Patent Application
20140358101
The business of manufacturing and marketing disposable absorbent articles for personal care or hygiene (such as disposable diapers, training pants, adult incontinence undergarments, feminine hygiene products, breast pads, care mats, bibs, wound dressing products, and the like) is relatively capital intensive and highly competitive. To maintain or grow their market share and thereby maintain a successful business, manufacturers of such articles must continually strive to enhance their products in ways that serve to differentiate them from those of their competitors, while at the same time controlling costs so as to enable competitive pricing and the offering to the market of an attractive value-to-price proposition.
One way in which some manufacturers may seek to enhance such products is through enhancements to softness. Parents and caregivers naturally seek to provide as much comfort as they can for their babies, and utilizing products such as disposable diapers that they perceive as relatively soft provides reassurance that they are doing what they can to provide comfort in that context. With respect to other types of disposable absorbent articles that are designed to be applied and/or worn close to the skin, an appearance of softness can reassure the wearer or caregiver that the article will be comfortable.
Thus, manufacturers may devote efforts toward enhancing the softness of the various components used to make such articles, such as various web materials, including nonwoven web materials formed from polymer fibers, and laminates thereof, forming the articles. Such laminates may include, for example, laminates of polymer films and nonwoven web materials forming the backsheet components of the articles.
It is believed that humans' perceptions of softness of a nonwoven web material can be affected by tactile signals, auditory signals and visual signals.
Tactile softness signals may be affected by a variety of the material's features and properties that have effect on its tactile feel, including hut not limited to loft, fiber shape, thickness and density, basis weight, microscopic pliability and flexibility of individual fibers, macroscopic pliability and flexibility of the nonwoven web as formed by the fibers, surface friction characteristics, number of loose fibers or free fiber ends, and other features.
Among materials commonly used for manufacturing nonwoven web materials to be used as components of absorbent articles, polypropylene and polyethylene resins are predominant, for reasons of cost, availability, and amenability to processing, i.e., fiber spinning. Between fibers of equal size formed of these two types of polymers, polypropylene fibers tend to have comparatively greater mechanical strength and stiffness, and tend to exhibit comparatively higher coefficients of friction (i.e., tend to have a less slippery feel) with the skin. By comparison, polyethylene fibers tend to have comparatively less mechanical strength and stiffness (i.e., more pliability), and tend to exhibit comparatively lower coefficients of friction (i.e., have a more slippery feel) with the skin. Additionally, fibers formed of polyethylene tend to impart a relatively greater degree of visible and tactilely perceptible “fuzz” to a nonwoven web, as a result of comparatively lower fiber and bond strength.
When these fibers are used to form a nonwoven web, they will impart these attributes to the web. Thus, in forming nonwoven web materials, various attempts have been made to impart desirable characteristics of polypropylene and polyethylene components, while compensating for the shortcomings of each. Generally, mechanical strength of the nonwoven web material is desired for dimensional stability in processing in the manufacture of articles, and to impart structural strength to the articles, in which the web material is a component. Pliability and a lower coefficient of friction a may be desired for a pliant and silky feel, and good drape, contributing to perceptions of tactile softness.
An additional factor affecting the relative proportions of each polymer type that may be used is cost. It is believed that, historically, fibers comprising polyethylene resin have tended to be more expensive to produce than those made from polypropylene resin.
While attempts to manufacture nonwoven web materials in various configurations to find a balance of desirable attributes from these and other materials have achieved some success to date, there is always room for improvement.
a is a schematic side elevation view depicting equipment and components in a process for manufacturing a nonwoven web.
b is a schematic side elevation view depicting equipment and components in a process for hydrojetting a nonwoven web.
“Absorbent article” refers to devices that absorb and contain body exudates, and, more specifically, refers to devices that are placed against or in proximity to the body of the wearer to absorb and contain the various exudates discharged from the body. Absorbent articles may include diapers, training pants, adult incontinence undergarments and pads, feminine hygiene products, breast pads, care mats, bibs, wound dressing products, and the like. As used herein, the term “exudates” includes, but is not limited to, urine, blood, vaginal discharges, breast milk, sweat and fecal matter.
