CRYSTALLIZATION TIME

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S.S.N. 62/785,261, filed December 27, 2018, herein incorporated by reference.

BACKGROUND

[0002] The present disclosure relates to methods for forming spunbond materials from polymer compositions, and to composites and articles formed from such spunbond materials.

[0003] Nonwoven fabrics comprised of processed polymers are in high demand for their use in multiple kinds of products including clothing and hygienic fabrics such as diapers, surgical masks, surgical gowns, and the like. Of the nonwoven fabrics, spunbond fabrics are particularly attractive because of the breathability such fabrics offer. In addition, many spunbond process lines are in existence, which allows for a substantial degree of manufacturing throughput.

[0004] Spunbond processes typically involve passing a polymer composition through an extruder (optionally in combination with one or more additives such as coloring agents, resin modifiers, and the like), in which the polymer composition is melted. The molten polymer composition passes through a spinneret comprising a plurality of small holes through which the molten polymer composition passes, thereby forming molten polymer composition filaments. Cool or quench air is passed over the filaments as they exit, with the aim of cooling the filaments so as to solidify them, before they are deposited onto a collection surface such as a moving belt where the filaments form a web. Frequently, spunbond processes employ some means of bonding to bond the filaments of the web together as they move along the collection surface. Examples include hydroentanglement, needlepunching, thermal bonding, and chemical bonding. After the fabrics are bonded, they may be further treated as they move farther along the moving collection belt (e.g., by dyeing, resin coating, or the like), after which they are rolled up and ready for shipment. For more details on spunbond processes in general, see Lim, H. A Review of Spun Bond Process. Journal of Textile and Apparel, Technology and Management, Vol. 6, Issue 3 (Spring 2010).

[0005] Typically, polymers such as styrene-block copolymers, olefin block copolymers (OBCs), thermoplastic polyurethanes (TPUs), polyester-polyurethane copolymers (such as spandex, also known as elastane), polypropylenes, high density polyethylenes, polyesters, polyamides, and others are used in the polymer compositions in these spunbond processes. An alternative to such polymer compositions typically used in spunbond processes is desired. [0006] Various attempts at using polymer compositions comprising 100% or nearly 100% of an elastomer such as a propylene-ethylene copolymer have been made. The difficulty encountered in such attempts is one of trade-offs: in order to obtain properties suitable for processing of the polymer composition (e.g., one or more of sufficiently high MFR, melt strength, and crystallinity, and/or sufficiently rapid crystallizability), the elasticity of the final product is frequently impaired. For instance, chain scission of polymer chains to result in shorter average chains (and therefore higher MFR, as desired for good processability) tends to impair the elasticity of the resulting article. To overcome these shortfalls in elastomeric compositions such as propylene-ethylene copolymers, blends are frequently used instead, combining high-MFR polymers with low-MFR polymers, and/or combining high- and low- crystallinity polymers, to form the polymer composition to be processed into spunbond and other nonwoven materials. While some of these solutions may provide the desired processability, they suffer from excessive complication, poor elastic properties of the resultant nonwoven, or both. On the other hand, modifying the compositions to improve simplicity and/or elasticity of the end product frequently results in compositions that are not easily processed. Obtaining a suitably low MFR for the maintenance of elastic properties typically requires the extrusion of the polymer composition to be operated at higher temperatures; however, this, in turn, means that the polymer composition will not crystallize as readily or as quickly upon being extruded, such that, by the time it is deposited onto a collecting surface from the extruder, it will still be too tacky and amorphous, making it incapable of further adequate processing (e.g., further bonding, calendering, rolling up, and the like).

[0007] Background references may include U.S. Patent Nos. 6,218,010; 6,342,565; 6,525,157; 6,635,715; 7,863,206; and 8,013,093 that describe previous attempts to use propylene-ethylene copolymers in spunbonding processes. This attempt encountered significant difficulty in processing the propylene-ethylene copolymer, such that significant amounts of high-MFR polypropylene were required in the blend just to obtain suitable processability (which significantly impaired the desired elasticity and tensile strength of the resulting nonwovens).

SUMMARY

[0008] The present disclosure relates to methods for forming spunbond materials from polymer compositions, and to composites and articles formed from such spunbond materials. More specifically, the present invention uses a nucleator in conjunction with a propylene- ethylene copolymer to decrease the polymer crystallization time, which makes the propylene- ethylene copolymer more processable. [0009] A first embodiment is a method comprising: extruding a polymer composition to form a plurality of filaments, wherein the polymer composition comprises 75 wt% to 99 wt% of a propylene-ethylene copolymer, 0.5 wt% to 15 wt% of a propylene-based thermoplastic polymer, and 0.005 wt% to 1 wt% of a nucleator; and forming a spunbond material from the plurality of filaments.

[0010] A second embodiment is a spunbond fabric made by the method of the first embodiment.

[0011] A third embodiment is a spunbond fabric having a machine direction (MD) and a cross direction (CD) comprising a polymer composition that comprises 75 wt% to 99 wt% of a propylene-ethylene copolymer, 0.5 wt% to 15 wt% of a propylene-based thermoplastic polymer, and 0.005 wt% to 1 wt% of a nucleator.

[0012] A fourth embodiment is an article formed from the spunbond fabric of the third embodiment. The article may be selected from the group consisting of diaper tabs, side panels, leg cuffs, top sheet, back sheet, tapes, feminine hygiene articles, swim pants, infant pull up pants, incontinence wear components, and bandages.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] 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.

