Patent Application
20060094320
The present invention relates to nanofiber materials, and, in particular, to gradient nanofiber materials and methods for making same.
This application is related to U.S. patent application Ser. No. ______, commonly assigned, filed on same date herewith and entitled, “Composite Nanofiber Materials and Methods for Making Same,” which is hereby incorporated herein by reference.
Products made from fibrous materials are useful in a wide variety of applications such as personal care products and garments, filtration devices, and the like. Such products can be absorbent or non-absorbent. These fibrous materials have a number of properties, such as specific surface chemistries or other material properties, which affect their performance.
Absorbent products, for example, are used in a variety of applications from absorbent garments to wipe cloths. With absorbent products, it is important to have a sufficiently large surface area to allow for adequate absorption. In some instances, such as in absorbent garments, wicking is a very important feature. In many of these products it is desirable for the material to be either hydrophobic or hydrophilic, depending on its use. In some instances it is important for a product to have discrete areas with distinct properties.
Therefore, there is a need in the art to provide fibrous materials having improved properties.
A gradient material comprising at least two types of nanofibers distributed non-uniformly throughout the material to form one or more gradients is provided. In one embodiment, the at least two types of nanofibers intertwine to form a single layer of material, i.e., are at least partially physically intertwined, i.e., entangled with one another in a multi-component material. Such intertwining can occur when both types of nanofibers are deposited substantially simultaneously in an overlapping region. In another embodiment, the at least two types of nanofibers combine to form a plurality of layers. The nanofibers can be any suitable type of nanofiber, including electrospun fibers, protein nanofibers, cellulose nanofibers, hollow nanofibers, bacterial nanofibers, inorganic nanofibers, hybrid nanofibers, splittable nanofibers and combinations thereof. The at least two types of nanofibers in the layers may be intertwined, especially at the interface between the two layers, or portion of the at least two types of fibers may be bonded to each other to provide layer integrity.
In another embodiment, the gradient material comprises at least two types of electrospun fibers distributed non-uniformly throughout the material to form one or more gradients. In one embodiment, the at least two types of electrospun fibers intertwine to form a single layer of material. In one embodiment, the at least two types of electrospun fibers combine to form a plurality of layers, i.e., a multi-layer material. The at least two types of electrospun fibers are distributed non-uniformly within one or more of the plurality of layers to form one or more planar gradients, i.e., gradients in the plane of the layers, and/or between one or more of the plurality of layers to form one or more thickness direction gradients, i.e., z-direction gradient (z-direction is the direction normal to the plane of the layers). In one embodiment, the at least two types of electrospun fibers are produced from a single polymer or polymer blend and at least two types of electrospinning methods or from at least two different polymers or polymer blends and one or more types of electrospinning methods.
Any suitable materials can be used for the electrospun fibers. In one embodiment, polymers and/or polymer blends are used as the electrospun fibers, with no other materials present and/or only trace amounts of other fibers present, such as ceramics and/or titania. In one embodiment, the polymers and/or polymer blends are selected from the group consisting of polylactides, polylactic acids, polyolefins, polyacrylonitrile, polyurethane, polycarbonate, polycaprolactone, polyvinyl alcohol (PVA), cellulose, chitosan nylon (e.g., Nylon 6, Nylon 406, Nylon 6-6, etc.), polystyrene, proteins, and the like, or combinations thereof, further including combinations of polymers and polymer blends as described herein. Suitable solvents for each polymer, polymer combination or polymer blend can be selected from solvents known to those skilled in the art. In other embodiments, the electrospun fibers are made from materials other than polymers, such as ceramics.
Embodiments of the invention further comprise a product having one or more components made from a gradient electrospun material. The invention further comprises an absorbent article or other disposable article, health care product or consumer article made from a composite electrospun material having at least two types of electrospun fibers distributed non-uniformly to form one or more gradients. In one embodiment, at least one of the one or more gradients is a surface chemistry gradient, such as a contact angle gradient.
Embodiments of the invention further comprise a process for producing nanofibers of a first type; producing nanofibers of a second type; and combining the nanofibers of the first and the second type to produce a gradient nanofiber material. In one embodiment, the nanofibers of the first type and the nanofibers of the second type are applied sequentially to the moving substrate. In one embodiment, the nanofibers of the first type and the nanofibers of the second type are applied substantially simultaneously to the moving substrate, and, in one embodiment, are substantially intertwined in at least a portion of the resulting electrospun material. The resulting gradient nanofiber material can have a gradient in the thickness and/or planar directions. In one embodiment, the nanofibers are electrospun fibers formed by any suitable method, including with the use of a needle and/or slot, or a plurality of needles and/or slots or orifices of any suitable shape and size.
Embodiments of the present invention are useful for any type of disposable garment, including, but not limited to absorbent articles such as diapers, training pants, adult incontinence, feminine care garments, and the like, as well as disposable articles such as hospital garments (defined herein to include surgical gowns, hair or head coverings (e.g., shower caps, hairnets, surgical caps, etc.), shoe covers, face masks, disposable patient gowns, laboratory coats, surgical gloves, and the like), other medical and surgical good including, but not limited to, sterile wrap, wound covers, hemostatic articles, further including any type of glove, glove liner, and so forth. Embodiments of the present invention are also useful for many other types of consumer products, including, but not limited to, wipes, air filters, water filters, absorbent pads, electrostatic webs, dust filters for computer media such as floppy disks and hard disks, and so forth.
Materials described herein can provide strong and varying surface effects, such as wicking. In one embodiment, hydrophobic fibers have a sufficiently small diameter to create a lotus effect.
In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific preferred aspects in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that electrical, chemical, mechanical, procedural and other changes may be made without departing from the spirit and scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims, along with the full scope of equivalents to which such claims are entitled.
A gradient material comprising at least two types of nanofibers, such as a plurality of electrospun fibers, distributed non-uniformly is provided. The gradient can be one or more thickness direction gradients, one or more planar direction gradients or both. A process for forming a gradient material by combining various types of nanofibers, such as electrospun fibers, in a non-uniform manner is also provided.
Definitions of certain terms used throughout the specification are provided first, followed by a description of various embodiments of the present invention, an example and a brief conclusion.
As used herein, the term “disposable absorbent garment” refers to a garment that typically includes a bodyside liner and an absorbent element adapted for receiving and retaining body fluids or waste. The absorbent element typically includes an absorbent material such as cellulosic fibers, tissue layers, fibrous nonwoven webs and/or superabsorbent material. Often, such garments include a body chassis for supporting the absorbent element, which itself can include multiple components, such as an absorbent core, surge layer and so forth. Such garments include, for example, incontinence undergarments, which are typically configured with a self-supporting waist band, or diapers, and the like, which can be secured on the user with tabs, belts and the like. The body chassis can include a liquid permeable top sheet or film secured to an outer cover or backsheet, i.e., liner, which can be liquid permeable or impermeable, depending on whether an additional backsheet, i.e., barrier, is provided. Typically, the absorbent element is disposed between the body chassis and the user. The body chassis can take many forms, including for example, a pant-like or underwear type undergarment described herein, which includes a self-supporting waistband extending circumferentially around the waist of the user. Alternatively, the body chassis can be a diaper or like garment, which is secured around the user with various fastening means or devices known by those of skill in the are, including for example and without limitation tabs, belts and the like. The chassis can include elastic regions formed along the edges of the crotch region and around the leg openings, so as to form a gasket with the user's crotch and legs.
