus attenuated. To accomplish this, the filaments are attenuated by passing through a venturi device in which due to pressurized air flow, accelerates and/or attenuates the filaments. Increasing the air velocity within the venturi device may be done by a variety of methods described in the art, including raising the air pressure within the venturi device. Typically, increasing this air velocity (for example by increasing air pressure) results in increased filament velocity and greater filament attenuation. The higher the air pressure, the more the polymer melts of the bi-component fibers are accelerated and so attenuated, in terms of speed and denier of the fiber that is formed therefrom. To achieve finer fibers, high air pressures are desirable. However, this is balanced by the tendency for the filaments to break due to excessive pressure. The polymer melts of the bi-component fibers described herein can be attenuated using higher air pressures than is typical in other spunbond processes. In any embodiment, the attenuating air pressure used in the spunbonding process is greater than 2000 Pa or 3000 Pa or 4000 Pa or 6000 Pa, and less than 600 kPa or 500 kPa or 400 kPa in other embodiments; and is within a range from 2000 Pa or 3000 Pa or 4000 Pa to 8000 Pa or 10,000 Pa or 15,000 Pa in other embodiments. Such air pressure may be generated in a closed area where the fibers are attenuated such as a “cabin,” and the air pressure therein is sometimes referred to as a “cabin pressure.”
Air attenuation can be accomplished by any means such as described and the process is not limited to any particular method of attenuating the filaments. In any embodiment, the venturi effect to attenuate the fibers is obtained by drawing the filaments of polymer melts of the bi-component fibers using an aspirator slot (slot draw), which runs the width of the machine. In another embodiment, the venturi effect is obtained by drawing the filaments through a nozzle or aspirator gun. Multiple guns can be used, since orifice size can be varied to achieve the desired effect. Bi-component fibers thus formed are collected onto a screen (“wire”) In any embodiment, or porous forming belt in another embodiment to form a fabric of the filaments. Typically, a vacuum is maintained on the underside of the belt to promote the formation of a uniform fabric and to remove the air used to attenuate the filaments and creating the air pressure. The actual method of air attenuation is not critical, as long as the desirable accelerating air velocity, (often reflected by the air pressure), and hence venturi effect, is obtained to attenuate the bi-component fibers.
Pressure in the die block in any embodiment is generated by a gear pump. The method of forming the pressure in the die block is not critical, but the pressure inside the die block ranges from 35 bar to 50 bar (3500 kPa to 5000 kPa) In any embodiment, and from 36 bar to 48 bar (3600 kPa to 4800 kPa) in another embodiment, and from 37 bar to 46 bar (3700 kPa to 4600 kPa) in yet another embodiment.
The melt temperature in the die of the polymer melts of the bi-component fibers ranges from 200° C. to 260° C. In any embodiment, and from 200° C. to 250° C. in yet another embodiment, and ranges from 210° C. to 245° C. in yet another embodiment.
In certain embodiments, the spunbond line throughput is within a range from 150 kg/hr or 170 kg/hr to 200 kg/hr or 270 kg/hr to 300 kg/hr. In certain other embodiments, the spunbond line throughput per hole is within a range from 0.20 grams/hole/minute or 0.30 grams/hole/minute or 0.40 grams/hole/minute to 0.60 grams/hole/minute or 0.70 grams/hole/minute or 0.90 grams/hole/minute.
In certain embodiments, the spunbond process is conducted at a spinning speed within a range from 700 m/min or 900 m/min or 1100 m/min or 1300 m/min or 1500 m/min to 2000 m/min, or 2500 m/min, or 3000 m/min, or 3500 m/min, or 4000 m/min, or 4500 m/min, or 5000 m/min.
In forming propylene-based fabrics, there are any number of ways of dispersing or distributing the bi-component fibers to form a uniform fabric. In any embodiment, a deflector is used, either stationary or moving. In another embodiment, static electricity or air turbulence is used to improve fabric uniformity. Other means may also be used as is known in the art. In any case, the formed fabric typically passes through compression rolls to improve fabric integrity. The fabric, in any embodiment, is then passed between heated calender rolls where the raised lands on one roll bond the fabric at certain points to further increase the spunbonded fabric integrity. The compression and heated calender can be isolated from the area where the filaments are formed in any embodiment.