[0014] FIG. 1 is an illustration of a typical hysteresis curve provided for purposes of illustrating the determination of various elasticity properties described herein.

[0015] FIG. 2 is an illustration of an ideal hysteresis curve.

[0016] FIG. 3 is the 100% hysteresis curve for the first cycle in the machine direction (MD) for control and nucleated inventive samples.

[0017] FIG. 4 is the 100% hysteresis curve for the second cycle in the MD for control and nucleated inventive samples.

[0018] FIG. 5 is the 100% hysteresis curve for the first cycle in the cross direction (CD) for control and nucleated inventive samples.

[0019] FIG. 6 is the 100% hysteresis curve for the second cycle in the CD for control and nucleated inventive samples.

DETAILED DESCRIPTION

[0020] The present disclosure relates to methods for forming spunbond materials from polymer compositions, and to composites and articles formed from such spunbond materials. More specifically, the present invention uses a nucleator in conjunction with a propylene- ethylene copolymer to decrease the polymer crystallization time, which makes the propylene- ethylene copolymer more processable.

[0021] The compositions of the present invention include polymer compositions that comprise 75 wt% to 99 wt% of a propylene-ethylene copolymer, 0.5 wt% to 15 wt% of a propylene-based thermoplastic polymer, and 0.005 wt% to 1 wt% ppm of a nucleator. Without being limited by theory, it is believed that as spunbond filaments of the foregoing composition cool and solidify, the nucleator causes the propylene-based thermoplastic polymer to crystallize more rapidly than in the absence of the nucleator. Then, the crystallized propylene-based thermoplastic polymer acts as nucleation sites for the propylene-ethylene copolymer to crystallize. Therefore, the entire polymer composition crystallizes more quickly than without the nucleator.

Propylene-Ethylene Copolymer

[0022] The propylene-ethylene copolymer is preferably a propylene-ethylene random copolymer having crystalline regions interrupted by non-crystalline regions. Without being limited by theory, it is believed that the non-crystalline regions may result from regions of non- crystallizable polypropylene segments and/or the inclusion of comonomer units. The crystallinity and the melting point of the propylene-ethylene random copolymer are reduced compared to highly isotactic polypropylene by the introduction of errors (stereo and region defects) in the insertion of propylene and/or by the presence of comonomer.

[0023] Preferably, however, the introduction of comonomer is limited to specific amounts, so as to maintain adequately high crystallinity of the copolymer for spunbond processing purposes. Thus, the copolymer preferably has an ethylene content of about 1.5 wt% to about 20 wt%, or about 5 wt% to about 10 wt%, or about 10 wt% to about 15 wt% based upon the total weight of the propylene-ethylene copolymer. Propylene-derived units form the balance of the copolymer of such embodiments (that is, the copolymer comprises about 80 wt% to about 98.5 wt% propylene, or about 90 wt% to about 95 wt%, or about 85 wt% to about 90 wt%).

[0024] The propylene-ethylene copolymer has a melt flow rate (MFR) of about 10 g/10 min (dg/min) to about 120 g/10 min, or about 15 g/10 min to about 100 g/10 min, or about 25 g/10 min to about 50 g/10 min, or about 10 g/10 min to about 40 g/10 min. The MFR is measured in accordance with ASTM D1238-13 at 230°C and 2.16 kg weight.

[0025] The propylene-ethylene copolymer may have a single peak melting transition as determined by differential scanning calorimetry (DSC). In one embodiment, the copolymer has a primary peak transition of about 60°C to about 70°C (preferably about 60°C to about 65 °C), with a broad end-of-melt transition of about 80°C to about 105°C, such as about 85°C to about 95 °C, or about 88°C to about 92°C.

[0026] The peak“melting point” (“T _m ”) is defined as the temperature of the greatest heat absorption within the range of 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 _m of the copolymer. The propylene-ethylene copolymer may have a T _m ranging from a low of any one of about 58°C, 59°C, 60°C, 61°C, 62°C, 63°C, 64°C, and 65°C, to a high of any one of about 62°C, 63 °C, 64°C, 65 °C, 66°C, 67°C, 68°C, 69°C, and 70°C, provided the high is greater than the low.

[0027] The method of determination by DSC is as follows: DSC data may be obtained using a Perkin-Hlmer DSC 7. About 5 mg to about 10 mg of a sheet of the polymer to be tested should be pressed at approximately 200°C to 230°C, then removed with a punch die and annealed at room temperature for 48 hours. The samples should then be sealed in aluminum sample pans. The DSC data should be recorded by first cooling the sample to -50°C and then gradually heating it to 230°C at a rate of 10°C/minute. Keep the sample at 230°C for 10 minutes before a second cooling-heating cycle is applied. Both the first and second cycle thermal events should be recorded. The melting temperature is measured and reported during the second heating cycle (or second melt).

[0028] The DSC procedure may be continued to determine the heat of fusion and the degree of crystallinity of the polymer sample. The percent crystallinity (X%) should be calculated using the formula, X%=[area under the curve (Joules/gram)/B(Joules/gram)]*100, where B is the heat of fusion for the homopolymer of the major monomer component. These values for B may be found from the Polymer Handbook, Fourth Edition, published by John Wiley and Sons, New York 1999. A value of 189 J/g (B) is used as the heat of fusion for 100% crystalline polypropylene, the major component of the propylene-ethylene copolymer of various embodiments described herein.