As used herein, the term “nonwoven web” refers to a structure or a web of material that has been formed without use of traditional fabric forming processes, such as weaving or knitting, to produce a structure of individual fibers or threads that are intermeshed, but not in an identifiable, repeating manner as is found in typical woven webs. Non-woven webs can be formed by a variety of conventional processes such as, for example, meltblowing processes, spunbonding processes, film aperturing processes, hydroentangling, coform production, airlaying, and staple fiber carding processes. Meltblown (MB) web and spunbond (SB) webs are both examples of “meltspun” webs.
As used herein, the term “coform” refers to a nonwoven material of air-formed matrix material comprising thermoplastic polymeric MB fibers and a multiplicity of individualized absorbent fibers, typically of at least microfiber size or larger, such as, for example, wood pulp fibers disposed throughout the matrix of MB fibers and engaging at least some of the MB fibers to space the MB fibers apart from each other. The absorbent fibers are interconnected by, and held captive within, the matrix of MB fibers by mechanical entanglement of the MB fibers with the absorbent fibers. The mechanical entanglement and interconnection of the MB fibers and absorbent fibers alone form a coherent integrated fibrous structure. The coherent integrated fibrous structure can be formed by the MB fibers and the absorbent fibers without any adhesive, molecular or hydrogen bonds between the two different types of fibers. The absorbent fibers can be distributed uniformly throughout the matrix of MB fibers to provide a homogeneous material. These materials can be prepared according to the descriptions in U.S. Pat. No. 4,100,324 to Anderson et al., U.S. Pat. No. 5,508,102 to Georger et al. and U.S. Pat. No. 5,385,775 to Wright, all commonly assigned, and hereby incorporated herein by reference.
As used herein the term “polymer” refers to and generally includes, but is not limited to, homopolymers, copolymers, such as, for example, block, graft, random and alternating copolymers, terpolymers, etc. and blends and modifications thereof. Polymers can include, but are not limited to, polylactides, polylactic acids, polyolefins, polyacrylonitrile, polyurethane, polycarbonate, polycaprolactone, polyvinyl alcohol (PVA), cellulose, chitosan nylon (e.g., nylon 6, nylon 406, nylon 6-6, etc.), polystyrene, proteins, and the like, or combinations thereof. Unless otherwise specifically limited, the term “polymer” is intended to include all possible geometrical configurations of the material. These configurations include, but are not limited to, isotactic, syndiotactic and random symmetries. Suitable solvents for each polymer can be selected from solvents known to those skilled in the art, including, but not limited to, sulfuric acid, formic acid, chloroform, tetrahydrofuran, dimethyl formamide, water, acetone, and combinations thereof. As used herein the term “polymer blends” refers to combinations of various types and amounts of polymers as well as blends of polymers with other materials, such as those described below.
Polymer blends or systems for forming fibers from single polymers can be selected from any suitable polymers, as can the corresponding solvents used in electrospinning. By way of example only, several representative polymer systems suitable for electrospinning include the following: Silk fibroin, optionally with added polymers such as poly(ethylene oxide) to improve processability or other properties, as disclosed by H. J. Jin et al., “Electrospinning Bombyx Mori Silk with Poly(ethylene oxide),” Biomacromolecules, Vol. 3, No. 6, November-December 2002, pp. 1233-1239; polyaniline in sulfuric acid or other solvents, optionally doped with a blend of polyaniline and polystyrene (PS) and/or polyethylene oxide (PEO) dissolved in a solvent such as chloroform, as disclosed by M. J. Díaz-de León, “Electrospinning Nanofibers of Polyaniline and Polyaniline/(Polystyrene and Polyethylene Oxide) Blends,” Proceeding of The National Conference on Undergraduate Research (NCUR) 2001, University of Kentucky, Mar. 15-17, 2001, Lexington, Ky.; polyacrylonitrile-acrylamide (PAN-AA) copolymers dissolved in organic solvents, such as N,N-dimethylformnamide (DMF), described by A. V. Mironov, “Nanofibers based on associating polyacrylonitrile-acrylamide copolymers produced by electrospinning, ” 2nd International Conference on Self-Assembled Fibrillar Networks (in Chemistry, Physics and Biology), Poster Session, Autrans, France, Nov. 24-28, 2001. (Reported polymer concentrations ranged from 6.4 to 14.9 wt. % in DMF; Nylon 6 in formic acid, e.g., about 10-20% nylon in the solvent); polyurethane in a 1:1 mixture of tetrahydroftiran (THF) and dimethyl formamide (DMF), or other ratios of THF and DMF, ranging from 0 to 100% of either solvent. Polyurethane concentration may be, for example, from about 5% to 25% on a mass basis in the solvent; polyvinyl alcohol and/or PEO in water; and polylactic acid and biotin or other proteinaceous materials in a mixture of acetone and chloroform. Suitable solvents for each polymer blend or system can be selected from solvents known to those skilled in the art.
As used herein, the term “longitudinal,” refers to or relates to length or the lengthwise direction, and in particular, the direction running between the front and back of the user. The term “laterally,” as used herein means situated on, directed toward or running from side to side, and in particular, a direction running from the left to the right of a user. The terms “upper,” “lower,” “inner,” and “outer” as used herein are intended to indicate the direction relative to the user wearing an absorbent garment over the crotch region. For example, the terms “inner” and “upper” refer to a “bodyside,” which means the side closest to the body of the user, while the terms “outer” and “lower” refer to a “garment side.”
As used herein, the term “machine direction” or “MD” refers to the direction of travel of the forming surface or moving substrate onto which fibers are deposited during formation of a nonwoven fibrous material, such as the electrospun composite material of the present invention.
As used herein, the term “cross-machine direction” or “CD” refers to a direction which is essentially perpendicular to the machine direction defined above.
As used herein, the terms “meltblown fibers” or “MB fibers” refers to fibers formed by extruding a molten thermoplastic material through a plurality of fine, usually circular, die capillaries as molten threads or filaments into a high velocity gas (e.g., air) stream which attenuates the filaments of molten thermoplastic material to reduce their diameter, which can be to microfiber diameter. Thereafter, the MB fibers are carried by the high velocity gas stream and are deposited on a collecting surface to form a web of randomly disbursed MB fibers. Meltblown fibers are considered herein to be a type of “coarse” fiber.
As used herein, the term “spun-bonded fibers” refers to fibers which are at least micro-sized fibers or larger and which are formed by extruding a molten thermoplastic material as filaments from a plurality of fine, usually circular, capillaries of a spinnerette with the diameter of the extruded filaments then being rapidly reduced as by, for example, by reductive drawing or other well-known spunbonding mechanisms. The production of spun-bonded nonwoven webs is illustrated in patents such as, for example, in U.S. Pat. No. 4,340,563 to Appel et al., commonly assigned, and hereby incorporated herein by reference. Spun-bonded fibers are considered herein to be a type of “coarse” fiber.
