Nonwoven webs made from multicomponent filaments and methods for forming nonwoven webs

Abstract

Multicomponent filaments, nonwoven webs prepared from the multicomponent filaments, and methods for forming nonwoven webs are disclosed. According to the present invention, the multicomponent filaments contain a crimp enhancing additive. Specifically, the crimp enhancing additive is added to the polymer component such that the crystallization rate and / or the curing rate of the polymer component is increased. Use of the crimp enhancing additive in one of the polymer components of the multicomponent filaments allows the multicomponent filaments to develop inherent crimp without the use of any post-crystallization / curing heat treatment. The method produces a web having improved fabric density and softness properties. The crimp enhancing additive incorporated into the filaments is a polyolefin homopolymer, particularly a polypropylene homopolymer.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Provisional Application No. 63 / 290,801, filed on December 17, 2021, which is expressly incorporated herein by reference in its entirety. Technical Field

[0003] The present invention as a whole relates to multicomponent filaments, nonwoven webs prepared from the multicomponent filaments, and methods for forming the nonwoven webs. According to the present invention, the multicomponent filaments contain a curl enhancing additive. More specifically, the present invention relates to incorporating an additive into one of the polymers used to prepare the multicomponent filaments. The additive can produce an inherent curl in the multicomponent filaments without using any post-crystallization / curing curl treatment. The method produces a web having improved fabric density and softness properties. The curl enhancing additive incorporated into the filaments is a polyolefin homopolymer, particularly a polypropylene homopolymer. Background Art

[0004] Nonwoven fabrics are used to prepare a variety of products that require specific levels of softness, strength, uniformity, liquid handling properties (such as absorbency), and other physical properties. These products include towels, industrial wipes, incontinence products, filtration products, baby care products (such as baby diapers), absorbent feminine care products, and clothing (such as safety and other protective clothing). These products are often made from multiple layers of nonwoven fabrics to achieve the desired combination of properties. For example, a disposable baby diaper made from a polymer nonwoven fabric may include a soft, porous lining layer that fits against the baby's skin, a firm, soft, non-permeable outer cover, and one or more inner liquid handling layers that are soft, fluffy, and absorbent.

[0005] Nonwoven fabrics (such as the aforementioned nonwoven fabrics) are typically prepared by melt spinning of thermoplastic materials, including by a spunbond process. Such fabrics prepared by a spunbond process are sometimes referred to as spunbond materials or spunbond nonwoven polymer webs. Spunbond nonwoven polymer webs are typically prepared from thermoplastic materials by extruding the thermoplastic material through a spinneret and drawing the extruded material into filaments with a high velocity gas stream to form a random web on a collecting surface.

[0006] Spunbond materials with desired combinations of physical properties, particularly softness, strength, and absorbency, have been produced, but limitations have been encountered. For example, for some applications, polymer materials such as polypropylene may have a desired level of strength, but not a desired level of softness. On the other hand, in some cases, materials such as polyethylene may have a desired level of softness, but not a desired level of strength.

[0007] To produce nonwoven materials having a desired combination of physical properties, spunbond nonwoven polymer fabrics made from multicomponent or bicomponent filaments and fibers have been developed. Multicomponent polymer fibers or filaments comprise two or more polymer components that remain distinct, and bicomponent polymer fibers or filaments comprise two polymer components that remain distinct. As used herein, the terms "filament" and "fiber" mean strands of material and may be used interchangeably. In certain embodiments, the filaments of the present invention may be continuous, or the filaments of the present invention may be discontinuous and thus have a defined length. The first and subsequent components of the multicomponent filaments are disposed in substantially different regions across the cross-section of the filament and extend continuously along the length of the filament. Typically, one component exhibits different properties from the other component such that the filament exhibits the properties of both components. For example, one component may be relatively stiff polypropylene while the other component may be relatively soft polyethylene. The end result is a stiff yet soft nonwoven fabric. However, if one of the polymers is non-recyclable, using different polymers in the multicomponent filaments can make the recycling of the multicomponent filaments and the webs made from the multicomponent filaments impractical or impossible because it is difficult to separate the polymers for extracting the recyclable polymer.

[0008] To increase the bulk or fullness of the multicomponent nonwoven web to improve fluid management behavior or enhance the "cloth-like" feel of the web, the bicomponent filaments or fibers are typically crimped. The multicomponent filaments can be mechanically crimped or, if suitable polymers are used, can be naturally crimped. As used herein, a naturally crimped filament is a filament that is crimped by activating latent crimps contained within the filament. For example, in one embodiment, the filament can be naturally crimped by subjecting the filament to a gas such as a heated gas after drawing.

[0009] Generally speaking, it is much better to construct filaments that can be naturally crimped than to have to crimp the filaments by a separate mechanical process. However, difficulties have been encountered in the past in producing filaments that are naturally crimped to the extent required for a particular application. In addition, it has been found very difficult to produce naturally crimped thin filaments (such as filaments having a linear density less than two deniers). Specifically, the draw forces used to produce thin filaments typically prevent or remove any significant latent crimp properties that the filaments may contain. Accordingly, there is a current need for a method of producing multicomponent filaments having enhanced inherent crimp properties without the need to use a separate crimping process (e.g., mechanical crimping). In addition, there is a need for nonwoven webs made from such filaments and methods for forming such webs. Summary of the Invention

[0010] The present invention recognizes and addresses the foregoing drawbacks and other drawbacks of existing art configurations and methods.

[0011] Accordingly, an object of the present invention is to provide a multi-component filament having an inherent crimp property.

[0012] Another object of the present invention is to provide an improved nonwoven web, including a spunbond web, and a method for forming the nonwoven web.

[0013] Another object of the present invention is to provide a nonwoven polymer fabric containing highly crimped filaments and a method for economically preparing the nonwoven polymer fabric.

