WO2008024426A2 - Nanosilver-containing absorbent articles - Google Patents

Abstract

The present invention provides hygienic absorbent articles, such as feminine sanitary napkins, tampons and disposable diapers, having antimicrobial activity that can minimize odors caused by body fluids. The articles of the invention include an absorbent member such as an elongated absorbent portion or pad that contains an antibacterial amount of substantially immobilized nanosilver particles or particles containing silver ions, preferably encased in a granule of a soluble carrier such as dextran, and the like, or a water-insoluble, but water- swellable superabsorbent polymer (SAP).

Description

NANOSILVER-CONTAINING ABSORBENT ARTICLES

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No. 60/839,759 filed on August 24, 2006, which is incorporated herein by reference. FIELD OF THE INVENTION

This invention relates to nanosilver-containing absorbent hygienic articles such as feminine napkins, tampons, bed pads and diapers for absorbing bodily fluids. More particularly, this invention relates to absorbent hygienic articles that include an antimicrobial amount of colloidal metallic silver or silver ions dispersed therein. BACKGROUND OF THE INVENTION

Colloidal silver and silver ions are generally considered to be safe and effective biocides. Common forms of biocidal silver materials include colloidal metallic silver (e.g., nanocrystalline silver or "nanosilver"), as well as silver ion-containing materials. Silver functions as a biocide by interrupting the metabolism of bacteria. For example, silver ions can be absorbed into bacterial cells, resulting a disruption of membrane transport mechanisms, respiration, and electron transfer. Various forms of silver materials that have been investigated as bacteriocidal agents include powdered silver metal, metal-substituted zeolites, metal-plated non-woven fabrics, and silver cross-linked polymeric materials.

Nanotechnology involves the manufacture and use of solid materials having dimensions in the nanometer (10"⁹ meter) range, typically on the order of about 0.1 nm to about 100 nm. Recently, nanotechnology has found uses in a variety of fields, including medical applications. The individual particles of colloidal silver have particle sizes in the nanometer range.

Colloidal silver has been recognized as a safe and effective antibacterial agent for over 200 years, and has been used in oriental medicine for many centuries. Colloidal silver has been used for antibacterial purposes in the human body. The advent of modern antibiotics has supplanted most medicinal uses for colloidal silver, however. Due to the rising number of antibiotic resistant bacteria, a need has arisen for antimicrobial agents that do not induce drug resistance. It has been found that colloidal silver is such an agent.

Antibacterial cloth containing biocidal metallic particles, such as copper, silver, and zinc, particularly incorporated into zeolites, has been known in the field for many years. Many methods for incorporating metal ions directly into fabrics and fibers have been proposed. Methods for directly incorporating metals into fabrics and fibers generally have led to expensive and heavy products. In addition, silver particles tend to migrate and separate during handling and storage of products containing such particles. .

SUMMARY OF THE INVENTION

The present invention provides nanosilver-containing absorbent hygienic articles, such as feminine sanitary napkins, tampons, bed pads, diapers, and the like having antimicrobial activity and adapted to minimize odors due to absorbed body fluids, likelihood of bed sores, etc. The absorbent hygienic articles of the invention include an absorbent member (e.g., an elongated body portion or pad) that contains an antimicrobial amount of substantially immobilized nanosilver particles or particles containing silver ions, preferably encased in a granule of a soluble carrier such a dextran, and the like, or a water-insoluble, but water- swellable superabsorbent polymer (SAP).

BRIEF DESCRIPTION OF THE DRAWINGS

In the Drawings, FIGURE 1 depicts a feminine sanitary napkin of the invention.

FIGURE 2 depicts a perspective view of feminine sanitary napkin of the invention.

FIGURE 3 depicts a perspective view of a tampon of the invention. FIGURE 4 depicts a perspective view of a tampon of the invention. FIGURE 5 depicts a cross-sectional view of a tampon of the invention. FIGURE 6 depicts a disposable diaper of the invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the hygienic articles of manufacture embodying the present invention, the absorbent member can comprise any absorbent material that is capable of absorbing and/or retaining body fluids (e.g., menses and/or urine). The absorbent member can be manufactured in a wide variety of sizes and shapes and from a wide variety of liquid-absorbing materials, depending on the intended end use of the article. A representative, non-limiting list of useful materials includes cellulosic materials, such as rayon, cotton, wood, pulp, creped cellulose wadding, tissue wraps and laminates, peat moss, and chemically stiffened, modified, or cross-linked cellulosic fibers; synthetic materials, such as polyester fibers, polyolefin fibers, absorbent foams, absorbent sponges, superabsorbent polymers (SAP), absorbent gelling materials; formed fibers, such as capillary channel fibers and multilimbed fibers; combinations of materials, such as synthetic fibers and wood pulp including coformed fibrous structures (e.g., those materials described in Anderson et al., U.S. Pat. No. 4,100,324); or any equivalent material or combinations of materials, or mixtures of these. The foregoing materials can be treated with a nanosilver antimicrobial solution such as the nanosilver-containing antimicrobial finishing or sizing agent commercially available from Shanghai Huzheng Nano Technology Co., Ltd., Shanghai 201204, China, for example, to impart antimicrobial properties to the liquid absorbing material.

