Patent Grant
7670665
This invention relates to body facing layers of disposable absorbent articles such as sanitary napkins. In particular, this invention relates to topsheets having improved fluid handling properties.
Disposable absorbent articles such as disposable diapers, incontinence products, catamenial products and the like are widely used, and much effort has been made to improve the effectiveness and functionality of these articles. In general such articles have a fluid permeable body-facing layer, often referred to as a topsheet, a fluid impermeable garment-facing layer, often referred to as a backsheet, and an absorbent core sandwiched between the topsheet and the backsheet. Other components, such as acquisition layers, secondary topsheets, and adhesive fasteners are also well known in the art.
Conventional body-facing layers, i.e., topsheets, used in disposable absorbent typically exhibit a tradeoff between improved acquisition of gushes of fluid and improved dryness. For example, topsheets can be made relatively hydrophilic to quickly wet out and acquire gushes of fluid, but this same relative hydrophilicity causes the topsheet to feel wet next to the wearer's skin, i.e., dryness is compromised. Various material and component structures have been proposed in the past to provide for either improved gush acquisition or improved rewet, but the properties have remained linked, one being inversely proportional to the other.
It is known that providing for a certain amount of compression-resistant thickness, or caliper, in a topsheet aids in reducing rewet. For example, three-dimensional formed film topsheets such as those known as DRI-WEAVE® topsheets on ALWAYS® sanitary napkins marketed by The Procter & Gamble Co. are known to provide for low rewet, i.e., better dryness, compared to typical nonwoven topsheets. However, some consumers express a dislike for polymer film topsheets and prefer topsheets made of nonwoven materials.
Furthermore, known topsheets typically are not designed specifically for absorption of high viscosity fluids such as runny bowel movements, wound exudates, blood, and menses. As a result, typical topsheets can leak, stain, and contribute to poor skin health due to prolonged contact with the wearer's skin.
Accordingly, there is a need for an improved topsheet for a disposable absorbent article capable of providing for high gush acquisition rates and yet also providing for improved dryness.
Additionally, there is a need an improved topsheet for a disposable absorbent article capable of providing for high gush acquisition rates and yet also providing for improved dryness that is comfortable to the wearer.
Finally, there is a need for a method of relatively inexpensively making a topsheet for a disposable absorbent article capable of providing for high gush acquisition rates and yet also providing for improved dryness.
An absorbent article having a topsheet, a backsheet, and an absorbent core disposed between the topsheet and the backsheet. The topsheet has a first side and a second side, the first side being a body-facing side. The topsheet defines a CD-MD plane and includes a fibrous nonwoven web and tufts, the tufts having fibers of the fibrous nonwoven web. The topsheet further includes first, second and third zones, each zone being characterized in a Z-direction by the zone fiber orientation, wherein the first and third zones are displaced relative to each other and each include fibers having portions orientated substantially parallel to said CD-MD plane of the topsheet. The second zone is intermediate and adjacent to the first and third zones, the second zone including substantially reoriented fibers that are substantially vertically oriented with respect to the CD-MD plane of said topsheet.
Web 1 has a first side 3 and a second side 5, the term “sides” being used in the common usage of generally planar two-dimensional webs, such as paper and films that have two sides when in a generally flat condition. Each precursor web 20 and 21 has a first surface 12 and 13, respectively, and a second surface 14 and 15, respectively (shown in
In one embodiment, first side 3 of web 1 is defined by exposed portions of the first surface 13 of second precursor web 21 and at least one, but preferably a plurality of, discrete tufts 6 which are integral extensions of the fibers of a nonwoven first precursor web 20. Each tuft 6 can comprise a plurality of looped, aligned fibers 8 extending through second precursor web 21 and outwardly from the first surface 13 thereof. In another embodiment each tuft 6 can comprise a plurality of non-looped fibers 18 (as shown in
As used herein, the term “nonwoven web” refers to a web having a structure of individual fibers or threads which are interlaid, but not in a repeating pattern as in a woven or knitted fabric, which do not typically have randomly oriented fibers. Nonwoven webs or fabrics have been formed from many processes, such as, for example, meltblowing processes, spunbonding processes, spunlacing processes, hydroentangling, airlaying, and bonded carded web processes, including carded thermal bonding. The basis weight of nonwoven fabrics is usually expressed in grams per square meter (gsm). The basis weight of the laminate web is the combined basis weight of the constituent layers and any other added components. Fiber diameters are usually expressed in microns; fiber size can also be expressed in denier, which is a unit of weight per length of fiber. The basis weight of laminate webs suitable for use in an article of the present invention can range from 10 gsm to 100 gsm, depending on the ultimate use of the web 1.
The constituent fibers of nonwoven precursor webs 20 and/or 21 can be polymer fibers as known in the art. The fibers can be monocomponent, bicomponent, and/or biconstituent, non-round (e.g., capillary channel fibers), and can have major cross-sectional dimensions (e.g., diameter for round fibers) ranging from 0.1-500 microns. The constituent fibers of the nonwoven precursor webs may also be a mixture of different fiber types, differing in such features as chemistry (e.g. PE and PP), components (mono- and bi-), shape (i.e. capillary channel and round) and the like. The constituent fibers can range from about 0.1 denier to about 100 denier.
As used herein, “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 with the diameter of the extruded filaments then being rapidly reduced. Spunbond fibers are generally not tacky when they are deposited on a collecting surface. Spunbond fibers are generally continuous and have average diameters (from a sample of at least 10) larger than 7 microns, and more particularly, between about 10 and 40 microns.
As used herein, the term “meltblowing” refers to a process in which fibers are 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, usually heated, gas (for example air) streams which attenuate the filaments of molten thermoplastic material to reduce their diameter, which may be to microfiber diameter. Thereafter, the meltblown fibers are carried by the high velocity gas stream and are deposited on a collecting surface, often while still tacky, to form a web of randomly dispersed meltblown fibers. Meltblown fibers are microfibers which may be continuous or discontinuous and are generally smaller than 10 microns in average diameter.
