US 3561447 A
Description (OCR text may contain errors)
United States Patent lnventor Robert R. Alexander Sudbury, Mass.
Appl. No. 807,055
Filed Mar. 13,1969
Patented Feb. 9, 1971 Assignee The Kendall Company Boston, Mass.
a corporation of Massachusetts FLUSHABLE SANITARY NAPKIN 7 Claims, 1 Drawing Fig.
US. Cl 128/290, 117/140; 156/328; 161/146 lnt.Cl A6lf 13/16 Field of Search 117/140,
 References Cited UNITED STATES PATENTS 3,081,197 3/1963 Adelman 117/140 3,106,207 10/1963 Dudley Y 128/290 3,370,590 2/ 1968 Hokanson et al. 128/284UX 3,371,666 3/1968 Lewing 128/296 3,480,016 1 H1969 Constanza et 128/284 Primary Examiner-Charles F. Rosenbaum Attorney-John F. Ryan ABSTRACT: A bonded nonwoven fabric suitable for use as a flushable cover for a disposable diaper or a sanitary napkin is produced by bonding a thin web of textile-length fibers with a fugitive binder comprising a mixture of a soft acrylic binder and a polyvinyl alcohol. Such a fabric has sufficient tensile strength to function usefully as a cover whether dry or damp, but then, after use, may be readily disposed of by flushing since it disintegrates into a thin fibrous slurry when agitated in water.
PATENTEU man man FLUSHABLE SANITARY NAPKIN *The present'invention relates to nonwoven fabrics in which textile-length fibers'are bonded by abinding agent whose adherence to the fibers imparts to the fabric a substantial degree of fabric strength when dry. or damp, but which allows the disposable diapers, sanitary napkins, incontinent pads, surgical dressings, and the like, has created a disposal problem. Especially when such products are soiled or stained from usage, incineration is a cumbersome and offensive expedient. Recourse is frequently had to flushing the nonwoven covers in a water closet, but this introduces the hazard of clogged plumbing. Moreover, most bonded nonwoven fabrics are only slowly attacked by bacterial decomposition in a cesspool, septic tank, or sewerage system. Decomposition by bacterial attach is much more rapid if the fibers comprising the fabric are more or less individually separated from each other.
It is with improvements in the art of producing what will be termed herein flushable nonwoven fabrics that the present invention is concerned. Byflushable is meant not simply that the fabric can be bodily deposited in and flushed through a water closet, but that soaking the fabric in an excess of water, with even mild agitation, will cause the cover to release the bonding and so disintegrate into its component fibers. The use of such a cover as a wrapper around an absorbent core of unbonded flushable fibers results in an article which can be totally disposed of in a water closet with minimal danger of clogging the plumbing.
It is the primary object of this invention to provide a soft, conformable,and flushable nonwoven fabric for such use.
It is a further object of the invention to provide a nonwoven fabric which whether dry or damp has sufficient strength and toughness to serve as a covering for a diaper or sanitary napkin, but which when agitated in an excess of water by reason of its fugitive, bonding will disintegrate into a suspension of unbonded fibers.
lt is another object of the invention to provide a sanitary napkin which disintegrates completely into a fibrous slurry when agitated in water.
Other objects of the invention will appear from the following description thereof and the drawing, in which:
The FIGURE is a perspective view, partially cut away, of a sanitary napkin of this invention.
ln the FIGURE there is shown a sanitary napkin l comprising an absorbent core 12 and an external nonwoven covering 14 in intimate contact with said core. The shape and thickness, as well as the composition of the core, are conventional, as are the degree of overlap of the covering nonwoven fabric, and the method of sealing or securing the overlap if such an operation is desired.
Advantage is taken in this invention that a polymeric bonding agent such a polyvinylalcohol is known to swell strongly and eventually dissolve in water at room temperature. Polyvinyl alcohol is prepared by the saponification of polyvinyl acetate, and is considered to be principally a polymerized 1-3 glycol, (-CH,CHOH-CH,-CHOH),,. The saponification of the polyvinyl acetate is not complete, but in the polyvinyl alcohols of commerce, between 76 percent and 98 percent of the acetyl groups are replaced by hydroxyl groups. Polyvinyl alcohols saponified to between 76 percent and 98 percent are generally soluble in cold water.
