1. Field of the Invention
This invention relates to a lofty, nonwoven material produced from continuous fibers in which the lofty character of the nonwoven material is the result of the fibers comprising the web being oriented in a z-direction, that is outside of the plane of the orientation of the web, of the nonwoven material. These materials are particularly suitable for use in a broad range of applications including fluid management (surge), air and liquid filtration, acoustic and thermal insulation, packing material, absorbents, and cleaning materials. More particularly, these materials are suitable for use as surge, spacer layers, filtration materials and absorbent layers in personal care absorbent products including disposable diapers, incontinence garments, and feminine care products such as sanitary pads and napkins, and in face masks, surgical gowns, sterile wraps and surgical drapes. In addition, this invention relates to methods for producing such lofty, nonwoven materials.
2. Discussion of Related Art
Absorbent personal care articles such as sanitary pads and napkins, disposable diapers, incontinent-care pads and the like are widely used, and much effort has been made to improve their effectiveness and functionality. These articles generally include a liquid absorbent material backed by a liquid-impervious barrier sheet. To enhance the sense of comfort, the absorbent material has a facing of a material which masks at least the body-facing surface of the product. The purpose of this cover material is to help structurally contain the absorbent material and to protect the wearer from continuous direct contact with moisture from previously wetted absorbent material. The cover material is typically of relatively low basis weight nonwoven fabric. Improved product performance has been obtained in these products through the incorporation of a surge management material disposed between the cover material and the absorbent material. The surge management material is made from a relatively high basis weight, low density, that is, thick, nonwoven web material.
In nonwoven webs, the fibers comprising the web are generally oriented in the x-y plane of the web and the resulting nonwoven web material is relatively thin, that is lacking in loft or significant thickness. Loft or thickness in a nonwoven web suitable for use in personal care absorbent articles promotes comfort (softness) to the user, surge management and fluid distribution to adjacent layers.
In order to impart loft or thickness to a nonwoven web, it is generally desirable that at least a portion of the fibers comprising the web be oriented in the z-direction. Conventionally, such lofty nonwoven webs are produced using staple fibers. See, for example, U.S. Pat. No. 4,837,067 which teaches a nonwoven thermal insulating batt comprising structural staple fibers and bonding staple fibers which are entangled and substantially parallel to the faces of the batt at the face portions and substantially perpendicular to the faces of the batt, and U.S. Pat. No. 4,590,114 which teaches a batt including a major percent of thermo-mechanical wood pulp fibers stabilized by the inclusion of a minor percent of thermoplastic fibers including staple length thermoplastic fibers. Alternatively, conventional high loft forming processes rely on pre-forming processes such as fiber crimp formed on a flat wire or drum, and post-forming processes such as creping or pleating of the formed web.
In contradistinction to the known art, the present invention does not first form a web of material and pleat it. Rather, fibers are looped, or bent, on themselves without being first being formed into a material web. These fiber level loops, running between the major surfaces of the resultant web, are aggregated in the cross machine direction to form structures running in the cross machine direction which are herein sometimes called “waves” or “folds” to distinguish them from “pleats” which refer to structures in preformed web or mesh material that has been folded on itself.
Accordingly, it is one object of this invention to provide a high loft, low density nonwoven web material comprising substantially continuous fibers as opposed to staple fibers traditionally used in the manufacture of such nonwoven materials.
This and other objects of this invention are addressed by a lofty, nonwoven material comprising a nonwoven web comprising a plurality of substantially continuous fibers, which may be crimped or linear, oriented in a z-direction of the nonwoven web. The substantially continuous fibers are preferably spunbond and/or meltblown. In accordance with one embodiment of this invention, a support structure may be attached to at least one face of the nonwoven web, thereby providing strength to the high loft nonwoven web. This laminate structure provides support for the high loft structure, strength for winding, converting, etc., and a boundary layer to either enhance or retard fluid flow into the lofty absorbent structure in products such as disposable diapers, incontinence garments, and absorbent feminine care products including sanitary pads and napkins.
The lofty, nonwoven material of this invention is produced in accordance with one embodiment of this invention by a process in which a plurality of substantially continuous fibers are directed into a variable nip, resulting in bending of the fibers and formation of a nonwoven web. Within the nip the fibers may be subjected to a vacuum from both sides of the nip, either equally or differentially, producing a lofty, nonwoven web having a plurality of the substantially continuous fibers oriented in a z-direction.
In accordance with another embodiment of this invention, the lofty, nonwoven material is produced by directing a plurality of continuous, substantially linear, filament fibers through a slot formed by two opposed surfaces whereby the substantially continuous fibers bend from contact with the two opposed surfaces, which may be differential speeds or vacuum, or both, thereby forming a lofty, nonwoven web having a plurality of as-formed z-direction fibers.