[0029] The propylene-ethylene copolymer may have heat of fusion (H _f ) of about 17.5 to about 25 J/g, or about 18 to about 22 J/g, or about 19 to about 20 J/g. The propylene-ethylene copolymer may have a percent crystallinity of about 5% to about 15%, or about 9% to about 11%, or about 10% to about 10.5%. H _f and percent crystallinity are determined according to the DSC procedure as described above. [0030] The propylene-ethylene copolymer may have a density of about 0.850 g/cm ³ to about 0.920 g/cm ³ , or about 0.860 g/cm ³ to about 0.890 g/cm ³ , or about 0.860 g/cm ³ to about 0.870 g/cm ³ , at room temperature as measured per ASTM D1505-18.

[0031] The propylene-ethylene copolymer may have a weight average molecular weight (“Mw”) of about 100,000 g/mole to about 130,000 g/mole, or about 115,000 g/mole to about 125,000 g/mol. The propylene-ethylene copolymer may have a number average molecular weight (“Mn”) of about 40,000 g/mole to about 60,000 g/mole, or about 50,000 g/mole to about 55,000 g/mol. The propylene-ethylene copolymer may have a z-average molecular weight (“Mz”) of about 180,000 g/mole to about 200,000 g/mole, or about 185,000 g/mole to about 195,000 g/mol. The propylene-ethylene copolymer may have a molecular weight distribution MWD (defined as Mw/Mn) ranging from about 1.6 to about 3.25, or about 1.75 to about 2.25, or about 1.9 to about 2.1.

[0032] The propylene-ethylene copolymer may have a Shore A Hardness (as determined in accordance with ASTM D2240-15el) of about 60 to about 80, or about 65 to about 75, or about 69 to about 72.

[0033] The Vicat softening temperature of the propylene-ethylene copolymer (determined in accordance with ASTM D1525-17el) may be about 40°C to about 60°C, or about 48°C to about 52°C, or about 49°C to about 52°C.

[0034] Processes suitable for preparing the propylene-ethylene copolymer may in some embodiments include metallocene-catalyzed or Ziegler-Natta catalyzed processes, including solution, gas-phase, slurry, and/or fluidized bed polymerization reactions. Suitable polymerization processes are described in, for example, U.S. Patent Nos. 4,543,399; 4,588,790; 5,001,205; 5,028,670; 5,317,036; 5,352,749; 5,405,922; 5,436,304; 5,453,471; 5,462,999; 5,616,661; 5,627,242; 5,665,818; 5,668,228; and 5,677,375; PCT Publications WO 96/33227 and WO 97/22639; and European Publications EP-A-0 794 200, EP-A-0 802 202, and EP-B- 634 421, the entire contents of which are incorporated herein by reference.

[0035] In certain preferred embodiments, the propylene-ethylene copolymer is a reactor blend. That is, it is a blend of effluents from two or more polymerization reactor zones, such as parallel solution polymerization reactors, each zone including a metallocene-catalyzed polymerization process. Particularly suitable are those polymerization processes and reactors as described in U.S. Patent Nos. 6,881,800 and 8,425,847, which are incorporated herein by reference.

[0036] Although propylene-ethylene copolymers are described above as having only two monomers (i.e., propylene and ethylene), in some embodiments, the propylene-ethylene copolymers can have a comonomer in addition to ethylene, and/or having comonomer(s) different from ethylene, so long as the MFR, T _m , and crystallinity (or H _f ) of the propylene- ethylene copolymers remain within the ranges described above with respect to the propylene- ethylene copolymers. For instance, the propylene-ethylene copolymers may be a propylene-a- olefin copolymer comprising units derived from propylene and one or more comonomer units derived from a C4 to C20 a-olefin in addition to, or instead of, ethylene. The propylene- a-olefin copolymer may optionally further comprise one or more comonomer units derived from dienes. In some embodiments, then, the a-olefin comonomer units may derive from, for example, 1- butene, 1-hexane, 4-methyl- 1-pentene and/or 1-octene. In one or more embodiments, the diene comonomer units may derive from 5-ethylidene-2-norbornene, 5-vinyl-2-norbomene, divinyl benzene, 1,4-hexadiene, 5-methylene-2-norbomene, 1 ,6-octadiene, 5-methyl- 1 ,4-hexadiene, 3,7-dimethyl-l,6-octadiene, 1,3-cyclopentadiene, 1 ,4-cyclohexadiene, dicyclopentadiene, or a combination thereof.

[0037] The polymer compositions described herein can include 75 wt% to 99 wt% of a propylene-ethylene copolymer, or 80 wt% to 99 wt% of a propylene-ethylene copolymer, or 90 wt% to 99 wt% of a propylene-ethylene copolymer.

Propylene-Based Thermoplastic Polymer

[0038] As described above, the propylene-based thermoplastic polymer is believed to crystallize first and act as a nucleator for the crystallization of the propylene-ethylene copolymer. The polymer compositions described herein can include 0.5 wt% to 15 wt% of a propylene-based thermoplastic polymer, or 1 wt% to 10 wt% of a propylene-based thermoplastic polymer, or 0.5 wt% to 5 wt% of a propylene-based thermoplastic polymer.