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. In addition, unless otherwise specifically limited, the term “polymer” includes all possible geometric configurations of the material. The configurations include, but are not limited to, isotactic, atactic, syndiotactic, and random symmetries.
As used herein, the term “monocomponent” fiber refers to a fiber formed from one or more extruders using 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, antistatic properties, lubrication, hydrophilicity, etc. These additives, for example titanium dioxide for coloration, are generally present in an amount less than about 5 weight percent and more typically about 2 weight percent.
As used herein, the term “bicomponent fibers” refers to fibers which have been formed from at least two different 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. The polymers are arranged in substantially constantly positioned distinct zones across the cross-section of the bicomponent fibers and extend continuously along the length of the bicomponent fibers. The configuration of such a bicomponent fiber may be, for example, a sheath/core arrangement wherein one polymer is surrounded by another, or may be a side-by-side arrangement, a pie arrangement, or an “islands-in-the-sea” arrangement.
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. Biconstituent fibers do not have the various polymer components arranged in relatively constantly positioned distinct zones across the crosssectional area of the fiber and the various polymers are usually not continuous along the entire length of the fiber, instead usually forming fibrils which start and end at random. Biconstituent fibers are sometimes also referred to as multiconstituent fibers.
As used herein, the term “non-round fibers” describes fibers having a non-round cross-section, and include “shaped fibers” and “capillary channel fibers” as are known in the art. Such fibers can be solid or hollow, and they can be tri-lobal, delta-shaped, and are preferably fibers having capillary channels on their outer surfaces. The capillary channels can be of various cross-sectional shapes such as “U-shaped”, “H-shaped”, “C-shaped” and “V-shaped”. One preferred capillary channel fiber is T-401, designated as 4DG fiber available from Fiber Innovation Technologies, Johnson City, Tenn. T-401 fiber is a polyethylene terephthalate (PET).
As used herein, the term “integral” as in “integral extension” when used of the tufts 6 refers to fibers of the tufts 6 having originated from the fibers of the precursor webs 20 and/or 21. Therefore, the looped fibers 8 and non-looped fibers 18 of tufts 6, can be plastically deformed and extended fibers of the first precursor web 20, and are, therefore, integral with first precursor web 20. Similarly, for embodiments wherein second precursor web 21 is a nonwoven comprising similarly extensible fibers, the fibers of second precursor web 21 can contribute to tufts 6. As used herein, “integral” is to be distinguished from fibers introduced to or added to a separate precursor web for the purpose of making tufts, as is commonly done in conventional carpet making, for example.
The number, spacing, and dimensions of tufts 6 can be varied to give varying texture to first side 3 of web 1. For example, if tufts 6 are sufficiently closely spaced the first side 3 of web 1 can have a terry cloth-like feel. Alternatively, tufts 6 can be arranged in patterns such as lines or filled shapes to create portions of a laminate web having greater texture, softness, bulk, absorbency or visual design appeal. For example, when tufts 6 are arranged in a pattern of a line or lines, the tufts can have the appearance of stitching. Tufts 6 can also be arranged to form specific shapes, such as designs, words or logos. Likewise, the size dimensions, such as the height, length and width of individual tufts 6 can be varied. Single tufts can be as long as about 3 cm in length and can be made alone or dispersed among tufts of various sizes.
First precursor web 20 can be a fibrous woven or nonwoven web comprising fibers having sufficient elongation properties to have portions formed into tufts 6. As described more fully below, tufts are formed by urging fibers out-of-plane in the Z-direction at discrete, localized, portions of first precursor web 20. The urging out-of-plane can be due to fiber displacement, i.e., the fiber is able to move relative to other fibers and be “pulled,” so to speak, out-of-plane. More often, however, for most nonwoven first precursor webs 20, the urging out-of-plane is due to the fibers of tufts 6 having been at least partially plastically stretched and permanently deformed to form tufts 6. Therefore, in one embodiment, depending on the desired height of tufts 6, the constituent fibers of a nonwoven first precursor webs 20 can exhibit an elongation to break of at least about 5%, more preferably at least about 10%, more preferably at least about 25%, more preferably at least about 50%, and more preferably at least about 100%. Elongation to break can be determined by simple tensile testing, such as by use of Instron tensile testing equipment, and can generally be found on material data sheets from suppliers of such fibers or webs.
It can be appreciated that a suitable nonwoven first precursor web 20 should comprise fibers capable of experiencing sufficient plastic deformation and tensile elongation, or are capable of sufficient fiber mobility, such that looped fibers 8 are formed. However, it is recognized that a certain percentage of fibers urged out of the plane of the first surface 12 of first precursor web 20 will not form a loop, but instead will break and form loose ends. Such fibers are referred to herein as “loose” fibers or “loose fiber ends” 18 as shown in
First precursor web 20 can be a fibrous woven or nonwoven web comprising elastic or elastomeric fibers. Elastic or elastomeric fibers can be stretched at least about 50% and return to within 10% of their original dimension. Tufts 6 can be formed from elastic fibers if the fibers are simply displaced due to the mobility of the fiber within the nonwoven, or if the fibers are stretched beyond their elastic limit and are plastically deformed.
For use as a topsheet in the present invention, first precursor web 20 can be relatively hydrophilic compared to second precursor web 21. In a preferred embodiment first precursor web 20 is also hydrophilic compared to the skin of the wearer of an article of the present invention. In this manner, fluid in contact with the topsheet of the present invention can be wetted out onto the fibers of first precursor web, conducted by capillarity action through the openings 4 of the second precursor web 21 to underlying components of an article of the present invention. While actual measures of hydrophilicity or hydrophobicity are not considered to be critical (only relative hydrophilicity/hydrophobicity between the first precursor web 20 and the second precursor web 21), in general, first precursor web 20 can be considered hydrophilic if it exhibits a contact angle with water of less than about 70 degrees. If first precursor web is not naturally hydrophilic (i.e., the polymer properties are not hydrophilic), it can be rendered hydrophilic by methods known in the art, for example, by application of a surfactant to the fibers and/or the web.
