|Publication number||US3683916 A|
|Publication date||Aug 15, 1972|
|Filing date||Jan 11, 1971|
|Priority date||Jan 11, 1971|
|Also published as||CA964979A1|
|Publication number||US 3683916 A, US 3683916A, US-A-3683916, US3683916 A, US3683916A|
|Inventors||Frederick K Mesek, Virginia L Rapke|
|Original Assignee||Frederick K Mesek, Virginia L Rapke|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (7), Referenced by (32), Classifications (10)|
|External Links: USPTO, USPTO Assignment, Espacenet|
United States Patent Mesek et al.
[ DISPOSABLE DIAPER  Inventors: Frederick K. Mesek, 929 Clyde Ave, Downers Grove, 111. 60515; Virginia L. Rapke, 15333 Maple Dr., Oak Forest, Ill. 60452 221' Filed: Jan. 11, 1971 21 Appl.No.: 105,195
Related US. Application Data  Continuation-in-part of Ser. No. 861,689, Sept.
29, 1969, abandoned.
. 151 3,683,916 [451 Aug. 15, 1972 3,595,235 7/1971 Jespersen .l ..128/284 Primary Examiner-Charles F. Rosenbaum Att0rney-Michael Q. Tatlow, Harold L. Warner and Robert L. Minier 5 ABSTRACT A disposable multi-layered diaper of high absorptive capacity is provided which comprises as a first layer to be brought into contact with an infant's skin, a porous, fibrous non-woven bonded facing web of controlled wettability made of mixed long and short fibers. A second layer in juxtaposition to the facing layer, is a highly porous batt of short cellulosic fibers which are loosely compacted throughout the thickness of the batt, to provide a layer which has greater wettability that that of the facing web. The outermost backing layer of the diaper is an impervious sheet directly adhered to its adjacent layer, which may be the second layer, over a widely distributed area of adhesion. in some embodiments of the invention there may be provided one or more layers between the highly porous batt and the impervious backing sheet, for example, an additional highly porous batt or a plurality of sheets of creped cellulose wadding.
24 Claims, 8 Drawing Figures Patented Aug. 15, 1972 2 Sheets-Sheet 1 5 M W M M Patented Aug. 15, 1972 2 Sheets-Sheet 2 321a), Zz/
DISPOSABLE DIAPER CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of our application Ser. No. 861,689, filed on Sept. 29, 1969 and now abandoned.
BACKGROUND OF THE INVENTION Disposable diapers provide substantial advantages in convenience over diapers intended to be laundered and reused, particularly when they are used away from home. In recent years, many different disposable diapers have been proposed and some have been successful in the marketplace. However, even the successful diapers are inadequate in functioning properties,
and their success has come because consumers are resigned to accepting inadequate performance as part of the price for convenience.
One design criterion which has not heretofore been met adequately is the desire to keep moisture away from the surface of the diaper which comes into contact with the infants skin and thereby avoid skin irritation and infection.
Another important criterion is lack of stiffness and ready confonnability to the body of the infant for maximum comfort.
In one form of prior disposable diaper, creped cellulose wadding is used as the sole absorbent material, covered with a permeable paper-like facing material on the side to be brought into contact with the infants skin and covered with an impervious plastic sheet on the outside. In such a diaper, the wadding becomes more or less uniformly saturated with urine as the infant voids and there is thus a substantial amount of moisture only a papers thickness away from the infants skin. In use, the weight of the infant presses the paper-like facing layer against the saturated wadding so that substantial amounts of moisture pass through the facing into contact with the infants skin.
In addition, in the prior art form of disposable diaper, the limited absorptive capacity of the cellulose wadding makes it necessary to prevent excess urine from wetting the infants outer clothing or bed clothes. This diaper provides a folded-over edge of the impermeable plastic sheet which is put into direct contact with the infants skin to make an impermeable envelope to hold the excess urine. However, the prolonged direct contact of plastic to the infants skin can cause irritation and infection.
Finally, both the paper-like facing material and the creped wadding of this prior art diaper are relatively stiff, making for an uncomfortable diaper, particularly when sufficient wadding is present to absorb a reasona ble amount of urine.
SUMMARY OF THE INVENTION In accordance with this invention, a diaper is provided which, within a volume small enough to be consistent with comfort,
a. handles the full volume of one or more discharges of urine;
b. rapidly draws (funnels) the urine away from the infants skin, leaving a relatively dry layer in contact therewith; and
c. keeps the absorbed urine from wetting outer garments or bed clothes.
Specifically, these functions are accomplished by a multi-layer. diaper comprising, in juxtaposed relationship in the order named, a fibrous facing layer of a mixture of short and long fibers, usually cellulosic fibers, bonded one to the other, which facing layer is intended to be brought into contact with the infants skin, a highly porous batt of loosely compacted short cellulosic fibers, and an impervious backing sheet adhered to the loosely compacted cellulose batt throughout the area of the interface therebetween. Optionally, a layer comprising a second loosely compacted batt of cellulosic fibers or a layer comprising a plurality of sheets of creped cellulose wadding may be interposed between the first-named cellulosic batt and the impervious backing sheet.