Also, a manufactured absorbent article, e.g., sanitary napkin, tampon, bed pad, diaper, and the like, can be sprayed with a nanosilver-bearing sizing agent or immersed into a bath containing such a sizing agent, followed by drying, to provide the desired amount of nanosilver in the finished hygienic article of manufacture.

Preferably, the absorbent member comprises a fibrous mass in which nanosilver granules are distributed and are substantially immobilized. Preferably, nanosilver particles (about 0.1 to 100 nanometers in diameter, e.g., mean particle size) are distributed throughout the absorbent member. These particles can be present in the form of a finely divided powder or associated with a micro fiber carrier, a SAP that is a water-insoluble, but water-swellable particulate, such as a hydrocolloid, a hydrosol, and the like. The nanosilver particles preferably are - A -

incorporated into the water-insoluble, but water-swellable particles so that as these particles swell upon contact with a body fluid the nanosilver particles contained therein are available to contact the body fluid and exert the desired antimicrobial effect.

Suitable for this purpose is a water-insoluble, but water-swellable material, which is a particulate absorbent material having at least about 25 percent of its molecular structure composed of hydrophilic groups, and which is capable of retaining water in an amount that is at least ten times the dry weight of the absorbent material, and preferably about fifteen to seventy times the dry weight, or more. These particulate materials have a particle size of about 1 to about 10³ microns. A more complete description of these particles is set forth herein below.

Illustrative of the water-insoluble, but water-swellable particles having nanosilver distributed therein and suitable for use in practicing this invention are the so-called superabsorbent polymeric materials, which are water-insoluble, for example, the cross-linked polyacrylamides, cross-linked sulfonated polystyrenes, mixtures of the foregoing, and the like. Preferred are the hydrolyzed polyacrylamides having general Formula (T):

wherein Y is a hydrogen, ammonium, or an alkali metal ion, m is an integer having a value of 1 to 100, n is an integer having a value of 0 to 100, the sum of m plus n is 100, and Z is an integer having a value of 1 to 30, where Z times 100 is equal to the number of monomer units between crosslinks. These materials are known in the art and are described in U.S. Pat. No. 3,229,769 and U.S. Pat. No. 3,670,731.

The aforesaid polyacrylamide-type absorbent materials can be prepared by cross-linking a linear polyacrylamide with a non-conjugated divinyl compound such as methylene-bis-acrylamide. Alternatively, an acrylamide can be copolymerized. The polymerization techniques for these materials are known in the art and include the use of peroxide catalysts, photopolymerization with a riboflavin activator, and similar methods.

The cross-linking compound can be present in an amount of about 500 to about 5,000 parts per million parts of the polymerizate. Other illustrative non-conjugated divinyl cross-linking compounds are 1,4-divinylbenzene, N,N-diaHylacrylamide, diallylamine, diallylmethacrylamide, 2,5-dimethyl-l-,7-octadiene, p,p'-diisopropenylbenzene, 2,8-dimethyl-l,8-nonadiene, diethyleneglycol divinyl ether, and the like.

Particularly preferred particulate polyacrylamides for the present purposes are those in Formula (I) that are hydrolyzed and wherein Y is sodium or potassium, n has a value of about 10 to about 70, and Z has a value of about 2 to 20. Most preferred are the hydrolyzed polyacrylamides wherein Y is a sodium, n has a value of about 20 to about 40, and Z has a value of about 4 to about 15.

The cross-linked polystyrene sulfonates suitable for the present purposes can be represented by Formula (II):

wherein X is a hydrogen, ammonium, or alkali metal ion, and W is an integer having a value of about 100 to 3,000 and defines the number of monomer units between crosslinks. The foregoing crosslinked polystyrene sulfonates are well known in the art and are described in U.S. Pat. No. 3,670,731. The polystyrene sulfonates of Formula (H) can be prepared by copolymerizing styrene with a non-conjugated divinyl compound such as divinylbenzene in the presence of a polymerization catalyst such as benzoyl peroxide. To produce the desired particulate form of this absorbent material, a suspension stabilizer, such as gelatin or polyvinyl alcohol, can be added to the polymerization mixture. The produced polymer is then sulfonated by heating in the presence of concentrated sulfuric acid at a temperature of about 100° C.

Another grouping of suitable particulate absorbent materials comprises cross-linked poly(alkylene oxides) and the alkyl-substituted phenyl ethers thereof. The cross-linked poly(alkylene oxides) contain at least one of the units having a structure shown in Formula (Ht) and Formula (IV):

wherein R¹, R², R³ and R⁴ can be hydrogen, lower alkyl, lower alkenyl, and aryl, preferably methyl, vinyl, and phenyl, respectively.