Second precursor web 21 can be virtually any web material, the only requirement being that it be less hydrophilic, and even hydrophobic relative to first precursor web 20, and that it have sufficient integrity to be formed into a laminate by the process described below. In one embodiment, second precursor web can be a film or a nonwoven web having sufficiently less elongation properties relative to first precursor web 20, such that upon experiencing the strain of fibers from first precursor web 20 being urged out-of-plane in the direction of second precursor web 21, second precursor web 21 will rupture, e.g., by tearing due to extensional failure, such that portions of first precursor web 20 can extend through, (i.e., “punch through” so to speak), second precursor web 21 to form tufts 6 on first side 3 of web 1, as shown in
A representative tuft 6 for the embodiment of web 1 shown in
As can be appreciated by the description herein, in many embodiments of web 1 openings 4 will have a distinct linear orientation and a longitudinal axis, which is oriented parallel to the longitudinal axis L of its corresponding tuft 6. Likewise, openings 4 will also have a transverse axis generally orthogonal to longitudinal axis in the MD-CD plane.
As shown in
In one embodiment flaps 7 do not contribute significantly to the material of tufts 6, and particularly do not contribute significantly to the tactile quality of tufts 6. In one embodiment, therefore, the laminate web 1 comprises at least two layers (i.e., precursor webs 20 and 21), but at least one of the layers (i.e., precursor web 21 in
In one embodiment, flaps 7 may extend out of plane significantly, even being as high, so to speak, as the tufts 6 themselves. In this embodiment flaps 7 can cause the tufts 6 to be more resilient and less susceptible to flattening due to compressive or bending forces. In one embodiment, therefore, the laminate web 1 comprises at least two layers (i.e., precursor webs 20 and 21), and both layers affect the tactile qualities of tufts 6.
Tufts 6 can be, in a sense, “punched through” second precursor web 21 and can be “locked” in place by frictional engagement with openings 4. In some embodiments, for example, the lateral width of opening 4 (i.e., the dimension measured parallel to its transverse axis) can be less than the maximum width of the tooth that formed the opening (per the process described below). This indicates a certain amount of recovery at the opening that tends to constrain tuft 6 from pulling back out through opening 4. The frictional engagement of the tufts and openings provides for a laminate web structure having permanent tufting on one side that can be formed without adhesives or thermal bonding.
Tufts 6 can be spaced sufficiently closely so as to effectively cover first side 3 of web 1. In such an embodiment, both sides of web 1 appear to comprise nonwoven fibers integral with first precursor web 20, with a difference between the two sides 3 and 5 being a difference in surface texture. Therefore, in one embodiment, a topsheet of the present invention can be described as a laminate material of two or more precursor webs, wherein both sides of the laminate web are substantially covered by fibers from only one of the precursor webs. Specifically, a topsheet of the present invention can be described as comprising a first relatively hydrophobic component (i.e., second precursor web 21) and a second relatively hydrophilic component (i.e., first precursor web 20) wherein the relatively hydrophilic component extends through the relatively hydrophobic component and is disposed on both sides (i.e., sides 3 and 5) of said topsheet.
As shown in
In contrast, non-looped fibers 18 are integral with, but only begin in first or second precursor webs 20 and/or 21 and have a free end extending outwardly in the Z-direction from first side 3 of web 1. Loose fibers 18 can also have a generally uniform alignment described as having a significant or major vector component parallel to the Z-CD plane.
For both looped fibers 8 and loose fibers 18, the alignment is a characteristic of tufts 6 prior to any post-manufacture deformation due to winding onto a roll, or compression in use in an article of manufacture. As used herein, a looped fiber 8 oriented at an angle of greater than 45 degrees from the longitudinal axis L when viewed in plan view, as in
The orientation of looped fibers 8 in the tufts 6 is to be contrasted with the fiber composition and orientation for first or second precursor webs 20 and 21 (if a nonwoven web is used for second precursor web 21), which, for nonwoven webs is best described as having a substantially randomly-oriented fiber alignment. In a woven web embodiment, the orientation of the looped fibers 8 in tufts 6 could be the same as described above, but the fibers of woven precursor webs would have the orientation associated with the particular weaving process used to make the web, e.g., a square weave pattern.
In the embodiment shown in
In some embodiments, due to the preferred method of forming tufts 6, as described below, another characteristic of tufts 6 comprising predominantly looped, aligned fibers 8, can be their generally open structure characterized by open void area 10 defined interiorly of tufts 6. By “void area” is not meant an area completely free of any fibers; the term is meant as a general description of the general appearance of tufts 6. Therefore, it may be that in some tufts 6 a loose fiber 18 or a plurality of loose fibers 18 may be present in the void area 10. By “open” void area is meant that the two longitudinal ends of tuft 6 are generally open and free of fibers, such that tuft 6 can form something like a “tunnel” structure in an uncompressed state, as shown in
Void area 10 is believed to contribute to the surprising fluid handling properties of web 1 when used as a topsheet on a disposable absorbent article, as described more fully below. By having generally open ends tufts 6 provide for “lateral entry” of fluids, particularly viscous fluids having solid components, such as menses.
One way of describing the structure of web 1 is with respect to the three-dimensional fiber orientation in the Z-direction, as shown in
In one preferred embodiment of web 1 for use as a topsheet on a disposable article, both precursor webs 20 and 21 are nonwoven webs, with second precursor web 21 being relatively hydrophobic with respect to first precursor web 20 (and, preferably, the skin or hair of the wearer), and both contribute fibers to tufts 6 in a relatively layered manner. In such a topsheet, as described more fully below with respect to
As a consequence of a preferred method of making web 1, the second side 5 of web 1 exhibits discontinuities 16 characterized by a generally linear indentation defined by formerly random fibers of the second surface 14 of first precursor web 20 having been urged directionally (i.e., in the “Z-direction” generally orthogonal to the MD-CD plane as shown in
From the description of web 1 comprising at least a nonwoven first precursor web 20, it can be seen that the fibers 8 or 18 of tuft 6 can originate and extend from either the first surface 12 or the second surface 14 of first precursor web 20. Of course the fibers 8 or 18 of tuft 6 can also extend from the interior 28 of first precursor web 20. The fibers 8 or 18 of tufts 6 extend due to having been urged out of the generally two-dimensional plane of first precursor web 20 (i.e., urged in the “Z-direction” as shown in
Therefore, from the above description, it is understood that in one embodiment web 1 can be described as being a laminate web formed by selective mechanical deformation of at least a first and second precursor webs, at least the first precursor web being a nonwoven web, the laminate web having a first side, the first side comprising the second precursor web and a plurality of discrete tufts, each of the discrete tufts comprising a plurality of tufted fibers being integral extensions of at least the first precursor web and extending through the second precursor web; and a second side, the second side comprising the first precursor web.