Disposable diapers are usually rectangular in configuration, the longer dimension being adapted to extend from the back of the infant's waist to the front of his waist, while the shorter dimension is limited to what can comfortably fit around the infants waist and between his legs. In a diaper in which urine discharge tends to spread evenly in the wetted area, any discharge to a mid-point of the diaper is likely to spread to its side edges before it reaches its ends and before the absorptive capacity of the diaper is fully utilized. In the preferred embodiments of the diaper of this invention, flow or urine is preferentially directed longitudinally of the rectangular diaper to compensate for the dimensional inequality and to more or less equalize the spread of urine to each edge of the diaper.
In the embodiment of the diaper which includes a layer of creped cellulose wadding, preferential longitudinal urine flow is achieved by orienting the wadding layer so that its machine direction is transverse to the length of the diaper and the ridges of the creping run parallel to the length of the diaper. In those embodiments of the diaper in which the impervious sheet is adhered directly to a loosely compacted, highly porous batt, the adhesion between the sheet and the batt throughout the interface between them is along spaced parallel lines running the length of the diaper, thus tending to channel liquid flow between the adhesive lines.
The fibrous facing layer of the diaper is of porous construction and its fibers have less wettability for water than the fibers of the adjacent loosely compacted batt, resulting in a tendency for liquid to flow from the facing layer into the batt. The creped cellulose wadding, when used, has a smaller average pore size than the loosely compacted fibrous batt, resulting in a tendency for liquid to flow from the batt into the wadding.
The respective elements of the multi-layer diaper of the invention cooperate in that (l) urine flowing into a small area on the outer surface of the facing layer, flows preferentially into the underlying batt rather than to other areas of the facing layer, thus tending to contain wetting of the facing layer to a restricted region and to move the urine away from the infants skin; (2) urine flowing through a small region of the interface between the facing layer and the loosely compacted batt tends to spread laterally within the batt (or batts) because of the greater wettability and wicking action of the fibers therein; (2a) when a creped wadding layer is used, the urine flowing thereinto tends to spread more rapidly than in the loosely compacted batt, thus tending to restrict wetting in the batt to an area of moderate size and to move the urine farther from the infants skin; (3) urine which might pass through the loosely compacted batt (or batts, or through the batt and wadding) during discharge is held back by the impervious backing sheet for sufficient time to permit absorption of the urine within the region of the batt to take place, especially when urine flow is rapid; and (4) urine is excess of the rapid absorptive capacity of the loosely compacted batt (or batts, or of the batt and wadding) is forced back by the impervious layer into the dry portion of the batt for take-up at a slower rate, thus effecting utilization of the full absorptive capacity of the batt.
In the preferred embodiment of this invention, the facing layer is coextensive in dimension with the impervious backing sheet and there is no fold-over of the latter on to the forward face of the diaper. In this embodiment, the complete face of the diaper which is brought into contact with the infant is of fibrous material, and there is no plastic layer or similar impervious layer on that face. Thus, the diaper avoids the clamminess and possible irritation and infection which result from direct contact between the plastic material and the skin.
Our copending application Ser. No. 6,864, filed Jan. 29, 1970 and now US. Pat. No. 3,612,055, relates to a diaper having a facing layer made of a bonded web of long and short fibers, a highly porous loosely compacted batt of short cellulosic fibers and an impervious backing sheet, and also having a paper-like densified, highly compacted cellulosic fibrous layer integral with the loosely compacted batt and on the face thereof adjacent to the impervious sheet. In the present invention, by contrast, the loosely compacted batt of cellulosic fibers has substantially no density gradient in its thickness dimension and in one embodiment, is bonded directly to the impervious backing sheet.
One purpose of the densified layer, or skin, of the diaper of Ser. No. 6,864, is to enhance the rate of absorption of urine so that it can be absorbed quickly following a rapid discharge. In the embodiment of this invention wherein the creped cellulose wadding is used, it serves the same function as the densified layer, or skin, i.e., to speed up the rate of urine absorption while at the same time (when properly oriented) tending to equalize the spread of urine to the side and end edges of the diaper.
For some uses, however, the ultimate absorptive capacity of the diaper may be more important than its rate of absorption, and the diaper which utilizes only the loosely compacted batt short cellulosic fibers has a higher absorptive capacity for the same total weight of absorbent than the diaper which utilizes a batt having a densified skin of cellulosic fibers. In an overnight diaper for a very small infant, for example, the total discharge of several voidings may make added absorptive capacity desirable while the rate of discharge in any one voiding may not be so great as to tax the absorption rate of the loosely compacted batt, so that advantage may be taken of the higher ultimate absorptive capacity per unit weight of the loosely compacted batt having no density gradient over that of a batt in which a portion of the fibers are highly compacted.