The cross-linked polymers of the type shown in Formulas (ET) and (IV) are described in U.S. Pat. No. 3,783,872 and can be formed by preparing a substantially homogeneous aqueous solution of a water-soluble compound having the Formula (V):

wherein R¹ -R⁴ are the same as in Formulas (IH) and (IV), above, R⁵ and R⁶ are hydrogen, alkyl or alkaryl, and K is an integer having a value greater than 1, and subjecting the prepared solution to ionizing radiation for a time period sufficient to render the dissolved reactants insoluble. The preferred compounds within the purview of Formula (V) are ethylene oxide polymers having a reduced viscosity of at least about 0.5 and up to about 75, or an aqueous viscosity of about 225 centipoise (cP) to about 12,000 cP, measured as a solution of about 1 weight percent concentration at 25° C.

Particularly suitable are the ethylene oxide homopolymers and the ethylene oxide copolymers, terpolymers, and the like, containing up to about 50 percent by weight at least one other lower olefin oxide such as propylene oxide, butylene oxide, styrene oxide, and the like.

Still other suitable particulate polymeric absorbent materials are polyelectrolytes such as the water-insoluble, cross-linked copolymers of maleic anhydride and ethylene, as well as the hydrophilic maleic anhydride copolymers with vinyl methyl ether, divinyl ether, vinyl acetate, isobutylene, styrene, and similar unsaturated monomers. Generally, the foregoing polymeric polyelectrolytes are prepared by reacting ethylene or other unsaturated monomer or mixtures thereof, as previously described, with the acid anhydride in the presence of a peroxide catalyst in an aliphatic or aromatic hydrocarbon which is a solvent for the monomers but a nonsolvent for the interpolymer formed. Suitable solvents include benzene, toluene, xylene, chlorinated benzene and the like. While benzoyl peroxide is usually the preferred catalyst, other peroxides such as acetyl peroxide, butyryl peroxide, ditertiary butyl peroxide, lauroyl peroxide, and the like, or any of the numerous azo catalysts, are satisfactory since they are soluble in organic solvents.

The copolymer preferably contains substantially equimolar quantities of the olefin residue and the anhydride residue. Generally, the copolymer will have a degree of polymerization of about 8 to about 10,000, preferably about 100 to about 5,000, and a molecular weight of about 1,000 to about 1,000,000, preferably about 10,000 to 500,000.

The properties of the polymer, such as molecular weight, for example, are regulated by proper choice of the catalyst and control of one or more of the variables such as ratio of reactants, temperature, and catalyst concentration or the addition of regulating chain transfer agents, such as diisopropylbenzene, propionic acid, alkyl aldehydes, or the like. The product is obtained in solid form and is recovered by filtration, centrifugation, or the like. Removal of any residual or adherent solvent can be effected by evaporation using moderate heating.

Numerous of these polymers are commercially available.

Particularly useful copolymers are those derived from ethylene and maleic anhydride in approximately equimolar proportions. Such materials are commercially available in various molecular weights, e.g., having molecular weights of about 2,000-3,000, 20,000-30,000, and 60,000-80,000, any of which may be used for preparation of products employed in the present invention, since insolubilization by crosslinking leads to an indefinite molecular weight product. The maleic anhydride copolymers thus obtained have repeating anhydride linkages in the molecule, which are readily hydrolyzed by water to yield the acid form of the copolymer, rate of hydrolysis being proportional to temperature.

In addition, some of the aforementioned absorbent materials that are anchored on the open network structures in accordance with the present invention are initially water-soluble at a certain water temperature, but are rendered substantially water-insoluble once the water is removed by vaporization, or by irradiation while in an aqueous solution in a manner known in the art, prior to the vaporization of the water carrier.

Another preferred type of particulate absorbent material suitable for the present purposes is a graft copolymer of a water-insoluble polysaccharide such as starch or cellulose having hydrophilic chains of carboxylate-, and/or carbamide-bearing moieties.

Water-insoluble starch or a wide variety of cellulosic fibers can be utilized as starting materials for producing graft copolymers of this general type. Typical such cellulosic fibers are: cotton, cotton linters, wood pulp, bagasse pulp, jute, rayon, and the like. The polysaccharide chains are then modified by grafting thereon a hydrophilic chain of general Formula (VI):

in which A and B are selected from the group consisting of -OR⁹, -OM, -ONH₄ and -NH₂, wherein R⁷, R⁸, and R⁹ are selected from the group consisting of hydrogen and alkyl having 1 to 4 carbon atoms, wherein r is an integer having a value of 0 to about 5000, s is an integer having a value of 0 to about 5000, r plus s is at least 500, p is an integer having a value of zero or 1 , q is an integer having a value of 1 to 4 and M is an alkali metal ion.

Preferred hydrophilic chains are hydrolyzed polyacrylonitrile chains and copolymers of polyacrylamide and sodium polyacrylate. In another preferred embodiment both ionizable polymeric moieties and non-ionizable polymeric moieties can be grafted on the same polysaccharide backbone.

