Thin, Flexible Absorbent Pads

Abstract

Thin, absorbent pads with soft, flexible edges. The pad structure comprises a fluid pervious non-woven cover sheet, a central absorbent batt of comminuted wood pulp fibers, and a fluid-impervious backing element. Each element is coextensive with the others. The integrity of the central absorbent batt is maintained in the x and y directions by adhering the cover sheet and fluid impervious backing element to the respective top and bottom surfaces of the central batt by light applications of flexible adhesive, and in the z direction by hydrogen bonding of the wood pulp fibers in selected areas. The selected areas of hydrogen bonding comprise a spaced pattern of embossment lines which extend generally longitudinally of the pad and intersect the edges and ends of the pad at spaced intervals. The pad may be adapted for secure placement on a suitable support such as a snug-fitting undergarment by the use of pressure sensitive adhesive on the backing element or by increasing the frictional properties of the bottom side by the use of flexible foam or other friction increasing materials.

Description

BACKGROUND OF THE INVENTION

This invention relates to improvements in the structure of very thin absorbent pads primarily for feminine hygiene which may be used for undergarment protection between menstrual periods as well as for absorbing light flow between and during periods.

There are a number of prior art patents relating to thin absorbent pads for the above purposes. The pad structure defined in these patents broadly fall into two categories. One in which the main absorbent medium comprises multiple plies of creped absorbent tissue commonly called cellulose wadding, and the other in which the main absorbent medium is an airformed batt of comminuted wood pulp fibers commonly known as fluff.

This invention relates to improvements in the latter type of pad in which the main absorbent medium is fluff.

In prior art pads where fluff is the main absorbent component, it has always been considered necessary to confine or bind the short wood pulp fluff fibers in some way to prevent undesirable dusting of the short fibers which would otherwise occur. One common way of accomplishing this is to enclose the fluff batt in a tissue or nonwoven wrap as is taught for example in U.S. Pat. No. 2,826,200 issued Mar. 11, 1958. Another way to prevent dusting is to cover the tops, sides and ends of the pad with a nonwoven wrapper as shown in U.S. Pat. No. 3,575,175 issued Apr. 20, 1971. Still another way is to cover or adhesively bind the surface fibers and then seal all the pad edges by highly compressing the pad around its entire periphery as taught in British Pat. No. 1,071,191 published Jun. 7, 1967. Adhesive binder to secure all or part of the fluff fibers to each other has also been used in combination with some of the above structures.

While the above structures do accomplish the job of fiber confinement in various ways and do minimize or prevent dusting out of the fibers, some disadvantages in comfort and disposability remain when such structures are used for absorbent pads which contact the body as in feminine hygiene uses. In addition the cost of the confining elements special adhesive combination and multiple operations necessary to assemble the prior art pads add undesirably to the final cost of the product.

An encircling outerwrap of nonwoven material with an all fluff central batt and a thin film baffle for example, is relatively quite an expensive component when very thin pads are involved. In addition because of the inherent flexibility of thin pads, such wrappers tend to wrinkle excessively at the fold lines along the pad edges when the pad is arcuately bent into the usual shape which results when worn for catamenial uses.

When, as taught in the prior art, the entire periphery of the pad is compacted or compressed sufficiently to seal the edges with or without supplementary adhesive, relatively harsh and sharp edges are formed which, because of the resulting cardboard-like structure, tend to wrinkle and form undesirable abrasive edges during use. Continuous peripheral embossing also limits the thickness of the absorbent element which can be satisfactorily used and still remain sealed at the edges.

In the structure disclosed herein it has been found that a suitable pad can be provided, in which the short fibered fluff comprising the absorbent material in the central pad terminates at the peripheral edges without employing an enclosing wrapper or continuous peripheral sealing. The pad described herein can also be produced at low cost. While the resulting pad may dust moderately at the unbonded edge areas this slight disadvantage is overshadowed by the more important advantage of providing comfortable soft edges for the user. In emergencies, the pad may also be disposed of in a toilet since the main fluff element will delaminate and break apart as water destroys the hydrogen bonding in the embossed line areas hereinafter described thus permitting dispersion of the major portion of the fibers when the pad is agitated in water during the flushing action.