[0039] Propylene-based thermoplastic polymers include those polymers that primarily comprise units derived from the polymerization of propylene. In certain embodiments, at least 96% of the units of the propylene -based thermoplastic polymer derive from the polymerization of propylene. That is, the propylene-based thermoplastic polymer may be a random propylene copolymer having a comonomer content of 4 wt% or less based upon the total weight of the random propylene copolymer. Example of comonomers include the a-olefin comonomer units described above relative to the propylene-ethylene copolymers. Alternatively, the propylene- based thermoplastic polymer is a homopolymer of polypropylene.

[0040] The propylene-based thermoplastic polymers may have a melting temperature (T _m ) that is greater than 120°C, or greater than 155°C, or greater than 160°C. In some embodiments, the propylene-based thermoplastic polymers may have a T _m that is less than 180°C, or less than 170°C, or less than 165°C. [0041] The propylene-based thermoplastic polymers may have a heat of fusion (H _f ) that is equal to or greater than 80 J/g, or greater than 100 J/g, in or greater than 125 J/g, or greater than 140 J/g as measured by DSC.

[0042] The propylene-based thermoplastic polymers may include crystalline and semi crystalline polymers. These polymers may be characterized by a crystallinity of at least 40% by weight, or at least 55% by weight, or at least 65%, or at least 70% by weight as determined by DSC. Crystallinity may be determined by dividing the heat of fusion of a sample by the heat of fusion of a 100% crystalline polymer, which is assumed to be 189 J/g for isotactic polypropylene.

[0043] In general, the propylene-based thermoplastic polymers may be synthesized having a broad range of molecular weight and/or may be characterized by a broad range of MFR. For example, the propylene-based thermoplastic polymers can have an MFR of at least 2 g/10 min, or at least 4 g/10 min, or at least 6 g/10 min, or at least 10 g/10 min, where the MFR is measured according to ASTM D1238-13, 2.16 kg at 230°C. In some embodiments, the propylene-based thermoplastic polymer can have an MFR of less than 2,000 g/10 min, or less than 400 g/10 min, or less than 250 g/10 min, or less than 100 g/10 min, or less than 50 g/10 min, where the MFR is measured according to ASTM D1238-13, 2.16 kg at 230°C.

[0044] The propylene-based thermoplastic polymers may have an Mw of from about 50 to about 2,000 kg/mole, or from about 100 to about 600 kg/mole. They may also have a Mn of from about 25 kg/mole to about 1,000 kg/mole, or from about 50 kg/mole to about 300 kg/mole, as measured by GPC with polystyrene standards.

[0045] The propylene-based thermoplastic polymers include a homopolymer of a high- crystallinity isotactic or syndiotactic polypropylene. This polypropylene can have a density of from about 0.85 g/cm ³ to about 0.91 g/cm ³ , with the largely isotactic polypropylene having a density of from about 0.90 g/cm ³ to about 0.91 g/cm ³ . Optionally, the propylene based thermoplastic polymer includes isotactic polypropylene having a bimodal molecular weight distribution.

[0046] The propylene-based thermoplastic polymers may be synthesized by any appropriate polymerization technique known in the art such as, for example, slurry, gas phase, or solution, using catalyst systems such as conventional Ziegler-Natta catalysts or other single site organometallic catalysts like metallocenes, or non-metallocenes.

Nucleators

[0047] Nucleating agents can be present in the polymer compositions of the present disclosure at 0.005 wt% to 1 wt%, or 0.01 wt% to 0.5 wt%, or 0.05 wt% to 0.1 wt%. The amount of nucleating agent depends on the efficacy thereof. For example, sodium benzoate is a relatively weak nucleator and should be used in higher concentrations as compared to a more potent nucleator like HYPERFORM® HPN-68L (available from Milliken Chemicals).

[0048] Examples of nucleating agents include, but are not limited to, sodium benzoate, talc, HYPERFORM® additives (e.g., HPN-68L), MILLAD® additives (e.g., MILLAD® 3988, available from Milliken Chemicals), and organophosphates (e.g., NA-11 and NA-21, available from Amfine Chemicals).

[0049] The nucleator can be added to the components of the polymer composition as is. Alternatively, the nucleator can be blended with the propylene-based thermoplastic polymer before adding it to the components of the polymer composition. Typically, this is called a nucleator master batch.

Additives

[0050] The polymer compositions of some embodiments optionally include one or more additives. Any additive known to be suitable in a spunbonding process may be employed with the propylene-ethylene copolymers.

[0051] In some preferred embodiments, any additives are present in the polymer composition in an amount of 10 wt% or less, or 6 wt% or less, such as 3 wt% or less. In various embodiments, the additive(s) are present in amounts less than or equal to 10 wt%, 9 wt%, 8 wt%, 7 wt%, 6 wt%, 5 wt%, 4 wt%, 3 wt%, 2 wt%, 1 wt%, and 0.5 wt% based upon the weight of the polymer composition.

[0052] Examples of additives include, but are not limited to, stabilizers, antioxidants, fillers, slip aids (or, alternatively, slip agents or slip additives), colorants, mold release agents, waxes, and processing oils. Primary and secondary antioxidants include, for example, hindered phenols, hindered amines, and phosphites. Other additives such as dispersing agents, for example, ACROWAX™ C (available from Lonza), can also be included. Catalyst deactivators may also be used including, for example, calcium stearate, hydrotalcite, and calcium oxide, and/or other acid neutralizers known in the art.