While the detailed mechanism by which the grafting of the hydrophilic chain or chains onto a starch or a cellulosic backbone is not fully known, it is believed that grafting takes place through a free radical mechanism whereby the free radical is situated on the backbone, which serves as a reducing agent, and the hydrophilic chain is attached to the starch or cellulosic reducing agent through a carbon linkage. The produced graft copolymer using a cellulosic backbone is of the type shown in Formula (VH):

wherein L represents the hydrophilic chain of Formula (VI), above. The graft copolymer using a starch backbone is substantially similar to that represented by Formula (VI) except that a starch backbone is present in lieu of a cellulosic backbone. The foregoing hydrophilic chains are polymers of an olefinically unsaturated carboxylic acid or a derivative thereof with itself or in approximately equimolar amounts with at least one other monomer copolymerizable therewith. The resulting polycarboxylic acid-type polymers can be of the nonvicinal type including those containing monomer units such as acrylic acid, acrylic anhydride, methacrylic acid, crotonic acid or their respective derivatives, including partial salts, amides and esters thereof, or of the vicinal type including maleic acid, itaconic acid, citraconic acid, alpha-dimethyl maleic acid, alpha-butyl maleic acid, fumaric acid, aconitic acid, as well as partial salts, amides and esters thereof. Anhydrides of any of the aforesaid acids can also be employed. Comonomers which can be used with the above functional monomers include alpha-olefms such as ethylene, propylene, isobutylene, 1-butene, 2-butene.

The initial copolymers of anhydrides with another monomer can be converted to carboxyl-containing copolymers by reaction with water, and carboxylate-contaming moieties, such as ammonium or alkali salts thereof, by reaction with aqueous solutions of alkali metal compounds such as sodium hydroxide, potassium hydroxide, and the like, or with aqueous ammonia.

The copolymers are formed in a known manner by reacting admixtures of the desired monomers in the presence of a peroxide catalyst in a suitable solvent for the monomers.

The obtained copolymers are conveniently identified in terms of their monomelic constituents. However, the names so applied to the copolymers refer to the molecular structure of the polymer and are not limited to the polymers prepared by the copolymerization of the specific monomers. In many instances, the identical copolymers may be prepared from other monomers and converted to the desired copolymer by a subsequent chemical reaction. A preferred hydrophilic polymer chain can be prepared by several methods known in the art. Illustrative of such methods are the following:

(1) Polymerize acrylonitrile and hydrolyze with an alkaline solution to form alkali salts of polyacrylic acid. (2) Polymerize an alkyl acrylate such as methyl acrylate ethyl methacrylate, and the like, and hydrolyze with an alkaline solution to form alkali salts of polyacrylic acid.

^• (3) Polymerize an alkyl acrylate such as methyl acrylate, ethyl acrylate, butyl acrylate, and the like, and partially hydrolyze so as to produce ionizable and non-ionizable polymeric moieties grafted on the polysaccharide backbone.

(4) Polymerize acrylic acid or alkali salts of acrylic acid.

(5) Polymerize methacrylonitrile and hydrolyze with acids to form polymethacrylic acid or hydrolyze with an alkaline solution to form alkali salts of polymethacrylic acid.

(6) Polymerize methacrylic acid or alkali salts of methacrylic acid.

(7) Polymerize acrylamide, optionally followed by hydrolysis.

(8) Polymerize methacrylamide, optionally followed by hydrolysis.

(9) Form copolymers of any of the above monomers or copolymerize with a small amount of non-hydrolyzable monomers.

Methods of graft-copolymerizing olefinically-unsaturated chains onto cellulose and starch are also known in the art. Thus, grafting of the hydrophilic material onto a starch or cellulose backbone can be accomplished simultaneously with the formation of the hydrophilic polymeric material in an aqueous medium, because the peroxide catalyst used to copolymerize the various monomers forms a redox catalyst system in combination with a reducing agent and thus also serves to effect chain transfer onto the starch or cellulose backbone. Suitable reducing agents for this purpose are eerie ion, ferrous ion, cobaltic ion ammonium persulfate, cuprous ion, and the like. The desired ions can be supplied in the form of salts such as eerie ammonium nitrate, ferrous ammonium sulfate, and the like. Graft copolymerization of olefinically-unsaturated chains can also be effected by irradiation (ultraviolet-, gamma-, or X-radiation) or by heating in an aqueous medium in the presence of an emulsifier.

Powdered starch or cellulose fibers or pulp can be slurried in water containing a graft copolymerization catalyst system and the monomer or monomers added to the slurry and polymerized in situ at ambient temperatures or above depending on the catalyst employed. In this manner, a portion of the formed hydrophilic polymer may also be physically entrapped into the polysaccharide backbone material during the polymerization process. The preparation of suitable starting materials for practicing the present invention is also illustrated in U.S. Pat. No. 3,256,372.