SUMMARY OF THE INVENTION

The pad of this invention comprises a thin elongate air felted absorbent batt of intermingled wood fluff fibers, a fluid pervious nonwoven cover sheet and a fluid impervious film backing sheet. The absorbent batt, cover sheet and backing film are all coextensive with each other.

The nonwoven cover sheet may be any of the many known types of pervious non-woven materials in common use as wrappers for sanitary napkins, the most common of which comprises carded rayon fibers of staple length bonded by a flexible adhesive.

In the preferred embodiment, the entire under-surface of the cover sheet is secured to the top of the fluff batt by a very thin adhesive layer. Preferably, the adhesive is applied to the top surface fibers of the fluff batt in the form of an atomized spray of aqueous based adhesive prior to placing the cover sheet material onto the batt.

The cover sheet is then placed on top of the sprayed batt and the fibers in the fluff batt are caused to bond to the cover sheet by the simultaneous application of heat and pressure. While moderate overall pressure is applied to bond the cover sheet to the batt, a critical consideration is to bond the fibers in selected areas by using heavy pressure sufficient to provide hydrogen bonding in areas defined by a pattern of narrow spaced lines of compression. Many suitable patterns may be used. A particularly preferred pattern comprises spaced longitudinally extending lines arranged in a sinuous pattern with the lines terminating at points spaced from each other around the pad periphery. The spacing between the lines of compression and the width of the lines is preferably such that the non-woven cover area between lines is not highly stressed in order that the batt areas between lines remains substantially uncompressed and thus provide soft, resilient, cushioned areas. Another important consideration is that the primary direction of the impressed lines be in the longitudinal direction of the pad and that the major portion of the edge area of the pad remain unbonded to retain its softness and resiliency.

After the batt and overlying cover sheet are integrated by heat and pressure, and the fluff fibers are hydrogen bonded by line embossing, the embossed pad structure is secured to a plastic film backing to complete the pad structure. Preferably such securement is obtained by an intermittent pattern of adhesive applied to the surface of the underlying film, with the spacing between adhesive areas being sufficient to permit easy flexing of the completed pad structure.

The completed pad may be used in combination with a tight fitting undergarment without supplementary attachment means if desired. Preferably, however, pressure sensitive adhesive is disposed on a portion of the bottom surface of the plastic film and covered with a removable protective strip which may be peeled off by the user for more positive attachment purposes. The bottom surface may alternatively be provided with a thin, flexible, high friction material such as synthetic sponge of polyurethane or the like which will help retain it in position on an undergarment by frictional engagement therewith.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a plan view of one embodiment of the pad of the invention.

FIG. 2 is a plan view of a modified pad shape.

FIG. 3 is an enlarged section taken along line 3--3 of FIG. 1.

FIG. 4 is a section similar to FIG. 3 showing a modification thereof.

FIG. 5 is a perspective view of the bottom of another embodiment of the pad.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the plan view of FIG. 1 there is shown a substantially elliptical pad having a top cover sheet 12 of non-woven material with a pattern of spaced longitudinally extending line embossments 14 impressed therein. Undulating line embossments 14 extend the full length of the pad and intersect the ends and edges of the pad at intervals indicated at 15, leaving major portions 16 of the periphery unembossed and therefore unbonded in the z-direction.

FIG. 2 illustrates an oblong tapered pad with undulating line embossments 14 of a similar nature.

The internal structure of the pad is shown in FIG. 3 which is an enlarged section taken along line 3--3 of FIG. 1. As shown therein, fiber batt 17 of absorbent wood pulp fibers is heavily compressed along line embossments 14 and by being so heavily compressed provide hydrogen bonding of the wood pulp fibers in areas 18. It is this hydrogen bonding which provides the fluff batt 17 with sufficient integrity to prevent delamination in the z-direction. Cover sheet 12 is puffed up in rounded cushion-like contours between the line embossments 14 where uncompressed and unbonded portions of fiber batt 17 press upwardly against cover sheet 12 between embossments.