[0053] In one or more embodiments, useful slip aids include those compounds or molecules that are incompatible with the polymeric matrix of the fibers and therefore migrate to the surface of the fiber, once formed. In one or more embodiments, the slip aids form a monolayer over the surface (or a portion thereof) of the fiber. In these or other embodiments, useful slip aids are characterized by relatively low molecular weight, which can facilitate migration to the surface. Types of slip aids include fatty acid amides as disclosed in Handbook of Antiblocking, Release and Slip Additives, George Wypych, Page 23. Examples of fatty acid amides include, but are not limited to, behenamide, erucamide, N-(2-hdriethyl) erucamide, Lauramide, N,N'- ethylene-bis-oleamide, N,N'-ethylene bisstearmide, oleamide, oleyl palmitamide, stearyl erucamide, tallow amide, and mixtures thereof.

[0054] Other additives include, for example, fire/flame retardants, plasticizers, vulcanizing or curative agents, vulcanizing or curative accelerators, cure retarders, processing aids, and the like. The aforementioned additives 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 or lubricants.

[0055] Any additive, may be included in the polymer composition in neat form, or as a master batch. When additives are present as a master batch, the % by weight of the additive master batch (that is, the wt% of the carrier resin-plus-additive) is taken as the amount of additive included in the polymer composition. Thus, where an additive is included in master batch form, 10 wt% of that additive would mean 10 wt% of the master batch (i.e., the combined amount of carrier resin and additive would be 10 wt%). Any suitable carrier resin may be used to form an additive master batch, such as polypropylene, polyethylene, propylene-ethylene copolymers, and the like.

Processing the Polymer Compositions

[0056] The formation of nonwoven fabrics from the foregoing polymer compositions may include manufacture of fibers by extrusion. The extrusion process may be accompanied by mechanical or aerodynamic drawing of the fibers. The fiber and fabrics of the present invention may be manufactured by any technique and/or equipment known in the art, many of which are well known. For example, spunbond nonwoven fabrics may be produced by spunbond nonwoven production lines produced by Reifenhauser GmbH & Co., of Troisdorf, Germany. The Reifenhauser system utilizes a slot drawing technique as described in U.S. Patent No. 4,820,142.

[0057] More particularly, spunbond or spunbonded fibers include fibers produced, for example, by the extrusion of molten polymer filaments from either a large spinneret having several thousand holes or with banks of smaller spinnerets containing, for example, as few as 40 holes. The temperature at which the spinneret is operated (i.e., the“melt temperature” of the extruder) may be about 270°C or less, or from about 180°C to about 260°C, or about 200°C to about 250°C. That is, processes according to some embodiments may include extruding the polymer composition through a spinneret at a temperature of about 270°C or less, or from about 180°C to about 270°C. Throughput preferably ranges from about 0.10 ghm (gram/hole/min) to about 0.30 ghm, or from about 0.15 ghm to about 0.25 ghm.

[0058] After exiting the spinneret, the molten filaments are quenched by a cross-flow air quench system, then pulled away from the spinneret and attenuated (drawn) by high speed air. There are generally two methods of air attenuation, both of which use the Venturi effect. The first method draws the filament using an aspirator slot (slot draw), which may run the width of the spinneret or the width of the machine. The second method draws the filaments through a nozzle or aspirator gun. Filaments formed in this manner may be collected on a collecting surface, such as a screen (“wire”) or porous forming belt to form a web of cooled fibers. The web can then be passed through compression rolls and then between heated calender rolls where raised lands on one or both rolls bond the web at points covering, for example, 10% to 40% of its area to form a nonwoven fabric (e.g., point-bonding). In another embodiment, welding of the deposited fibers can also be effected using convection or radiative heat. In yet another embodiment, fiber welding can be effected through friction by using hydro entangling or needle punch methods.

[0059] The fibers and/or webs may furthermore be annealed. Annealing may be carried out after the formation of fiber in continuous filament or fabrication of a nonwoven material from the fibers. Annealing may partially relieve the internal stress in the stretched fiber and restore the elastic recovery properties of the blend in the fiber. Annealing has been shown to lead to significant changes in the internal organization of the crystalline structure and the relative ordering of the amorphous and semicrystalline phases. This may lead to recovery of the elastic properties. 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), may be adequate for the restoration of the elastic properties in the fiber.

[0060] Thermal annealing of the fibers can be conducted by maintaining the fibers (or fabrics made from the fibers) at temperatures, for example, between room temperature up to 160°C, or alternatively to a maximum of 130°C for a period between a few seconds to less than 1 hour. A typical annealing period is 1 to 5 minutes at about 100°C. The annealing time and temperature can be adjusted based upon the composition employed. In other embodiments, the annealing temperature ranges from 60°C to 130°C, or may be about 100°C.

[0061] In certain embodiments, for example conventional continuous fiber spinning, annealing can be done by passing the fiber through a heated roll (godet) without the application of conventional annealing techniques. Annealing may desirably be accomplished under very low fiber tension to allow shrinking of the fiber in order to impart elasticity to the fiber. The above-referenced passing of fibers through heated calender rolls may accomplish such annealing steps. Similar to fiber annealing, the nonwoven web may desirably be formed under low tension to allow for shrinkage of the web in both machine direction (MD) and cross direction (CD) to enhance the elasticity of the nonwoven web. In other embodiments, the bonding calender roll temperature ranges from 35°C to 85°C, or at a temperature of about 60°C. The annealing temperature can be adjusted for any particular blend. These calender roll temperatures may be less than typically used due to the high concentration of the elastomer component (e.g., propylene-ethylene copolymer as described above) in the polymer composition being processed.