DESCRIPTION OF THE DRAWINGS The invention is more readily understood by reference to the drawings, in which:
FIG. 1 is a perspective view, partly in cross section, of an open unfolded diaper in accordance with one embodiment of this invention;
FIG. 2 is a partial cross section of the diaper of FIG. 1 taken along plane 2-2, illustrating the internal configuration of the embodiment of FIG. 1;
FIG. 3 is a partial cross section similar to FIG. 2, illustrating an alternate embodiment of the invention;
FIG. 4 is a partial cross section similar to FIG. 2, illustrating another alternate embodiment of the invention in which two cellulosic batts are interposed between the impervious sheet and the facing layer;
FIG. 5 is a perspective view on a reduced scale of the diaper of FIGS. 1 and 2 in its configuration after being put on the infant;
FIG. 6 is a perspective view, partially in phantom, illustrating one manner in which the diaper of FIGS. 1 and 2 may be folded, and the manner of partially opening the diaper for use;
FIG. 7 is a partial cross section of the folded diaper of FIG. 6, taken along plane 7-7; and
FIG. 8 is a perspective view, partly in cross section, of an open unfolded diaper in accordance with the embodiment utilizing a layer of creped wadding.
DETAILED DESCRIPTION OF THE INVENTION Referring to the drawings, and particularly to FIGS. 1 and 2, the diaper assembly 10, when fully opened and laid out flat, comprises a lowermost water-impervious sheet 12 which is rectangular in shape, a highly waterabsorbent fibrous pad, or batt 14, which is also rectangular in shape, but smaller than the impervious sheet and centrally disposed thereon, and an overlying facing layer 16 of fibrous material, which is also rectangular in shape, equal in dimension, and coterminous with the impervious sheet and in contact therewith in the marginal portions of the diaper extending peripherally beyond the absorbent pad, i.e., in the portions 16b and 12b of facing layer 16 and impervious sheet 12, respectively. The batt 114 is adhered to the impervious sheet by bead lines of adhesive 22 substantially throughout the interface therebetween. Marginal portions 162; and 12b are also adhered to each other by bead lines 22 of adhesive.
In the preferred embodiment of the invention, moisture impervious sheet 112 is formed of polyethylene having a thickness of approximately 0.001. The sheet may be smooth, or may be embossed to improve its drape and feel. Other suitable flexible moisture impervious sheets may be used in accordance with the invention, such as, for example, polyethylene terephthalate sheets having a thickness of about 0.005 inch.
Batt 14 is formed of loosely compacted short cellulose fibers, such as wood pulp fibers, or cotton linters, or mixtures thereof, which are primarily held together by interfiber bonds requiring no added adhesive, as is known in the art. Briefly, this batt is a low bulk density coherent web of loosely compacted cellulose fibers preferably comminuted wood pulp fibers in the form of so-called fluff.
The term short fibers, as used herein, refers to fibers less than about one-fourth inch in length, in contrast to long fibers, or textile length fibers which are longer than about one-fourth inch in length, and generally are between about one-half and 2 inches in length. The former are substantially less costly than the latter. The classification of short fibers by length may be carried out by the Clark Classification procedure described in the test manual of The Technical Association of Pulp and Paper Industry (TAPPI-T233 SU64).
The density of batt 14 should be, above about 0.07 gm./cc., and preferably between about 0.10 and 0.20 gm./cc. The foregoing density values are applicable to the diaper as produced. In storage and handling, the loft or thickness of the batt is increased to some extent, resulting in lowered densities.
Facing layer 16 is made up of a mixture of fibers consisting predominantly of short cellulosic fibers such as wood pulp fibers or cotton linters, in amounts of about 75 percent to about 98 percent, the balance being textile length fibers such as rayon. Short cellulosic fibers such as wood pulp fibers or cotton linters are substantially less expensive than textile length cellulosic fibers such as cotton and rayon, and this low cost is a factor in reducing the cost of the facing layer component of the diaper of this invention.
In the facing layer, the short fibers are in uniform admixture with 2 to 25 percent by weight of textile length fibers, such as 1.5 denier rayon fibers uniformly cut to llinch length. The short and long fibers are randomly and substantially uniformly dispersed and bonded with a bonding agent such as a self-cross-linking acrylic emulsion. The facing web is also treated with a wetting agent to partially counteract the water-repellency of the bonding agent and bring the facing layer to the desired degree of wettability. Facing layers of this character are described in greater detail in commonly owned copending U.S. Pat. application Ser. No. 729,784.