[0014] Another object of the present invention is to provide a method for causing inherent crimp in multi-component filaments.

[0015] Another object of the present invention is to provide a method for causing inherent crimp in multi-component filaments, which is carried out by adding a crimp enhancing additive to one of the components of the filaments.

[0016] Yet another object of the present invention is to provide an inherently crimped filament containing about 90% or more of polypropylene.

[0017] Another object of the present invention is to provide multi-component filaments having at least about five crimps per inch on average and nonwoven webs prepared from such filaments.

[0018] These and other objects of the present invention are achieved by providing a method for forming a nonwoven web. The method includes a step of melt spinning multi-component filaments. The filaments include a first polymer component and a second polymer component. The second polymer component has a faster curing rate and / or crystallization rate than the first polymer component. The second polymer component contains a crimp enhancing additive. The crimp enhancing additive includes a polyolefin homopolymer having a melt flow rate of less than about 20 g / 10 min. The crimp enhancing additive causes the multi-component filaments to have inherent crimp when the filaments cure and / or crystallize.

[0019] Once melt spun, the multi-component filaments are drawn onto a forming surface to form the nonwoven web. Thereafter, the multi-component crimped filaments are formed into a nonwoven web for various applications.

[0020] In one embodiment, the multi-component filaments have at least about five crimps per inch on average. Preferably, the multi-component filaments have at least about five crimps per inch on average.

[0021] In one embodiment, the multi-component filaments contain greater than about 90% by weight of polypropylene. Preferably, the multi-component filaments contain greater than about 95% by weight of polypropylene. Preferably, the multi-component filaments contain greater than about 97% by weight of polypropylene.

[0022] In one embodiment, the crimp enhancing additive comprises a polypropylene homopolymer. In one embodiment, the crimp enhancing additive is present in the second component in an amount between about 5 wt% and 50 wt% based on the weight of the second component. Preferably, the crimp enhancing additive is present in the second component in an amount between about 20 wt% and 30 wt% based on the weight of the second component.

[0023] These and other objects of the present invention are also achieved by providing a nonwoven web comprising multicomponent filaments having inherent crimp without heat treatment, wherein the multicomponent filaments have at least about five crimps per inch on average.

[0024] In one embodiment, the multicomponent inherently crimped filaments are prepared from at least a first polymer component and a second polymer component. In one embodiment, the second polymer component comprises a crimp enhancing additive, and when solidifying and / or crystallizing from a molten state, the second component exhibits a faster solidification rate and / or crystallization rate than the first component.

[0025] In one embodiment, the multicomponent filaments of the nonwoven web have at least about five crimps per inch on average. Preferably, the multicomponent filaments have at least about twenty crimps per inch on average.

[0026] In one embodiment, the nonwoven has a TS7 softness of about 4 or less as measured by a TSA analyzer.

[0027] In one embodiment, the multicomponent filaments of the nonwoven web comprise greater than about 90% polypropylene by weight. Preferably, the multicomponent filaments of the nonwoven web comprise greater than about 95% polypropylene by weight. Preferably, the multicomponent filaments of the nonwoven web comprise greater than about 97% polypropylene by weight.

[0028] In one embodiment, the crimp enhancing additive is a polypropylene homopolymer. In one embodiment, the crimp enhancing additive is present in the second component in an amount between about 5 wt% and 50 wt% based on the weight of the second component. Preferably, the crimp enhancing additive is present in the second component in an amount between about 20 wt% and 30 wt% based on the weight of the second component.

[0029] In one embodiment, the nonwoven web contains multicomponent filaments having a denier between about 1 and about 2.5. In another embodiment, the nonwoven web has a fabric density of less than about 76 kg / m3.

[0030] These and other objects of the present invention are also achieved by providing a multicomponent filament having the composition described herein. The multicomponent filament comprises a first polymer component and a second polymer component. The second polymer component has a faster curing rate and / or crystallization rate than the first polymer component. The second polymer component contains a crimp enhancing additive. The multicomponent filament exhibits inherent crimp without heat treatment. The multicomponent filament has an average of at least about five crimps per inch. Preferably, the multicomponent filament has an average of at least about twenty crimps per inch.

[0031] In one embodiment, the multicomponent filament comprises greater than about 90% polypropylene by weight. Preferably, the multicomponent filament comprises greater than about 95% polypropylene by weight. Preferably, the multicomponent filament comprises greater than about 97% polypropylene by weight.

[0032] In one embodiment, the crimp enhancing additive is a polypropylene homopolymer. In one embodiment, the crimp enhancing additive is present in the second component in an amount between about 5 wt% and 50 wt% based on the weight of the second component. Preferably, the crimp enhancing additive is present in the second component in an amount between about 20 wt% and 30 wt% based on the weight of the second component.

[0033] In one embodiment, the multicomponent filament is continuous. In one embodiment, the multicomponent filament is discontinuous.

[0034] Other objects, features, and aspects of the present invention are discussed in more detail below. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] A complete and enabling disclosure of the present invention, including the best mode thereof, to one of ordinary skill in the art, is more particularly set forth in the remainder of the specification, including reference to the accompanying drawings, in which:

[0036] Figure 1 is a schematic view of a process line for preparing an embodiment of the present invention.

[0037] Figure 2A is a schematic view showing a cross-section of a filament prepared according to an embodiment of the present invention, wherein polymer components A and B are arranged side by side.

[0038] Figure 2B is a schematic view showing a cross-section of a filament prepared according to an embodiment of the present invention, wherein polymer components A and B are arranged in an eccentric skin / core arrangement.

[0039] The repeated use of reference numerals in the specification and drawings is intended to represent the same or analogous features or elements of the present invention. Detailed Embodiments

[0040] Those of ordinary skill in the art will understand that this discussion is only a description of exemplary embodiments and is not intended to limit the broader aspects of the present invention, which are embodied specifically as exemplary structures.

