This invention relates to absorbent articles that contain superabsorbent polymers, and the methods of making such articles. More particularly, this invention relates to absorbent cores used in absorbent articles.
Currently available absorbent articles include tissues that contain superabsorbent polymers (SAP), and air laid composites containing SAP particles and/or superabsorbent fibers. Traditional methods of absorbent article manufacture use SAP applied as a solid particulate material. Although the SAP particles in such absorbent articles afford the advantage of providing very high water absorbency, many of the particles shake out during preparation of the articles on high speed manufacturing machines.
One attempt to deal with the issue of shake-out is described in U.S. Pat. No. 5,641,561 to Hansen et al. Hansen et al. described absorbent composites made of fibrous material (e.g. cellulosic or synthetic material) and SAP particles that are bound to the fiber via hydrogen bonding binder molecules. SAP particles are mixed with bleached kraft fluff, heated and spread out to dry. The binder adheres the SAP particles to the fibers. The dried product is then fed through a hammermill and shunted to an airlay line to produce a web containing 40% SAP particles attached to individual fibers.
U.S. Pat. No. 5,593,399 to Tanzer discloses an absorbent article, namely a diaper, having two layers attached by an adhesive to provide attached zones and unattached zones to form pocket regions. Tanzer describes the use of SAP particles located within the pocket regions of the article to provide an absorbent laminate.
Another difficulty with absorbent products is that they sometimes exhibit a problem known as “gel blocking.” This refers to the tendency of SAP particles, when evenly distributed in an absorbent matrix, to swell so much upon imbibing a fluid that they occlude the interstitial voids in the matrix, thereby restricting or preventing further fluid flow. The result is a tendency for leakage when a second flow of liquid occurs, since much of the SAP is inaccessible to the liquid due to the blocking effect. Thus, much of the SAP is inefficiently used.
Another problem with absorbent products is strength in that, upon exposure to a fluid, the entire substrate may become or remain wet. Because of such wetting, the strength may be diminished, leading to tearing problems.
Thus there remains a need for an improved absorbent article design that overcomes one or more of the foregoing problems associated with conventional designs.
In one exemplary aspect, the invention provides an absorbent article comprising a barrier layer, a cover layer extending substantially parallel to the barrier layer, and a superabsorbent polymer interposed between the cover layer and the barrier layer. The superabsorbent polymer is adhered to the article in a pattern configured to distribute fluid in the absorbent article, wherein at least one portion extending essentially completely across the absorbent article is substantially devoid of the superabsorbent polymer.
According to one exemplary embodiment, the absorbent article optionally includes a tissue layer interposed between the cover layer and the barrier layer. The superabsorbent polymer is optionally provided on the tissue layer in a pattern configured to distribute fluid in the absorbent article.
In another exemplary aspect, the invention provides a method of making an absorbent article. The method includes positioning a superabsorbent polymer adjacent a barrier layer in a pattern to form at least one region including the superabsorbent polymer and at least one region substantially devoid of the superabsorbent polymer extending essentially completely across the barrier layer, thereby providing the region substantially devoid of superabsorbent polymer with greater tear resistance than the region including the superabsorbent polymer. A cover layer is attached substantially parallel to and substantially coextensive with the barrier layer, thereby interposing the superabsorbent polymer between the barrier layer and the cover layer.
In yet another exemplary embodiment, the method includes positioning a liquid comprising a superabsorbent precursor adjacent a barrier layer in a pattern to form at least one region including the superabsorbent precursor and at least one region substantially devoid of the superabsorbent precursor extending essentially completely across the barrier layer, thereby providing the region substantially devoid of superabsorbent polymer with greater tear resistance than the region including the superabsorbent polymer. The superabsorbent precursor is converted to a superabsorbent polymer, thereby forming at least one region including the superabsorbent polymer and at least one region devoid of the superabsorbent polymer. A cover layer is coupled substantially parallel to and substantially coextensive with the barrier layer, thereby interposing the superabsorbent polymer between the barrier layer and the cover layer.
This invention will now be described with reference to specific embodiments selected for illustration in the drawings, wherein similar numbers indicate similar features. It will be appreciated that the spirit and scope of this invention are not limited to the embodiments selected for illustration. Instead, the scope of this invention is defined separately in the appended claims. Also, it will be appreciated that the drawings are not rendered to any particular proportion or scale.