Facing layers suitable for use in this invention have fabric weights in the range of 1 to 5 oz./yd. and densities less than 0.15 gm./cc. generally in the range between 0.05 and 0.1 gm./cc. The dry strength of the facing layer, for a fabric having a weight of about 1.5 oz./yd. is at least 0.15 lbs/in. of width in the machine direction and at least 0.08 lbs/in. of width in the cross direction. The fabrics have unusually good elongation, loft, softness and drape characteristics in comparison to prior products incorporating any substantial amount of short fibers.
An important aspect of this invention is the provision for selective wettability between the facing layer and the loosely compacted batt of short cellulosic fibers, such that the. moisture is selectively drawn from the facing layer into the batt.
The less wettable of the fibrous elements of the diaper of FIG. 1 is facing layer 16. However, even in the facing layer the ability to be wetted by water is desired. Water repellency in the facing layer is not desired since, at the desired fiber densities in the facing layer, water repellency can prevent the liquid from penetrating into the facing layer and the absorbent layers behind it, just as a tent fabric holds back penetration of rain water. For this reason, the facing layer is usually treated with a wetting agent, such as an anionic surfactant, to moderate and reduce the water repellency which may be imparted to the short and long fibers of the web by the bonding agent which bonds them into an integral layer. After treatment with a wetting agent, the facing layer is receptive to penetration by urine but remains less wettable than the batt.
A useful parameter of wettability is the liquid-fiber contact angle for the individual fiibers of the layer, the contact angle approaching for fibers which are difficultly wettable, exceeding 90 for fibers which are highly water repellent and approaching zero for fibers which are highly wettable by water. The liquid-fiber contact angle may be determined from interface high speed photographs of individual dry fibers, held in a clamp, and advanced into the wetting liquid (water) at a rate of 0.5 cm/sec. by techniques known in the art.
In any particular facing layer, the liquid-fiber contact angle for individual fibers may vary considerably because of uneveness of distribution of the water-repellent bonding agent and unevenness of distribution of wetting agent. Nevertheless, a liquid-fiber contact angle between about 30 and about 60 for most (over 50 percent) of the individual fibers in a random selection provides suitable wettability in the facing layer, and a liquid-fiber contact angle between about 40 and about 60 is preferable.
Batt It is substantially more wettable than the facing layer and tends to draw liquid away from the facing layer. The individual fibers of the batt are extremely wettable, generally having liquid-fiber contact angles below about 15 and approaching zero in the optimum embodiment.
The relative wickability, or preferential absorptivity for water, between facing layer 16 and batt M is affected by both the relative densities of the layers and the relative wettability of the individual fibers in each layer. The facing layer is sometimes more dense than the batt, tending to provide greater wickability in the facing layer, but even the, the individual fibers of the batt have substantially smaller liquid-fiber contact angles than those of the facing layer, overcoming the density difference and providing a substantial overall increase in capillary pressure to absorb liquid into the body of the batt.
When urine if voided into an area in facing layer 16, it partially wets the facing layer and is absorbed therein, spreading out to a limited extent to form a roughly circular wetted zone therein. When the urine passes through the facing layer and comes into contact with the fibers of batt it, it is preferentially absorbed into the batt because of the enhanced wettability thereof. It spreads within the batt to wet a zone of larger area therein or wets to the edges of the batt, depending on the amount of urine passed.
On occasions when a substantial amount of urine has been voided rapidly, the wetted area of the batt becomes saturated and excess urine, aided by the presence of impervious sheet l2 and its adherence to the loosely compacted batt in a discontinuous pattern substantially throughout the interface therebetween, flows into the previously dry portions of the batt, and finally into the previously dry portions of the facing layer. It is to be noted, however, that such flow from the impervious sheet is from the outermost portions of the diaper inward so that most of the facing layer remains dry until all other fibrous portions of the diaper are saturated.
There is cooperation between the loosely compacted batt and impervious sheet 12 to which it is adhered. A voiding of urine usually takes place within a short time, and the rate or absorption of the diaper might be overwhelmed during this short period in spite of the diapers ultimate capacity to absorb the amount of liquid voided. The impervious sheet serves to hold the urine and keep it from wetting the bed clothes or outer clothing so that the absorptive portions of the diaper can have the time to function. In addition, since the impervious sheet is adhered to the fluff of the batt over a widely distributed area, the sheet serves as an anchor to stabilize the fluff of the batt against migration of the loosely compacted fibers.
In the embodiment of this invention wherein the loosely compacted batt of short cellulosic fibers is adhered directly to the impervious sheet, it is preferred to adhere the two layers by bead lines 22 of adhesive which run lengthwise of the maximum diaper dimension. These bead lines of adhesive coact with the impervious sheet and tend to channel the urine flow lengthwise so that the liquid tends to spread in a roughly elliptical pattern rather than in a circular one.
When urine spreading in the loosely compacted batt of the diaper reaches an edge of the batt, it tends to flow to some extent out of the diaper and into the bed clothes or outer garments of the infant. Any edge of the batt may be the first to be reached by the spreading urine, depending on the position of the infant and the distribution of his weight during and after urine discharge. However, on the average, the urine is more likely to reach one or more side edges before it reaches an end edge because the batt has less width than length so that any point of discharge is likely to be closer to a side edge than to an end edge.