The fact that the polyvinyl alcohol is too soluble in water renders it unsuitable for use alone as a binder for a nonwoven napkin or diaper cover, since it loses its bonding power rather readily when merely damp, and the fabric becomes incapable of retaining and enclosing the absorbent filler element. For example, a carded fleece of textile-length rayon fibers, bonded with polyvinyl alcohol alone, has adequate dry strength but has no measurable strength in either the machine or cross direction when damp.
By damp is not meant that the nonwoven cover is completely saturated and dripping wet, since it rarely if ever reaches that condition in actual use, being in intimate contact with a large mass of other absorbent material. Damp strength is therefore measured by wetting a nonwoven fabric with excess water and then quickly blotting it between absorbent paper towels or blotting paper until it has substantially ceased to transmit water to the blotting medium. The moisture content of the fabric will be found to be somewhere between percent and percent of the fabric weight when it is in the damp condition.
There are many methods available for cross-linking polyvinyl alcohol to insolubilize it, including reacting the alcohol with formaldehyde, phenol-formaldehyde, or melamine-formaldehyde, or cross-linking with metallic salts such as those of chromium, iron, copper, titanium, aluminum, and others. Unfortunately, they are not useful in the process of this invention. since the insolubilization is irreversible, and the cross-linked polyvinyl alcohol binder would remain water insoluble. Furthermore, the cross-linking reaction embrittles the binder and renders it stiff and harsh.
in contrast to the behavior of polyvinyl alcohol, aqueous dispersions of acrylic resins are used as bonding agents for nonwoven fabrics where wet strength is a desirable property of the fabric. Such binders are typified by the polymerized or copolymerized esters of acrylic and methacrylic acids wherein the ester group contains up to eight carbon atoms; acrylonitrile; and mixtures and modifications thereof. Such binders may be selected to yield soft, conformable nonwoven fabrics, but unfortunately their high wet strength renders the fabrics nonflushable: that is, nonwoven fabrics prepared from acrylic binders remain bonded when agitated in water, and do not disintegrate into a suspension of individual fibers or clumps of fibers.
. It has not been found that if a soft acrylic polymeric bonding agent and a portion of water-soluble polyvinyl alcohol are deposited together and substantially uniformly on a web of unspun and unwoven textile-length fibers and dried thereon, the
resulting product has sufficient strength when damp to serve as a cover for a disposable diaper or a sanitary napkin, but will disintegrate into individual fibers or clumps of fibers when gently agitated in an excess of water.
binder formulation comprising between 35 percent and 65 percent of a soft acrylic polymer and between 65 percent and 35 percent polyvinyl alcohol, used to bond a lightweight web of textile-length fibers, will yield a napkin or diaper cover which when damp (80 percent-B0 percent water content) will have a tensile strength of at least 0L3 pounds per inch-wide strip, but which will disintegrate into a thin slurry of small clumps of fibers within 20 seconds when mildly agitated in excess water. By contrast, the use of polyvinyl alcohol alone results in nonwoven fabrics with no measurable damp tensile strength, and the use of acrylics alone results in products which do not disintegrate in water and are therefore not flushable.
As a starting base material for the fabrics of this invention there may be used carded, garnetted, or air-laid webs of cotton, rayon, acetate, nylon, polyester, or others of the wellknown textile fibers of such length that they may be dry-assembled into a fleece or web, in distinction to the web processing of shorter papermaking fibers. For reasons of hydrophilicity, ease of separation when agitated in water, and cost, viscose rayon fibers are the material of choice. It has been found that rayon fibers of about 1 inch in staple length will yield, on disintegration, a thinner slurry than longer rayon fibers, 1.5 inches or more: about 1 inch staple length is therefore preferred. For diaper or napkin covers, a weight range of 10 to 20 grams per square yard is suitable.
Polyvinyl alcohol tends to form a film which is rather stiff and brittle, and its nature is not substantially changed by the presence of an acrylic binder. To enhance the softness of products designed for use as napkin covers, therefore, it is preferred that the polyvinyl alcohol be plasticized by, for example, a glycol such as glycerine, ethylene glycol, diethylene glycol, or other recommended glycol plasticizers for polyvinyl alcohol. The softness and esthetic appeal of the products of this invention preferable may be further enhanced by distributing the binder not uniformly throughout the web, but in a set of discrete and spaced-apart lines extending transversely across the web, in the manner known in the art as line bonding. Alternatively, the cover may be bonded by so-called spot bonding, by a set of broken transverse or oblique lines; by an overall diamond of lozenge print pattern; or by any of the other well-known and widely practiced patterns of discontinuous bonding. in this connection, therefore, it is understood that when reference is made to the binder being distributed substantially uniformly on the web, it is not meant that the whole extent of the web must be bonded, but that the binder is substantially uniform in composition in those areas where it is applied.