As used herein, the term “coarse fibers” refers to fibers larger in size than nanofibers, to include microfibers as well as fibers larger than micro-sized fibers having diameters greater than about 100 microns, such as about 200 to about 500 microns or greater, with exemplary ranges of about 100 to about 2000 microns or about 200 to about 900 microns. Examples of coarse fibers include, but are not limited to, meltblown (MB) fibers, spun-bonded fibers, paper-making fibers, pulp fibers, fluff, cellulose fibers, nylon staple fibers, and the like.
As used herein, the term “microfibers” refers to small diameter fibers having an average diameter not greater than about 100 microns and not less than about 0.5 microns, with an exemplary range of about four (4) to about 50 microns. Examples of microfibers include, but are not limited to, meltblown (MB) fibers, spun-bonded fibers, paper-making fibers, pulp fibers, fluff, cellulose fibers, nylon staple fibers and the like, although such materials can also be made larger in size than microfiber-sized. Microfibers can further include ultra microfibers, i.e., synthetic fibers having a denier per filament (dpf) of between about 0.5 and about 1.5, provided that the fiber diameter is at least about 0.5 microns.
As used herein, the term “nano-sized fibers” or “nanofibers” refers to very small diameter fibers having an average diameter not greater than about 1500 nanometers (nm). Nanofibers are generally understood to have a fiber diameter range of about 10 to about 1500 nm, more specifically from about 10 to about 1000 nm, more specifically still from about 20 to about 500 nm, and most specifically from about 20 to about 400 nm. Other exemplary ranges include from about 50 to about 500 nm, from about 100 to 500 nm, or about 40 to about 200 nm. In instances where particulates are present and heterogeneously distributed on nanofibers, the average diameter of a nanofiber can be measured using known techniques (e.g., image analysis tools coupled with electro microscopy), but excluding the portions of a fiber that are substantially enlarged by the presence of added particles relative to the particle free portions of the fiber.
As used herein, the term “electrospinning” refers to a technology which produces nano-sized fibers referred to as electrospun fibers from a solution using interactions between fluid dynamics and charged surfaces. In general, formation of the electrospun fiber involves providing a solution to an orifice in a body in electric communication with a voltage source, wherein electric forces assist in forming fine fibers that are deposited on a surface that may be grounded or otherwise at a lower voltage than the body. In electrospinning, a polymer solution or melt provided from one or more needles, slots or other orifices is charged to a high voltage relative to a collection grid. Electrical forces overcome surface tension and cause a fine jet of the polymer solution or melt to move towards the grounded or oppositely charged collection grid. The jet can splay into even finer fiber streams before reaching the target and is collected as an interconnected web of small fibers. The dried or solidified fibers can have diameters of about 40 nm, or from about 10 to about 100 nm, although 100 to 500 nm fibers are commonly observed. Various forms of electrospun nanofibers include branched nanofibers, tubes, ribbons and split nanofibers, nanofiber yarns, surface-coated nanofibers (e.g., with carbon, metals, etc.), nanofibers produced in a vacuum, and so forth. The production of electrospun fibers is illustrated in many publication and patents, including, for example, P. W. Gibson et al, “Electrospun Fiber Mats: Transport Properties,” AIChE Journal, 45(1): 190-195 (January 1999), which is hereby incorporated by reference.
As used herein, the term “type” such as when referring to “different types of fibers” refers to fibers having “a substantially different overall material composition” with measurably different properties, outside of “average diameter” or other “size” differences. That is, two fibers can be of the same “type” as defined herein, yet have different “average diameters” or “average diameter ranges.” (However, in the present invention, it is intended that fibers of a certain “average diameter” or “average diameter range,” namely nano-sized fibers, are used). Although fibers are of different “types” when they have a substantially different overall material composition, they can still have one or more components in common. The “substantially different overall material composition” may be characterized in that at least one component comprising a first weight percent of at least 1 weight percent in a first fiber type (based on measurement of a representative sample size, such as a sample of at least 10 grams of collected fibers) has a substantially different second weight percent in a second fiber type, wherein the absolute value of the difference between the second weight percent and the first weight percent is at least the smaller of 5% and one-half of the first weight percent. Alternatively, the absolute value of the difference between the second weight percent and the first weight percent is at least the smaller of 10% and one-half of the first weight percent. The contact angle of the material in the first fiber type may differ from the contact angle of the material in the second fiber type by at least 10 degrees, more specifically by at least 20 degrees. For example, pure polyethylene oxide fibers and polyethylene oxide fibers coated with particles, such as silica colloidal particles or containing fillers, wherein the fillers are present at a level of 2 wt % or greater, may be considered two different “types” of fibers herein. Likewise, electrospun fibers made from a polymer blend with a first polymeric component present at a level of at least 10 wt % would be considered a different fiber type relative to electrospun fibers made from a polymer blend that was substantially free of the first polymeric component. Fibers of different “types” can also have a completely different content, each made of a different polymer for example, or one made from a polymer fiber and the other from a titania fiber, or a ceramic fiber and a titania fiber, and so on.
As used herein, the term “gradient electrospun material” refers to a multi-component material in which nano-sized fibers of at least two different “types” which have been produced by electrospinning are present and non-uniformly distributed to create one or more gradients or heterogeneity in one or more directions. The gradient in a “gradient electrospun material” provides discrete areas having measurable differences in surface chemistry (e.g., wicking, contact angle, etc.) or other material properties, including, but not limited to, density, pore size, surface charge, zeta potential, and so forth, resulting from the presence of fibers of different types, i.e., of substantially different material composition. Materials having minor variations in fiber distribution, which do not cause measurable differences in surface chemistry or other material properties, are not considered gradient electrospun materials. For example, inherent non-uniform distribution of fibers due to the effects of the orifice used, current, etc., does not create a gradient electrospun material. Likewise, differences in density or basis weight of a given material from a single fiber type, possibly due to edge effects in electrospinning (lower mass at the edges of the formation region) are not considered gradients. Likewise, differences within a single fiber due to multiple components in the fiber (e.g., bicomponent electrospun fibers, e.g., polymer/titania fiber) which may be called a “gradient” by persons skilled in the art, are generally not considered to produce an electrospun gradient material as defined herein, but may nevertheless be used as a single component thereof. Differences within a single electrospun fiber are produced, for example, by using two concentric needles to release a coaxial jet of two different fluids into an electrospinning environment. See, for example, “Hollow Nanofibers in a Single Step,” Chemical and Engineering News, Vol. 82, No. 17, Apr. 26, 2004, p. 6 (non-hollow bicomponent fibers can be produced by similar means). The gradient can be in the thickness or z-direction such that the material is a layered material. The gradient can also be in the planar or x/y-direction (CD or MD). The gradient can also be in both the thickness and planar directions. A “gradient electrospun material” is to be distinguished from a “composite electrospun material” (which may or may not contain a gradient), described in U.S. patent application Ser. No. ______, commonly assigned, filed on same date herewith and entitled, “Composite Nanofiber Materials and Methods for Making Same” (hereinafter “Composite Application”). The “composite electrospun materials” are defined therein to be materials containing fibers of two different average diameters, namely nano-sized fibers and coarse-sized fibers. Although some skilled in the art may also refer to a material which has two different “types” of fibers but with each fiber type having substantially the same average diameter or average diameter range (such as the gradient electrospun materials described herein) as being a “composite,” the various embodiments of the present invention are not considered to be a “composite” as defined in the Composite Application, supra, since the fibers used herein are all substantially of the same average diameter or average diameter range, i.e., nano-sized fibers, and no fibers of another average diameter or average diameter range, such as coarse fibers, are used. Similarly, although some skilled in the art may also refer to two different “phases” in the same fiber as a composite (e.g., islands of a first polymer in a matrix of a second on a scale smaller than a fiber diameter, or surface regions on a fiber relatively enhanced in concentration of one component relative to its concentration in the interior regions of the fibers), such fibers are not encompassed in the term “composite” as defined in the Composite Application, supra, but are otherwise considered to be two different “types” of fibers as defined herein.