Nonwoven Materials

[0062] The nonwoven material resulting from the processing of various embodiments may be spunbond nonwoven material, e.g., a spunbond fabric or fiber. The spunbond material may exhibit hysteresis in either or both of the machine direction (MD) and cross direction (CD) in a second cycle of testing of 45% or less, or 10% to 45%, or 20% to 40%, or 25% to 35%. “Hysteresis” is defined and determined according to the description in the“Examples” section below for“hysteresis (%).”

[0063] The nonwoven material may also exhibit permanent set (after 2 cycles of testing) 0% to 20%, or 2% to 15% or 4% to 10% (again, in either or both of the MD and CD).

[0064] The nonwoven material may further exhibit 50% unloading force, on 2nd cycle and in either or both of MD and CD, of greater than or equal to 0.1 N/5cm to 5.0 N/5 cm, or 0.5 N/5cm to 4.0 N/5 cm, or 1 N/5cm to 3.0 N/5 cm. The 50% unloading force can be determined on the basis of a spunbond fabric having a basis weight of 10 grams per square meter (gsm).

[0065] The nonwoven material may also or instead exhibit a peak load of 10 N or less, or 1 N to 10 N, or 2 N to 8 N, or 5 N to 10 N in the CD. The nonwoven material may also or instead exhibit a peak load of 20 N or less, or 1 N to 20 N, or 5 N to 15 N, or 10 N to 20 N in the MD.

[0066] “Permanent set,”“50% unloading force,” and“Peak Load” are each defined and determined on a second cycle of hysteresis testing according to the description given below in the“Examples” section, in particular in the discussion of hysteresis testing.

[0067] Further, the nonwoven material may also exhibit superior tensile strength and elasticity, such as elongation at maximum strain of greater than or equal to 250%, or greater than or equal to 270%, or greater than or equal to 277%. The tensile strength of the nonwoven material in the MD and/or CD may be such that the material can withstand a force (that is, the breaking force of the nonwoven material may be) of 6 N to 30 N, or 10 N to 25 N or 15 N to 20 N.

[0068] Each of the aforementioned elasticity properties (i.e., permanent set, 50% unloading force, and hysteresis %), and each of the aforementioned tensile strength properties (i.e., breaking force, elongation at maximum strain) are measured on the basis of a nonwoven material having basis weight of 10 gsm or greater, or about 10 gsm to 500 gsm, or about 10 gsm to 100 gsm, or about 25 gsm to 200 gsm, or about 50 gsm to 300 gsm, or about 100 gsm to 500 gsm.

Composites

[0069] The spunbond materials of various embodiments may form a nonwoven fabric layer of a multilayer composite. For instance, the spunbond material may, during its processing or after processing, be combined with one or more layers of other woven or nonwoven material, such as one or more other spunbond layers, one or more meltblown layers, and the like, to form a composite. Suitable composites include S, SS, SSS, SMS, MSM, MSxM, SMxS, SMM, MMS, and the like, where each S represents a spunbond layer in the composite, and each M represents a meltblown layer in the composite (with each sub-script x representing an integer from 1-10, indicating repetition of the labeled layer). The spunbond material described hereinabove may form any one or more of the spunbond layers in the composites of such embodiments.

[0070] Another example is an SSMMS construction, wherein the outer S substrate may be a bi-component stretch laminate (for example, PE sheath/PP core), the inner S may be an elastic nonwoven web, the meltblown (M) layers may comprise one or more crystalline polyolefins (PP, PE), propylene-based elastomers, and blends thereof, and the outer S layer may comprise a bi-component web with an elastic nonwoven core and a polyolefin sheath. The elastic nonwovens may further be modified by any suitable additives known to those skilled in the art, such as titanium dioxide to improve opacity.

Spunbond Articles

[0071] The fibers and nonwoven fabrics of the present invention may be employed in several applications. In one or more embodiments, they may be advantageously employed in diapers and/or similar personal hygiene articles, for example in such applications as diaper tabs, side panels, leg cuffs, top sheet, back sheet, tapes, feminine hygiene articles, swim pants, infant pull up pants, incontinence wear components, and bandages. In particular, they can be employed as the dynamic or stretchable components of these articles such as, but not limited to, the elastic fastening bands. In other embodiments, the fibers and nonwoven fabrics may be fabricated into other protective garments or covers such as medical gowns or aprons, surgical drapes, sterilization wraps, wipes, bedding, or similar disposable garments and covers. These materials may also find applications in protective covers, home furnishing such as bedding, carpet antiskid padding, wall coverings, floor coverings, window shades, scrims, and any other application in which traditional fabrics have been used previously.

[0072] In other embodiments, the fibers and fabrics of the present invention can be employed in the manufacture of filtration media (gas and liquid). For example, particular applications include use in functionalized resins where the nonwoven fabric can be electrostatically charged to form an electret.

[0073] Further, the fibers and fabrics of the present invention may be employed in any of the structures and other end-use applications, or in conjunction with any of the additives and other compositions described in U.S. Patent Nos. 7,902,093; 7,943,701; and 8,728,960.