The extension of fibers 8 or 18 can be accompanied by a general reduction in fiber cross sectional dimension (e.g., diameter for round fibers) due to plastic deformation of the fibers and Poisson's ratio effects. Therefore, the aligned looped fibers 8 of tuft 6 can have an average fiber diameter less than the average fiber diameter of the fibers of first or second precursor webs 20 or 21. It is believed that this reduction in fiber diameter contributes to the perceived softness of the first side 3 of web 1, a softness that can be comparable to cotton terry cloth, depending on the material properties of the first precursor web 20. It has been found that the reduction in fiber cross-sectional dimension is greatest intermediate the base 17 and the distal portion 3 of tuft 6. This is believed to be due to the preferred method of making, as disclosed more fully below. Briefly, it is believed that portions of fibers at the base 5 and distal portion 3 of tufts 6 are adjacent the tip of teeth 110 of roll 104, described more fully below, and are frictionally locked and immobile during processing. Thus, the intermediate portions of tufts 6 are more free to stretch, or elongate, and accordingly, can experience a corresponding fiber cross sectional dimension reduction.
Referring to
In
The method of making a web 1 in a commercially-viable continuous process is depicted in
The process and apparatus of the present invention is similar in many respects to a process described in U.S. Pat. No. 5,518,801 entitled “Web Materials Exhibiting Elastic-Like Behavior” and referred to in subsequent patent literature as “SELF” webs, which stands for “Structural Elastic-like Film”. However, there are significant differences between the apparatus and process of the present invention and the apparatus and process disclosed in the '801 patent, and the differences are apparent in the respective webs produced thereby. As described below, the teeth 110 of roll 104 have a specific geometry associated with the leading and trailing edges that permit the teeth to essentially “punch” through the precursor webs 20, 21 as opposed to, in essence, deforming the web. In a two layer laminate web 1 the teeth 110 urge fibers from precursor webs 20 and 21 out-of-plane by the teeth 110 pushing the fibers 8 through to form tufts 6. Therefore, a web 1 can have tufts 6 comprising loose fiber ends 18 and/or “tunnel-like” tufts 6 of looped, aligned fibers 8 extending away from the surface 13 of side 3, unlike the “tent-like” rib-like elements of SELF webs which each have continuous side walls associated therewith, i.e., a continuous “transition zone,” and which do not exhibit interpenetration of one layer through another layer.
Precursor webs 20 and 21 are provided either directly from their respective web making processes or indirectly from supply rolls (neither shown) and moved in the machine direction to the nip 116 of counter-rotating intermeshing rolls 102 and 104. The precursor webs are preferably held in a sufficient web tension so as to enter the nip 16 in a generally flattened condition by means well known in the art of web handling. As each precursor web 20, 21 goes through the nip 116 the teeth 110 of roll 104 which are intermeshed with grooves 108 of roll 102 simultaneously urge portions of precursor webs 20 and 21 out of the plane to form tufts 6. In one embodiment, teeth 110 in effect “push” or “punch” fibers of first precursor web 20 through second precursor web 21. In another embodiment teeth 110 in effect “push” or “punch” fibers of both first and second precursor webs 20 and 21 out of plane to form tufts 6.
As the tip of teeth 110 push through first and second precursor webs 20, 21 the portions of the fibers of first precursor web 20 (and, in some embodiments, second precursor web 21) that are oriented predominantly in the CD across teeth 110 are urged by the teeth 110 out of the plane of first precursor web 20. Fibers can be urged out of plane due to fiber mobility, or they can be urged out of plane by being stretched and/or plastically deformed in the Z-direction. Portions of the precursor webs urged out of plane by teeth 110 result in formation of tufts 6 on first side 3 of web 1. Fibers of precursor webs 20 and 21 that are predominantly oriented generally parallel to the longitudinal axis L, i.e., in the MD as shown in
It can be appreciated by the forgoing description that when web 1 is made by the apparatus and method of the present invention that the precursor webs 20, 21 can possess differing material properties with respect to the ability of the precursor webs to elongate before failure, e.g., failure due to tensile stresses. In one embodiment, a nonwoven first precursor web 20 can have greater fiber mobility and/or greater fiber elongation characteristics relative to second precursor web 21, such that the fibers thereof can move or stretch sufficiently to form tufts 6 while the second precursor web 21 ruptures, i.e., does not stretch to the extent necessary to form tufts. In another embodiment, second precursor web 21 can have greater fiber mobility and/or greater fiber elongation characteristics relative to first precursor web 20, such that both first and second precursor webs 20 and 21 form tufts 6. In another embodiment, second precursor web 21 can have greater fiber mobility and/or greater fiber elongation characteristics relative to first precursor web 20, such that the fibers of second precursor web 21 can move or stretch sufficiently to form tufts 6 while the first precursor web 20 ruptures, i.e., does not stretch to the extent necessary to form tufts.
The degree to which the fibers of nonwoven precursor webs are able to extend out of plane without plastic deformation can depend upon the degree of inter-fiber bonding of the precursor web. For example, if the fibers of a nonwoven precursor web are only very loosely entangled to each other, they will be more able to slip by each other (i.e., to move relative to adjacent fibers by reptation) and therefore be more easily extended out of plane to form tufts. On the other hand, fibers of a nonwoven precursor web that are more strongly bonded, for example by high levels of thermal point bonding, hydroentanglement, or the like, will more likely require greater degrees of plastic deformation in extended out-of-plane tufts. Therefore, in one embodiment, one precursor web 20 or 21 can be a nonwoven web having relatively low inter-fiber bonding, and the other precursor web 20 or 21 can be a nonwoven web having relatively high inter-fiber bonding, such that the fibers of one precursor web can extend out of plane, while the fibers of the other precursor web cannot. Optionally, a precursor web 20 or 21 may have a moderate level of inter-fiber bonding which maximizes the combination of fiber mobility which enables fibers to more easily extend out of the plane to form tufts and web stability which minimizes the collapsing of the tufts.