Hydrophilic chain loading on the polysaccharide backbone can vary from about 10 percent by weight to about 90 percent by weight, and preferably is about 40 to about 80 percent by weight of the graft copolymer.

An extremely water-swellable absorbent material suitable for the present purposes is a starch derivative commercially available from General Mills

Chemicals, Inc. under the designation "SG Polymer". This material is prepared by alkaline hydrolysis of starch polyacryloninϊle. The product is polymeric and comprises starch and a synthetic polymer composed of sodium acrylate and acrylamide. Proportions of starch and the synthetic polymer in the product are approximately 2:3, and the proportions of sodium acrylate and acrylamide in the polymer are approximately 3:1.

The term "water-insoluble" means that the product concerned does not dissolve in water or aqueous solutions at ambient temperatures, even though it does have characteristics such as high degree of swelling due to solvation by water, even to the extent of existence in a gel form. Such characteristics are imparted by cross-linking as previously described. The degree of cross-linking, i.e., cross-linking density, relates to the percentage of interchain linkages relative to the total functional units of the polymer.

Alternatively, the nanosilver can be dispersed within granules of a dried, water-soluble polymeric material, such as a dextran. Non-limiting examples of suitable dextran materials include dextran 40 (approximately 40,000 molecular weight) and dextran 70 (approximately 70,000 molecular weight). With such water-soluble materials, the polymer can be partially dissolved in water or made into an aqueous paste of a hydrated polymer. The nanosilver can be then be mixed with resulting hydrated polymer. The resulting mixture can then be dried to produce silver-containing granules. Referring to FIGS. 1 and 2, there is shown an embodiment of the present invention, a feminine sanitary napkin 20.

The sanitary napkin 20 has a main body 22 with a first transverse side 26 defining a front portion thereof and a second transverse side 28 defining a rear portion thereof. Each of these sides is arcuate in shape. The main body also has two longitudinal sides, namely a longitudinal side 30 and a longitudinal side 32.

The sanitary napkin 20 has a thickness usually less than about 5 mm. Preferably, the thickness is less than 3.5 mm, more preferably less than 3 mm, and most preferably, it is of about 2.8 mm.

The sanitary napkin 20 has a longitudinal centerline 34 that is an imaginary line bisecting the sanitary napkin 20 in two identical halves.

Projecting laterally outward from each of the longitudinal sides 30, 32 is a flap 38, 40 (respectively). The flaps 38, 40 are in the shape of an isosceles trapezoid with the top adjoining the longitudinal side and the base at the distal end. The main body 22 also has an imaginary transverse centerline 36 perpendicular to the longitudinal centerline 34 and simultaneously bisecting the flaps 38, 40.

The main body 22 is of a laminate construction and preferably comprises a liquid-permeable cover layer 42, an absorbent system 44, and a fluid- impervious barrier layer 50. The absorbent system has preferably two components, namely a first absorbent layer 46 (commonly known as "transfer layer") and a second absorbent layer 48 (commonly known as "absorbent body"). Alternatively, a single layer, namely the second absorbent layer 48, can form the absorbent system 44. Each of these layers is described in hereinbelow.

The cover layer 42 may be a relatively low density, bulky, high-loft non-woven web material. The cover layer 42 may be composed of only one type of fiber, such as polyester or polypropylene or it may be composed of bi-component or conjugate fibers having a low melting point component and a high melting point component. The fibers may be selected from a variety of natural and synthetic materials such as nylon, polyester, rayon (in combination with other fibers), cotton, acrylic fiber and the like and combinations thereof. An example is the non-woven cover layer of sanitary napkins sold by Johnson & Johnson Inc. of Montreal, Canada under the trademark STAYFREE ULTRA-THIN COTTONY DRY COVER.

Bi-component fibers maybe made up of a polyester layer and a polyethylene sheath. The use of appropriate bi-component materials results in a fusible non- woven fabric. Examples of such fusible fabrics are described in U.S. Pat. No. 4,555,430'. Using a fusible fabric increases the ease with which the cover layer may be mounted to the adjacent first absorbent layer and/or to the barrier layer.

The cover layer 42 preferably has a relatively high degree of wettability, although the individual fibers comprising the cover may not be particularly hydrophilic. The cover material preferably also contains a large number of relatively large pores. This is because the cover layer 42 is intended to take-up body fluid rapidly and transport it away from the body and the point of deposition. Therefore, the cover layer contributes little to the time taken for the napkin to absorb a given quantity of liquid (penetration time). The fibers which make up the cover layer 42 should not lose their physical properties when they are wetted. In other words, they should not collapse or lose their resiliency when subjected to water or body fluid. The cover layer 42 may be treated to allow fluid to pass through it readily. The cover layer 42 also functions to transfer the fluid quickly to the other layers of the absorbent system 44. Thus, the cover layer 42 is wettable, hydrophilic and porous. When composed of synthetic hydrophobic fibers such as polyester or bi-component fibers, the cover layer 42 may be treated with a surfactant to impart the desired degree of wettability.