As used herein, the term “gradient nanofiber material” refers to a multi-component material in which nano-sized fibers of at least two different “types” which have been produced by any method known in the art are present and non-uniformly distributed to create one or more gradients or heterogeneity in one or more directions. (See above definition of “gradient electrospun material” for additional detail, including further discussion of the terms “gradient,” “type,” and so forth, all of which is fully applicable with a “gradient nanofiber material”).
As used herein, the term “single layer of material” or “single-layered material” refers to a material composed of a single thickness which can be variable in size.
As used herein, the term “plurality of layers” or “multi-layered material” refers to a “stack” of single-layered materials, which in some instances, can have small areas of intertwining or blending between the layers (such as shown in
In another alternative embodiment, any or all of the needles 104A, 104B and 104C may be replaced with a slot or other orifice of any suitable shape or size. In another embodiment (not shown), the needles can comprise a metal body shielded with an outer insulating material (e.g., a dielectric coating), with the tip exposed to allow fluid to pass therethrough.
Although in this embodiment, three types of electrospun fibers 114A, 114B and 114C from three different polymer sources 102A, 102B and 102C, respectively, are being added in sequence onto a moving collection substrate 108, the invention is not so limited. Any number of different types of electrospun fibers can be deposited on the moving collection substrate 108 to produce a gradient material as described herein. In one embodiment, two types of electrospun fibers are used. In one embodiment, three types of electrospun fibers are used. In other embodiments, more than three types of electrospun fibers are used.
The collection substrate 108 can be a fabric containing coarse fibers, the surface of a roll or drum, an endless belt, and so forth, and can alternatively comprise metal, such as a woven metal wire fabric or metallic coating, and can be electrically conductive (e.g., a woven or nonwoven web comprising electrically conductive polymers), although the invention is not so limited. Electrospinning can also be used to apply a low-basis weight functional coating applied uniformly or heterogeneously (e.g., in a pattern or with in-plane or z-directional gradients in chemistry) to one or both surfaces of a substrate such as a paper towel, a wound dressing, a disposable garment, a surgical gown, a glove, a shoe liner, a medical implant, an injection-molded device such as a catheter, filter materials (e.g., for air or water filtration) and so forth. In one embodiment, the collection substrate 108 is a carrier wire. In the embodiment shown in
As the polymer solutions from polymer sources 102A, 102B and 102C are injected through the needles 104A, 104B and 104C at high electrical potential, nano-sized electrospun fibers 114A, 114B and 114C are formed by electrospinning as is understood by those skilled in the art. The electrospun fibers 114A, 114B and 114C are successively deposited onto the collection substrate 108 to form a gradient electrospun material 116. Depending on the type and manner of this deposit, the resulting gradient electrospun material 116 can have heterogeneity in one or more directions, i.e., one or more gradients in one or more directions. Specifically, a gradient material made according to the process of
In the embodiment shown in
Although the gradient electrospun material 116 shown in
In one embodiment, a material property of the gradient electrospun material 116 averaged over an approximately 1-centimeter (cm) by 1-cm area square area in the material varies in the plane of the material such that the average parameter varies substantially monotonically along a linear path of about 5 cm in length (alternatively, of about 3 cm in length or about 10 cm in length) such that the average property at the beginning of the path differs by more than a predetermined value (e.g., by about 20% or about 50% of the higher of the two values) from that at the end of the path. For example, a contact angle gradient includes a gradient wherein the average contact angle averaged over an approximately 1 cm square region in the gradient electrospun material 116, such as a gradient electrospun web, is about 20 degrees in one portion of the web, and then rises along a linear path in the web reaching a portion of the web that is relatively more hydrophobic, such that a region about 5 cm away from the first region may have an average contact angle of about 60 degrees, or, more generally, may differ by about 20 degrees or more. In other embodiments, the average fiber size varies by about 30% or more, or by about 100% or more, along an approximately 5-cm path in the plane of the gradient electrospun material 116. For z-direction gradients, fiber properties averaged over a stratum of the gradient electrospun material 116 representing about 20% of the thickness of the material varies from adjacent strata by about 20% or more or about 50% or more of a physical property such as fiber diameter or surface energy, or by about 20 degrees or more for contact angle.
The gradients can be formed in any suitable manner, such as by varying the source location and/or rate and/or angle of delivery of one or more types of fibers being added to the moving substrate, including oscillating the electrospun delivery means such as the needle, varying the rate of production and/or distribution of fibers, varying the speed of the moving collection substrate, varying polymer temperatures, varying the applied voltage, varying the electrospun fiber characteristics (e.g., needle characteristics, use of slots, etc.), and so forth. Any of these parameters can be varied in time as well, to create MD variations. In one embodiment, the gradient electrospun materials of the present invention have a surface chemistry gradient, wherein the high surface area of electrospun fibers coupled with the gradient in surface chemistry across the material, provides a material with regions of super-hydrophilicity and/or super-hydrophobicity, including optional regions that repel liquids according to the “lotus effect” discussed herein.