An absorbent article and method of making such an article are provided. More specifically, exemplary embodiments of this invention relate to an absorbent article wherein liquid superabsorbent polymer has been applied either directly to a fluid-impermeable barrier layer or to a porous core positioned adjacent the barrier layer, in any of a variety of patterns. The absorbent core may be covered with a woven or non-woven, fluid-permeable cover layer on the surface opposite that of the barrier layer. A nonlimiting example of such an absorbent article is an underpad designed to provide fluid protection for beds and other external surfaces. Other absorbent articles such as diapers, incontinence pads, and feminine hygiene pads, may also be made according to this invention.
As used herein, the terms “liquid SAP” and “liquid superabsorbent polymer” mean a liquid comprising one or more crosslinked or uncrosslinked superabsorbent polymers in dispersed or dissolved form, or a liquid comprising one or more superabsorbent precursors, or a combination of these. Superabsorbent precursors include inter alia oligomers and monomers that, after placement on a substrate, are subsequently converted, for example by polymerization and/or crosslinking, to a superabsorbent polymer.
Application of liquid SAP to an absorbent article provides the article with added total absorbent capacity, thereby reducing the amount of core material needed to obtain a targeted total capacity. Since less material is needed to obtain targeted total absorption capacity, a thin absorbent material may be provided by the present invention. Thus, in order to provide an “ultra-thin” absorbent core, use of the liquid superabsorbent reduces the number and/or thickness of layers needed to obtain a targeted total absorbent capacity. This type of construction affords a thinner product, desirable for comfort and/or cost savings on material consumption and handling. The liquid SAP may be applied to the core. For some applications, no core at all may be used, with SAP being only on the barrier layer of the absorbent article.
The core 108 may be preferably made of any cellulosic material such as for example tissue or paper towel sheets, especially when a lower product cost is desired. The use of tissue is also advantageous in providing a low weight pad, and one of good wet integrity. Pulp may also be used in the core. Specifically, core 108 may comprise a single layer of defibrated pulp embossed for rapid fluid absorption and dispersion. Other types of cores may also be used. Nonlimiting examples include fibrous webs made of natural or synthetic fibers, for example, woven fabric, non-woven fabric, paper and knit fabric. Also, hydrophilic fibers such as wood pulp, cotton, wool, rayon, acetate, and vinylon, for example may be used for making core 108. An air laid composite may also be used. As discussed elsewhere, the care can also be eliminated from the absorbent article.
The barrier layer 102 may be made of any liquid impermeable material such as polyethylene, polypropylene, a copolymer thereof, polyester, and bi-component fibers. Other suitable materials include acrylic, nylon, and polyvinyl chloride. The barrier layer 102 prevents the passage of liquid and covers the underside of the absorbent article for protection against leakage.
Cover layer 106 may be formed of a woven or non-woven material, such as a substrate of thermoplastic fibers, or an apertured film. Materials used for cover layers are well known in the art and are selected from materials that are fluid permeable; that is, they allow the passage of liquid therethrough. The cover layer 106 and the barrier layer 102 are typically attached to the core 108 by means of adhesive 110, but other means may also be used in addition or instead.
One type of adhesive 110 that may be used is a hot melt pressure-sensitive adhesive. Such adhesives typically comprise one or more base polymers, one or more tackifying resins, a plasticizer, one or more waxes, and a filler and/or a pigment. Base polymers include for example polyethylene, amorphous polypropylene, ethylene-vinyl acetate copolymers, or block copolymers. Tackifying resins include for example hydrocarbon resins, rosin esters, or terpene-based resins made from such feedstocks as alpha pinene, beta pinene, limonene, dipentene, and related materials. Wax types include paraffin, microcrystalline, or synthetic waxes. Plasticizer types include for example polybutene and mineral oil. Other additives may include for example antioxidants such as sterically hindered phenols, phosphites, synergists or amides. In addition, other types of adhesive such as cold glue emulsions or cohesives may be used.
SAP 106 is positioned by applying a liquid SAP in a pattern designed to ensure that absorption of the insult will occur primarily where the liquid superabsorbent is applied. Thus, the liquid SAP permits a controlled application of the SAP especially in specific patterns, as will be discussed below. Also, by using liquid SAP, the manufacturer may be able to make a finished product on converting lines without pulp hammer mills, if that is desired.
Numerous liquid SAPs are known in the art. Nonlimiting examples of liquid SAPs suitable for use with this invention will now be described. In all cases, the final result is the formation of a superabsorbent polymer adhered to one or both of the barrier layer and the core.
U.S. Pat. No. 4,944,963 to Dabi, incorporated herein by reference, describes forming a terpolymer of methyl methacrylate, acrylic acid, and glycidyl methacrylate, with the terpolymer subsequently being neutralized. The resulting solution is applied to a polyester fibrous weave in an aqueous form. Excess solution is removed by vacuum, and the fiber/polyester composite is heated for 20 minutes at 120° C. to create a structure of 40% fibrous weave and 60% crosslinked polymer.