Backing element 19 is a thin film, such as polyethylene, which is adhesively attached to batt 17 and which film retains its substantially planar configuration.

Cover sheet 12 is bonded to batt 17 over its entire common interface with batt 17 by a light layer of adhesive applied as hereinafter described, while film backing element 19 is intermittently bonded to the bottom surface of batt 17 by a spaced pattern of adhesive printed on the upper surface of the film 19 before assembling the pad into its final form.

Referring again to FIG. 1, unbonded edge portions 16 also retain a plumped up cushion-like configuration similar to that shown between embossments in FIG. 3 and thereby provide the pad with the desired soft edges.

The FIG. 4 pad structure is the same as that of the FIG. 3 pad except that a layer of lightweight synthetic sponge 20 such as polyurethane foam is additionally laminated to the backing element 19. The foam 20 provides a high friction surface which assists in maintaining the pad in place when the pad is worn with a tight-fitting undergarment.

In FIG. 5 a perspective view of the underside of a completed pad is shown wherein another means for attaching the pad to an undergarment is illustrated. As shown in FIG. 5 the backing element 19 has applied thereto a narrow band of pressure sensitive adhesive 22 which is covered by a peelable strip of protective release paper 24 or the like.

When the FIG. 5 pad is worn in combination with an undergarment, protective strip 24 is first peeled off and the exposed pressure sensitive adhesive 22 is then utilized to adhere the pad to the crotch area of the undergarment. Generally, the use of pressure sensitive attachment means for absorbent pads is well known in the art and is disclosed herein merely as a preferred embodiment.

While only two pads shapes are illustrated in the drawings, it is understood that various other elongate configurations may be used including a variety of geometric forms such as rectangular, oblate, diamond, hexagonal and the like.

Additionally while the line embossments are shown as uniformly spaced and substantially parallel undulating lines, other longitudinally extending patterns may be used. Important considerations are: that the lines be spaced sufficiently apart to prevent undue compression of the batt between lines; that the compressed bonded areas be of narrow width for the same reason; that they extend substantially longitudinally of the pad; and that where they intercept the edges they be spaced from one another to minimize edge compression or bonding. Typical dimensions for the line embossments comprise a width of about 1/32 inch and a spacing of about 1/4 inch to 3/8 inch. An objective of the line embossing arrangement, in addition to providing the hydrogen bonding which is the primary means for providing z direction integrity in the pads, is to provide the entire surface of the pad including the edges with a soft, cushion-like structure.

Another objective of the line embossments is to direct the migration of the absorbed flow in the longitudinal direction especially since the edges of the pad are unsealed and it is therefore desirable to keep any of the absorbed fluid away from these edges as long as possible. The longitudinally extending embossments serve this purpose well as conduits which due to their compressed condition provide small pores in the batt which enhance capillary suction pressures.

Undulating or wavy lines are also preferred for the line embossments because when the pad is bent into its arcuate shape during use, the wavy or undulating lines were found to flex much more readily than straight lines do and thus produce only small scale wrinkles which do not appear to interfere with tactile comfort as large scale wrinkles have been found to do.

As indicated throughout this specification, the primary purpose of the line embossing is to bind the short wood pulp fibers together by means of hydrogen bonding. As is well known in the papermaking art, hydrogen bonding of wood pulp fibers are bonds which develop when the hydroxyl groups of adjacent fibrillae in the cellulosic fibers form hydrogen bonds when a paper web is dried. In this instance the bonds are formed during the embossing process. Such bonding is also the sole means for maintaining the strength and integrity of the batt in the z direction in the pads disclosed herein. Sufficient strength and integrity in the x and y directions are of course provided by the adhesive attachment of the cover sheet and backing element to the batt as previously described. The x, y, and z designations are used herein in the customary manner, i.e., x and y are the transverse and longitudinal directions respectively, while the z direction is perpendicular thereto.