“Absorbent core” means a structure typically disposed between a topsheet and backsheet of an absorbent article for absorbing and containing liquid received by the absorbent article. The absorbent core may also include a cover layer or envelope. The cover layer or envelope may comprise a nonwoven. In some examples, the absorbent core ma include one or more substrates, an absorbent polymer material, and a thermoplastic adhesive material/composition adhering and immobilizing the absorbent polymer material to a substrate, and optionally a cover layer or envelope.
“Bicomponent” refers to fiber having across-section comprising two discrete polymer components, two discrete blends of polymer components, or one discrete polymer component and one discrete blend of polymer components. “Bicomponent fiber” is encompassed within the term “Multicomponent fiber.” A Bicomponent fiber may have an overall cross section divided into two or more subsections of the differing components of any shape or arrangement, including, for example, coaxial subsections, core-and-sheath subsections, side-by-side subsections, radial subsections, etc.
“Film”—means a skin-like or membrane-like layer of material formed of one or more polymers, which does not have a form consisting predominately of a web-like structure of consolidated polymer fibers and/or other fibers.
“Like chemistry,” with respect to two structures formed of polymeric material(s), means that the respective polymeric material(s) of the two structures is/are capable of mixing together at a temperature of 300° C. or lower, to form a mixture that behaves as a single thermodynamic phase.
“Monocomponent” refers to fiber formed of a single polymer component or single blend of polymer components, as distinguished from Bicomponent or Multicomponent fiber.
“Multicomponent” refers to fiber having a cross-section comprising more than one discrete polymer component, more than one discrete blend of polymer components, or at least one discrete polymer component and at least one discrete blend of polymer components. “Multicomponent fiber” includes, but is not limited to, “Bicomponent fiber.” A Multicomponent fiber may have an overall cross section divided into subsections of the differing components of any shape or arrangement, including, for example, coaxial subsections, core-and-sheath subsections, side-by-side subsections, radial subsections, etc.
A “nonwoven” or “nonwoven web” is a manufactured sheet or web of directionally or randomly oriented fibers, consolidated and thermally, mechanically or chemically bonded together by friction, fusion, cohesion, hydrogen-bonding, adhesion, or one or more patterns of bonds and bond impressions created through localized compression and/or application of heat or heating energy, or a combination thereof. The term does not include fabrics which are woven, knitted, or stitch-bonded with yarns or filaments. The fibers may be of natural or man-made origin and may be staple or continuous filaments or be formed in situ. Commercially available fibers have diameters ranging from less than about 0.001 mm to more than about 0.2 mm and they come in several different forms: short fibers (known as staple, or chopped), continuous single fibers (filaments or monofilaments), untwisted bundles of continuous filaments (tow), and twisted bundles of continuous filaments (yarn). The size of the fibers in cross section, which may be substantially circular or non-circular, can also be expressed in denier and ranges from 0.001 denier to 400 denier, or more typically from 0.001 denier to 10 denier. Nonwoven fabrics can be formed by many processes such as meltblowing, spunbonding, solvent spinning, electrospinning, and carding, and bonding using thermal, chemical and mechanical means (e.g., calendering, hydro-entangling, and air-thru-bonding). The basis weight of nonwoven fabrics is usually expressed in grams per square meter (gsm)
As noted in the Background, generally, polyethylene fibers tend to have a more slippery tactile feel than polypropylene fibers. They also tend to be more pliable, and possess less mechanical (tensile) strength. Thus, it may be desirable to form a web having a surface layer formed of polyethylene fibers to impart a slippery, silky feel to the web. Such a layer, however, may be more susceptible to fraying and pilling (formation of small tangled balls or rolls of fibers) with rubbing wear such as may be encountered, for example, by the outer cover of a disposable diaper during wear. Fraying and pilling may undesirably lead to consumer perceptions of poor quality, and structural weakening of the material.
Referring to
The web also may have a second outer accumulation of second fibers 120. The second fibers 120 also may be formed of one or more polymers such as polypropylene, selected to impart desirable attributes such as mechanical strength to the web.
The first and second outer accumulations of respective first and second fibers 110, 120, may be disposed in such a manner as to form respective first and second oppositely-facing macroscopic web outer surfaces 112, 122.