Preferably, the thus formed fabrics (bonded or unbonded) are exposed to a cooling environment to a temperature below 50° C., or 45° C., or 40° C., or 45° C., or 40° C., or within a range from 20° C. to 50° C. Cooling can be effected by any means such as cooling air, or chill rollers. Following the cooling, the fabrics are heated, preferably on a calender roll, heated air or heated oven environment or the like, to a temperature of at least 50° C., or 55° C., or 60° C., or 65° C., or 70° C., or 75° C., or 80° C., or 85° C., or 90° C., or within a range from 50° C., or 55° C. to 80° C., or 90° C., or 100° C., or 125° C., or 155° C. More particularly, heat may be applied by any suitable method known in the art, such as heated air, infrared heaters, heated nipped rolls, or partial wrapping of the fabric or laminate around one or more heated rolls or steam canisters, and the like. Heat may also be applied to the grooved rolls themselves. It should also be understood that other grooved roll arrangement are equally suitable, such as two grooved rolls positioned immediately adjacent to one another. The percent bonded area is typically 18% to 25% of the fabric. It is possible, and preferable to decrease the bonding area, for example, to 10% to 15% of the fabric to enhance the loftiness of the fabrics and preserve the curling of fibers.
Various additional potential processing and/or finishing steps known in the art, such as slitting, treating, printing graphics, and the like, may be performed without departing from the spirit and scope of the invention. For instance, the fabric or laminate comprising the fabric may optionally be mechanically stretched in the cross-machine and/or machine directions to enhance extensibility. In any embodiment, the fabric or laminate may be coursed through two or more rolls that have grooves in the CD and/or MD directions. Such grooved satellite/anvil roll arrangements are described in US 2004/0110442 and US 2006/0151914 and U.S. Pat. No. 5,914,084. For instance, the fabric or laminate may be coursed through two or more rolls that have grooves in the CD and/or MD directions. The grooved rolls may be constructed of steel or other hard material (such as a hard rubber). Besides grooved rolls, other techniques may also be used to mechanically stretch the composite in one or more directions. For example, the composite may be passed through a tenter frame that stretches the composite. Such tenter frames are well known in the art and described, for instance, in US 2004/0121687.
No matter how formed and oriented, the propylene-based fabrics comprise fibers having an average diameter of less than 20 or 17 or 15 or 12 μm in certain embodiments, alternatively from 0.5, or 1, or 2, or 3, or 4 to 12, or 15, or 17, or 20 μm, and/or a denier (g/9000 m) of less than 2.0 or 1.9 or 1.8 or 1.6 or 1.4 or 1.2 or 1.0 in certain embodiments, alternatively from 0.2, or 0.4 or 0.6 to 1.0, or 1.2 or 1.4 or 1.6 or 1.8, or 2.0. Such fabrics, when oriented at a temperature (calender set temperature) within a range from 110 to 150° C. have a MD Tensile Strength (WSP 110.4 (05)) of greater than 20 or 25 N/5 cm in certain embodiments. The fabrics have a CD Tensile Strength (WSP 110.4 (05)) of greater than 10 N/5 cm or 15 N/5 cm when oriented at a temperature (calender set temperature) within a range from 110° C. to 150° C. in other embodiments.
In certain embodiments, the one or more propylene-based fabrics may form a laminate either with itself or with other secondary layers. The lamination of the various layers can be done such that CD and/or MD orientation is imparted into the fabric or laminate, especially in the case where the laminate includes at least one elastomeric layer. Many approaches may be taken to form a laminate comprising an elastomeric film and/or fabric layer which remains elastomeric once the laminate layers are bonded together. One approach is to fold, corrugate, crepe, or otherwise gather the fabric layer prior to bonding it to the elastomeric film. The gathered fabric is bonded to the film at specified points or lines, not continually across the surface of the film. While the film/fabric is in a relaxed state, the fabric remains corrugated or puckered on the film; once the elastomeric film is stretched, the fabric layer flattens out until the puckered material is essentially flat, at which point the elastomer stretching ceases.
Another approach is to stretch the elastomeric film/fabric, then bond the fabric to the film while the film is stretched. Again, the fabric is bonded to the film at specified points or lines rather than continually across the surface of the film. When the stretched film is allowed to relax, the fabric corrugates or puckers over the unstretched elastomeric film.
Another approach is to “neck” the fabric prior to bonding it to the elastomer layer as described in U.S. Pat. Nos. 5,336,545, 5,226,992, 4,981,747, and/or 4,965,122. Necking is a process by which the fabric is pulled in one direction, which causes the fibers in the fabric to slide closer together, and the width of the fabric in the direction perpendicular to the pulling direction is reduced. If the necked fabric is point-bonded to an elastomeric layer, the resulting laminate will stretch somewhat in a direction perpendicular to the direction in which the fabric was pulled during the necking process, because the fibers of the necked fabric can slide away from one another as the laminate stretches.