The cover layer 42 can also be made of polymer film having large pores. The film accomplishes the function of quickly transferring body fluid to the inner layers of the absorbent system. Apertured co-extruded films such described in U.S. Pat. No. 4,690,679 and available on sanitary napkins sold by Johnson &

Johnson Inc. of Montreal, Canada could be useful as cover layers in the present invention. The cover layer 42 may be embossed to the remainder of the absorbent system 44 in order to aid in promoting hydrophilicity by fusing the cover to the next layer. Such fusion maybe effected locally, at a plurality of sites or over the entire contact surface of cover layer 42 absorbent system 44. Alternatively, the cover layer 42 may be attached to the absorbent system 44 by other means such as by adhesion.

Adjacent to the cover layer 42 on its inner side and bonded to the cover layer 42- is a first absorbent layer 46 that forms part of the absorbent system 44. The first absorbent layer 46 provides the means of receiving body fluid from the cover layer 42 and holding it until an underlying second absorbent layer has an opportunity to absorb the fluid, and therefore serves as a fluid transfer or acquisition layer.

The first absorbent layer 46, preferably, is more dense and has a larger portion of smaller pores than the cover layer 42. These attributes allow the first absorbent layer 46 to contain body fluid and hold it away from the outer side of the cover layer 42, thereby preventing the fluid from re-wetting the cover layer 42 and its surface. However, the first absorbent layer 46 is not so dense as to prevent the passage of the fluid through the layer 46 into the underlying second absorbent layer 48. The first absorbent layer 46 may be composed of fibrous materials, such as wood pulp, polyester, rayon, flexible foam, or the like, or combinations thereof. The first absorbent layer 46 may also comprise thermoplastic fibers for the purpose of stabilizing the layer and maintaining its structural integrity. The first absorbent layer 46 maybe treated with surfactant on one or both sides in order to increase its wettability, although generally the first absorbent layer 46 is relatively hydrophilic and may not require treatment. The first absorbent layer 46 is preferably bonded on both sides to the adjacent layers, i.e. the cover layer 42 and an underlying second absorbent layer 48.

Materials particularly suitable for use in the first absorbent layer 46, which contribute to reducing the penetration time have a density in the range of about 0.04 to 0.05 g/cc, a basis weight in the range from about 80 to 110 g/m² and a thickness in the range of about 2 to 3 mm and in particular, a thickness of 2.6 mm. Examples of materials suitable for the first absorbent layer are through air bonded pulp sold by Buckeye of Memphis, Term, under the trade name VIZORB 3008, which has a basis weight of 110 g/m² and VIZORB 3010, which has a basis weight of 90 g/m². Adjacent to and bonded to the first absorbent layer 46 is the second absorbent layer 48.

In one embodiment, the first absorbent layer 46 has a central width that is at least-about the same as the central width of the second absorbent layer 48. In a specific embodiment, this central width is greater than about 64 mm. In another embodiment, the first absorbent layer 46 has a central width that exceeds the central width of the second absorbent layer 48. The term "central width" refers to a specific area of a layer, such as an absorbent layer determinable as follows. A reference point on the sample layer that is disposed beneath the center of the vaginal orifice, when worn, is located. A plane parallel to the transverse centerline 36 and 3.75 centimeters forward from the reference point in the direction of the wearer's mons pubis is located. Another plane parallel to the lateral centerline 36 and 5.0 centimeters rearward from the reference point in the direction of the wearer's buttocks is also located. The greatest flat-out, uncompressed, unmanipulated, lateral width of the sample layer between the two planes is the absorbent width of the sample layer.

The central width of the absorbent system, when the absorbent system includes a plurality of absorbent layers, is the central width of the layer of the absorbent system that has the largest central width. In a specific example, the central width of the absorbent system exceeds 64 mm. In one embodiment, the second absorbent layer 48 is a blend or mixture of cellulosic fibers and superabsorbent disposed in and amongst fibers of that pulp.

In a specific example, the second absorbent layer 48 is a material containing from about 40 weight percent to about 90 weight percent cellulosic fibers, and about 5 weight percent to about 60 weight percent SAP (superabsorbent polymers) granules that include nanosilver. The SAP material has a water content of less than bout 10 weight percent. As used herein, the phrase "weight percent" means weight of substance per weight of final material. By way of example, 10 weight percent SAP means 10 g/m² SAP per 100 g/m² basis weight of the material.