[0041] The present invention generally relates to multi-component filaments, nonwoven webs produced from the filaments (including spunbond webs), and methods for forming nonwoven webs from the filaments. Specifically, the filaments are inherently crimped, for example, in a helical arrangement. The crimp of the filaments can increase bulk, softness, and drape. The nonwoven web also has improved fluid management properties and has an enhanced cloth-like appearance and feel.

[0042] The multi-component filaments for use in the present invention contain at least two polymer components. The polymer components can be in, for example, a side-by-side configuration or an eccentric core-shell configuration. The polymer components are selected from semi-crystalline and crystalline thermoplastic polymers that have different crystallization rates and / or curing rates from each other to cause the filaments to have inherent crimp. More specifically, one of the polymer components has a faster curing rate and / or crystallization rate than the other polymer component.

[0043] As used herein, the curing rate and / or crystallization rate of a polymer refers to the rate at which a softened or molten polymer hardens and forms a fixed structure. It is believed that the curing rate and / or crystallization rate of a polymer is affected by different parameters, including the melting temperature and crystallization rate of the polymer. For example, a rapidly curing and / or crystallizing polymer typically has a melting point that is about 10°F or more, more desirably about 20°F or more, and most desirably about 30°F or more higher than a polymer having a slower curing rate and / or crystallization rate. However, it should be understood that even if the crystallization rates of two polymer components are significantly different, they can have similar melting points.

[0044] It is believed that the inherent crimp of the multi-component filaments is caused in the filaments due to differences in the shrinkage properties between the polymer components (i.e., differences in curing rate and / or crystallization rate).

[0045] The present invention relates to adding a crimp enhancing additive to one of the polymer components to cause that component to have a faster curing rate and / or crystallization rate. In this way, the difference in curing rate and / or crystallization rate between the two (or more) polymer components produces multi-component filaments that exhibit inherent crimp. Specifically, the crimp enhancing additive of the present invention is a polyolefin homopolymer, preferably a polypropylene homopolymer.

[0046] As used herein, "intrinsic crimp" means that a multicomponent filament develops crimp after curing and / or crystallization without the use of any further crimping processes, i.e., processes that create or activate the crimp. Previous methods of creating crimp in multicomponent filaments required additional steps to generate, enhance, or activate the crimp in the filaments. These steps included using heat during filament drawing to activate the crimp or ventilating and drying or using an air knife. In contrast, the multicomponent filaments of the present invention exhibit a high degree of crimp without the use of any of these additional or subsequent crimping processes. Thus, the present invention allows for the use of simplified and less energy-intensive methods to produce highly crimped multicomponent filaments and nonwoven webs formed therefrom.

[0047] In one embodiment, the multicomponent filament has at least about five crimps per inch on average. Preferably, the multicomponent filament has at least about 10 crimps per inch, or at least about twenty crimps per inch, or at least about 30 crimps per inch, or at least about 40 crimps per inch or at least about 50 crimps per inch.

[0048] It has also been found that in addition to producing multicomponent filaments with intrinsic crimp, the crimp enhancing additives of the present invention provide many other beneficial effects and advantages. For example, fabrics and webs prepared from the filaments have a higher bulk and a lower density. By preparing a web with a lower density, less material is required to prepare a web of a specified thickness, and thus the cost of producing the web is lower. It has also been found that the web, in addition to having a lower density, is more cloth-like, has a softer hand, and is more stretchable.

[0049] The webs and fabrics of the present invention are particularly suitable for the preparation of a variety of products, including liquid and gas filters, personal care products, and apparel materials. Personal care products include baby care products (such as disposable baby diapers), child care products (such as training pants), and adult care products (such as incontinence products and feminine care products). Suitable apparel includes safety clothing, work clothing, and the like.

[0050] As described above, the fabrics of the present invention can be prepared from continuous or discontinuous multicomponent polymer filaments comprising at least a first polymer component and a second polymer component. A preferred embodiment of the present invention is a polymeric fabric comprising continuous bicomponent filaments, the continuous bicomponent filaments comprising a first polymer component A and a second polymer component B. The bicomponent filaments have a cross-section, a length, and an outer peripheral surface. The first component A and the second component B are disposed in substantially different regions on the cross-section of the bicomponent filament and extend continuously along the length of the bicomponent filament. In some embodiments, the second component B continuously forms at least a portion of the outer peripheral surface of the bicomponent filament along the length of the bicomponent filament.

[0051] For example, the first component A and the second component B can be arranged side by side as shown in Figure 2A and can also be arranged in an eccentric skin / core configuration as shown in Figure 2B such that the resulting filaments exhibit an inherent helical crimp. The polymer component A is the core of the filament and the polymer component B is the skin in the skin / core arrangement. Methods for extruding multicomponent polymer filaments into such arrangements are well known to those of ordinary skill in the art.

[0052] The polymer component A and the polymer component B must be selected such that the resulting bicomponent filaments can form an inherent crimp. Preferably, the polymer component B has a faster curing rate than the polymer component A. For example, in one embodiment, the polymer component B can have a higher melting temperature than the polymer component A. In one embodiment, the curing rate and / or crystallization rate of the second component is at least about 5% faster than the curing rate and / or crystallization rate of the first component. Preferably, the curing rate and / or crystallization rate of the second component is at least about 10%, at least about 15%, at least about 20%, at least about 25%, at least about 30%, at least about 40%, at least about 50%, at least about 60%, at least about 70%, at least about 80%, at least about 90% or at least about 100% faster than the curing rate and / or crystallization rate of the first component.