Laminates

This invention further provides a laminate comprising one or more layers of a nonwoven fabric comprising bi-component fibers described herein.
Preferably, the laminates are allowed to cool, if previously heated, to a temperature below 50° C., or 45° C., or 40° C., or 45° C., or 40° C., or within a range from 20° C. to 50° C. Cooling can be effectuated by any means such as cooling air, or chill rollers. Following the cooling, the fabrics are activated such as by heating the laminates in a similar fashion to activation of the individual fabrics described above. In particular the laminates may be heated, preferably on a calender roll, heated air or heated oven environment or the like, to a temperature of at least 50° C., or 55° C., or 60° C., or 65° C., or 70° C., or 75° C., or 80° C., or 85° C., or 90° C., or within a range from 50° C., or 55° C. to 80° C., or 90° C., or 100° C., or 120° C. More particularly, heat may be applied by any suitable method known in the art, such as heated air, infrared heaters, heated nipped rolls, or partial wrapping of the fabric or laminate around one or more heated rolls or steam canisters, and the like. Heat may also be applied to the grooved rolls themselves. It should also be understood that other grooved roll arrangement are equally suitable, such as two grooved rolls positioned immediately adjacent to one another.
Yet another approach is to activate the laminate by a physical treatment, modification or deformation of the laminate, said activation being performed by mechanical means. For example, the laminate may be incrementally stretched by using intermeshing rollers, as discussed in U.S. Pat. No. 5,422,172, or US 2007/0197117 to render the laminate stretchable and recoverable. Finally, the film or fabric may be such that it needs no activation and is simply formed onto and/or bound to a secondary layer to form a laminate.
In some embodiments, the laminates comprising one or more secondary layers comprising other fabrics, nets, coform fabrics, scrims, and/or films prepared from natural and/or synthetic materials. The materials may be extensible, elastic or plastic in certain embodiments. In particular embodiments, the one or more secondary layers comprise materials selected from the group consisting of polypropylene, polyethylene, plastomers, polyurethane, polyesters such as polyethylene terephthanlate, polylactic acid, polyvinyl chloride, polytetrafluoroethylene, styrenic block copolymers, ethylene vinyl acetate copolymers, poly amide, polycarbonate, cellulosics (e.g., cotton, Rayon™, Lyocell™ Tencil™), wood, viscose, and blends of any two or more of these materials. Any secondary layer may also comprise (or consist essentially of) any material that is elastic, examples of which include propylene-α-olefin elastomer, natural rubber (NR), synthetic polyisoprene (IR), butyl rubber (copolymer of isobutylene and isoprene, IIR), halogenated butyl rubbers (chloro-butyl rubber: CIIR; bromo-butyl rubber: BUR), polybutadiene (BR), styrene-butadiene rubber (SBR), nitrile rubber, hydrogenated nitrile rubbers, chloroprene rubber (CR), poly chloroprene, neoprene, EPM (ethylene-propylene rubber) and