The channeling or urine lengthwise by the coaction of the bead lines of adhesive and the impervious sheet tends to equalize the spread or urine to the end edges and side edges so that substantially the full absorptive capacity of the batt may be utilized before any edge is reached.
The embodiment of FIG. 2, described above, is one of the simplest and most economical forms of the present invention. For superior performance, however, the embodiment of FIG. 3 may be preferred. The construction of FIG. 3 is similar to that of FIG. 2, except that the facing layer is cut wider than the impervious sheet and is folded under on itself in the marginal portions to provide a thicker and heavier border. The underfolded portion of the facing layer is shown as 16c and the bight as 16d.
Since facing layer 16 has substantial body and strength, folding it over at the marginal portions of the diaper enhances the strength of the diaper and provides additional tear resistance where pins are used. In addition, the configuration of FIG. 3 improves the balance and feel of the diaper and provides better sealing where the edge portions come into contact with the thighs of the infant when the diaper is pinned in place.
Another advantage of the FIG. 3 embodiment is derived from the fact that the folding-over of the facing layer compresses it at the inner surface of the fold and stretches it at the outer surface of the bend to produce a lower density at the outermost edge of the folded facing layer. When the diaper is thoroughly saturated with urine to the edges of the facing layer, the urine will tend to be held in the densificd inner portion of the fold in preference to the less dense outermost edge and will thereby tend to be held within the diaper.
It is to be noted that in both FIGS. 2 and 3, the facing layer as assembled into the diaper (whether folded or not) is coterrninous with the impervious sheet and there is no folding over of the impervious sheet to envelope any edge of fibrous material. Thus, there is no portion of the upper surface of the diaper (as shown in FIGS. 2 and 3) which is covered with any plastic material, and no plastic material comes into direct contact with the infants skin when the diaper is affixed in position by pins or tabs. Prolonged direct contact of plastic material with an infants skin can cause irritation and infection but, nonetheless, is employed in prior art disposable diapers to provide an impervious seal to the infants skin. The superior absorptive capacity of the diaper of this invention and its superior functioning make such plastic-to-skin contact unnecessary.
In the embodiment of FIG. 4, there are two loosely compacted batts of short cellulosic fibers disposed between facing layer 16 and impervious sheet 12, batt 14, similar to the batt of the same designation in the embodiment of FIG. 2, and a second, larger batt 20, similar to batt 14 except for its dimensions. The overall effect is to provide a stepped cross section as shown in FIG. 4. I
When an infants weight rests on the stepped construction of FIG. 4, there is a tendency for the uncompressed absorbent material of loosely compacted batts 14 and 20 to become partially compressed by the weight. Since there is a greater thickness of material in the center of the stepped construction of FIG. 4 than at the margins, there will be greater pressure (and hence more compression) at the center. This results in a smaller effective capillary radius in the center section. With a given liquid, the capillary force increases with narrower capillary-radii, resulting in greater wick-ability of the more highly compressed center portion of the FIG. 4 construction as compared to the less compressed marginal portions. In the case of a night diaper designed to hold several voidings, the construction of FIG. 4 helps to keep the urine in place in the central portion of the diaper and away from the edges from which it might leak out.
At the interface between loosely compacted batts 14 and 20 there is an intermingling of their respective surface fibers tending to coalesce the two batts into one. This surface intermingling, aided by the loose degree of compaction at each surface, tends to transmit to batt 14 from batt 20 the stability against lateral migration which batt 20, in turn, gets from its overall adhesion to the impervious sheet.
The diaper of this invention is normally packaged and sold in a folded condition. FIG. 6 illustrates the diaper of FIG. 1 in a folded state and also illustrates, in phantom, the diaper in a partially opened state, ready for application onto the lower torso and thighs of an infant. FIG. 7 is a partial cross section of the folded diaper of FIG. 6, taken along plane 7 7 thereof.
As shown in FIGS. 6 and 7, the side margins12b and 16b of the impervious sheet 12 and the facing web 16, together with a portion of batt 14, are folded inwardly in a first fold to provide as the uppermost layer of the fold, a portion of the moisture impervious sheet designated in FIG. 7 as 12c. This sub-assembly is then folded outwardly along each edge in a second fold to cover the first folded portion and to expose the edge portion of the facing web (designated as 16d) as the upper layerv of the double fold. In the preferred embodiment, each double fold at the edge of the diaper comprises approximately one-third of the resulting trans verse dimension of the folded diaper, leaving approximately one-third of the width of the folded diaper as a central unfolded and uncovered portion.