An inner accumulation of third fibers 130 may be included, and may be disposed, to some extent, approximately between the first and second outer accumulations. Through appropriate processing such as described below, third fibers from the inner accumulation of fibers 130 may further be interlaced among the first and second fibers, and may protrude outwardly from the macroscopic web surfaces 112, 122.
The third fibers 130 may be formed entirely of polyethylene, or may include polyethylene components, such that they include surfaces of polyethylene with a desirable slippery feel. In one example, the third fibers 130 may in bicomponent fibers having polyethylene components. The bicomponent fibers may have any suitable configuration by which the polyethylene component is present at, or forms, outer surfaces of the fibers. For example, bicomponent fibers may have a side-by-side arrangement in which polyethylene forms one longitudinal side and longitudinal portion of the outer surface of the fiber. In another example, bicomponent fibers may have a sheath-core arrangement in which polyethylene forms an outer sheath about a core formed of the second component. The second component of the bicomponent fiber may be polypropylene, but may also be another polymer or blend of polymers suitably selected.
The nonwoven web material 105 may bear an impressed pattern of thermal bonds 140. The bonds may be formed by passing a butt of fibers through the nip between a pair of calender/bonding rollers. At least one of the rollers may have formed on its cylindrical rolling surface a pattern of bonding protrusions and recessed areas, where the bonding protrusions are shaped and arranged so as to impress the desired pattern of thermal bonds, with the desired shape(s) in the nonwoven web material. At least one of the rollers may be supplied with heating energy, so that heat wilt be transferred from the roller(s) to the fibers and cause them to melt and at least partially fuse beneath the bonding protrusions, as the batt passes through the nip.
Thus, in the example depicted in
Other selections of polymers to achieve similar effects can be made. The main polymer component of the first and second fibers can be selected from the general class of polypropylenes, particularly isotactic polypropylenes with a typical fiber-grade melt-flow rate such as ranging from, for example, 10 to 50 g/10 min MFR. They may be isotactic PP created with Ziegler-Natta-type catalysts or from metalocene catalysts, commonly abbreviated zn- or m-type i-PP. The third fibers may contain polymer components with a relatively lower softening or melting point than first or second fibers, and can be selected from polyethylene, ethylene-propylene copolymers, or from polypropylenes with lower isotacticity, such as syndiotactic or less stereo-regular polypropylenes; all of which achieves a lower softening and melting point while at the same time providing for a more slippery tactile property on the fiber surface.
The compositions may also include other additives like anti-oxidant packages, pigments and dyes, etc.
An appropriately configured pattern of thermal bonds 140 may serve to cause the first fibers 110 and second fibers 120 to form outer networks of bonded fibers that tend to contain and restrain third fibers 130. At the same time, as explained further below, third fibers 130 may be caused to be interlaced among the first fibers 110 and second fibers 120, and to protrude through the outer macroscopic surfaces formed thereby, so as to be exposed for purposes of imparting a slippery, silky tactile feel to the nonwoven web material.
It is not necessary that the layered accumulations of first fibers 110 and second fibers 120 are similar or identical in loft or thickness, basis weight, fiber size, fiber cross-sectional shape, fiber longitudinal shape, fiber directional bias or orientation, or fiber material composition. For example, the accumulation of second fibers 120 may have a greater density or number of fibers per unit area or unit volume, differently sized fibers, differently shaped fibers, fibers of different composition, etc., compared with the accumulation of first fibers 110. It is preferred, however, that first fibers 110 and second fiber 120 or at least components thereof have like chemistry such that the fibers 110, 120 or portions thereof will readily fuse and form robust bonds at bond sites 142.
a schematically illustrates an example of equipment configuration and a process by which the nonwoven web material schematically depicted in
Following spinning, the second combination batt 134 may be conveyed into the nip between a pair of calender/bonding rollers 208, 210. One or both of the rollers 208, 210 may be supplied with heating energy, so as to be transferred to the fibers in the nip. One or both of the rollers 208, 210 may have formed on the cylindrical rolling surface thereof a pattern of shaped bonding protrusions and recessed areas, such that a like pattern of bonds of like shapes is impressed on the second combination batt 134 as it passes through the nip. Heating energy may be supplied to an extent sufficient to cause melting and fusing of the first and second fibers 110, 120. As a result, a consolidated and bonded web 150, bearing bonds 140, exits the nip.