In one embodiment, for a given maximum strain (e.g., the strain imposed by teeth 110 of apparatus 100), it is beneficial that second precursor web 21 actually fail under the tensile loading produced by the imposed strain. That is, for the tufts 6 comprising only, or primarily, fibers from first precursor web 20 to be disposed on the first side 3 of web 1, second precursor web 21 must have sufficiently low fiber mobility (if any) and/or relatively low elongation-to-break such that it locally (i.e., in the area of strain) fails in tension, thereby producing openings 4 through which tufts 6 can extend.
In another embodiment it is beneficial that second precursor web 21 deform or stretch in the region of induced strain, and does not fail, such that tuft 6 includes portions of second precursor web 21 result.
In one embodiment second precursor web 21 has an elongation to break in the range of 1%-5%. While the actual required elongation to break depends on the strain to be induced to form web 1, it is recognized that for most embodiments, second precursor web 21 can exhibit a web elongation-to-break of 6%, 7%, 8%, 9%, 10%, or more. It is also recognized that actual elongation-to-break can depend on the strain rate, which, for the apparatus shown in
Relative to first precursor web 20, second precursor web 21 can have lower fiber mobility (if any) and/or lower elongation-to-break (i.e., elongation-to-break of individual fibers, or, if a film, elongation-to-break of the film) such that, rather than extending out-of-plane to the extent of the tufts 6, second precursor web 21 fails in tension under the strain produced by the formation of tufts 6, e.g., by the teeth 110 of apparatus 100. In one embodiment, second precursor web 21 exhibits sufficiently low elongation-to-break relative to first precursor web 20 such that flaps 7 of opening 4 only extend slightly out-of-plane, if at all, relative to tufts 6. In general, for embodiments in which tufts 6 comprise primarily fibers from first precursor web 20, it is believed that second precursor web 21 should have an elongation to break of at least 10% less than the first precursor web 20, preferably at least 30% less, more preferably at least 50% less, and even more preferably at least about 100% less than that of first precursor web 20. Relative elongation to break values of webs used in the present invention can be measured by means known in the art, such as by standard tensile testing methods using standard tensile testing apparatuses, such as those manufactured by Instron, MTS, Thwing-Albert, and the like.
In one embodiment second precursor web 21 can comprise substantially all MD-oriented fibers, e.g., tow fibers, such that there are substantially no fibers oriented in the CD. For such an embodiment of web 1 the fibers of second precursor web 21 can simply separate at the opening 4 through which tufts 6 extend. In this embodiment, therefore, second precursor web 21 need not have any minimum elongation to break, since failure or rupture of the material is not the mode of forming opening 4.
The number, spacing, and size of tufts 6 can be varied by changing the number, spacing, and size of teeth 110 and making corresponding dimensional changes as necessary to roll 104 and/or roll 102. This variation, together with the variation possible in precursor webs 20, 21 permits many varied webs 1 having varied fluid handling properties for use in a disposable absorbent article. As described more fully below, a web 1 comprising a nonwoven/film first precursor web/second precursor web combination can also be used as a component in disposable absorbent articles. However, a nonwoven/nonwoven precursor web/second precursor web combination wherein fibers from both webs contribute to tufts 6 is also suitable.
An enlarged view of teeth 110 is shown in
As shown in
At higher line speeds, i.e., relatively higher rates of processing of the web through the nip of rotating rolls 102 and 104, like materials can exhibit very different structures for tufts 6. The tuft 6 shown in
Therefore, from the above description, it is understood that in one embodiment web 1 can be described as being a laminate web formed by selective mechanical deformation of at least a first and second precursor webs, at least the first precursor web being a nonwoven web, the laminate web having a first side, the first side comprising the second precursor web and a plurality of discrete tufts, each of the discrete tufts comprising fibers integral with but extending from the first precursor web and fibers neither integral with nor extending from the first precursor web.
Although it is believed that the distinct fiber orientation observed at the distal portion of tufts 6, e.g., mat 19, is due primarily to processing rates, it is also believed to be affected by other parameters, such as fiber type and basis weight of the precursor webs 20 and 21 as well as processing temperatures that can affect the degree of fiber-to-fiber bonding. Matting of fibers is believed to occur on the portion of tuft 6 associated during manufacturing with the tip of tooth 110 of roll 104. It is believed that frictional engagement of the fibers at the tip of the teeth “lock” the fibers in place, thereby limiting fiber elongation and/or fiber mobility, two mechanisms believed to permit formation of tufts 6. Therefore, once locked, so to speak, in position, fibers adjacent tooth 110 tip can be broken, and, due to the random entanglement of the precursor web as well as possible cold welding of fibers due to pressure and friction, the broken fibers 11 become and remain lodged in mat 19 at the distal end 3 of tufts 6.
Precursor webs having relatively higher basis weights generally have relatively more fiber 11 portions in mat 19. In one sense, it appears as if most of the fiber content of the precursor webs in the immediate vicinity of a tooth tip 110 during manufacture can be simply displaced in the Z-direction to the distal portion 3 of tufts 6, resulting in mat 19. First precursor webs 20 comprising relatively low elongation fibers, or fibers with relatively low fiber-to-fiber mobility (e.g., relatively limited capability for fiber reptation) appear to result in relatively few fibers becoming and remaining lodged in mat 19 at the distal end 3 of tufts 6. Fiber-to-fiber mobility can be increased by reducing or eliminating the fiber-to-fiber bonds. Thermal bonds can be completely eliminated (i.e., avoided by not bonding), or reduced in certain nonwoven webs to increase fiber-to-fiber mobility. Similarly, hydroentangled webs can be less entangled to increase fiber-to-fiber mobility. For any precursor web 20, lubricating it prior to processing as disclosed herein can also increase fiber-to-fiber mobility. For example, a mineral oil lubricant can be applied to first precursor web 20 prior to it entering the nip 116 of rolls 102 and 104. Additionally, a plasticizing agent, such as petrolatum, can be added to some synthetic fiber webs, such as polyethylene or a polyethylene and polypropylene web, to increase extensibility.