The diaper is held in its folded condition by two small central spots of adhesive 24 applied between the main body of the diaper and the overlying sides 16b of the facing web, one spot on each folded side of the diaper. When the diaper is to be put on the infant, the folds are opened on one side of each of the adhesive spots, as shown in phantom in FIG. 6, and the open portion of the diaper is put under the infants buttocks while the folded portion is raised into the crotch region. The final form of the diaper is shown in perspective on a reduced scale in FIG. 5.
In one form of the invention, as illustrated in FIGS. and 6, the diaper is provided with adhesive tabs 26, each having a fixed end secured to the impervious sheet 12 and a free end wherein the adhesive surface is covered with a facing sheet 32. Facing sheets 32 are removed to expose the adhesive surfaces when the diaper is applied to the infant, as in the configuration shown in FIG. 5, and the free ends of the adhesive tabs are secured to opposite corners of the diaper.
FIG. 8 illustrates the embodiment of this invention wherein a creped cellulose wadding layer 18 is interposed between cellulosic batt 14 and impervious sheet 12. Preferably, layer 18 comprises at least two plies of wadding. However, since the creped cellulose wadding layer is not primarily relied on in this diaper for its total absorptive capacity, it is preferred that layer 18 contain no more than four plies of wadding to avoid excessive stiffness in the diaper.
The creped wadding is preferably oriented in the diaper of FIG. 8 so that its machine direction is trans-' verse to the length of the diaper and its creped ridges run longitudinally. In this manner a preference toward longitudinal flow of urine is imparted to the diaper.
At the interface between loosely compacted batt 14 and creped cellulose wadding 18 the surface fibers of the batt become entangled in the crimps of the wadding making for a firm bond-between the layers without the necessity of utilizing an adhesive between them. The wadding is, in turn, adhered to the impervious sheet throughout the area of the interface between them in the same manner as the loosely compacted batt is adhered to the impervious sheet in the embodiment of FIG. 2.
Suitable fibrous structures for making batts 14, used in this invention, are made from short cellulosic fibers obtained by the grinding or comminution of compacted wood pulp fibers (pulpboard) or cotton linters. The compacted cellulosic material is at a moisture content of 5-10 weight percent (or is slightly moistened to bring it to that range) before being subjected to the grinding operation so that the fibers produced by grinding have sufficient moisture to have the capability of developing weak interfiber hydrogen bonds which give some coherence to the batt.
The batts are initially formed by air blowing the slightly moist cellulosic fibers onto a support at a total weight of about 2 to about 10 oz./yd. and then subjecting the air blown fibers to heavy compression. The small amount of moisture which may, when required, be added to cellulosic pulpboard is uniformly distributed throughout the air blown fibers by the grinding and air blowing operations, and after compression, this moisture provides weak hydrogen bonding to give some integrity to the body of the batt.
The short fibers used in making batts 14 of this invention are generally entirely fibers of wood pulp or cotton linters. However, other cellulosic fibers may be used as well as blends of cellulose fibers with other fibers such as silk, wool, nylon and cellulose acetate. Highly purified kraft paper pulp fibers have proven to be most satisfactory for most applications.
The pulpboard used to make the loosely compacted batts is usually ground down to individual short fibers in the mill. However, in one preferred embodiment, some of the pulpboard fibers are not completely comminuted and remain joined to other fibers in small clumps, generally smaller than about one-fourth inch across. It has been found that the presence of such small clumps of fibers in the batt provides islands of in creased tenacity for holding liquid. When an infants weight on one portion of the batt densifies that portion and tends to concentrate the liquid in the densified portion, the presence of clumps of fibers elsewhere in the batt tends to hold the liquid in place. Preferably from about 2 to about 10 weight percent of the fibers should be in the form of such clumps, which are uniformly and randomly distributed throughout the cellulosic batt so that they do not alter the substantially zero density gradient of the batt in its thickness dimension.
There are weak hydrogen bonds in the loosely compacted batt of short cellulosic fibers providing sufficient strength to maintain the integrity of the batt in ordinary handling, and additional strength, or integrity, is obtained by adhesion of the batts to the impervious layer, or polyethylene film, either directly, or through an intervening layer.
In the embodiments of FIGS. 2v and 3 in which a single loosely compacted batt of short cellulosic fibers is directly adhered to the polyethylene film, the adherence is preferably obtained by the application of parallel lines or beads of adhesive to the film before bringing it into contact with the batt. As explained above, the parallel beads of adhesive disposed lengthwise of the diaper tend to channel the flow of urine lengthwise to utilize as much of the diaper length as possible for absorption before the urine reaches the diaper sides. The use of parallel beads of adhesive also achieves adhesion between the batt and the film throughout their interface without the excessive stifiness which would result if adhesive were applied as a continuous film.
Close overall adhesion between the batt and the polyethylene film, as contrasted "to marginal adhesion, prevents the formation of substantial spaces between them in which uncontrollably large amounts of free, unabsorbed urine can accumulate. In addition, overall adhesion to the polyethylene film tends to stabilize the loosely compacted batt and tends to keep its fibers from bunching by transverse migration.