A suitable method for fabricating the pads will now be described. In manufacturing the pads a thin uniform continuous batt of intermingled wood pulp fibers is first formed by suitable airlaying methods. Many methods for airlaying wood fibers are known, so there is no need to describe such methods here. It is also well known that airlaid batts have little self integrity because even though the fibers in the batt are intermingled, no chemical bonding is developed in dry forming and since the fibers are so short little tensile strength is derived from mere mechanical entanglement. Airlaid batts are therefore very weak and easily destroyed when tensile forces are applied. To obtain batts with structural integrity some supplementary bonding means is therefore required. This is particularly true when the batt is thin, i.e., in the range of 1/16 inch to 1/4 thick as used herein.

Because of the inherent structural weakness of unbonded airlaid batts it is therefore necessary during subsequent converting operations for the formed batt to be carried on suitable supporting means such as the wire mesh fabric on which it is formed during the airlaying process. Alternatively, the batt could be formed on woven or non-woven scrim which could then be retained with the batt and become an integral part of the finished pad, if desired. However, the latter modifications adds to the final cost, and since these pads are intended to be disposable low cost pads, the inclusion of scrim may not be desirable from a cost standpoint.

After the batt is formed it is sprayed with a light application of an atomized spray of an aqueous-based flexible adhesive. Amounts in the range of 5 to 15 grams per square yard are appropriate. In general, acrylic latexes are preferred for use as the adhesive. It is desirable to use latexes or other aqueous-based adhesives because it is necessary to moisturize the wood fluff fibers at some stage in the process in order to obtain the previously mentioned hydrogen bonding, and aqueous-based adhesives facilitate this.

After the adhesive is sprayed onto the batt, a cover sheet of fluid-pervious non-woven material is then applied to the surface of the batt on which the adhesive has been sprayed. This laminate is lightly pressed between two rolls to slightly adhere the cover sheet and batt and is next passed under a bank of infrared lamps or other heating means to partially set the adhesive and to help condition the batt to a point where the moisture is uniformly distributed through the batt in the amount of about 10 to 20 percent by weight. Further moisture conditioning of the laminate may be done before embossing by spraying the laminate with water at this point in the process. The laminate is then passed through a high pressure nip comprised of a top embossing roll having the desired pattern and a lower heated roll. As the conditioned laminate is passed through the nip, the high pressure exerted on the moisture-conditioned batt by the raised land areas of the embossing roll develops the hydrogen bonding of the fibers in only the compressed area of the batt. Nip pressures in the range of about 70-85 psi and temperatures of about 300.degree. to 350.degree.F are suitable for this purpose. Heat is utilized to help drive off residual moisture and to further set the adhesive. The preferred density of the batt in the compressed and hydrogen bonded areas is in the range of about 0.40 grams per cubic centimeter to about 1.0 grams per cubic centimeter. In the uncompressed areas preferred densities are approximately 0.03 grams per cubic centimeter to about 0.15 grams per cubic centimeter.

The laminated batt and cover sheet are then passed through another light pressure nip where a film backing element having a patterned adhesive on the surface is applied to the bottom of the batt to complete the laminated structure.

The continuous laminate then goes through further processing machinery where pads of the desired shape and dimension are cut out, and where pressure sensitive adhesive or friction increasing means may also be applied to the bottom surface.

The hydrogen bonding along the embossed lines, which is provided during fabrication, has been found to be of sufficient strength to retain the integrity of the batt, and thus the entire structure, during normal use. In the event the pad is disposed of in a toilet, or inadvertently dropped therein, these hydrogen bonds are swiftly destroyed as the water penetrates the batt. The batt will then delaminate and permit the major portion of the wood pulp fibers to disperse during normal flushing action. The cover sheet and backing element, of course, will not disperse but they are considered sufficiently flexible to pass through a normally functioning toilet system without difficulty.