While not wishing to be bound by theory, it is believed that if the fibers of the first precursor web have a highly curvilinear shape, e.g., curled fibers, the resultant tufts 6 will have more looped fibers 8 and less broken fibers 18 as compared to more linear fiber conformations. It is believed that such fiber conformations have a lesser chance of bridging between two adjacent teeth, and, as a result they are less prone to be stretched beyond their breaking point, and thus have a greater chance of forming complete loop structures. Furthermore, such curvilinear-shaped fibers can be made by using eccentric bicomponent fibers, or side-by-side bicomponent fibers, such as bicomponent fibers consisting of polyethylene and nylon.
It has been found that certain nonwoven webs, such as carded webs comprising staple-length fibers, when used as a precursor web produce very few looped fibers 8 in tufts 6, so that the tufts 6 produced in these webs may not be described as comprising a plurality of looped, aligned fibers 8 as described above with respect to
Therefore, from the above description, it is understood that in one embodiment web 1 can be described as being a laminate web formed by selective mechanical deformation of at least a first and second precursor webs, at least the first precursor web being a nonwoven web, the laminate web having a first side, the first side comprising the second precursor web and a plurality of discrete tufts, the tufts comprising a plurality of fibers integral with but extending from said first region.
In preferred embodiments precursor webs are nonwoven web in which there are minimal fiber-to-fiber bonds. For example, the precursor web can be a nonwoven web having a pattern of discrete thermal point bonds, as is commonly known in the art for nonwoven webs. In general, however, it is believed to be desirable to minimize the number of bond points and maximize the spacing so as to allow for some fiber mobility and dislocation at during formation of tufts 6. In general, utilizing fibers having relatively high diameters, and/or relatively high extension to break, and/or relatively moderate or high fiber mobility, results in better and more distinctly formed tufts 6.
Although web 1 is disclosed in preferred embodiments as a two layer web made from two precursor webs, it is not necessary that it be limited to two layers. For example, a three-layer or more laminate can be made from three or more precursor webs, as long as one of the precursor webs can extend out-of-plane to form tufts. In general, it is not necessary that adhesive or other bonding means be utilized to make laminate web 1. The constituent layers of web 1 (e.g., precursor webs 20 and 21 and any other layers) can be held in a face-to-face laminated relationship by virtue of the “locking” effect of the tufts 6 that extend through openings 4 in second precursor web 21. In some embodiments it may be desirable to use adhesives or thermal bonding or other bonding means, depending on the end use application of web 1. For example, a web 1 comprising bicomponent fiber nonwoven webs can be through-air bonded after formation of tufts 6 to provide for layer-to-layer adhesion for greater peel strength and for increased tuft stability. Additionally, it may be desirable to apply adhesive to a portion of one of the precursor webs. For example, in some embodiments adhesive or thermal bonding between layers can be selectively applied to certain regions of web 1. In the case of adhesive application, for example, adhesive can be applied in a continuous manner, such as by slot coating, or in a discontinuous manner, such as by spraying, extruding, and the like. Discontinuous application of adhesive can be in the form of stripes, bands, droplets, and the like.
In a multilayer web 1 each precursor web can have different material properties, thereby providing web 1 with beneficial properties with respect to use as a topsheet in a disposable absorbent article, as described more fully below. For superior fluid handling, for example, first precursor web 20 can be comprised of relatively hydrophilic fibers. Second precursor web 21 can be polymer film, e.g., a polyethylene film or an apertured polyethylene film, and can be hydrophobic or rendered hydrophobic. The tufts 6 of such a web could form an upper layer, i.e., a body-contacting layer when used as a topsheet on a disposable absorbent article. Fluid deposited upon the upper, relatively hydrophilic tufts is quickly transported away from the relatively hydrophobic film to the portion of the first precursor web underlying the second film precursor web layer. One reason for the observed rapid fluid transport is the capillary structures formed by the generally aligned fibers 8, 18 of tufts 6. The fibers 8, 18 form directionally-aligned capillaries between adjacent fibers, and the capillary action is enhanced by the general convergence of fibers near proximal portion 7 of tufts 6.
In another embodiment, first precursor web 20 can be comprised of relatively hydrophilic fibers. Second precursor web 21 can be comprised of fibers that are relatively hydrophobic or rendered hydrophobic (i.e., exhibit a contact angle with water of greater than about 70 degrees). The tufts 6 of such a web could comprise fibers from both precursor webs to form a relatively hydrophobic upper layer, i.e., a body-contacting layer when used as a topsheet on a disposable absorbent article. Fluid deposited upon the web 1 can have lateral entry contact into voids 10 to reach relatively hydrophilic fibers, however, and thereby be quickly transported away to underlying components of the absorbent article. One reason for the observed rapid fluid transport in either structure is believed to be the capillary structures formed by the generally aligned fibers 8, 18 of tufts 6. The fibers 8, 18 form directionally-aligned capillaries between adjacent fibers, and the capillary action is enhanced by the general convergence of fibers near proximal portion 7 of tufts 6.
It is believed that the rapid fluid transport is further increased due to the ability of fluid to enter the web 1 via the voids 10 defined by looped tufts 6. This “lateral entry” capability and/or capillary action, and/or the hydrophilicity gradient afforded by the structure of web 1 makes web 1 an ideal material for optimal fluid handling for disposable absorbent articles. In particular, a multilayer web 1 can provide for even greater improvement in fluid handling characteristics.