Example Fmbodiments

[0074] A first embodiment is a method comprising: extruding a polymer composition to form a plurality of filaments, wherein the polymer composition comprises 75 wt% to 99 wt% of a propylene-ethylene copolymer, 0.5 wt% to 15 wt% of a propylene-based thermoplastic polymer, and 0.005 wt% to 1 wt% of a nucleator; and forming a spunbond material from the plurality of filaments. This embodiment may optionally include one or more of the following: Element 1: wherein the propylene-ethylene copolymer has an ethylene content of 1.5 wt% to 20 wt% and a propylene content of 80 wt% to 98.5 wt% based upon the total weight of the propylene-ethylene copolymer; Element 2: wherein the propylene-ethylene copolymer has a melt flow rate (MFR) (ASTM D-1238, 2.16 kg weight @ 230°C) of 10 g/10 min to 120 g/10 min; Element 3: wherein the propylene-based thermoplastic polymer is a homopolymer of propylene; Element 4: wherein the propylene-based thermoplastic polymer is a random propylene copolymer having a comonomer content of 4 wt% or less based upon the total weight of the random propylene copolymer; Element 5: wherein the polymer composition consists of the propylene-ethylene copolymer, the propylene -based thermoplastic polymer, and the nucleator; Element 6: wherein the polymer composition consists of the propylene-ethylene copolymer, the propylene-based thermoplastic polymer, the nucleator, and a slip aid; Element 7: wherein the polymer composition further comprises one or more additives selected from the group consisting of a stabilizer, an antioxidant, a filler, a slip aid, a colorant, a mold release agent, a wax, and a processing oil; and Element 8: wherein the polymer composition is extruded through a spinneret at a melt temperature of 270°C or less, thereby forming the plurality of filaments. Example of combinations include, but are not limited to, Elements 1 and 2 in combination and optionally in further combination with one of Elements 3 and 4; one of Elements 5-7 in combination with Elements 1 and/or 2 and optionally in further combination with one of Elements 3 and 4; one of Elements 5-7 in combination one of Elements 3 and 4; and Element 8 in combination with one or more of Elements 1-7.

[0075] A second embodiment is a spunbond fabric made by the method of the first embodiment optionally including one or more of Elements 1-8.

[0076] A third embodiment is a spunbond fabric having a machine direction (MD) and a cross direction (CD) comprising a polymer composition that comprises 75 wt% to 99 wt% of a propylene-ethylene copolymer, 0.5 wt% to 15 wt% of a propylene-based thermoplastic polymer, and 0.005 wt% to 1 wt% of a nucleator. This embodiment may optionally include one or more of the following: Element 1; Element 2; Element 3; Element 4; Element 5, Element 6; Element 7; Element 9: wherein the spunbond fabric exhibits a permanent set of 20% or less in either or both of the MD and the CD, said permanent set being determined on the basis of said spunbond fabric having a basis weight of greater than 10 gsm; Element 10: wherein the spunbond fabric exhibits either or both of (i) a 50% unloading force in the MD less than or equal to 2.5 N/5 cm, and (ii) a 50% unloading force in the CD less than or equal to 0.9 N/5 cm, said 50% unloading force determined on the basis of said spunbond fabric having a basis weight of 10 gsm or greater; Element 11: wherein the spunbond fabric exhibits a hysteresis of 45% or less in either or both of the MD and the CD of the spunbond fabric, said hysteresis being determined on the basis of said spunbond fabric having a basis weight of 10 gsm or greater; and Element 12: wherein the spunbond fabric exhibits either or both of (i) a peak load of 20 N or less in the MD, and (ii) a peak load of 10 N or less in the CD, said peak loads being determined on the basis of said spunbond fabric having a basis weight of 10 gsm or greater. Example of combinations include, but are not limited to, Elements 1 and 2 in combination and optionally in further combination with one of Elements 3 and 4; one of Elements 5-7 in combination with Elements 1 and/or 2 and optionally in further combination with one of Elements 3 and 4; one of Elements 5-7 in combination one of Elements 3 and 4; one or more of Elements 9-12 in combination with one or more of Elements 1-7; and two or more of Elements 9-12 in combination.

[0077] A fourth embodiment is an article formed from the spunbond fabric of the third embodiment optionally including one or more of Elements 1-7 and 9-12. Further, the article may be selected from the group consisting of diaper tabs, side panels, leg cuffs, top sheet, back sheet, tapes, feminine hygiene articles, swim pants, infant pull up pants, incontinence wear components, and bandages. [0078] Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as molecular weight, reaction conditions, and so forth used in the present specification and associated claims are to be understood as being modified in all instances by the term“about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the embodiments of the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claim, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques

[0079] 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.

[0080] 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.

[0081] To facilitate a better understanding of the embodiments of the present invention, the following examples of preferred or representative embodiments are given. In no way should the following examples be read to limit, or to define, the scope of the invention.