In the embodiment of FIG. 4 the stabilization of batt 20 by adhesion to the polyethylene layer is transmitted to some extent to batt 14 by reason of the intermingling of the fibers of the two batts at the interface between them.
In the embodiment of FIG. 8 adhesion of the creped cellulose wadding to the polyethylene film is also throughout the area of their interface. Such adhesion counteracts the tendency of the wadding to bunch up; and the stabilization of the wadding is transmitted to the fluff of the cellulosic batt by the adhesion of the batt to the wadding by entanglement of fibers of the batt into the crimps of the uppermost ply of the wadding.
The adhesive bonding the polyethylene film to its adjacent layer need not be in the form of parallel bead lines when the adjacent layer is creped cellulose wadding as described in FIG. 8 or in other applications in which the longitudinal channeling function may be dispensed with. The adhesive may also be applied in other patterns, such as spaced dots or other forms of so-called island bonds, but fairly close overall adhesion between the polyethylene film and its adjacent layer is required and no portion of the film should be more than about two inches from a point of adhesion. In the absence of such close overall adhesion, the fluff of the batt will not derive stabilization directly or indirectly from the polyethylene sheet and spaces for the collection of unabsorbed urine will be created by separation of the polyethylene sheet from its adjacent layer in regions where they are not adhered to each other.
The facing layer, as described above, contains between 75 percent and 98 percent by weight of short fibers, not exceeding about one-fourth inch in length. The average short fibers are from about one-sixteenth to about three-sixteenth inch in length. The facing layer is prepared by first forming a web of randomly laid dry fibers of the desired mix of short and long lengths, the web having a density from about 0.09 gm/cc. to about 0.025 gm/cc. measured by ASTM Method D-l777 at 0.16 pounds/square inch.
Facing layers having weights between about 1 and about ounces per square yard are generally suitable for use in this invention. One particular facing layer which has been used with satisfaction is composed of approximately 15 percent textile-length fibers such as uniformly cut one and one-half inch 1.5 denier rayon fibers and 85 percent fibers of individualized second cut cotton linters. This facing layer is made on a web laying device to a weight of 2 oz./yd. This layer is then conveyed into a bonder including a suction means, and a bonding agent such as a self-cross-linking acrylic emulsion is applied. One bonding agent which has been employed with considerable success is a latex of a polyethyl-acrylate copolymer containing small amounts of acrylonitrile and a cross-linking monomer sold under the trademark I-IYCAR 2600 X 120. The bonding agent should preferably be of the low viscosity type with a viscosity less than 5 centipoises.
To avoid excessive water repellency, a surfactant, preferably an anionic surfactant, is included in the binder suspension. A typical surfactant which has been found to be suitable is the ionic sulfonated alkyl ester sold under the trademark Triton GR-5.
The composition of the binder suspension and the amount of suction at the suction slot is controlled in a typical application so as to give the fabric a dry solids add-on of 6 percent based on the fabric weight, of which about 0.15 percent is the amount of surfactant. A suitable range for the amount of binder is from about 4% percent to about 9 percent, based on fabric weight.
The wet web is conveyed into a drying oven having a temperature of 3l0320 E, where it is dried and the resin binder cured. The resultant material has a density of 0.05 to 0.07 grams/co, and a dry strength of about 1.4 lbs./in. of width in the cross direction. The wet strengths are about 0.9 lbs./in. of width in the machine direction and about 0.5 lbs/in. of width in the cross direction.
The bonding agent in the facing layer tends to provide the layer with greater dimensional stability than the batt which contains no bonding agent. When the diaper is wet with urine and the infants weight is on a portion thereof, both the facing layer and the batt will be compressed under the weight, but the batt is more subject to compression because it contains no bonding agent. This increased compaction in the batt enhances the margin of wickability which it normally has in comparison to the facing layer (even when dry and uncompressed) and tends to hold the liquid strongly against migration into the facing layer where it could wet the infants skin.
If desired, the facing layer may be made with a veneer of long fibers on one or both surfaces thereof, in place of or in addition to the long fibers intermixed with the short fibers. Such constructions are described in the above mentioned commonly owned application Ser. No. 729,784.
In another embodiment, the facing layer may be made substantially entirely of textile length fibers bonded together with a resinous bonding agent. This embodiment can provide a facing layer of greater strength, but it is not preferred because it is' more expensive and because the strength of the short fiber-containing facing material is adequate in most instances.
In all embodiments of the invention, the adherence of the impervious layer to the batt, continuously or discontinuously, over substantially the entire interface between them is important because it prevents substantial separation between the two and the creation of substantial spaces in which substantial amounts of free liquid urine can accumulate. The adherence of the impervious layer to the batt cellulosic layer, directly or through an intervening layer, effects a dimensional stabilization of the batt against transverse movement and thereby brings about some stabilization of the loosely compacted fiber fluff of the batt layer.