While acrylic latexes are preferred for use as the bonding material between the cover sheet and the batt and also to secure the batt to the backing element, other flexible adhesives of similar nature may be used. Suitable adhesives, among the acrylics for example, included ethyl and methyl acrylates and their copolymers, and copolymers of ethyl acrylates, acrylamides and acrylic acid. Other suitable adhesives include vinyl resins such as vinyl acetates and vinyl chlorides and combinations thereof, other synthetic latexes such as butadiene, acrylonitrile and styrene and copolymers thereof, natural gums, starches and the like. Aqueous based adhesives are preferred of course for reasons mentioned earlier. That is, in order for the hydrogen bonding to occur, the batt must be properly conditioned with moisture, and the light spray application of an aqueous-based adhesive assists in achieving this purpose. A surfactant may be added to the latex in amounts of 4 to 5 percent by weight based on latex solids in order to maintain absorbency. Any suitable surfactants may be employed for this purpose. Particularly suitable are sulfated or sulfonated organic compounds representative of which are the sodium diamyl to sodium dioctyl sulfosuccinates, sodium lauryl sulfates, sodium sulfoethyl methyl oleyl amides, and sodium sulfonates of alkylated phenols or benzenes. When any of these are employed they should be non-toxic in nature, of course.

While the pad may be used in its basic form, it is preferred that it be provided with some garment attachment means. A preferred means is a strip of pressure-sensitive adhesive as described with respect to FIG. 5. A thin, flexible foam layer such as polyurethane may also be used. Patches of friction increasing hot melts or the like may also be used.

The cover sheet may also be comprised of various materials and still function. A preferred material is a non-woven web of stable length rayon fibers. Other fibers including absorbent and non-absorbent synthetics may be used. Spunbonded webs of continuous filaments such as polyethylene, polypropylene, polyesters, nylon and the like may also be used. When the latter hydrophobic webs are used the pad retains a much drier surface when in use and such webs are sometimes preferred for that reason.

Claims

What is claimed is:

1. An elongate thin absorbent pad with soft flexible edges, said pad comprising a fluid pervious cover sheet of non-woven fibers, a central absorbent batt of comminuted wood pulp fibers, and a fluid impervious backing element; said cover sheet, absorbent batt, and backing element being coextensive; the entire undersurface of said cover sheet being secured to said batt by a light overall layer of flexible adhesive which does not penetrate into the batt; said cover sheet and said batt having a spaced pattern of line embossments impressed therein; said line embossments extending primarily in the longitudinal direction of said pad and intersecting the edges and ends of said pad at spaced intervals; said line embossments defining areas of said batt in which the fibers have been moisture conditioned and sufficiently compacted in the z direction to form hydrogen bonds between those fibers disposed in said line embossment areas; said backing element being secured to the bottom of said batt by discrete adhesive segments disposed in a spaced pattern; the adhesive between said cover sheet and said backing element respectively serving to attach only the respective surface fibers of the batt to said cover sheet and backing element in the adhesive areas; the integrity of said batt in the z direction between cover sheet and backing sheet being provided solely by said hydrogen bonding; and the fibers in the ends and edges of said batt being free of z-direction bonding except where intersected by said line embossments.

2. The absorbent pad of claim 1 wherein said batt has a thickness in the range of about 1/16 inch to about 1/4 inch.

3. The absorbent pad of claim 1 wherein said line embossments have an undulating configuration.

4. The absorbent pad of claim 1 wherein the density of said batt in the area of said line embossments is in the range of about 0.4 grams per cubic centimeter to about 1.0 grams per cubic centimeter.

5. The absorbent pad of claim 4 wherein the density of said batt in the area between said line embossments is in the range of about 0.03 grams per cubic centimeter to about 0.15 grams per cubic centimeter.

6. The absorbent pad of claim 1 wherein said fluid impervious backing element is a thin plastic film.

7. The absorbent pad of claim 1 wherein said backing element has an area of pressure sensitive adhesive applied to the lower surface thereof and wherein said area of adhesive is covered with a removable protective sheet.

8. The absorbent pad of claim 1 wherein said backing element has applied to its lower surface a friction-increasing material.

9. The absorbent pad of claim 8 wherein said friction increasing material is a thin layer of flexible plastic foam.