[0053] Preferably, the polymer component A comprises polypropylene and the polymer component B also comprises polypropylene. When component A is polypropylene and component B is also polypropylene, the bicomponent filaments can contain greater than about 90 wt% polypropylene. More preferably, the bicomponent filaments can contain greater than about 95 wt% polypropylene and greater than about 97 wt% polypropylene.

[0054] In one embodiment, the weight ratio of the first polymer component (component A) to the second polymer component (component B) is from about 50:50 to about 90:10. Preferably, the weight ratio of the first polymer component (component A) to the second polymer component (component B) is from about 50:50 to about 65:35 or from about 50:50 to about 75:25.

[0055] Materials suitable for preparing the multicomponent filaments of the present invention include fiber grade polypropylene, such as, as determined by ASTM D1238, having a melt flow rate between about 20 g / 10 min and about 55 g / 10 min at 230 °C and a 2.16 kg load, such as PP3155E5 (a polypropylene homopolymer, obtained from ExxonMobil, Houston, Tex.).

[0056] In one embodiment, the crimp enhancing additive of the present invention is a polyolefin homopolymer. More preferably, the crimp enhancing additive is a polypropylene homopolymer. Preferably, the crimp enhancing additive is free of phthalates. For example, a commercially available product that can be used as the crimp enhancing additive is a polypropylene homopolymer, such as having an MFR (melt flow rate) of 14 g / 10 min at 230 °C and a 2.16 kg load and a density of 0.9 g / cm3 as determined according to ASTM D1238.

[0057] In one embodiment, the crimp enhancing additive is present in the second component (Component B) in an amount between about 5 wt% and 50 wt% based on the weight of the second component. Preferably, the crimp enhancing additive is present in the second component (Component B) in an amount between about 10 wt% and 40 wt% or between about 20 wt% and 30 wt% based on the weight of the second component.

[0058] In one embodiment, as determined according to ASTM D1238, the crimp enhancing additive has a melt flow rate (MFR) measured at a temperature of 230 °C and a 2.16 kg load of less than about 20 g / 10 min. Preferably, as determined according to ASTM D1238, the crimp enhancing additive has a melt flow rate (MFR) measured at a temperature of 230 °C and a 2.16 kg load between about 5 g / 10 min and 20 g / 10 min or between about 8 g / 10 min and about 16 g / 10 min or between about 10 g / 10 min and about 14 g / 10 min.

[0059] In one embodiment, the multicomponent filament comprises two polymer components A and B. Each of Component A and Component B may also contain minor additional ingredients. As used herein, the term "minor" means less than about 25 wt% of the component to which the ingredient is added. Additional ingredients suitable for the multicomponent filaments of the present invention include softness / fluffiness enhancers, pigments, and slip aids.

[0060] Suitable pigments include white pigments such as titanium dioxide and zinc oxide. Preferably, the pigment is a white pigment such as SCC-4837 (titanium dioxide, obtained from Standridge Color Corporation, Social Circle, Ga.). In one embodiment, the white pigment is present in the first component in an amount of about 1 wt% based on the weight of the first component. Preferably, the white pigment is present in the first component in an amount between about 0.5 wt% and about 3 wt% or between about 1.0 wt% and about 1.5 wt% based on the weight of the first component. In one embodiment, the white pigment is present in the second component in an amount of about 1 wt% based on the weight of the second component. Preferably, the white pigment is present in the second component in an amount between about 0.5 wt% and about 3 wt% or between about 1.0 wt% and about 1.5 wt% based on the weight of the second component. Preferably, the white pigment is present in both components in the amounts discussed above.

[0061] Suitable softness / fluffiness enhancers include polypropylene / polyethylene copolymers such as Vistamaxx 7050 (a polypropylene / polyethylene copolymer containing 13 wt% ethylene, having a mass flow rate of 45 g / 10 min at 230 °C and a 2.16 kg load as determined according to ASTM D1238, obtained from ExxonMobil) and Americhem 48137 (secondary fatty acid amide, obtained from Americhem of Cuyahoga Falls, OH.). In one embodiment, the softness / fluffiness enhancer is present in the first component in an amount between about 10 wt% and about 20 wt% based on the weight of the first component. Preferably, the softness / fluffiness enhancer is present in the first component in an amount between about 5 wt% and about 25 wt% based on the weight of the first component. In one embodiment, the softness / fluffiness enhancer is present in the second component in an amount of about 1.5 wt% based on the weight of the second component. Preferably, the softness / fluffiness enhancer is present in the second component in an amount between about 0.5 wt% and about 3 wt% based on the weight of the second component. Preferably, the softness / fluffiness enhancer is present in both components in the amounts discussed above.

[0062] Suitable slip aids include primary amides and secondary amides. The primary amide slip aids include erucamide (obtained from Sigma Aldrich, St. Louis, MO). In one embodiment, the slip aid is present in the first component in an amount of about 0.3 wt% based on the weight of the first component. Preferably, the slip aid is present in the first component in an amount between about 0.1 wt% and 1 wt% or between about 0.2 wt% and 0.5 wt% based on the weight of the first component. In one embodiment, the slip aid is present in the second component in an amount of about 0.3 wt% based on the weight of the second component. Preferably, the slip aid is present in the second component in an amount between about 0.1 wt% and 1 wt% or between about 0.2 wt% and 0.5 wt% based on the weight of the second component. Preferably, the slip aid is present in both components in the amounts discussed above.

[0063] In one embodiment, component A includes polypropylene, an ethylene / propylene copolymer, a secondary fatty acid amide, and a white pigment. In another embodiment, component B includes polypropylene, a crimping additive, a secondary fatty acid amide, and a white pigment. In one embodiment, component A includes polypropylene, an ethylene / propylene copolymer, a secondary fatty acid amide, and a white pigment, and component B includes polypropylene, a crimping additive, a secondary fatty acid amide, and a white pigment.