Next, the bonded web 150 may be conveyed past one or more banks of jets 214 which direct jets 216 of water at the web. (Variants of this process have been called, e.g., “hydrojetting,” “hydroneedling,” “hydroenhancing,” “hydroentangling,” and “hydroengorging.” Examples are described in U.S. Pat. Nos. 6,632,385; 6,803,103; 7,858,544; and RE40,362, and U.S. App. Pub. No. 20120179126.) As the web is conveyed past the jets, it may be carried and supported by a suitable belt 212 formed of a permeable mesh. When the water jets 216 impinge the fibers of the bonded web 150, they can displace and tease the fibers and thereby cause the third fibers 130 to be interlaced among the first fibers 110 and second fibers 120. With suitable configurations of jets 214 and water pressures, third fibers 130 may be pushed between and/or among first fibers 110 and/or second fibers 120 and outwardly, to an extent that they are present at the macroscopic web surfaces 112, 122 formed by the first fibers 110 and second fibers 120. In the configuration suggested in
In another alternative, however, the web 150 may be exposed to hydro jetting on both sides, to displaces some of third fibers 130 toward both macroscopic surfaces. As suggested in
Such a hydrojetting step may be employed to displace third fibers 130 within the web such that they are desirably interlaced between and/or among the first fibers 110 and/or second fibers 120, extend through the layers thereof, and are present and exposed to the touch at the first and/or second macroscopic surfaces 112, 122, in a bonded, hydrojetted nonwoven web material as suggested in
In another alternative, jets of fluid other than water may be directed at the web 150 to displace fibers therewithin and drive fibers inside the fiber matrix among and between other fibers, to cause them to be interlaced therewith and to be present at a macroscopic surface. Jets of gas such but not limited to air may be employed.
In still another alternative, a needlepunching process may be employed to displace fibers within the web structure. Needlepunching involves pushing banks of needles, having forward-oriented barb structures, through the web, in a direction transverse or orthogonal to a macroscopic surface thereof. As the needles advance through the web, the barb structures catch some of the individual fibers within the web and carry them along therewith as the needles advance, driving the caught fibers forward between and among the other fibers in the web, and toward the macroscopic surface facing away from the distal ends of the needles. Needlepunching processes are described in, for example, U.S. Pat. App. Pub. No. 2013/0067706.
In still another alternative, a tufting process as described in, for example, U.S. Pat. No. 7,553,532, may be employed to displace fibers in an interior layer toward or to an outer macroscopic surface.
It may be noted that thermal bonding and the resulting bonds have the effect of partially locking fibers in place within the web, making it more difficult to displace fibers within the bonded web by hydrojetting or other fiber displacing technique described above, without breaking the bonds and losing some of the benefits of bonding and/or the desirable mechanical strength of the web. In other words, in some circumstances, energy sufficient to displace fibers from an inner layer to the outer macroscopic surfaces may also be sufficient to substantially alter the bonded structure of the web and degrade its mechanical properties (e.g., tensile strength).
However, if the third fibers 130 are formed of a material that has greater ductility than first fibers 110 and/or second fibers 120, when impinged and pushed by hydrojetting or other displacing mechanism they can plastically deform (lengthen) within the web structure to extend out to the macroscopic surfaces, under energy that is not so great as will substantially degrade the web structure. Since polythylene-based resins are generally more ductile than polypropylene-based resins, forming first and second (e.g., outer) layers of fibers 110, 120 of polypropylene and a third layer of fibers 130 of polyethylene is believed advantageous and thereby suitable for purposes herein. Other combinations of resins having suitable properties and relationships of properties, however, are contemplated, in which outer layers of fiber hafts have a first ductility and one or more inner layers of fiber bans have a second, higher ductility. Both displacement and reorientation of fibers (in the thickness direction) as well as a permanent stretching deformation of the fibers or portions of the third fibers are possible mechanisms that lead to the desired effect of having softer-feeling fibers present at a macroscopic surface, white still having them contained and restrained so as not to be subject to undesirable fuzzing and/or pilling.