For example, if the process of either
However, not all non-uniform areas are considered “gradients” as defined herein. For example, non-uniform areas 240 near the edge of the single-layered material in
In contrast to
Although relatively simple gradients in primarily the thickness direction and/or the planar direction have been discussed and illustrated, in practice, more complex gradients or gradients of other kinds can be formed in any other number of configurations as well according to manufacturing practices known in the art, including suitable modifications of any of the processes discussed herein and shown in
Gradient electrospun materials having a gradient in just the x and/or y-directions, i.e., a single layered material with one or more planar gradients, as illustrated in
Gradient electrospun materials having one or more gradients in both the z-direction and within the plane, as illustrated in
The electrospun fibers themselves can be produced by varying methods as is known in the art, to alter specific measurable properties as desired, thus creating different “types” of fibers as defined herein. In one embodiment a complex electrode system is used to produce the electrospun fibers comprising slots or openings (instead of or in addition to needles) for high shear gas flow to entrain the electrospun fibers. Useful geometries can then be adapted such as uniaxially aligned ceramic electrospun fibers as described by Li, et al, in “Electrospinning of Polymeric and Ceramic Nanofibers as Uniaxially Aligned Arrays,” Nano Letters, vol. 3, no. 8, Jul. 8, 2003, pp. 1167-1171, hereby incorporated herein by reference. In other embodiments titania nanofibers or alumina-borate oxide fibers are produced, which can also be aligned, if desired. Additionally, ceramic nanofibers comprising titania/polymer or anatase nanotubes can also be used, such as those described by Dan Li , et al., in “Direct Fabrication of Composite and Ceramic Hollow Nanofibers by Electrospinning,” Nano Letters, vol. 4, no. 5, Mar. 30, 2004, pp. 933-938, hereby incorporated herein by reference.
The collection substrate 108 in any of the processes described herein can be moving at any useful speed in the MD, such as about 0.1 to about one (1) cm/sec or greater. In one embodiment, the MD speed is greater than about one (1) cm/sec up to about 400 cm/sec or greater. Generally, the slower speeds are useful for producing gradient materials with machine direction gradients controlled by dynamically modifying electrospinning conditions during production, while the higher speeds are useful for steady-state products or materials with gradients in the cross-machine direction (CD) achieved by generating electrospun fibers from two or more sources spaced apart in the cross-direction, or for producing z-direction gradients under steady-state conditions, although any suitable speed can be used as desired. In one embodiment, the speed ranges from about five (5) to 200 cm/sec. In another embodiment, the speed ranges from about 0.1 to about 50 cm/sec. In another embodiment, the speed ranges from about 0.5 to ten (10) cm/sec. In one embodiment, the speed is varied during the operation, i.e., in time, to allow for varying amounts of fibers to be deposited in the MD.
In another embodiment, the grounding electrode is a rotating, translating or stationary grounded surface with slots to allow aerodynamic forces to overcome the electrostatic attraction to the grounded surface, thereby allowing electrospun fibers to be blended into a stream of other electrospun fibers. In yet another embodiment, the electrospinning process is performed in a vacuum. Other methods can produced branched fibers, tube fibers, nanoballs, ribbon fibers, split fibers, electrospun yarns, and surface coated fibers, as is known in the art.
In one embodiment, filler materials and other solids such as any type of particle (e.g., superabsorbent particles, odor control materials such as talc, zeolites or activated carbon particles or silica, opacifiers, graphite, graphite nanoparticles, carbon nanotubes, silica nanoparticles, colloidal metals such as silver or gold, etc.), as well as kaolin or other minerals or fillers, antimicrobials, elastomeric materials such as elastomeric polyurethanes and the like, are embedded in the gradient electrospun material to create fibers of different types (when the filler materials are present at a level of 2 wt % or greater of the fiber plus filler material combined) as compared with fibers of the similar material composition but without filler materials. Such materials can be useful in providing skin-health benefits in skin-contacting layers of garments or in absorbent articles, or for providing a variety of other benefits in consumer goods.
Methods of attaching superabsorbent particles or other particles to fibers using binders are disclosed in U.S. Pat. No. 6,596,103, “Method of Binding Binder Treated Particles to Fibers,” issued Jul. 22, 2003 to Hansen et al. and U.S. Pat. No. 6,425,979, “Method for Making Superabsorbent Containing Diapers,” issued Jul. 30, 2002 to Hansen et al., both of which are hereby incorporated herein by reference. Mechanical means for delivering superabsorbent particles to a structure via air entrainment are disclosed in U.S. Pat. No. 6,709,613, “Particulate Addition Method and Apparatus,” issued Mar. 23, 2004 to Chambers et al., hereby incorporated herein by reference.
Superabsorbents useful in embodiments of the present invention can be chosen from classes based on chemical structure as well as physical form. These include, for example, superabsorbents with low gel strength, high gel strength, surface cross-linked superabsorbents, uniformly cross-linked superabsorbents, or superabsorbents with varied cross-link density throughout the structure. Superabsorbents may be based on chemistries that include, but are not limited to, poly(acrylic acid), poly(iso-butylene-co-maleic anhydride), poly(ethylene oxide), carboxymethyl cellulose, poly(vinyl pyrrollidone), poly(-vinyl alcohol), and the like. Other details regarding the use of superabsorbent particles for absorbent articles are disclosed in U.S. Pat. No. 6,046,377, “Absorbent Structure Comprising Superabsorbent, Staple Fiber, and Binder Fiber,” issued Apr. 4, 2000 to Huntoon et al., and U.S. Pat. No. 6,376,011, “Process for Preparing Superabsorbent-Containing Composites,” issued Apr. 23, 2002 to Reeves et al., both of which are hereby incorporated herein by reference.
In one embodiment elastomeric fibers, such as elastomeric polyurethanes, are used to create breathable stretchable films. In one embodiment a layer of electrospun nanofibers are deposited on a film or nonwoven web of electrospun fibers, such as an apertured film or elasticized web, in order to provide a breathable moisture barrier layer attached to a layer providing other functionality, such as texture, elasticity, integrity or bulk. In an alternative embodiment, the electrospun fibers are deposited on a rubbery elastomeric electrospun material to improve the tactile properties of the material. Elastomeric-containing materials are useful in products such as diapers, training pants, feminine napkins, hospital gowns, wraps for placement on the body, sterile wrap, wound dressings, articles of clothing, wipes for surface cleaning, athletic gear, and the like.
In one embodiment, a small amount of conductive polymer is added to the electrospun fiber to provide ions in the gas or melt phases. The conductive polymer can also serve as an initial layer on the collecting substrate to help modify or control the electrical field or modify the formation of the electrospun material. In a particular embodiment, about one (1) to about five (5)%, by weight, conductive polymer material is added to the electrospun fiber. In one embodiment, the conductive polymer is a 5-membered ring which includes a nitrogen, such as polypyrliodne, and the like. The use of conductive polymers is useful in biosensor applications, such as wetness sensors and the like.
In one embodiment, some or all of the composite electrospun material comprises hydrophobic fibers of sufficiently small diameter to simulate the lotus effect in their hydrophobicity and self-cleaning abilities. The lotus effect refers to the lotus leaf's extreme hydrophobicity, wherein minute hydrophobic bumps on the surface allow water and other liquid to roll off the surface. Known commercial mimicry of the lotus effect has relied on nanoparticles, such as small particles of wax, arranged as small bumps on a surface. In embodiments of the present invention, nanofibers are used as the hydrophobic fibers. See, for example, U.S. Pat. No. 6,660,363 to Barthlott and U.S. Patent Application 2002/0150724 to Nun et al., both of which are hereby incorporated herein by reference.