In one embodiment, web 1 comprises a nonwoven first precursor web 20 comprising a spunbond nonwoven having a basis weight of about 80 gsm, and comprising polyethylene/polypropylene (sheath/core) bicomponent fibers having an average diameter of about 33 microns, and a second precursor web comprising a polyethylene film having a basis weight of 20 gsm. In this embodiment, web 1 has about 24 tufts 6 per square centimeter, the tufts 6 having a plurality of looped, aligned fibers 8, each of which has an average fiber diameter of about 18 microns. A web of this type can be beneficially used as a topsheet for disposable absorbent articles, as shown below with reference to
In one embodiment, as depicted schematically in
Web 1 is especially useful as a topsheet 206 of sanitary napkin 200. Web 1 as described with respect to
The topsheet 206 can comprise two layers, i.e., one layer corresponding to each precursor web, and the first precursor web could be considered to be a secondary topsheet. But since the two webs are joined into a laminate composite, they are referred to herein as a topsheet 206. The basis weights of the precursor webs can be varied due to cost and benefit considerations. In general, a web 1 having a total basis weight of between about 20 gsm and 100 gsm is desirable for use as a topsheet 206 in a disposable absorbent article, such as a sanitary napkin. Second precursor web 21 can be a nonwoven web or a polymer film web. When made as a hydrophilic/hydrophobic (one web with respect to the other) nonwoven/film laminate, web 1 has been found to combine the softness and fluid capillarity of fiber tufts with the rewet prevention of a fluid impermeable polymer film. Likewise, when made as a hydrophilic/hydrophobic (one web with respect to the other) nonwoven/nonwoven laminate, web 1 has also been found to combine consumer-acceptable softness with excellent gush fluid acquisition and rewet properties.
It is well known in the sanitary napkin field, as illustrated by Table 1 below, and illustrated on the graph of
Therefore, when rewet and gush acquisition rate are graphed on orthogonal axes, the data show a very well known and predictable trend showing that as dryness improves, gush acquisition rates decrease. By way of example, the data in Table 1, which is graphed in
Samples 1-4 were all purchased current market products. All values are averages with n=10.
The PP/Rayon nonwovens were a carded blend of 70% 2.2 denier polypropylene(PP)/30% 5 denier rayon, available from PGI Nonwovens under the designation 164-253-6.
The 25 gsm Bico PE/PP nonwovens were relatively hydrophobic spunbond bicomponent PE/PP (sheath/core) fiber nonwoven webs obtained from BBA Nonwovens, Washougal, Wash. under the designation 074YLCO09U.
The hydrophilic BiCo PE/PP was a 30 gsm relatively hydrophobic spunbond bicomponent PE/PP (sheath/core) fiber nonwoven web obtained from BBA Nonwovens, Washougal, Wash. under the designation 088YLCO09U.
The “4DG” fibers were surfactant treated PET, crimped, 2-inch cut length fibers having a cross-section exhibiting channels that can act as fluid capillaries, obtained from Fiber Innovation Technologies, Johnson City, Tenn. Such fibers are sometimes referred to as capillary channel fibers.
The “round” fibers were surfactant treated PET, crimped, 2-inch cut length fibers having a round cross-sectional shape, obtained from Wellman, Inc., Charlotte, N.C. under the designation Type 204.
The “% PET fibers” refers to the percentage of PET fibers in the first precursor web. In all Samples 3-14, these fibers are blended with relatively hydrophilic 6 denier co-PET crimped, 2-inch cut length bicomponent binder fibers (higher melting PET core/low melting point PET sheath) obtained from Kanematsu USA, Gastonia, N.C. under the designation LM651. All percentages refer to weight percent.
Particularly in the Samples using relatively stiff fibers, such as PET fibers, the data showed results heretofore unobtainable, both improved gush acquisition rates, and improved dryness (lowered rewet). Such a surprising finding—both dryness and gush acquisition rate exhibiting a significant directional improvement with the use of the present invention-prompted further testing, this time using a more readily duplicated fluid, namely Paper Industry Fluid, commonly referred to as PIF. PIF is a well-known fluid used for simulating relatively high viscosity fluids such as menses. Additional testing using PWF was performed according to the Gush Acquisition Rate and Rewet method described below. The results of the PIF testing are shown in Tables 2 and 3. Table 2 shows the results of testing the web of the present invention in place of the topsheets on two well-known existing market products. Table 3 shows the results of testing the web of the present invention over current airfelt core of the type used in Always® Maxi Regular sanitary napkins, available from The Procter & Gamble Co., Cincinnati, Ohio.
In general it is noted that certain samples tested with AMF were duplicated using PIF and the results were seen to correlate in a proportional manner, with the PIF giving more modest improvements for both rewet and acquisition rate. That is, for a given sample, testing with PWF shows proportionally poorer values for both dryness and gush acquisition rate than does testing with AMF. However, even with the use of PIF, as shown in Tables 2 and 3, the tested values continue to be better in both gush acquisition rate and rewet than existing products. Therefore, tested values using AMF, menses, and/or consumer experience are each expected to be exhibit better results than those shown in the Tables below.
The Samples listed in Table 2 were store-purchased and tested according to the Test Method detailed below. The values shown for Gush Acquisition Rate and Rewet are averages of 10 tests for each value. In the “as purchased” condition, each Sample was tested without modification of the product. As shown in Table 2, for each product additional samples were tested after replacement of the existing topsheet with a web of the present invention as described below. This was accomplished by carefully removing the existing topsheet (and, if necessary any secondary topsheets) so as to not disturb the underlying absorbent core, and thereafter, placing a topsheet of the present invention over the core in a manner to simulate a machine made product. The webs of the present invention used in the testing shown in Table 2 had the following composition:
First precursor web: 45 gsm carded nonwoven web comprising a blend of 80% relatively hydrophilic 30 denier crimped, shaped, 2-inch cut length PET fibers obtained from Fiber Innovation Technologies, Johnson City, Tenn., under the designation 4DG, and 20% relatively hydrophilic 6 denier co-PET crimped, 2-inch cut length bicomponent binder fibers (higher melting PET core/low melting point PET sheath) obtained from Kanematsu USA, Gastonia, N.C. under the designation LM651.