EXAMPLES

Hysteresis Testing

[0082] Hysteresis tests were carried out as follows. Test samples measuring 150 mm length by 50 mm width were stretched to 100% elongation at a cross-head speed of 500 mm/min. At the point of 100% elongation, the samples were held for 1 second before being allowed to return to the starting position, also at a speed of 500 mm/min. The samples were then held in the un-stretched position for 30 seconds, and the elongation cycle was repeated a second time. During the second cycle, the percent elongation reached at a load of 0.1 N was measured. The test was conducted at 20°C and 50% relative humidity. The extension of the sample was plotted against the load (force) applied to stretch the sample through each cycle, generating a hysteresis curve. From the hysteresis curve, one can also determine peak load (N), 50% unloading force (N/5 cm) (also referred to as retractive force at 50%), permanent set, and hysteresis (%). The hysteresis properties of each fabric sample can be tested in either the machine direction (MD) or cross direction (CD).

[0083] FIG. 1 is a generic model hysteresis curve provided for purposes of illustrating the determination of hysteresis data herein. As shown in FIG. 1, the first cycle provides data to generate the curve OACD. The second cycle provides data to generate the curve EBCD'.

[0084] “Peak load” is the force exerted upon the sample when it is at maximum elongation during the hysteresis testing. In FIG. 1, the peak load is the Y-axis value at point A.

[0085] “50% unloading force” is the force per width of sample (N/5 cm) exerted by a sample at 50% elongation, measured as the sample retracts from 100% elongation during the first hysteresis cycle. In FIG. 1, the 50% unloading force is the Y-value at point H.

[0086] “Permanent set” quantifies the increase in length experienced by the sample after completion of the first cycle of extension and relaxation, representing how much the sample has been permanently stretched as a result of the first extension and relaxation cycle. With reference to FIG. 1, it can be seen that as all force is removed after the first cycle, the extension of the sample does not return to 0; instead, it lies at a point D. The permanent set can be determined by dividing the line OD by the line OF (representing the maximum extension of the sample during testing), and multiplying by 100%. That is, with reference to FIG. 1, permanent set is (OD/OF) times 100%.

[0087] “Hysteresis (%)” is defined as the quotient of hysteresis divided by mechanical hysteresis. Hysteresis and mechanical hysteresis are determined from the hysteresis curve. With reference to FIG. 1, hysteresis (%) may be determined as the area defined by curve OACD, divided by the area defined by OAFO, multiplied by 100%. That is, with reference to FIG. 1, hysteresis (%) is (OACD/OAFO) times 100%.

[0088] For visual reference regarding hysteresis, FIG. 2 illustrates an ideal hysteresis curve for elastic materials, indicating an approximate conformity to Hooke's law (and illustrating a return of the elastic material to its original length upon removal of the strain, that is, a permanent set of 0%). Desirably, for a given basis weight, a nonwoven will exhibit a combination of (i) low hysteresis; (ii) low permanent set; (iii) high 50% unloading force; and (iv) low peak load; all properties being determined in the 2nd cycle of hysteresis testing.

[0089] Example 1. Nonwoven fabrics were produced from three different polymer compositions according to Table 1 under the process parameters according to Table 1. Table 1 - Nonwoven Fabric Composition and Process Parameters

* VISTAMAXX™ is a propylene-ethylene copolymer commercially available from

ExxonMobil).

* Nucleator Master Batch = polypropylene resin (EXXONMOBIL™ PP3155, available from ExxonMobil Chemical Company) with 1 wt% nucleator (HYPERFORM® HPN-68L, available from Milliken Chemical)

** Slip Master Batch = polypropylene resin (EXXONMOBIL™ PP3155, available from ExxonMobil Chemical Company) with 15 wt% slip additive [0090] The crystallinity and physical properties are provided in Tables 2 and 3, respectively. The T1/2 data is the speed at which the fibers crystallize. The inventive Sample 1 crystallizes significantly faster than Comparative 1 because Sample 1 has the nucleator incorporated therein.

Table 2 - Fiber Crystallinity Properties

Table 3 - Fiber Physical Properties

* Did not break at machine force limitation.

[0091] FIG. 3 is the 100% hysteresis curve for the first cycle in the MD for control and nucleated inventive samples. FIG. 4 is the 100% hysteresis curve for the second cycle in the MD for control and nucleated inventive samples. FIG. 5 is the 100% hysteresis curve for the first cycle in the CD for control and nucleated inventive samples. FIG. 6 is the 100% hysteresis curve for the second cycle in the CD for control and nucleated inventive samples. The nonwoven fabric hysteresis data for 100% elongation and 200% elongation are provided in Tables 4 and 5, respectively. The figures make evident that the Sample 1 has a narrower and lower hysteresis that is closer to the ideal hysteresis curve for an elastomeric composition.

Table 4 - Nonwoven Fabric Hysteresis (100% Elongation)

Table 5 - Nonwoven Fabric Hysteresis (200% Elongation)

* Fiber broke.

[0092] 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. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular illustrative embodiments disclosed above may be altered, combined, or modified and all such variations are considered within the scope and spirit of the present invention. The invention illustratively disclosed herein suitably may be practiced in the absence of any element that is not specifically disclosed herein and/or any optional element disclosed 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. All numbers and ranges disclosed above may vary by some amount. Whenever a numerical range with a lower limit and an upper limit is disclosed, any number and any included range falling within the range is specifically disclosed. In particular, every range of values (of the form,“from about a to about b,” or, equivalently, “from approximately a to b,” or, equivalently, “from approximately a-b”) disclosed herein is to be understood to set forth every number and range encompassed within the broader range of values. Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee. Moreover, the indefinite articles“a” or“an,” as used in the claims, are defined herein to mean one or more than one of the element that it introduces.