The resulting gradient electrospun materials are most often webs. Such webs can be textured (e.g., molded to a three-dimensional shape, such as by forming against or subsequently molding against an Uncreped Through-Air Dried (UCTAD) fabric, such as the “ironman” design known in the art), apertured, slit, embossed, colored, combined with other materials, such as other absorbent materials in layered structures, joined to elastomeric webs and so forth. Additionally or alternatively, some or all portions of the materials can be chemically treated after at least some of the electrospun fibers have been deposited to modify surface chemistry and to optionally create or enhance surface chemistry gradients in the web. Such treatments can include, for example, fluorochemicals.
In addition to electrospun fibers, it is also possible to use other types of nanofibers in any of the various embodiments described herein. For example, in one embodiment hollow nanofibers are used for improved thermal insulation, acoustic insulation, dialysis materials, membrane filtration, reverse osmosis filters, chemical separations, etc. Formation of hollow nanofibers can be achieved by a technique described by I. G. Loscertales et al, in J. Am. Chem. Soc. 126, 5376 (2004), hereby incorporated herein by reference, which yields hollow fibers with nanometer-sized interior diameters in a single step. The method exploits electrohydrodynamic forces that form coaxial jets of liquids with microscopic dimensions. By the injection of two immiscible or poorly miscible liquids through a pair of concentric needles at high voltage, coaxial jets of liquids are formed. An outer shell solidifies around an interior liquid that can be evaporated or otherwise removed after the fibers are formed, yielding hollow fibers. With this method, hollow silica fibers can be spun with fairly uniform-sized inner diameters measuring a few hundred nanometers. The shells can be formed via sol-gel chemistry from tetraethylorthosilicate around cores of common liquids such as olive oil and glycerin. Many other compounds, such as ceramic materials and ceramic/polymer combinations, can also be used to form hollow fibers.
In another embodiment, cellulose nanofibers are produced according to methods known in the art in which cellulose is dissolved in a solvent and then electrospun. Suitable solvents can include N-methylmorphomine-N-oxide (NMMO), zinc chloride solutions, and the like. Particles can be present as a suspension or dispersion in the solution being used to make the fibers and combined with the electrospun fibers during the formation process. Alternatively, a particle-forming precursor can be present, or the particles can be added as a dry powder or entrained in a mist or spray as nanofibers are being produced. Charge on the particles or the entraining droplets can be added to enhance delivery of the particles to the electrospun web. Suitable particles can include silver (e.g., nanoparticles of silver), superabsorbent particles that can be entrained or entrapped in electrospun fibers (typically added external to electrospinning needles), minerals such as titanium dioxide or kaolin, odor control agents such as zeolites, sodium bicarbonate, or activated carbon particles, and the like.
In one embodiment protein nanofibers, such as fibrinogen fibers, elastin-mimetic fibers, etc., are combined with the coarse fibers. In one embodiment inorganic and hybrid (organic/inorganic) nanofibers are used. In one embodiment, polysaccharide nanofibers made from bacteria (e.g., bacterial cellulose) are used.
In another embodiment nanofibers known as splittable fibers are used, in which a fiber, such as a microfiber, is exposed to a swelling agent such as sodium hydroxide to cause it to split into numerous small filaments, or “islands-in-the-sea” fibers, in which a precursor fiber comprises multiple filaments (islands) in a removable matrix (sea) that typically is dissolved away. See, for example, http)://www.ifj.com/issue/october98/story8.html. By way of example, islands-in-the-sea nanofibers can be polypropylene islands in a PVA sea, polyester islands in a polyethylene sea, and so forth. Fiber diameter can be from about 0.1 to about four (4) microns.
In one embodiment, fibers prepared by nanofabrication techniques such as printing, atomic force microscopy assembly, or any of the techniques known for producing the setae in gecko-like adhesives, as described in U.S. patent application Ser. No. 10/747,923, entitled “Gecko-like Fasteners for Disposable Articles,” filed Dec. 29, 2003, are used. Two or more such techniques can also be combined to produce a gradient nanofiber web.
Gradient nanofiber webs produced by the methods described herein can have varying properties depending on a number of parameters such as the percentage of nanofibers, the type of nanofibers, presence of ions in the gas or melt phases, all of the other process variables noted herein, and so forth. In one embodiment the gradient nanofiber webs are gradient electrospun webs having a high porosity (e.g., at least about 20%) with relatively low pore sizes (e.g., less than about 5 microns). Such features are important in several types of absorbent products, filters of many kinds, medical goods, and so forth. In one embodiment, the porosity of a gradient electrospun material is about 10 to about 95%, such as from about 50 to about 90%, or from about 30 to about 80%. In one embodiment, the pore size as measured by mercury porosimetry is from about 0.1 to about 10 microns, such as from about 0.5 to about 3 microns, or from about 0.1 to about 2 microns, or from about 0.2 to about 1.5 microns, or less than about 1 micron.
The use of gradient nanofiber materials in various products is discussed in more detail below, but, generally speaking, the materials of the present are useful in a wide variety of products, including absorbent articles such as diapers, training pants, feminine napkins, adult incontinence garments, and the like. In one embodiment, the materials are used as distribution materials to hold and/or move liquid. In one embodiment, materials which are both hydrophobic and porous, can not only be used as an absorbent material to help keep the skin dry, but can also be used as a covering which allows fluid to pass through. In one embodiment, the gradient nanofiber materials described herein are used in a non-absorbent article (e.g., gloves) or on a non-absorbent side of an absorbent article, e.g., an outer cover layer.
Such materials are useful for virtually any type of protective clothing, including any type of disposable garment, such as garments requiring varying surface properties, barrier clothing, and the like. For example, the gradient nanofiber materials described herein can be incorporated into any type of disposable garment including, but not limited to, hospital garments such as surgical gowns, hair or head coverings (e.g., shower caps, hairnets, surgical caps, etc.), shoe covers, disposable patient gowns, laboratory coats, face masks, surgical gloves (e.g., for wicking moisture away from the hand and/or improving barrier functions), other medical and surgical goods including, but not limited to, sterile wrap, wound covers, hemostatic articles, and so forth. Specifically, the gradient nanofiber materials of the present invention can help prevent fluids, such as bodily fluids, from penetrating the material and contacting the user. In one embodiment, the barrier is a breathable barrier, as is known in the art. In one embodiment, the gradient nanofiber material includes hydrophobic fibers for use as a breathable barrier. It should be noted that the materials are useful as breathable materials for any purpose, including, but not limited to gloves, liners (e.g., exterior or interior lining of a glove), barrier layers, outer covers, absorbent core linings, barrier tissue, cuffs, wings, waistbands, and the like, found in absorbent articles. Such materials are also useful in wipes (including two-sided wipes or wipes with gradients in surface chemistry or other properties), face masks, air filters, water filters, sterile wrap, and so forth.
The high surface area of the various gradient nanofiber materials described herein additionally allows such materials to be useful in filtration applications, such as to absorb odors, particles, and so forth. In one embodiment, the materials described herein are used in a high efficiency filtration device for water or air. In one embodiment the materials described herein are combined with conventional filtration materials, such as activated charcoal, and the like.