These and other objects and features of this invention will be better understood from the following detailed description taken in conjunction with the drawings wherein:
As used herein, the term “nonwoven web” or “nonwoven material” means a web having a structure of individual fibers, filaments or threads which are interlaid, but not in a regular or identifiable manner, such as in a knitted fabric and films that have been fibrillated. Nonwoven webs or materials have been formed from many processes such as, for example, meltblowing processes, spunbonding processes, and bonded carded web processes. The basis weight of nonwoven webs or materials is usually expressed in ounces of material per square yard (osy) or grams per square meter (gsm), and the fiber diameters usable are usually expressed in microns. (Note that to convert from osy to gsm, multiply osy by 33.91.)
As used herein, the term “z-direction” refers to fibers disposed outside of the plane of orientation of a web.
As used herein, the term “spunbond fibers” refers to small diameter fibers which are formed by extruding molten thermoplastic material as filaments from a plurality of fine, usually circular capillaries of a spinneret as taught, for example, by U.S. Pat. No. 4,340,563 to Appel et al. and U.S. Pat. No. 3,802,817 to Matsuki et al.
As used herein, the term “meltblown 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 converging high velocity gas streams (for example, airstreams) which attenuate the filaments of molten thermoplastic material to reduce their diameter, which may be to microfiber diameter. Such a process is disclosed, for example, by U.S. Pat. No. 3,849,241 to Butin.
As used herein, the term “microfibers” refers to small diameter fibers having an average diameter not greater than about 75 microns, for example, having an average diameter of from about 0.5 microns to about 50 microns, or more particularly, having an average diameter of from about 2 microns to about 40 microns.
As used herein, the term “polymer” 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. Furthermore, unless otherwise specifically limited, the term “polymer” also includes all possible geometric configurations of the material. These configurations include, but are not limited to, isotactic, syndiotactic, atactic and random symmetries.
As used herein, the term “personal care absorbent article” means disposable diapers, training pants, absorbent underpants, adult incontinence products, feminine hygiene products and the like.
As used herein, the term “homofilament” refers to a fiber formed from only one polymer. This is not meant to exclude fibers formed from one polymer to which small amounts of additives have been added for coloration, anti-static properties, lubrication, hydrophilicity, etc.
As used herein, the term “bicomponent fibers” refers to fibers which have been formed from at least two polymers extruded from separate extruders but spun together to form one fiber. Bicomponent fibers are also sometimes referred to as conjugate fibers or multicomponent fibers. Bicomponent fibers are taught by U.S. Pat. No. 5,382,400 to Pike et al.
As used herein, the term “biconstituent fibers” refers to fibers which have been formed from at least two polymers extruded from the same extruder as a blend. The tern “blend” is defined below. Biconstituent fibers are sometimes also referred to as multiconstituent fibers. Fibers of this general type are discussed in, for example, U.S. Pat. No. 5,108,827 to Gessner. As used herein, the term “blend” means a mixture of two or more polymers.
As used herein, the term “substantially continuous fibers” refers to fibers, including without limitation, spunbond and meltblown fibers, which are not cut from their original length prior to being formed into a nonwoven web or fabric. Substantially continuous fibers may have average lengths ranging from greater than about 15 centimeters to more than one meter, and up to the length of the web or fabric being formed. The definition of “substantially continuous fibers” includes fibers which are not cut prior to being formed into a non woven web or fabric, but which are later cut when the nonwoven web or fabric is cut, and fibers which are substantially linear or crimped.
The term “staple fibers” means fibers which are natural or cut from a manufactured filament prior to forming into a web, and which have an average length ranging from about 0.1–15 centimeters, more commonly about 0.2–7 centimeters.
As used herein, the term “through-air bonding” or “TAB” means the process of bonding a nonwoven, for example, a bicomponent fiber web in which air which is sufficiently hot to melt one of the polymers of which the fibers of the web are made is forced through the web.
Potential applications for the nonwoven web of this invention include personal care absorbent articles such as diapers, training pants, incontinence garments, feminine care products including sanitary pads and napkins, all surge materials, loop for look and loop, air filtration, liquid filtration, body scrub pads, oil sorb, baby wipes, industrial wipes, insulation and packaging material. In the case of filtration materials, the method of this invention greatly increases the surface area and volume available for filtration. In addition, the method of this invention may be suitable for producing coforms or composite materials incorporating high loft surge/pulp/superabsorbent material. And, for a Continuous roll of diapers, a composite material made by the present invention could be produced by ridging or ruffling a high loft surge/pulp/superabsorbent material laminate and placing it in between an outer cover and a liner, which would produce a laminate with all of the components of a diaper in a single step, which could be wound up and cut and placed later on converting machines.