U.S. Pat. No. 5,853,867 to Harada, incorporated herein by reference, describes a cationic absorbent polymer applied to a fibrous polyester weave as a monomer solution, with the monomer subsequently being polymerized on the weave by heating. Alternatively, preformed polymer may be applied. Halogenated alkyl quaternary salts of dialkylamino (meth)acrylates are effectively used for the production of the polymers, and include the halogenated alkyl quaternary salts of such monomers as N,N-dimethylaminoethyl (meth)acrylate; N,N-dimethylaminopropyl (meth)acrylate; N,N-diethylaminobutyl (meth)acrylate; N,N-diethylaminoethyl (meth)acrylate; and N,N-diethylaminopropyl (meth)acrylate; for example. As used herein, the term “(meth)acrylate” means methacrylate and/or acrylate. Such a cationic absorbent polymer may be applied in a suitable liquid form, such as for example a solution, by means of spraying or spreading to the supporting member and fixed thereto. Preferably, the fixation of the cationic absorbent polymer to the supporting member is attained by depositing a monomer or mixture of monomers in the form of an aqueous solution on the supporting member by means of impregnation, for example, and polymerizing or polycondensing the applied layer of the monomer solution.
Another suitable liquid SAP is disclosed in U.S. Pat. No. 6,417,425 to Whitmore et al., incorporated herein by reference. There is described a sprayable composition comprising a monomer such as acrylic acid, methacrylic acid, and/or salts of these; a crosslinker such as ethoxylated and propoxylated trimethylolpropane triacrylate derivatives such as SR-9035 and SR-492 available from Sartomer Co., Inc. of Exton, Pa.; a polymerization initiator such as 2,2′-azobis(2-(2-imidazole-2-yl))propane dihydrochloride, and solid superabsorbent particles prepared for example from acrylic acid and crosslinked with for example an unsaturated crosslinking agent such as tetraallyloxyethane, all in aqueous solution. The mixture can be sprayed onto a fibrous substrate and subsequently cured via heating or exposure to electron beam or ultraviolet radiation, to form a superabsorbent polymer matrix.
Liquid SAP applied to a core may penetrate essentially through the entire thickness thereof. In a preferred embodiment, however, the superabsorbent polymer 106 is more heavily concentrated on one surface of core 108. That surface is positioned adjacent the barrier layer 102 for the purpose of avoiding gel blocking. In other words, the side of the core 108 that contains the highest loading of the superabsorbent polymer 106 is positioned to face the barrier layer 102. Since SAP 106 swells when wet, it tends to occlude the microscopic fluid wicking channels between the pulp fibers. By positioning the side of core 108 having less (or no) SAP nearer the cover layer 104, which is adjacent the user's body, fluids pass through portions of the core 108 where there is a diminished chance of gel blocking, before the fluid finally reaches the heavier concentration of SAP near the barrier layer 102.
Such areas devoid of SAP, by virtue of being adjacent areas with SAP, remain drier than would be the case if there were SAP present in them. The result is that these areas retain much of their strength even when the absorbent article is wet, since the SAP imbibes most of the water. Thus the likelihood of accidental tearing of core 108 is reduced, according to an exemplary aspect of the invention. In addition, as seen in
The application of the liquid SAP may be performed in a variety of patterns as shown in
In
Similarly, the melt blown pattern of
The patterns of SAP shown in
While preferred embodiments of the invention have been shown and described herein, it will be understood that such embodiments are provided by way of example only. Numerous variations, changes and substitutions will occur to those skilled in the art without departing from the spirit of the invention.
For example, according to exemplary aspects of this invention, an absorbent article is optionally formed by application of SAP directly to a barrier layer of the absorbent article (see, for example,
According to one exemplary embodiment so configured, SAP is applied directly to a film barrier. The film barrier is optionally em bossed film and may be embossed to have a “male” side opposite a “female” defining cavities. If such an embossed film barrier is utilized, the SAP is preferably applied to the female side of the embossed film so as to at least partially fill the cavities. The SAP is optionally applied to such a film barrier in patterns to facilitate fluid distribution. To do so, a liquid SAP may be applied in a manner set forth previously.
It is intended that the appended claims cover all such variations as fall within the spirit and scope of the invention. The invention having been described, the following and their equivalents are now claimed.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/US04/16641 | 5/26/2004 | WO | 1/3/2007 |
Number | Date | Country | |
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60496720 | Aug 2003 | US |