In one embodiment, gradient nanofiber materials described herein are used in absorbent articles in the intake region to provide varying properties within a single material or web. For example, wicking properties provided by these materials provide fluid flow control, barrier properties, and so forth. Therefore, it is possible for one region to be hydrophobic, which aids in wicking moisture away from the skin, and another area to be hydrophilic, and therefore located away from the fluid target area.
In one embodiment one or more of the gradient nanofiber materials of the present invention are laminated to another layer known to provide strength, (e.g., such as a meltblown web, a polyolefin film or other film layer, an apertured film, a scrim layer, a tissue layer such as a cellulosic web having a basis weight of about 20 grams per square meter or greater, a woven layer, and the like). In this way, a sufficiently strong laminate is provided which is also capable of controlling surface properties (e.g., water deflection, etc.)
Portions of various garments or entire garments (for infants, children or adults), can be made using any of the gradient nanofiber materials described herein. In one embodiment, the materials made from the processes described herein are useful as an insert, which can be comprised of a fluid impervious backing sheet or outer cover, fluid pervious facing sheet or liner, absorbent core and an intake/distribution or surge layer.
In one embodiment, the outer cover serves as a fluid barrier and can be made from any suitable liquid impermeable material or a material treated to be liquid impermeable, including any of the gradient nanofiber materials described herein. In one embodiment, the outer cover is a laminate comprised of an inner liner layer and an outer film layer, such as a polyethylene film. In one embodiment, “Breathable stretch thermal laminate” (BSTL) is used for the outer cover. In an alternative embodiment the outer cover is an opaque sheet of material with an embossed or matte surface that is about one mil thick, although the invention is not so limited. In another alternative embodiment, the outer surface is made of extensible materials, such as necked, pleated (or micropleated) or creped nonwovens, including spunbond polypropylenes, bonded carded webs, or laminates of nonwovens and films, including gradient nanofiber materials, which are necked, pleated or creped so as to allow the outer cover to extend with minimal force, further including any type of gradient nanofiber material as described herein. For example, a suitable extensible material is a 60% necked, polypropylene spunbond having a basis weight of about 1.2 osy. In one embodiment, the polypropylene spunbond fibers are combined with one or more types of electrospun fibers. The cover sheet and outer cover can also be made of nonwovens, films, or composites of films and nonwovens or gradient nanofiber materials. For a further description of extensible materials, see U.S. patent application Ser. No. 09/855,182, filed on May 14, 2001, entitled, “Absorbent Garment with Expandable Absorbent Element,” commonly assigned, and hereby incorporated herein by reference.
The liner serves as a fluid barrier and can be made from any suitable material or materials, including the gradient nanofiber materials described herein. In one embodiment, the liner is made from any soft, flexible porous sheet that permits the passage of fluids therethrough, including, but not limited to, hydrophobic or hydrophilic nonwoven webs, wet strength papers, spunwoven filament sheets, and so forth, further including gradient nanofiber materials. In one embodiment, the inner bodyside surface is made from spunwoven polypropylene filaments or a gradient nanofiber material with spot embossing, further including a perforated surface or suitable surfactant treatment to aid fluid transfer. In one embodiment, the liner is a laminate comprised of an inner liner layer, which, in one embodiment, is made from the gradient nanofiber materials described herein, and an outer film layer, such as a polyethylene film. In one embodiment, “breathable stretch thermal laminate” (BTSL) is used for the liner.
The absorbent core or absorbent batt located between the outer cover and liner serves to absorb liquids, as is known in the art, and can be made from any suitable material, including any of the gradient nanofiber materials described herein. The absorbent batt can be any material that tends to swell or expand as it absorbs exudates, including various liquids and/or fluids excreted or exuded by the user. For example, the absorbent material can be made of airformed, airlaid and/or wetlaid composites of fibers and high absorbency materials, referred to as superabsorbents. In certain embodiments, different types of superabsorbent material may be used among the different types of products, such as diapers. The delivery of different superabsorbent materials may be achieved using a pulsed superabsorbent delivery system. For example, the absorbent structure in one type of diaper may include a superabsorbent material that provides adequate performance for many general-use situations but fails to deliver optimum performance under some use conditions. Suitable superabsorbent materials can be selected from natural, synthetic, and modified natural polymers and materials. The superabsorbent materials can be inorganic materials, such as silica gels, or organic compounds, such as crosslinked polymers. In one embodiment the superabsorbent is any type of composite electrospun material as described herein. The fibers can be fluff pulp materials or any combination of crosslinked pulps, hardwood, softwood, and synthetic fibers and electrospun fibers or other types of nanofibers. Suitable superabsorbent materials are available from various commercial vendors, such as Dow Chemical Company located in Midland, Mich., U.S.A., BASF, located in Portsmouth, Va., U.S.A., and Degussa, located in Greensboro, N.C., U.S.A. Typically, a superabsorbent material is capable of absorbing at least about 15 times its weight in water, and desirably is capable of absorbing more than about 25 times its weight in water.
Airlaid and wetlaid structures typically include binding agents, which are used to stabilize the structure. Other absorbent materials, alone or in combination, and including webs of carded or air-laid textile fibers, multiple plys of creped cellulose wadding, various super absorbent materials, various foams, such as synthetic foam sheets, absorbent films, and the like can also be used. The batt can also be slightly compressed or embossed in selected areas as desired. Various acceptable absorbent materials are disclosed in U.S. Pat. No. 5,147,343, entitled, “Absorbent Products Containing Hydrogels With Ability To Swell Against Pressure,” U.S. Pat. No. 5,601,542, entitled “Absorbent Composite,” and U.S. Pat. No. 5,651,862, entitled, “Wet Formed Absorbent Composite,” all of which are commonly assigned and hereby incorporated herein by reference. Furthermore, the proportions of high-absorbency particles can range from about zero (0) to about 100%, and the proportion of fibrous material from about zero (0) to about 100%.
In one embodiment, the absorbent batt is a folded absorbent material made of fibrous absorbent materials with relatively high internal integrity, including for example one made with thermoplastic binder fibers in airlaid absorbents, e.g., pulp, bicomponent binding fibers, and superabsorbents, which have higher densities in the folded regions, further including any type of composite nanofiber materials as described herein. In one embodiment, gradient composite electrospun materials are used. The higher density and resulting smaller capillary size in these regions promotes better wicking of the liquid. Better wicking, in turn, promotes higher utilization of the absorbent material and tends to result in more uniform swelling throughout the absorbent material as it absorbs the liquid. The intake/distribution layer is made from any suitable material to increase the weight of fluid intake retention.
The surge layer is made from any suitable material, including any of the gradient nanofiber materials described herein, and is designed to increase the weight of fluid intake retention.
Other details of conventional construction and materials of disposable garments are understood in the art and will not be discussed in detail herein. See, for example, U.S. Pat. No. 4,437,860 to Sigl, commonly assigned, which is hereby incorporated herein by reference.