EPDM rubbers (ethylene-propylene-diene rubber), epichlorohydrin rubber (ECO), polyacrylic rubber (ACM, ABR), silicone rubber, fluorosilicone rubber, fiuoroelastomers, perfiuoroelastomers, polyether block amides (PEBA), chlorosulfonated polyethylene (CSM), ethylene-vinyl acetate (EVA), thermoplastic elastomers (TPE), thermoplastic vulcanizates (TPV), thermoplastic polyurethane (TPU), thermoplastic olefins (TPO), polysulfide rubber, or blends of any two or more of these elastomers. In certain embodiments, the one or more elastic layers comprise propylene-a-olefin elastomer, styrene-butadiene rubber, or blends thereof. In yet other embodiments, the one or more elastic layers consist essentially of propylene-a-olefin elastomer(s). In a particular embodiment, styrenic-based elastomers (polymers comprising at least 10 wt % styrene or substituted-styrene-derived units) are absent from the multilayer fabric.
The secondary layer(s) may be in the form of films, fabrics, or both. Films may be cast, blown, or made by any other suitable means. When the secondary layers are fabrics, the secondary layers can be meltspun, dry-laid or wet-laid fabrics. The dry-laid processes include mechanical means, such as how carded fabrics are produced, and aerodynamic means, such as, air-laid methods. Dry-laid nonwovens are made with staple fiber processing machinery such as cards and garnetts, which are designed to manipulate staple fibers in the dry state. Also included in this category are nonwovens made from fibers in the form of tow, and fabrics composed of staple fibers and stitching filaments or yarns, namely, stitchbonded nonwovens. Fabrics made by wet-laid processes made with machinery associated with pulp fiberizing, such as hammer mills, and paperforming. Web-bonding processes can be described as being chemical processes or physical processes. In any case, dry- and wet-laid fabrics can be jet and/or hydroentangled to form a spunlace fabric as is known in the art. Chemical bonding refers to the use of water-based and solvent-based polymers to bind together the fibrous webs. These binders can be applied by saturation (impregnation), spraying, printing, or application as a foam. Physical bonding processes include thermal processes such as calendering and hot air bonding, and mechanical processes such as needling and hydroentangling. Spunlaid nonwovens are made in one continuous process: fibers are spun by melt extrusion and then directly dispersed into a web by deflectors or can be directed with air streams.
In certain embodiments, the propylene-based elastomer may be formed into coform fabrics. Methods for forming such fabrics are described in, for example, U.S. Pat. Nos. 4,818,464 and 5,720,832. Generally, fabrics of two or more different thermoplastic and/or elastomeric materials may be formed.
The nonwoven fabric of fibers can be used to make articles, such as personal care products, baby diapers, training pants, absorbent underpads, swim wear, wipes, feminine hygiene products, bandages, wound care products, medical garments, surgical gowns, filters, adult incontinence products, surgical drapes, coverings, garments, cleaning articles and apparatus.