Cellulosic fibers that can be used in the second absorbent layer 48 are well known in the art and include wood pulp, cotton, flax and peat moss. Wood pulp is preferred. Pulps can be obtained from mechanical or chemi-mechanical, sulfite, kraft, pulping reject materials, organic solvent pulps, etc. Both softwood and hardwood species are useful. Softwood pulps are preferred. It is not necessary to treat cellulosic fibers with chemical debonding agents, cross-linking agents and the like for use in trie present material. The second absorbent layer 48 can contain any superabsorbent polymer (S AP) with nanosilver particles distributed therein. SAPs are well known in the art. For the purposes of the present invention, the term "superabsorbent polymer" (or "SAP") refers to materials which are capable of absorbing and retaining at least about 10 times their weight in body fluids under a 0.5 psi pressure. The superabsorbent polymer particles of the invention may be inorganic or organic crosslinked hydrophilic polymers, such as polyvinyl alcohols, polyethylene oxides, crosslinked starches, guar gum, xanthan gum, and the like. The particles may be in the form of a powder, grains, granules, or fibers. Preferred superabsorbent polymer particles for use in the present invention are crosslinked polyacrylates, such as the product offered by Sumitomo Seika Chemcials Co., Ltd. of Osaka, Japan, under the designation of SA60N Type π*, and the product offered by Chemdal International, Inc. of Palatine, IL, under the designation of 2100 A* .

In a specific example, the second absorbent layer 48 is a material containing from about 50 to about 90 weight percent cellulosic fibers and, more specifically from about 60 to about 80 weight percent cellulosic fibers. Such a material may contain from about 5 to about 60 weight percent SAP, preferably from about 20 to about 55 weight percent SAP, even more preferably from about 30 to about 45 weight percent SAP, and most preferably about 40 weight percent SAP, and an antibacterial effective amount of nanosilver, preferably at least about 0.001 weight percent nanosilver. The aforementioned absorbent layers themselves can also be contacted with a nanosilver-containing sizing solution to provide additional nanosilver for antimicrobial efficacy.

FIGS. 3, 4 and 5 show a tampon 110 comprising an absorbent body 112, having an introduction end 114 and a withdrawal end 116, and a longitudinal main portion 118 therebetween. The tampon further has a constriction 120 and an end thereof. The tampon 110 is substantially enclosed within a cover 122 comprising fluid-imperious plastic material in the form of a resilient three- dimensional web having a multiplicity of perforations 124 diagrammatically drawn up in FIGS 3, 4 and 5. Said web comprises a coating composition, such as a nonionic surfactant, on its outer surface, at least in a portion corresponding to the constricted portion 120 of the tampon 110. A withdrawal cord 126 is attached to the tampon 110 and extends from the withdrawal end 116. Nanosilver containing granules of a SAP material are dispersed throughout absorbent body 112. Cover 122 can also be impregnated with nanosilver to provide a topical coating that contains nanosilver in an amount sufficient to minimize or ameliorate bacterial infections of the vagina, i.e., an antibacterial amount of nanosilver. Alternatively, cover 122 can be an apertured polymeric film or mesh that releases an effective amount of nanosilver or silver ions sufficient to suppress bacterial growth. Suitable for such purposes is a nanosilver loaded polymeric film available form Nanopac Co., Ltd., Suwon, Korea.

The web of fluid-impervious plastic material of the present invention can be manufactured by standard processes known to those of ordinary skill in the art. For example, the base film that is to be apertured can be extruded, cast, blown, or it may be formed in other processes that will be recognized by those of ordinary skill in the art. The base film can then be apertured by any of the known processes. Several examples include hot air aperturing, and water jet aperturing. The resulting apertured film can be slit to a desired width for use in manufacturing an absorbent article. Another preferred embodiment of the present invention is a disposable diaper containing an antibacterial amount of nanosilver distributed therein. FIG. 6 shows disposable diaper 200, having a main body 202 with a first transverse side 204 defining a front portion thereof and a second transverse side 206 defining a rear portion thereof. Main body 202 also has two longitudinal sides, namely a longitudinal side 208 and a longitudinal side 210. Each of these longitudinal sides is arcuate in shape to conform to the legs of a person wearing the diaper. Main body 202 is of a laminate construction comprising of a water- impervious outer sheet 212 and a water-permeable inner sheet 214, which are joined together around the peripheries thereof. Transverse sides 204 and 206 include elastic bands 216 and 218, respectively.

Diaper 200 has a longitudinal centerline 220 that is an imaginary line bisecting diaper 200 in two substantially identical halves. First absorbent pad

222 is disposed along longitudinal line 220 such that it is also bisected by line 220. Optionally, diaper 200 includes second absorbent pad 224 arranged perpendicular to pad 222 along the first transverse side 204 of diaper 200. Pads 222 and 224 are secured between sheets 212 and 214. Projecting laterally outward from each of the longitudinal sides 208 and 210, near second transverse side 206, is a flap 230, 232 (respectively). Flaps 230, 232 include a pressure sensitive adhesive coating on respective inner surfaces 234 and 236 thereof. Main body 202 also has an imaginary transverse centerline 240 perpendicular to the longitudinal centerline 220 and simultaneously bisecting the main body 202 perpendicular to centerline 220.