[0064] To combine the crimp enhancing additive with polymer component B, in one embodiment, the polymers can be dry blended and coextruded during the formation of the multicomponent filaments. In an alternative embodiment, the crimp enhancing additive and polymer component B can be melt blended prior to forming the filaments of the present invention.

[0065] Reference will now be made to Figure 1 a method for producing multicomponent filaments and nonwoven webs in accordance with the present invention will be discussed in detail. The following method is similar to the method described in U.S. Patent No. 5,382,400 to Pike et al., which is incorporated herein by reference in its entirety.

[0066] See Figure 1 , which discloses process line 10 for preparing a preferred embodiment of the present invention. In some embodiments, the filaments described herein can be prepared, for example, by a "closed" or "open" spunbond system, as described below. Process line 10 is arranged to produce bicomponent continuous filaments, but it should be understood that the present invention includes nonwoven fabrics made from multicomponent filaments having more than two components. For example, the fabrics of the present invention can be made from filaments having three or four or more components.

[0067] The process line 10 includes a pair of extruders 12a and 12b for extruding polymer component A and polymer component B respectively. Polymer component A is fed from the first hopper 14a to the corresponding extruder 12a, and polymer component B is fed from the second hopper 14b to the corresponding extruder 12b. Polymer components A and 3 are fed from extruders 12a and 12b to the spinneret 18 through the corresponding polymer pipes 16a and 16b.

[0068] Spinnerets for extruding bicomponent filaments are well known to those of ordinary skill in the art and will not be described in detail here. Generally, the spinneret 18 includes a housing containing a spinning pack, which includes a plurality of plates stacked on top of each other and has an opening pattern arranged to generate flow paths for guiding polymer component A and polymer component B through the spinneret respectively. The spinneret 18 has openings arranged in one or more rows. The spinneret openings form a downwardly extending filament curtain when the polymer is extruded through the spinneret. For the purposes of the present invention, the spinneret 18 can be arranged to form side-by-side or eccentric sheath / core bicomponent filaments as shown in Figure 2A and 2B shown.

[0069] The process line 10 further includes a quench blower 20 positioned adjacent to the filament curtain extending from the spinneret 18. The air from the quench blower 20 quenches the filaments extending from the spinneret 18. The quenching air can be introduced from one side of the filament curtain as shown in Figure 1 shown, or from both sides of the filament curtain.

[0070] A fiber drawing unit or aspirator 22 is positioned below the spinneret 18 and receives the quenched filaments. Fiber drawing units or aspirators for melt spinning polymers are well known, as discussed above. A fiber drawing unit suitable for the method of the present invention includes a linear fiber aspirator of the type shown in U.S. Patent 3,802,817 and a teaching gun of the type shown in U.S. Patents 3,692,618 and 3,423,266, the disclosures of which are incorporated herein by reference.

[0071] Generally, the fiber drawing unit 22 includes an elongated vertical channel, and the fibers are drawn through the channel by suction air entering the channel from the side and flowing downward through the channel. A compressor (in an open system) or a blower (in a closed system) 24 supplies the suction air to the fiber drawing unit 22. The suction air draws the filaments and ambient air through the fiber drawing unit.

[0072] An annular porous forming surface 26 is positioned below the fiber drawing unit 22 and receives the continuous filaments from the outlet opening of the fiber drawing unit. The forming surface 26 travels around the guide roller 28. A vacuum device 30 positioned below the forming surface 26 where the filaments are deposited draws the filaments towards the forming surface.

[0073] The process line 10 further includes bonding equipment, such as a hot spot bonding roller 34 (shown in dashed lines) or a through-air bonding machine 36. The hot spot bonding machine and the through-air bonding machine are well-known to those skilled in the art and will not be disclosed in detail herein. Generally speaking, the through-air bonding machine 36 includes a perforated roller 38 for receiving the web and a hood 40 surrounding the perforated roller. Finally, the process line 10 includes a winding roller 42 for winding the finished fabric.

[0074] To operate the process line 10, the hoppers 14a and 14b are filled with the respective polymer components A and polymer components B. The polymer components A and B are melted and extruded by the respective extruders 12a and 12b through the polymer pipes 16a and 16b and the spinneret 18. Although the temperature of the molten polymer varies depending on the polymer used, when polypropylene is used for components A and B, the preferred temperature range during polymer extrusion is from about 370°F to about 530°F, and preferably in the range of 400°F to about 470°F.

[0075] When the extruded filaments extend below the spinneret 18, the air flow from the quench blower 20 quenches the filaments at least partially to form inherent helical crimps in the filaments. The quench air preferably flows in a direction substantially perpendicular to the length of the filaments at a temperature of about 45°F to about 90°F and a speed of about 100 feet per minute to about 400 feet per minute.

[0076] After quenching, the filaments are drawn into the vertical channel of the fiber drawing unit by an air flow (such as air) from the compressor or blower 24 through the fiber drawing unit 22. The fiber drawing unit is preferably located 30 to 60 inches below the bottom of the spinneret 18. During drawing and throughout the drawing process, the filaments develop inherent crimps during curing / crystallization.

[0077] The crimped filaments are deposited on the moving forming surface 26 through the outlet opening of the fiber drawing unit 22. The vacuum device 20 draws the filaments towards the forming surface 26 to form an unbonded nonwoven web of continuous filaments. The deposition pattern of the filaments on the forming surface is not critical. However, preferably, the filaments can be deposited evenly on the forming surface to produce a web with consistent properties. In the past, the web was usually first gently compressed with a compression roller and then hot spot bonded with the roller 34 or through-air bonded in the through-air bonding machine 36.