The invention will be illustrated by the following preferred example.
A carded web of 1.5 denier viscose rayon fibers, 1 inch long,
wrighing 12.6 grams per square yard, was bonded with an aqueous binder mixture consisting of:
Cellosize isa Union Carbide trademark for hydroxyl ethyl cellulose, and was used to thicken the binder mixture: Vinol is an Air-Reduction trademarked brand of polyvinyl alcohol: Triton is a trademarked wetting agent from Rohm and Haas; Poly M B225 is an acrylic ester-acrylonitrile polymer from Polymerics lnc.: Antiform AF is a Dow silicone antifoam.
Bonding was effected by printing the viscous binder onto the web by means of a print roll engraved with a series of shallow transverse grooves, one thirty-second inch wide, spaced 8 to the inch. Due to the aqueous nature of the binder mixture and the hydrophilicity of the rayon fibers, there is a certain amount of capillary spread in the width of the line of bonding agent, but for maximum enhancement of softness, it is preferred that at least 50 percent of the total area of the product should be substantially free of bonding agent.
The weight of the nonwoven fabric thus produced was 14.1 grams per square yard, indicating about 12 percent binder pickup. It has a machine direction tensile strength of 4.0 pounds when dampened to 130 percent water content. When gently agitated in water, a 4 inch square of the material was observed to disintegrate into a fibrous slurry or suspension in 18 seconds.
The products of this invention, though flushable, are marked by satisfactory resistance to damp abrasion, as well as by sufficient damp strength to serve satisfactorily as a cover for a disposable diaper or sanitary napkin. Such products combine an inner core of absorbent material, usually of inexpensive bulk material such as fluffed wood pulp, cellulose wadding, or the like, with a nonwoven cover wrapped or folded thereabout, said cover frequently being heat-sealed to itself to prevent displacement. In such structures, the absorbent core has many times the absorbent capacity of the cover, and performs the primary absorbing function. In this manner, a covering material in contact with such an absorbent core is generally found in a damp, rather than in a saturated, state.
Since the contents of the absorbent core are generally flushable, in that they disintegrate into a fibrous slurry in water, the use of the cover of this invention in such a structure leads to a sanitary napkin in which both cover and core are flushable, instead of different disposable techniques being required as in conventional.
1. A nonwoven fabric suitable for use as a covering for a disposable diaper or sanitary napkin:
having sufficient strength when damp to maintain its integri ty as a fabric; L
but capable of disintegrating into substantially individual nonunified fibers when gently agitated with an excess of water;
which comprises a web of textile-length fibers unified by a bonding medium which comprises between 35 percent and 65 percent of asoft acrylic polymeric binder; and between 65 percent and 35 percent of polyvinyl alcohol.
2. The product according to claim 1 in which the polyvinyl alcohol is plasticized by a water-soluble aliphatic glycol.
3. The product according to claim 1 in which the bonding agent is applied in the form of discrete, spaced-apart areas extending transversely across the fibrous web.
4. The product according to claim 3 in which the areas of bonding agent cover not more than 50 percent of the surface area of the fabric.
5. The product according to claim 1 in which the textilelength fibers are predominately of the order of approximately 1 inch in length.
6. The product according to claim I in which the soft acrylic bonding agent is a polymer copolymer of acrylonitrile and an acrylic ester of no more than eight carbon atoms in the ester group.
7. A wholly-flushable sanitary napkin comprising a flushable absorbent core and a nonwoven cover in intimate contact therewith:
said cover having sufficient strength when damp to maintain its integrity as a fabric and to contain the contents of the absorbent core;
but capable of disintegrating into substantially individual nonunified fibers when gently agitated with an excess of water;
said cover comprising a web of textile-length fibers unified by a bonding medium which comprises between 35 percent and 65 percent of a soft acrylic polymeric binder; and between 65 percent and 35 percent of polyvinyl alcohol.