Example Embodiments

A first embodiment is a method comprising: (a) extruding a bi-component fiber comprising: a first component comprising a first polypropylene homopolymer; and a second component comprising a blend that comprises a propylene-based elastomer and a second polypropylene homopolymer, wherein the blend has a melt flow rate that is at least 20% greater than or at least 20% less than a melt flow rate of the first polypropylene homopolymer; (b) cooling the bi-component fiber; and (c) thermally and/or mechanically activating the bi-component fiber to cause the bi-component fiber to curl. This embodiment may optionally include one or more of the following: Element 1: wherein a weight ratio of the propylene-based elastomer and the second polypropylene homopolymer in the blend is 10:90 to 90:10; Element 2: wherein a weight ratio of the propylene-based elastomer and the second polypropylene homopolymer in the blend is 40:60 to 90:10; Element 3: wherein a weight ratio of the propylene-based elastomer and the second polypropylene homopolymer in the blend is 10:90 to 60:40; Element 4: wherein the bi-component fiber is thermally activated by exposing the bi-component fiber to 50° C. to 150° C. for 1 second to 5 minutes; Element 5: wherein the bi-component fiber is thermally activated by exposing the bi-component fiber to 90° C. to 115° C. for 5 seconds to 15 seconds; Element 6: wherein the bi-component fiber is mechanically activated by exposing the bi-component fiber to a force of 0.01 N to 10 N; Element 7: wherein the bi-component fiber is mechanically activated by exposing the bi-component fiber to a force of 0.1 N to 5 N; Element 8: wherein the bi-component fiber after cooling is substantially straight and after activating has a shrinkage of a least 25%; Element 9: wherein the bi-component fiber after cooling is substantially straight and after activating has a shrinkage of a least 45%; Element 10: wherein a weight ratio of the first component and the second component in the bi-component fiber is 10:90 to 90:10; Element 11: wherein a weight ratio of the first component and the second component in the bi-component fiber is 40:60 to 80:20; Element 12: wherein a compositional cross-section is side-by-side, segmented, sheath/core, or island-in-the-sea; Element 13: the method further comprising: producing a nonwoven article with the bi-component fiber; and Element 14: the method further comprising: producing a laminated article with the bi-component fiber. Example combinations include, but are not limited to, one of Elements 1-3 in combination with one or more of Elements 4-7; one of Elements 1-3 in combination with one of Elements 8-9; one of Elements 1-3 in combination with one of Elements 10-11; one of Elements 1-3 in combination with one or more of Elements 12-14; one of Elements 10-11 in combination with one or more of Elements 4-7; one of Elements 10-11 in combination with one of Elements 8-9; one of Elements 10-11 in combination with one or more of Elements 12-14; one or more of Elements 4-7 in combination with one of Elements 8-9; one or more of Elements 4-7 in combination with one or more of Elements 12-14; and any combination of these combinations.
By “substantially straight” what is meant is that the fiber strand throughout its length has an overall bend from 180° of no more than ±10° or ±5°. For instance, there may be one, two or more bends or kinks in a strand, but overall the strand is substantially straight as defined here.
A second embodiment is a bi-component fiber comprising: a first component comprising a first polypropylene homopolymer; and a second component comprising a blend that comprises a propylene-based elastomer and a second polypropylene homopolymer, wherein the blend has a melt flow rate that is at least 20% greater than or at least 20% less than a melt flow rate of the first polypropylene homopolymer. This embodiment may optionally include one or more of the following: Element 1; Element 2; Element 3; Element 10; Element 11; and Element 12. Example combinations include, but are not limited to, one of Elements 1-3 in combination with one of Elements 10-11 and optionally in further combination with Element 12; one of Elements 1-3 in combination with Element 12; and one of Elements 10-11 in combination with Element 12.
A third embodiment is a nonwoven article comprising the bi-component fiber of the second embodiment, optionally including one or more of Elements 1-3 and 10-12.
A fourth embodiment is a laminated article comprising the bi-component fiber of the second embodiment, optionally including one or more of Elements 1-3 and 10-12.
One or more illustrative embodiments incorporating the invention embodiments disclosed herein are presented herein. Not all features of a physical implementation are described or shown in this application for the sake of clarity. It is understood that in the development of a physical embodiment incorporating the embodiments of the present invention, numerous implementation-specific decisions must be made to achieve the developer's goals, such as compliance with system-related, business-related, government-related and other constraints, which vary by implementation and from time to time. While a developer's efforts might be time-consuming, such efforts would be, nevertheless, a routine undertaking for those of ordinary skill in the art and having benefit of this disclosure.
While compositions and methods are described herein in terms of “comprising” various components or steps, the compositions and methods can also “consist essentially of” or “consist of” the various components and steps.
To facilitate a better understanding of the embodiments of the present invention, the following examples of preferred or representative embodiments are described. In no way should the following examples be read to limit, or to define, the scope of the invention.