The enhanced nonwoven web as described herein, and formed as described herein, may be used to form a component of an absorbent article, such as a diaper. For example, the nonwoven web may be used to form a topsheet, leg cuffs and/or backsheet. The nonwoven web may be used as an outer/outward-facing layer of a backsheet, wherein the backsheet is formed of a laminate having layers including a liquid-impermeable film and the nonwoven web.
The enhanced nonwoven web described herein may be hydrophobic or hydrophilic depending on the application and desired functions. When polyolefins are the materials used to form the respective fibers, no further surface treatment is required to make it suitable for use in applications where hydrophobicity is desired, e.g., a hydrophobic backsheet material, or hydrophobic cuff material. When hydrophilicity is desired, however, e.g., when the web is to be used as a topsheet material for a diaper or feminine hygiene pad, the web may be treated with a hydrophilic topical application. Alternatively, hydrophilic melt additive can be added to the polymer resin(s) from which the fibers forming the web are spun.
The diaper 10 generally may comprise a chassis 12 and an absorbent core 14 disposed in the chassis. The chassis 12 may comprise the main body of the diaper 10.
The chassis 12 may include a topsheet 18, which may be liquid pervious, and a backsheet 20, which may be liquid impervious. The absorbent core 14 may be encased between the topsheet 18 and the backsheet 20. The chassis 12 may also include side panels 22, elasticized leg cuffs 24, and an elastic waist feature 26. The chassis 12 may also comprise a fastening system, which may include at least one fastening member 46 and at least one landing zone 48.
The leg cuffs 24 and the elastic waist feature 26 may each typically comprise elastic members 28. One end portion of the diaper 10 may be configured as a first waist region 30 of the diaper 10. An opposite end portion of the diaper 10 may be configured as a second waist region 32 of the diaper 10. An intermediate portion of the diaper 10 may be configured as a crotch region 34, which extends longitudinally between the first and second waist regions 30 and 32. The crotch region 34 may include from 33.3% to 50% of the overall length of the diaper 10, and each of waist regions 30, 32 may correspondingly include from 25% to 33.3% of the overall length of the diaper 10.
The waist regions 30 and 32 may include elastic elements such that they gather about the waist of the wearer to provide improved fit and containment (elastic waist feature 26). The crotch region 34 is that portion of the diaper 10 which, when the diaper 10 is worn, is generally positioned between the wearer's legs.
The diaper 10 may also include such other features including front and rear ear panels, waist cap features, elastics and the like to provide better tit, containment and aesthetic characteristics. Such additional features are described in, e.g., U.S. Pat. Nos. 3,860,003 and 5,151,092.
In order to apply and keep diaper 10 in place about a wearer, the second waist region 32 may be attached by the fastening member 46 to the first waist region 30 to form leg opening(s) and an article waist. When fastened, the fastening system carries a tensile load around the article waist.
According to some examples, the diaper 10 may be provided with a re-closable fastening system or may alternatively be provided in the form of a pant-type diaper. When the absorbent article is a diaper, it may comprise a re-closable fastening system joined to the chassis for securing the diaper to a wearer. When the absorbent article is a pant-type diaper, the article may comprise at least two side panels joined to the chassis and to each other to form a pant. The fastening system and any component thereof may include any material suitable for such a use, including but not limited to plastics, films, foams, nonwoven, woven, paper, laminates, stretch laminates, activated stretch laminates, fiber reinforced plastics and the like, or combinations thereof. In some examples, the materials making up the fastening device may be flexible. In some examples, the fastening device may comprise cotton or cotton-like materials for additional softness or consumer perception of softness. The flexibility may allow the fastening system to conform to the shape of the body and thus, reduce the likelihood that the fastening system will irritate or injure the wearer's skin.