Second precursor web: 30 gsm relatively hydrophobic spunbond bicomponent PE/PP (sheath/core) fiber nonwoven web obtained from BBA Nonwovens, Washougal, Wash. under the designation 088YLCO09U.
The first and second precursor webs were processed by the method described in the specification above using the intermeshing rolls described above. Specifically, for each sample, the toothed rolls had a pitch P of 1.5 mm, an engagement E of 3.4 mm, and a uniform tooth height TH of 3.7 mm. The intermeshing rolls were rotated so as to process the webs at an approximate rate of about 3 m/min.
As shown by the data in Table 2, current market products exhibit a significant improvement in both rewet and acquisition rate by the use of a topsheet comprising a web of the present invention. The measured fluid handling parameters have a direct impact on consumer-desired properties. Therefore, by using topsheets comprising a web of the present invention, current market products can be significantly improved to deliver important consumer benefits.
Additional webs 1 of the present invention were produced with the same second precursor web as those used in Samples 1 and 2 of Table 2, but with varying first precursor web and fiber characteristics, as shown in Table 4. These webs were tested by the Acquisition Rate and Rewet test methods shown below to give the data shown in Table 3. For the data shown in Table 3, each topsheet was tested over airfelt absorbent cores removed from store-bought ALWAYS® Maxi Regular sanitary napkins.
Each of the Samples shown in Table 3 were processed with the first precursor web 20 indicated by the method described above using the intermeshing rolls described above. For each sample, the toothed rolls had a pitch P of 1.5 mm, an engagement E of 3.4 mm, and a uniform tooth height TH of 3.7 mm. The intermeshing rolls were rotated so as to process the webs at an approximate rate of about 3 m/min.
The “trilobal” fibers were surfactant treated PET, crimped, 2-inch cut length fibers having a triobal cross-sectional shape obtained from Fiber Innovation Technologies, Johnson City, Tenn.
The “4DG” fibers were surfactant treated PET, crimped, 2-inch cut length fibers having a cross-section exhibiting channels that can act as fluid capillaries, obtained from Fiber Innovation Technologies, Johnson City, Tenn. Such fibers are sometimes referred to as capillary channel fibers.
The “round” fibers were surfactant treated PET, crimped, 2-inch cut length fibers having a round cross-sectional shape, obtained from Wellman, Inc., Charlotte, N.C. under the designation Type 204.
The “% PET fibers” refers to the percentage of PET fibers in the first precursor web. In all Samples 3-14, these fibers are blended with relatively hydrophilic 6 denier co-PET crimped, 2-inch cut length bicomponent binder fibers (higher melting PET core/low melting point PET sheath) obtained from Kanematsu USA, Gastonia, N.C. under the designation LM651. All percentages refer to weight percent.
The web basis weight refers to the basis weight of the first precursor web only.
As can be seen from the Gush Acquisition Rate and Rewet results in Table 3, the web of the present invention provides for superior gush acquisition rates and dryness values compared to other, known topsheets (see, e.g., “as purchased” values in Table 2). On a graph similar to that shown in
In particular, from the results in Tables 2 and 3, it can be seen that a web of the present invention, when used as a topsheet in a disposable absorbent article, delivers both a gush acquisition rate of at least 0.11 ml/sec, and a rewet value much less than about 94 mg. In one embodiment a superior disposable absorbent article, such as a sanitary napkin, can be provided by utilizing a topsheet comprising a web of the present invention wherein the article exhibits a rewet value of less than about 75 mg and a fluid acquisition rate of at least about 0.5 ml/sec. In another embodiment, the article can exhibit a rewet value of less than about 25 mg and a fluid acquisition rate of at least about 1.0 ml/sec.
Without being bound by theory, it is believed that the superior fluid handling results can be attributed to at least two factors: (1) the hydrophilicity/hydrophobicity differences between the first and second precursor webs, respectively; and, (2) the presence of relatively stiff fibers in tufts 6 that can aid in retaining caliper under load. That is, relatively stiff fibers oriented generally in the Z-direction (e.g., as shown in
Table 4 below shows representative examples of other structures of webs 1 useful for components in articles of present invention, along with dimensions relative to the apparatus 100 used in the process to make them, as disclosed hereinabove. A brief description of each Sample listed follows Table 4.
As can be understood from the above description of webs 1 and apparatus 100 of the present invention, many various structures of webs 1 can be made without departing from the scope of the present invention as claimed in the appended claims. For example, webs 1 can be coated or treated with lotions, medicaments, cleaning fluids, anti-bacterial solutions, emulsions, fragrances, surfactants. In particular, relatively hydrophobic lotion having a hydrophilic/lipophilic balance (HLB) of less than or equal to 7. The lotion can be petrolatum-based and can comprise skin treatment agents and other ingredients as disclosed commonly-assigned U.S. patent application Ser. No. 10/444,241, which is hereby incorporated herein by reference. Web 1 can be treated such that only the distal ends of the tufts 6 have lotion applied thereto, such that the web 1 can be described as a web having a first side and a second side, wherein tufts at least partially originate in the second side and extending to a distal body-facing portion, the distal body-facing portion being relatively hydrophobic with respect to the second side.
Apparatus 100 can be configured to only form tufts 6 on a portion of the web 1, or to form varying sizes or area densities of tufts 6.
All documents cited in the Detailed Description of the Invention are, in relevant part, incorporated herein by reference; the citation of any document is not to be construed as an admission that it is prior art with respect to the present invention.
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.
Preparation of Paper Industry Fluid (PIF)
Reagents:
Procedure:
Viscosity Target:
This application is a continuation of U.S. application Ser. No. 10/737,307, filed Dec. 16, 2003, now U.S. Pat. No. 7,172,801 which is a continuation-in-part of U.S. application Ser. No. 10/610,299; filed Jun. 30, 2003, now abandoned, and which is a continuation-in-part of U.S. application Ser. No. 10/435,996, filed May 12, 2003 now abandoned, which is a continuation-in-part of U.S. application Ser. No. 10/324,661, filed Dec. 20, 2002, now abandoned.
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