Examples

Example 1. Bi-component fibers were produced with a side-by-side and a sheath/core compositional cross-section where the first component was a polypropylene homopolymer having an MFR (ASTM D1238-13, 2.16 kg, 230° C.) of 36 g/10 min and the second component was a 50:50 blend of the same polypropylene homopolymer and a polypropylene-polyethylene copolymer having an MFR (ASTM D1238-13, 2.16 kg, 230° C.) of 48 g/10 min (Sheath/Core Bi-Component Fiber and Side-by-Side Bi-Component Fiber). The blend had an MFR (ASTM D1238-13, 2.16 kg, 230° C.) of 45 g/10 min.
Control fibers were produced that consisted of the polypropylene homopolymer having an MFR (ASTM D1238-13, 2.16 kg, 230° C.) of 36 g/10 min (Single Component Fiber).
The weight ratio of the first component to the second component were varied from 20:80 to 80:20. After cooling the as-produced fibers, the bi-component and control fibers were thermally activated by exposure to 100° C. for 15 seconds, which resulted in curling of the filaments. The shrinkage (ASTM D2259-02(2016)) is reported in FIG. 1.
The control filaments have less than 7% shrinkage. Whereas, the bi-component fibers can have almost 80% shrinkage. As the weight ratio of the first component to the second component increases, so does the amount of shrinkage.
Example 2. FIG. 2A is a scanning electron micrograph of bi-component fibers having 40 wt % ExxonMobil™ PP3155E5 and 60 wt % of a 30:70 blend of ExxonMobil™ PP3155E5+Vistamaxx™7050 as-produced before mechanical activation, and FIG. 2B is that sample after mechanical activation by manually applying force with a brush. This illustrates the straight fibers as-produced and curled fibers after activation.
Example 3. Bi-component fibers were produced with a side-by-side compositional cross-section where the first component was a polypropylene homopolymer having an MFR (ASTM D1238-13, 2.16 kg, 230° C.) of 36 g/10 min and the second component was a 60:40 blend of the same polypropylene homopolymer and a polypropylene-polyethylene copolymer having an MFR (ASTM D1238-13, 2.16 kg, 230° C.) of 48 g/10 min.
FIGS. 3A and 3B is a light micrographs of the fibers as-produced before thermal activation, and FIGS. 3C and 3D is that sample after thermal activation at 100° C. for 15 seconds. This illustrates the straight fibers as-produced and curled fibers after activation.
Example 4. Bi-component fibers were produced with a side-by-side compositional cross-section or a sheath/core compositional cross-section according to the compositions in Table 1. Control fibers were produced that consisted of the polypropylene homopolymer having an MFR (ASTM D1238-13, 2.16 kg, 230° C.) of 36 g/10 min.

TABLE 1

			Comp. 1 to	Component 2
			Comp. 2 Wt.	Blend Ratio
Sample	Component 1	Component 2	Ratio	(Blend MFR)

1A	ExxonMobil ™	ExxonMobil ™	50/50	30/70
	PP3155E5	PP3155E5 +		(~45 g/10 min)
		Vistamaxx ™ 7050
1B	ExxonMobil ™	ExxonMobil ™	40/60	30/70
	PP3155E5	PP3155E5 +		(~45 g/10 min)
		Vistamaxx ™ 7050
1C	ExxonMobil ™	ExxonMobil ™	30/70	30/70
	PP3155E5	PP3155E5 +		(~45 g/10 min)
		Vistamaxx ™ 7050
1D	ExxonMobil ™	ExxonMobil ™	20/80	30/70
	PP3155E5	PP3155E5 +		(~45 g/10 min)
		Vistamaxx ™ 7050
2A	ExxonMobil ™	ExxonMobil ™	50/50	60/40
	PP3155E5	PP3155E5 +		(~28 g/10 min)
		Vistamaxx ™ 7020
2B	ExxonMobil ™	ExxonMobil ™	40/60	60/40
	PP3155E5	PP3155E5 +		(~28 g/10 min)
		Vistamaxx ™ 7020
2C	ExxonMobil ™	ExxonMobil ™	30/70	60/40
	PP3155E5	PP3155E5 +		(~28 g/10 min)
		Vistamaxx ™ 7020
2D	ExxonMobil ™	ExxonMobil ™	20/80	60/40
	PP3155E5	PP3155E5 +		(~28 g/10 min)
		Vistamaxx ™ 7020
3A	ExxonMobil ™	ExxonMobil ™	50/50	95/5
	PP3155E5	PP3155E5 +		(~48 g/10 min)
		Vistamaxx ™ 8880
3B	ExxonMobil ™	ExxonMobil ™	40/60	95/5
	PP3155E5	PP3155E5 +		(~48 g/10 min)
		Vistamaxx ™ 8880
3C	ExxonMobil ™	ExxonMobil ™	30/70	95/5
	PP3155E5	PP3155E5 +		(~48 g/10 min)
		Vistamaxx ™ 8880
3D	ExxonMobil ™	ExxonMobil ™	20/80	95/5
	PP3155E5	PP3155E5 +		(~48 g/10 min)
		Vistamaxx ™ 8880