For unitary absorbent articles, the chassis 12 and absorbent core 14 may form the main structure of the diaper 10 with other features added to form the composite diaper structure. While the topsheet 18, the backsheet 20, and the absorbent core 14 may be assembled in a variety of well-known configurations, preferred diaper configurations are described generally in U.S. Pat. No. 5,554,145 entitled “Absorbent Article With Multiple Zone Structural Elastic-Like Film Web Extensible Waist Feature” issued to Roe et al. on Sep. 10, 1996; U.S. Pat. No. 5,569,234 entitled “Disposable Pull-On Pant” issued to Buell et al. on Oct. 29, 1996; and U.S. Pat. No. 6,004,306 entitled “Absorbent Article With Multi-Directional Extensible Side Panels” issued to Robles et al. on Dec. 21, 1999.
The topsheet 18 may be fully or partially elasticized and/or may be foreshortened to create a void space between the topsheet 18 and the absorbent core 14. Exemplary structures including elasticized or foreshortened topsheets are described in more detail in U.S. Pat. No. 5,037,416 entitled “Disposable Absorbent Article Having Elastically Extensible Topsheet” issued to Allen et al. on Aug. 6, 1991; and U.S. Pat. No. 5,269,775 entitled “Trisection Topsheets for Disposable Absorbent Articles and Disposable Absorbent Articles Having Such Trisection Topsheets” issued to Freeland et al. on Dec. 14, 1993. In some examples, the topsheet 18 may be formed of an enhanced nonwoven web 105 as described above.
The backsheet 20 may be joined with the topsheet 18. The backsheet 20 may serve prevent the exudates absorbed by the absorbent core 14 and contained within the diaper 10 from soiling other external articles that may contact the diaper 10, such as bed sheets and clothing. Reining to
Suitable backsheet films include those manufactured by Tredegar Industries Inc. of Terre Haute, Ind. and sold under the trade names X15306, X10962, and X10964. Other suitable backsheet materials may include breathable materials that permit vapors to escape from the diaper 10 while still preventing liquid exudates from passing through the backsheet 20. Exemplary breathable materials may include materials such as woven webs, nonwoven webs, composite materials such as film-coated nonwoven webs, and microporous films such as manufactured by Mitsui Toatsu Co., of Japan under the designation ESPOIR and by EXXON Chemical Co., of Bay City, Tex., under the designation EXXAIRE. Suitable breathable composite materials comprising polymer blends are available from Clopay Corporation, Cincinnati, Ohio under the name HYTREL blend Pl 8-3097. Other examples of such breathable composite materials are described in greater detail in PCT Application No. WO 95/16746, published on Jun. 22, 1995 in the name of E. I. DuPont. Other breathable backsheets including nonwoven webs and apertured formed films are described in U.S. Pat. No. 5,571,096 issued to Dobrin et al. on Nov. 5, 1996.
In some examples, the backsheet of the present invention may have a water vapor transmission rate (WVTR) of greater than about 2,000 g/24 h/m2, greater than about 3,000 g/24 h/m2, greater than about 5,000 g/24 h/m2, greater than about 6,000 g/24 h/m2, greater than about 7,000 g/24 h/m2, greater than about 8,000 g/24 h/m2, greater than about 9,000 g/24 h/m2, greater than about 10,000 g/24 h/m2, greater than about 11,000 g/24 h/m2, greater than about 12,000 g/24 h/m2, greater than about 15,000 g/24 h/m2, measured according to WSP 70.5 (08) at 37.80 C. and 60% Relative Humidity.
The dimensions and values disclosed herein are not to be understood as being strictly limited to the exact numerical values recited. Instead, unless otherwise specified, each such dimension is intended to mean both the recited value and a functionally equivalent range surrounding that value. For example, a dimension disclosed as “40 mm” is intended to mean “about 40 mm.”
Every document cited herein, including any cross referenced or related patent or application, is hereby incorporated herein by reference in its entirety unless expressly excluded or otherwise limited. The citation of any document is not an admission that it is prior art with respect to any invention disclosed or claimed herein or that it alone, or in any combination with any other refer′ cc or references, teaches, suggests or discloses any such invention. Further, to the extent that any meaning or definition of a term in this document conflicts with any meaning or definition of the same term in a document incorporated by reference, the meaning or definition assigned to that term in this document shall govern.
While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention,