[0078] Finally, the finished web is wound onto a winding roll 42 for further processing or use. When used to prepare a liquid absorbent article, the fabric of the present invention can be treated with conventional surface treatment methods or contain conventional polymer additives that enhance the wettability of the fabric. For example, the fabric of the present invention can be treated with polyalkylene oxide-modified siloxanes and silanes (such as polyalkylene oxide-modified polydimethyl-siloxane), as disclosed in U.S. Patent 5,057,361. Such surface treatment methods enhance the wettability of the fabric.

[0079] The fabric of the present invention has a relatively high bulkiness. The helical crimp of the filaments produces an open web structure with a large number of void portions between the filaments, and the filaments are bonded at the contact points. In one embodiment, the nonwoven web of the present invention has a density of less than about 76 kg / m3. Preferably, the nonwoven web of the present invention generally has a density of less than about 75 kg / m3, or less than about 70 kg / m3, or less than about 60 kg / m3, or less than about 50 kg / m3, or less than about 40 kg / m3, or less than about 30 kg / m3, or less than about 25 kg / m3, or less than about 20 kg / m3 or less than about 10 kg / m3.

[0080] In one embodiment, the nonwoven web of the present invention has a basis weight of about 19 GSM (g / m2). Preferably, the nonwoven web of the present invention generally has a basis weight between about 10 GSM and about 60 GSM, or between about 15 GSM and about 40 GSM, or between about 20 GSM and about 30 GSM.

[0081] In one embodiment, the multicomponent filaments have a denier between about 1.0 and about 3. Preferably, the multicomponent filaments have a denier between about 1.0 and about 2.5 or between about 1.0 and 2.0.

[0082] In one embodiment, as measured by a TSA analyzer, the nonwoven has a TS7 softness of about 4 or less. Preferably, as measured by a TSA analyzer, the nonwoven has a TS7 softness of about 3 or less.

[0083] As discussed above, the crimp enhancing additive of the present invention allows for the production of highly crimped elongated filaments. In the past, it was difficult or even impossible to produce naturally crimped elongated filaments.

[0084] According to the present invention, filaments having an inherent crimp of at least about 10 crimps per inch can be produced at a linear density of less than 2 denier, especially less than about 1.2 denier. For most nonwoven webs, preferably the filaments have from about 10 crimps per inch to about 25 crimps per inch. Particularly advantageously, filaments having an inherent crimp within the above range can be produced according to the present invention at a lower linear density than in the past.

[0085] Hot melt bonding can be carried out according to U.S. Patent 3,855,046, the disclosure of which is incorporated herein by reference. When hot melt bonding is carried out, the fabric of the present invention exhibits a more cloth-like appearance and can be used, for example, as an outer covering layer for personal care products or as a clothing material.

[0086] Although Figure 1 the bonding methods shown are hot melt bonding and through-air bonding, it should be understood that the fabric of the present invention can also be bonded by other means, such as oven bonding, ultrasonic bonding, hydroentanglement or combinations thereof. Such bonding techniques are well known to those of ordinary skill in the art and will not be discussed in detail herein.

[0087] The bonding geometry used to form the nonwoven web can enhance the bulkiness, density and softness of the nonwoven web. In one embodiment, the bonding geometry has a bonding area between about 5% and about 25%. Preferably, the bonding geometry has a bonding area between about 8% and about 18%, or the bonding geometry has a bonding area of about 10%. In one embodiment, the bonding geometry has discrete shapes arranged in rows and columns, or an interlocking grid with a repeating geometry (such as a diamond or hexagon).

[0088] A spunbond-meltblown-spunbond (SMS) fabric is a three-layer nonwoven fabric. The SMS is composed of a spunbond polypropylene top layer, a meltblown polypropylene middle layer and a spunbond polypropylene bottom layer. The nonwoven web of the present invention is very suitable for use in SMS fabrics / layers. In one embodiment of the present invention, the SMS fabric / layer is formed from a top layer of the nonwoven web of the present invention, a meltblown polypropylene middle layer and a bottom layer of the nonwoven web of the present invention.

[0089] Once produced, the nonwoven web of the present invention can be used in a variety of different applications. For example, the web can be used in filtration products, liquid absorption products, personal care products, clothing and various other products.

[0090] Examples

[0091] The present invention can be better understood by reference to the following examples.

[0092] Example 1

[0093] The nonwoven web prepared according to the present invention has the following formulation:

[0094]

[0095]

[0096] A: Polypropylene homopolymer

[0097] B: Polypropylene / Polyethylene Copolymer

[0098] C: Secondary Fatty Acid Amide

[0099] D: Titanium Dioxide

[0100] E: Crimp Enhancement Additive

[0101] All formulations exhibit low density.

[0102] Example 2

[0103] The nonwoven web prepared according to the present invention has the following formulation:

[0104] Component A:

[0105] 87 wt% Polypropylene Homopolymer

[0106] 10 wt% Polypropylene / Polyethylene Copolymer

[0107] 1.5 wt% Secondary Fatty Acid Amide

[0108] 1.5 wt% Titanium Dioxide

[0109] Component B:

[0110] 67 wt% Polypropylene Homopolymer

[0111] 30 wt% Crimp Enhancement Additive

[0112] 1.5 wt% Secondary Fatty Acid Amide

[0113] 1.5 wt% Titanium Dioxide

[0114] These webs all have a GSM of 20 and a low density.

[0115] These and other modifications and variations of the present invention may be practiced by those of ordinary skill in the art without departing from the spirit and scope of the invention more specifically described in the appended claims. In addition, it should be understood that aspects of the various embodiments may be interchanged, in whole or in part. Further, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only and is not intended to limit the invention as further described in such appended claims.