The lofty or high loft nonwoven material of this invention comprises a nonwoven web comprising a plurality of substantially continuous fibers oriented in a z-direction of the nonwoven web. The substantially continuous fibers preferably are drawn in spunbond or meltblown processes. The substantially continuous fibers are preferably formed with polymers selected from the group consisting of polyolefins, polyamides, polyesters, polycarbonates, polystyrenes, thermoplastic elastomers, fluoropolymers, vinyl polymers, and blends and copolymers thereof. Suitable polyolefins include, but are not limited to, polyethylene, polypropylene, polybutylene, and the like; suitable polyamides include, but are not limited to, nylon 6, nylon 6/6, nylon 10, nylon 12 and the like; and suitable polyesters include, but are not limited to, polyethylene terephthalate, polybutylene terephthalate, polytrimethyl terephthalate, polylactic acid and the like. Particularly suitable polymers for use in the present invention are polyolefins including polyethylene, for example, linear low density polyethylene, low density polyethylene, medium density polyethylene, high density polyethylene and blends thereof; polypropylene; polybutylene and copolymers as well as blends thereof. Additionally, the suitable fiber forming polymers may have thermoplastic elastomers blended therein.
In accordance with one preferred embodiment of this invention, the substantially continuous fibers are bicomponent fibers. Particularly suitable polymers for forming the structural component of suitable bicomponent fibers include polypropylene and copolymers of polypropylene and ethylene, and particularly suitable polymers for the adhesive component of the bicomponent fibers includes polyethylene, more particularly linear low density polyethylene, and high density polyethylene. In addition, the adhesive component may contain additives for enhancing the crimpability and/or lowering the bonding temperature of the fibers, and enhancing the abrasion resistance, strength and softness of the resulting webs. The nonwoven web of the material of this invention has a basis weight in the range of about 0.25 osy to about 50 osy. To enhance the absorption characteristics of the nonwoven material, in accordance with one embodiment of this invention, the nonwoven web comprises an absorbent, for example, superabsorbent particles as a coform.
In accordance with one embodiment of this invention, a support structure is attached to at least one face of the nonwoven web so as to provide strength thereto. The resulting laminate structure provides support for the high loft structure, strength for winding, converting, etc., and a boundary layer to either enhance or retard fluid flow into the lofty absorbent structure. The support structure may include spunbond webs of various types including liners, perforated, micro-fiber, creped, etc., spunbond-meltblown-spunbond (SMS), meltblown, and/or films.
As used herein, the term “coform” means a process in which at least one meltblown diehead is arranged near a chute through which other materials are added to the web while it is forming. Such other materials may be pulp, superabsorbent particles, cellulose or staple fibers, for example. Coform processes are shown in commonly assigned U.S. Pat. No. 4,818,464 to Lau.
In a method for producing a lofty, nonwoven material in accordance with one embodiment of this invention,
In accordance with the embodiment shown in
Although shown as a combination of drum former 16 and forming surface 18, it will be apparent to those skilled in the art that variable nip 19 may be formed by other means, such as two drum formers, two opposed moving belts, etc.
In order to vary the 3-dimensional structure of the nonwoven web for a given fiber, the relative speeds of the drum former 16 and moving forming surface 18, as well as the height of the nip, and amount of vacuum may be varied. In accordance with one preferred embodiment of this invention, the speed of rotation of drum former 16 corresponds to the speed at which moving forming surface 18 is traveling. In accordance with another preferred embodiment of this invention, the speed at which drum former 16 is rotating is different from the speed of travel of moving forming surface 18. After forming in variable nip 19, the nonwoven web is integrally fixed, i.e., its structure is set by a hot air knife, adhesive, a calender, through-air-bonding unit, or the like and without laminate additions.
In accordance with one preferred embodiment of this invention, laminate structures are produced by unwinding and/or alternately producing and introducing one or more fabrics to be formed upon the web of the present invention. By either unwinding onto drum former 16 and/or web forming surface 18, applying adhesive in one or more possible places, and forming the lofty, nonwoven web as described hereinabove, a multi-layer laminate structure can be produced.
The loft and density of the nonwoven web produced in accordance with the method of this invention is defined in part by the distance between the two opposed surfaces 32, 33. The density of the nonwoven web may be controlled by adjustment of the speed at which the nonwoven web passes through slot 35 and/or by varying the width of slot 35. Slot 35 may be a fixed plate slot, but the dual wire system shown in
As stated above, spunbond and meltblown fibers can be used to produce the high loft nonwoven web of this invention. Single component (homofilament), bicomponent and biconstituent fibers can be used. Bicomponent fibers are preferred in accordance with one embodiment of this invention because they have the advantage that thermal bonding fiber crimp can be used to enhance lofty material properties. The fibers can also be either quenched (rapidly cooled), in which case the outer surface of the fibers is solidified, or unquenched in which case the outer surface of the fibers remains tacky. Unquenched fibers have the advantage of bonding to each other without a further bonding requirement. Thermoplastic fibers can be through-air bonded in a stuffed through-air bonder unit symbolically shown as arrow 36 in
Referencing
The fabric of
As seen in
While in the foregoing specification this invention has been described in relation to certain preferred embodiments thereof, and many details have been set forth for purpose of illustration, it will be apparent to those skilled in the art that the invention is susceptible to additional embodiments and that certain of the details described herein can be varied considerably without departing from the basic principles of the invention.
This application is a divisional application of U.S. patent application Ser. No. 09/537,564, filed 30 Mar. 2000 now U.S. Pat. No. 6,588,080, published Jul. 8, 2003.
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Child | 10463945 | US |