In one embodiment, the gradient nanofiber materials, such as gradient electrospun materials, produced according to the methods described herein are used in an absorbent article 502 as shown in
The absorbent article 502 comprises an absorbent chassis 504 and a fastening system 506 having a pair of fasteners, 508A and 508B to secure front and rear portions of the absorbent chassis 504 together. The fasteners 508A and 508B can be adhesive strips, mechanical fasteners, and the like. The absorbent chassis 504 defines a front waist region 510, a back waist region 512, a crotch region 514 interconnecting the front and back waist regions 510 and 512, respectively, an inner surface 516 which is configured to contact the wearer, and an outer surface 518 opposite the inner surface 516 which is configured to contact the wearer's clothing. In most embodiments, elastic 519 is present in the front waist region 510, the back waist region 512 and the crotch region 514 as shown. The crotch region 514 further includes containment flaps 521 as shown. Any of the components in the chassis 504 can include nanofibers, such as the electrospun gradient materials described herein. The absorbent chassis 504 also defines a pair of transversely opposed side edges 520 and a pair of longitudinally opposed waist edges, which are designated front waist edge 522 and back waist edge 524. The front waist region 510 is contiguous with the front waist edge 522, and the back waist region 512 is contiguous with the back waist edge 524.
The absorbent article further comprises an outer cover 526. In general, the outer cover 526 can comprise one or more layers of nanofibers on the outward facing surface. In one embodiment, the nanofibers are hydrophobic. The illustrated absorbent chassis 504 comprises a structure 528 which can be rectangular or any other desired shape, a pair of transversely opposed front side panels 530, and a pair of transversely opposed back side panels 532. The structure 528 and front and back side panels, 530 and 532, respectively, can comprise two or more separate elements, as shown in
The absorbent article 502, and, in particular, the outer cover 526 can comprise one or more appearance-related components such as printed graphics 534 on the front surface 536, a colored stretchable waist band 538, and so forth. Examples of appearance-related components include, but are not limited to: graphics; highlighting or emphasizing leg and waist openings in order to make product shaping more evident or visible to the user (e.g., a printed leg opening region 540); highlighting or emphasizing areas of the absorbent article 502 to simulate functional components such as elastic leg bands, elastic waistbands, simulated “fly openings” for boys, ruffles for girls; highlighting areas of the absorbent article 502 to change the appearance of the size of the absorbent article 502; registering wetness indicators, temperature indicators, and the like in the absorbent article 502; registering a back label, or a front label, in the absorbent article 502; and, registering written instructions at a desired location in the absorbent article 502.
The invention will be further described by reference to the following example, which is offered to further illustrate various embodiments of the present invention. It should be understood, however, that many variations and modifications may be made while remaining within the scope of the present invention.
Materials and Preparation
Polyethylene Oxide (PEO with a molecular weight (MW) of 100,000, Catalog No. 18, 198-6, from Sigma-Aldrich, having offices in Saint Louis, Mo., was used for the electrospun fibers. Three (3)% silica colloidal particle (340 nm) solution from Colloidal Dynamics, having offices in Warwick, R.I., was used as a filler particle to create a second type of electrospun fiber.
Two different types of electrospun fibers, each having a different composition, were created:
1. Electrospun fiber—Type No. 1 (hereinafter “ES1”): A 20% PEO solution was prepared by dissolving 1 g of PEO in 4 ml of ultra-filtered grade, distilled, deionized water with a resistivity reading of 18 MΩ.cm.
2. Electrospun fiber—Type No. 2 (hereinafter “ES2”): A 20% PEO solution was prepared by dissolving 1 g of PEO in 4 g of 3% silica colloidal particle (340 nm) solution to produce a different type of electrospun fiber (as compared with ES1) having a particle weight of approximately 13% (as compared with 0% particle weight for ES1). This was calculated as follows: (3% particles in solution)/(23% total solids in solution (particles plus PEO))=13% particles, by weight.
With the aid of a Model ‘22’ Syringe Pump from Harvard Apparatus, Inc., having offices in Holliston, Mass., both solutions were extruded at ambient temperature and pressure at a flow rate of approximately 100 uL/ml through separate Tygong brand tubings (1.6 mm id) to two positively charged metal bevel sharp-tipped B-D® brand needles (22 G×3.8 cm (1.5) in) made by Becton-Dickson & Co., having offices in Franklin Lakes, N.J. The needles were each isolated by a Teflon® brand tube for ease in handling the needles. The two needles were either placed at the same height, i.e., side-by-side position, approximately 3 cm apart or at different heights, approximately 1.5 cm apart. A High Voltage Supply ES30P/DDPD (having a low current power supply) from Gamma High Voltage Research, Inc., having offices in Ormand Beach, Fla., was utilized to establish the 18 kV electric potential gradient.
After each type of electrospun fibers were made (E1 and E2), gradient electrospun materials were made in two different ways. In one experiment, the gradient electrospun material was made with the needles in a side-by-side position. In another experiment, the gradient electrospun material was made with one needle higher than the other (but still side-by-side). Specifically, the higher needle was used to produce the second type of fibers containing the particles, ES2. In both instances, samples were collected at a grounded aluminum plate. For the side-by-side needle position, the aluminum plate was at approximately 10 cm below the tips. For the needles having varying heights, the aluminum plate was at approximately 10 cm below the end of the lower needle (ES1) and about 12 cm below the end of the upper needle (ES2).
Scanning Electron Microscope Images
SEM images were taken using S4500 Field Emission SEM, which operated at an accelerating voltage of 5 kV. An upper detector was used (pure SEI) at a working distance of about nine (9) mm. The samples were coated with approximately 20 nm chromium, and the images were taken at magnifications ranging from 10,000 to 45,000×.
In the embodiments described herein, mixtures of various nanofibers are created by using multiple discharge tubes containing different nanofiber-creating materials, such as polymers, each of which produce nanofibers which are deposited on a collection grid and combined with other nanofibers to form gradient nanofiber materials. Thus, for example, mixtures of hydrophobic and hydrophilic electrospun fibers can be created, such as combinations of polylactides or polyactic acid polymers, spun out of a solution and coupled with polyolefin nanofibers, such as polyethylene, spun from a melt. The resulting gradient nanofiber materials are useful, for example, in producing biodegradable webs for disposable absorbent articles. Such webs can be part of intake layers, protective covers, distribution materials, and outer covers of articles as described herein.
Embodiments of the present invention provide significant advantages over other fibrous products and methods for manufacture thereof. Nanofibers produced by electrospinning or other methods can produce materials having very large surface areas for a given weight. When these nanofibers are combined with other types of nanofibers as described herein, the resulting gradient materials can maintain similar porosity properties while providing a relatively low pore size and high surface area.
All publications, patents, and patent documents cited in the specification are incorporated by reference herein, each in their entirety, as though individually incorporated by reference. In the case of any inconsistencies, the present disclosure, including any definitions therein, will prevail.
Although specific aspects have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement that is calculated to achieve the same purpose may be substituted for the specific aspect shown. For example, although the invention has been described primarily in terms of electrospun fibers, it is to be understood that nanofibers of any type can be used. This application is intended to cover any adaptations or variations of the present invention. Therefore, it is manifestly intended that this invention be limited only by the claims and the equivalents thereof.