Claims

1. A method for forming a nonwoven web, the method comprising the steps of: Melt spinning a multicomponent filament, the filament comprising a first polymer component and a second polymer component, the second polymer component having a faster curing rate and / or crystallization rate than the first polymer component, the first polymer component containing polypropylene, the second polymer component containing polypropylene and a crimp enhancing additive, the crimp enhancing additive comprising a polyolefin homopolymer having a melt flow rate of less than 20 g / 10 min; Wherein the crimp enhancing additive is present in the second polymer component in an amount between 5 wt% and 50 wt% based on the weight of the second polymer component; Drawing the multicomponent filament onto a forming surface for forming the nonwoven web; And Wherein the crimp enhancing additive causes the multicomponent filament to develop inherent crimp when the filament cures and / or crystallizes.

2. The method for forming a nonwoven web according to claim 1, wherein the multicomponent filament has at least five crimps per inch on average.

3. The method for forming a nonwoven web according to claim 1, wherein the multicomponent filament has at least twenty crimps per inch on average.

4. The method for forming a nonwoven web according to claim 1, wherein the multicomponent filament comprises more than 90% by weight of polypropylene.

5. The method for forming a nonwoven web according to claim 1, wherein the multicomponent filament comprises more than 95% by weight of polypropylene.

6. The method for forming a nonwoven web according to claim 1, wherein the multicomponent filament comprises more than 97% by weight of polypropylene.

7. The method for forming a nonwoven web according to claim 1, wherein the nonwoven web has a basis weight of 19 GSM.

8. The method for forming a nonwoven web according to claim 1, wherein the nonwoven web has a basis weight between 10 GSM and 60 GSM.

9. The method for forming a nonwoven web according to claim 1, wherein the crimp enhancing additive is a polypropylene homopolymer.

10. The method for forming a nonwoven web according to claim 1, wherein the crimp enhancing additive does not contain phthalates.

11. The method for forming a nonwoven web according to claim 1, wherein the crimp enhancing additive is present in the second polymer component in an amount between 20 wt% and 30 wt% based on the weight of the second polymer component.

12. The method for forming a nonwoven web according to claim 1, wherein the crimp enhancing additive has a melt flow rate (MFR) measured at a temperature of 230 °C and a load of 2.16 kg according to ASTM D1238 between 8 g / 10 min and 16 g / 10 min.

13. The method for forming a nonwoven web according to claim 1, wherein the curing rate and / or crystallization rate of the second polymer component is at least 5% faster than the curing rate and / or crystallization rate of the first polymer component.

14. The method for forming a nonwoven web according to claim 1, wherein the curing rate and / or crystallization rate of the second polymer component is at least 50% faster than the curing rate and / or crystallization rate of the first polymer component.

15. The method for forming a nonwoven web according to claim 1, wherein the weight ratio of the first polymer component to the second polymer component is from 50:50 to 90:

10.

16. The method for forming a nonwoven web according to claim 1, wherein the weight ratio of the first polymer component to the second polymer component is from 50:50 to 65:

35.

17. The method for forming a nonwoven web according to claim 1, wherein the first polymer component comprises: polypropylene, propylene / ethylene copolymer, secondary fatty acid amide, and white pigment.

18. The method for forming a nonwoven web according to claim 1, wherein the second polymer component comprises: polypropylene, the crimp enhancing additive, secondary fatty acid amide, and white pigment.

19. The method for forming a nonwoven web according to claim 1, wherein the first polymer component comprises: polypropylene, propylene / ethylene copolymer, secondary fatty acid amide, and white pigment; and the second polymer component comprises: polypropylene, the crimp enhancing additive, secondary fatty acid amide, and white pigment.

20. The method for forming a nonwoven web according to claim 19, wherein the white pigment is present in the first polymer component in an amount of 1% by weight based on the weight of the first polymer component.

21. The method for forming a nonwoven web according to claim 19, wherein the white pigment is present in the second polymer component in an amount of 1% by weight based on the weight of the second polymer component.

22. The method for forming a nonwoven web according to claim 19, wherein the white pigment is present in each of the first polymer component and the second polymer component in an amount of 1% by weight based on the weight of the first polymer component and the second polymer component, respectively.

23. The method for forming a nonwoven web according to claim 1, wherein the nonwoven web is a spunbond web.

24. The method for forming a nonwoven web according to claim 1, wherein the multicomponent filaments are continuous.

25. The method for forming a nonwoven web according to claim 1, wherein the multicomponent filaments are discontinuous.

26. A nonwoven web comprising inherently crimped multicomponent filaments that have not been heat-treated, wherein the multicomponent filaments have at least five crimps per inch on average, and wherein the multicomponent filaments comprise: a first polymer component, the first polymer component comprising: polypropylene, propylene / ethylene copolymer, secondary fatty acid amide, and white pigment; and A second polymer component, said second polymer component comprising: Polypropylene, A crimp enhancing additive, said crimp enhancing additive comprising a polyolefin homopolymer having a melt flow rate of less than 20 g / 10 min, A secondary fatty acid amide, and A white pigment; Said crimp enhancing additive is present in said second polymer component in an amount between 5 wt% and 50 wt% based on the weight of said second polymer component.

27. The nonwoven web according to claim 26, wherein said multicomponent filaments have at least twenty crimps per inch on average.

28. The nonwoven web according to claim 26, wherein said multicomponent filaments have a denier number between 1 and 3.

29. The nonwoven web according to claim 26, wherein the nonwoven web has a fabric density of less than 76 kg / m3.

30. The nonwoven web according to claim 26, wherein said multicomponent filaments comprise greater than 90% by weight of polypropylene.

31. The nonwoven web according to claim 26, wherein said multicomponent filaments comprise greater than 95% by weight of polypropylene.

32. The nonwoven web according to claim 26, wherein said multicomponent filaments comprise greater than 97% by weight of polypropylene.