Example 5. Three sets of fibers were produced. First, a control set of fibers were produced in a side-by-side confirmation of ExxonMobil™ PP3155 and another polypropylene homopolymer (PP/PP Bi-Component Fiber). Second, a bi-component fiber of the invention was produced with Achieve™ Advanced PP3854 as the first component and ExxonMobil™ PP3155E5 as the second component in a side-by-side configuration (PP/Achieve Blend Bi-Component Fiber). Third, a blend of ExxonMobil™ PP3155 and Vistamaxx™7020 was produced as a monocomponent fiber (PP Blend Single Component Fiber). Each set of fibers was produced with different weight ratios of each component. The fibers were thermally activated by exposure to 100° C. for 15 seconds and the shrinkage was measured (see FIG. 4). The bi-component fiber of the invention is the only sample with appreciable shrinkage including up to 55% with 70 wt % of the first component and 30 wt % of the second component.
Therefore, the present invention is well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular embodiments disclosed above are illustrative only, as the present invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein.
While compositions and methods are described in terms of “comprising,” “containing,” or “including” various components or steps, the compositions and methods can also “consist essentially of” or “consist of” the various components and steps.

Claims

1. A method comprising:

extruding a bi-component fiber comprising:

a first component comprising a first polypropylene homopolymer; and

a second component comprising a blend that comprises a propylene-based elastomer and a second polypropylene homopolymer, wherein the blend has a melt flow rate that is at least 20% greater than or at least 20% less than a melt flow rate of the first polypropylene homopolymer;

cooling the bi-component fiber; and

activating the bi-component fiber to cause the bi-component fiber to curl wherein the step of activating is performed thermally, mechanically, or through a combination of thermal and mechanical action.

2. The method of claim 1, wherein a weight ratio of the propylene-based elastomer and the second polypropylene homopolymer in the blend is 10:90 to 90:10.

3. The method of claim 1, wherein a weight ratio of the propylene-based elastomer and the second polypropylene homopolymer in the blend is 40:60 to 90:10.

4. The method of claim 1, wherein the bi-component fiber is thermally activated by exposing the bi-component fiber to 50° C. to 150° C. for 1 second to 5 minutes.

5. The method of claim 1, wherein the bi-component fiber is thermally activated by exposing the bi-component fiber to 90° C. to 115° C. for 5 seconds to 15 seconds.

6. The method of claim 1, wherein the bi-component fiber is mechanically activated by exposing the bi-component fiber to a force of 0.01 N to 10 N.

7. The method of claim 1, wherein the bi-component fiber is mechanically activated by exposing the bi-component fiber to a force of 0.1 N to 5 N.

8. The method of claim 1, wherein the bi-component fiber after cooling is substantially straight and after activating has a shrinkage of a least 25%.

9. The method of claim 1, wherein the bi-component fiber after cooling is substantially straight and after activating has a shrinkage of a least 45%.

10. The method of claim 1, wherein a weight ratio of the first component and the second component in the bi-component fiber is 10:90 to 90:10.

11. The method of claim 1, wherein a weight ratio of the first component and the second component in the bi-component fiber is 40:60 to 80:20.

12. The method of claim 1, wherein a compositional cross-section is side-by-side, segmented, sheath/core, or island-in-the-sea.

13. The method of claim 1 further comprising producing a nonwoven article with the bi-component fiber.

14. The method of claim 1 further comprising producing a laminated article with the bi-component fiber.

15. A bi-component fiber comprising:

a first component comprising a first polypropylene homopolymer; and

a second component comprising a blend that comprises a propylene-based elastomer and a second polypropylene homopolymer, wherein the blend has a melt flow rate that is at least 20% greater than or at least 20% less than a melt flow rate of the first polypropylene homopolymer.

16. The bi-component fiber of claim 15, wherein a weight ratio of the propylene-based elastomer and the second polypropylene homopolymer in the blend is 10:90 to 90:10.

17. The bi-component fiber of claim 15, wherein a weight ratio of the first component and the second component in the bi-component fiber is 10:90 to 90:10.

18. The bi-component fiber of claim 15, wherein a compositional cross-section is side-by-side, segmented, sheath/core, or island-in-the-sea.

19. A nonwoven article comprising the bi-component fiber of claim 15.

20. A laminated article comprising the bi-component fiber of claim 15.