Absorbent pads 222, 224 preferably comprise cellulose fibers or other natural materials such as cotton fibers. Alternatively, synthetic fibers can be used, or a mixture of natural and synthetic fibers. Pads 222 and 224 can include multiple layers of fibers, if desired. A superabsorbent polymer and nanosilver are dispersed within the pads, as described herein for other embodiments. Absorbent pad 222 preferably contains at least about 25 percent by weight of a particulate superabsorbent material, and an antibacterial effective amount of nanosilver, preferably at least about 0.001 weight percent nanosilver. The nanosilver is encased within granules of the superabsorbent polymer. The water impervious outer sheet 212 preferably comprises a flexible, thin plastic film such as a polyethylene or polypropylene film, a polyester, or other suitable materials, which are well known in the disposable diaper art. Outer sheet 212 may also be made from a breathable material that is impermeable to fluids, but which allows for air and moisture vapor to be vented. Such breathable materials include blown or molded polyethylene films laminate with a nonwoven layer of spunbond or spunbond-meltblown-spunbond (SMS) material. The water permeable inner sheet 214 preferably is made from a material having properties like dryness and softness to the skin. Examples of suitable materials include a spunbond polypropylene, an apertured polyethylene film, and the like.

In FΪG. 6, absorbent pads 222, 224 are shown as having a generally rectangular shape. Typically, the pad 222 will have a length of about 200 to about

600 mm, and a width of about 50 to about 250 mm. Pad 224 typically has a length of about 50 to about 150 mm and a width of about 80 to about 250 mm. Pads 222, 224 typically have a thickness in the range of about 2-7 mm. Pads 222, 224 can have a shape other than rectangular, such as an hour-glass shape, if desired. The diapers of the invention can be made using standard manufacturing techniques that are well known in the disposable diaper art.

Example

S. G., a 47-year old mother of two complained of longstanding vaginal discharge. She had used some douching to treat the problem with mild success. She was in good health, working as a nurse practitioner. She did not have diabetes, or known venereal disease. She had not used any treatment for several months. She used, tampons for menstrual protection. On physical examination, no abnormalities were found. On pelvic examination there was a small amount of mucopurulent discharge. The vaginal mucosa was pink. There was a small cervical erosion. Pap smear was negative. The uterus and adexae were normal to palpation. A culture was taken for monilia, trichomonas, chlamydia, bacterial pathogens and viruses which showed only Gardnerella vaginalis. The patient was treated with a vaginal water douche daily followed by swabbing of the vagina daily and insertion of a nanosilver-containing, layered gauze (Acticoat 7^TM", Smith & Nephew). The gauze consisted of two layers of a fine silver-coated high density polyethylene mesh enveloping an inner core of silver-coated polyethylene mesh sandwiched between two layers of apertured non-woven fabric made from rayon and polyester. The gauze was inserted daily to cover the vaginal walls. After the fifth day, the gauze was removed. A culture taken two weeks later showed Gardnerella infestation to be gone. The clinical discharge was gone as far as the patient was concerned. The vaginal walls looked normal. The patient noted no side effects or complications.

As stated hereinabove, the absorbent hygienic articles of manufacture embodying the present invention include sanitary napkins, tampons, diapers, bed pads, and the like, and exhibit antimicrobial activity.

Numerous variations and modifications of the embodiments described above can be effected without departing from the spirit and scope of the novel features of the invention. It is to be understood that no limitations with respect to the specific embodiments illustrated herein are intended or should be inferred. It is, of course, intended to cover by the appended claims all such modifications as fall within the scope of the claims.

Claims

I CLAIM:

I . An absorbent hygienic article of manufacture having antimicrobial activity which comprises an absorbent member that contains an antibacterial amount of substantially immobilized nanosilver particles or silver ions.

2. A hygienic absorbent article having antimicrobial activity and adapted to minimize odors due to absorbed body fluids, which comprises an absorbent member that contains an antibacterial amount of substantially immobilized nanosilver particles or particles containing silver ions, the particles being encased in granules of a water soluble carrier or a water-insoluble, but water- swellable superabsorbent polymer (SAP).

3. The absorbent article of claim 2 wherein the absorbent member comprises absorbent fibers.

4. The absorbent article of claim 2 wherein the nanosilver particles are encased in a granules of a water soluble carrier.

5. The absorbent article of claim 4 wherein the water soluble carrier is a dextran.

6. The absorbent article of claim 2 wherein the nanosilver particles are encased in a granules of a water-insoluble, but water-swellable superabsorbent polymer.

7. The absorbent article of claim 2 wherein the absorbent member comprises at least about 0.001 weight percent of nanosilver particles.

8. The absorbent article of claim 2 wherein the nanosilver particles have a mean particle size in the range of about 0.1 to about 100 nm.

9. The absorbent article of claim 2 wherein the absorbent member comprises a fibrous mass in which nanosilver granules are distributed and are substantially immobilized.

10. A feminine sanitary napkin comprising an absorbent article of claim 2.

I I. A tampon comprising an absorbent article of claim 2.

12. A disposable diaper comprising an absorbent article of claim 2.

13. An absorbent hygienic article of manufacture having antimicrobial activity and comprising a fibrous absorbent member carrying substantially immobilized nanosilver in an antibacterial amount.