33. The nonwoven web according to claim 26, wherein the nonwoven web has a basis weight of 19 GSM.

34. The nonwoven web according to claim 26, wherein the nonwoven web has a basis weight between 10 GSM and 60 GSM.

35. The nonwoven web according to claim 26, wherein said crimp enhancing additive homopolymer is a polypropylene homopolymer.

36. The nonwoven web according to claim 26, wherein said crimp enhancing additive does not contain phthalates.

37. The nonwoven web according to claim 26, wherein said crimp enhancing additive is present in said second polymer component in an amount between 20 wt% and 30 wt% based on the weight of said second polymer component.

38. The nonwoven web according to claim 26, wherein said crimp enhancing additive has a melt flow rate (MFR) measured at a temperature of 230°C and a load of 2.16 kg according to ASTM D1238 between 8 g / 10 min and 16 g / 10 min.

39. The nonwoven web according to claim 26, wherein the nonwoven web has a TS7 softness of 4 or less as measured by a TSA analyzer.

40. The nonwoven web according to claim 26, wherein the weight ratio of said first polymer component to said second polymer component is from 50:50 to 90:

10.

41. The nonwoven web according to claim 26, wherein the weight ratio of said first polymer component to said second polymer component is from 50:50 to 65:

35.

42. The nonwoven web according to claim 26, wherein said white pigment is present in said first polymer component in an amount of 1 wt% based on the weight of said first polymer component.

43. The nonwoven web according to claim 26, wherein the white pigment is present in the second polymer component in an amount of 1% by weight based on the weight of the second polymer component.

44. The nonwoven web according to claim 26, wherein the white pigment is present in each of the first polymer component and the second polymer component in an amount of 1% by weight based on the weight of the first polymer component and the second polymer component, respectively.

45. The nonwoven web according to claim 26, wherein when solidifying and / or crystallizing from a molten state, the second polymer component exhibits a faster solidification rate and / or crystallization rate than the first polymer component.

46. The nonwoven web according to claim 45, wherein the solidification rate and / or crystallization rate of the second polymer component is at least 5% faster than the solidification rate and / or crystallization rate of the first polymer component.

47. The nonwoven web according to claim 45, wherein the solidification rate and / or crystallization rate of the second polymer component is at least 50% faster than the solidification rate and / or crystallization rate of the first polymer component.

48. The nonwoven web according to claim 26, wherein the multicomponent filaments are continuous.

49. The nonwoven web according to claim 26, wherein the multicomponent filaments are discontinuous.

50. A multicomponent filament comprising a first polymer component and a second polymer component, the second polymer component having a faster solidification rate and / or crystallization rate than the first polymer component, the first polymer component containing polypropylene, the second polymer component containing polypropylene and a crimp enhancing additive, wherein the multicomponent filament has inherent crimp without heat treatment, and wherein the multicomponent filament has at least five crimps per inch on average, wherein the crimp enhancing additive is a polypropylene homopolymer; the crimp enhancing additive is present in the second polymer component in an amount between 5% and 50% by weight based on the weight of the second polymer component.

51. The multicomponent filament according to claim 50, wherein the multicomponent filament has at least twenty crimps per inch on average.

52. The multicomponent filament according to claim 50, wherein the multicomponent filament has a denier number between 1 and 3.

53. The multicomponent filament according to claim 50, wherein the multicomponent filament comprises more than 90% by weight of polypropylene.

54. The multicomponent filament according to claim 50, wherein the multicomponent filament comprises more than 95% by weight of polypropylene.

55. The multicomponent filament according to claim 50, wherein the multicomponent filament comprises more than 97% by weight of polypropylene.

56. The multicomponent filament according to claim 50, wherein the first polymer component comprises: polypropylene, propylene / ethylene copolymer, secondary fatty acid amide, and white pigment; and the second polymer component comprises: polypropylene, the crimp enhancing additive, secondary fatty acid amide, and white pigment.

57. The multicomponent filament according to claim 50, wherein the crimp enhancing additive is free of phthalates.

58. The multicomponent filament according to claim 50, wherein the crimp enhancing additive is present in the second polymer component in an amount between 20 wt% and 30 wt% based on the weight of the second polymer component.

59. The multicomponent filament according to claim 50, wherein the crimp enhancing additive has a melt flow rate (MFR) measured at a temperature of 230 °C and a load of 2.16 kg according to ASTM D1238 between 8 g / 10 min and 16 g / 10 min.

60. The multicomponent filament according to claim 50, wherein the weight ratio of the first polymer component to the second polymer component is from 50:50 to 90:

10.

61. The multicomponent filament according to claim 50, wherein the weight ratio of the first polymer component to the second polymer component is from 50:50 to 65:

35.

62. The multicomponent filament according to claim 56, wherein the white pigment is present in the first polymer component in an amount of 1 wt% based on the weight of the first polymer component.

63. The multicomponent filament according to claim 56, wherein the white pigment is present in the second polymer component in an amount of 1 wt% based on the weight of the second polymer component.

64. The multicomponent filament according to claim 56, wherein the white pigment is present in each of the first polymer component and the second polymer component in an amount of 1 wt% based on the weight of the first polymer component and the second polymer component, respectively.

65. The multicomponent filament according to claim 50, wherein when solidifying and / or crystallizing from the molten state, the second polymer component exhibits a faster solidification rate and / or crystallization rate than the first polymer component.

66. The multicomponent filament according to claim 50, wherein the solidification rate and / or crystallization rate of the second polymer component is at least 5% faster than the solidification rate and / or crystallization rate of the first polymer component.

67. The multicomponent filament according to claim 50, wherein the solidification rate and / or crystallization rate of the second polymer component is at least 50% faster than the solidification rate and / or crystallization rate of the first polymer component.

68. The multicomponent filament according to claim 50, wherein the multicomponent filament is continuous.

69. The multicomponent filament according to claim 50, wherein the multicomponent filament is discontinuous.

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