It will be understood by those skilled in the art that variations and modifications of the specific embodiments described above may be employed without departing from the scope of the invention as defined in the appended claims.
What is claimed is:
1. A multi-layer diaper comprising (1) a porous facing layer in the form of a water-wettable bonded web of mixed long and short fibers, (2) a highly porous batt of short cellulosic fibers which are loosely compacted throughout the thickness of the batt, said batt having greater wettability to water than said facing layer and being disposed in face-to-face juxtaposition to said facing layer, and (3) a water-impervious backing sheet on the side of said loosely compacted batt opposite said facing layer, said backing sheet being adhered to its adjacent layer throughout the area of the interface between them.
2. The diaper of claim 1 wherein said loosely compacted batt has substantially no density gradient in its thickness dimension when in an unfolded state.
3. The diaper of claim 1 wherein said cellulosic fibrous batt is in direct contact with said water-impervious backing sheet.
4. The diaper of claim 1 wherein said cellulosic fibrous batt is in contact with a second highly porous batt of short cellulosic fibers which are loosely compacted throughout the thickness of the batt, on the side of said first named batt opposite said facing layer and said second highly porous fibrous batt is in direct contact with said water-impervious backing sheet.
5. The diaper of claim 1 wherein said cellulosic fibrous batt is in direct contact with a crimped cellulose wadding layer on the side of said batt opposite said facing layer and said crimped cellulose wadding layer is in direct contact with said water-impervious backing sheet.
6. The diaper of claim 1 wherein said water-impervious backing sheet is adhered directly to its adjacentlayer by an adhesive discontinuously distributed over the entire interface between them.
7. The diaper of claim 6 wherein said backing sheet is substantially rectangular and said adhesive is distributed in the form of parallel lines running longitudinally with respect thereto.
8. The diaper of claim wherein said layer of creped cellulose wadding is substantially rectangular in shape and is oriented so that the ridges of its crepe run longitudinally.
9. The diaper of claim 1 wherein said backing sheet and said facing layer are substantially rectangular and substantially coextensive, said batt is substantially rectangular, narrower than said backing sheet and facing layer, and centrally disposed with respect thereto to provide marginal portions of said diaper in which said backing sheet and said facing web are in direct contact with each other.
10. The diaper of claim 1 wherein the fiber content of said facing layer comprises from about 75 to about 98 weight percent of short fibers having a fiber length less than one-fourth inch and from about 2 to about 25 weight percent of long fibers having a fiber length between about one-half and about 2% inches.
11. The diaper of claim 1 wherein the fibers of said I facing layer are bonded together by a water repellent polymeric bonding agent and wherein the fibers of said facing layer are coated with a surfactant.
12. The diaper of claim 3 wherein said batt and said backing sheet are adhered to each other by an adhesive discontinuously distributed over the entire interface between them.
113. The diaper of claim 1 wherein said facing layer has a fabric weight of about 1 to. about 5 ounces per square yard and a density less than about 0.15 grams per cubic centimeter.
M. The diaper of claim l3 wherein said density is between about 0.05 and about 0.1 grams per cubic centimeter.
15. The diaper of claim 1 wherein said batt has a density between about 0.10 and about 0.20 grams per cubic centimeter.
16. The diaper of claim 1 wherein said batt contains among its loosely compacted fibers, randomly dispersed clumps of fibers, said clumps measuring no more than about one-fourth inch in their largest dimension and constituting from about 2 to about 10 percent of the weight of the loosely compacted batt.
17. A multi-layer diaper comprising l a porous facing layer in the form of a water-wettable bonded web of mixed long and short fibers, of which from about to about 98 weight percent are short fibers having a fiber length less than one-fourth inch and from about 2 to about 25 weight percent are long; fibers having a fiber length between about one-half and about 2% inches, said fibers being bonded together by a water repellent bonding agent and coated with a surfactant, (2) a highly porous, loosely compacted batt of short cellulosic fibers in face-to-face juxtaposition to said facing layer, having greater wettability to water than said facing layer and having substantially no density gradient in the thickness dimension when in an unfolded state, and
(3) a water-impervious backing sheet adhered directly to said loosely compacted batt on the face thereof opposite the face in juxtaposition to said facing layer by an adhesive discontinuously distributed over the entire interface between them, said backing sheet and facing layer being substantially rectangular and substantially coextensive and said batt being substantially rectangular, narrower than said backing sheet and facing layer and centrally disposed with respect thereto to provide marginal portions of said diaper in which said backing sheet and said facing layer are in direct contact with each other.
18. The diaper of claim l7 wherein said facing layer has a double thickness at its side marginal portions.
19. The diaper of claim 17 wherein at least 50 percent of the individual fibers in said facing web have liquid-fiber contact angles with respect to water between about 30 and about 60.
. 20. The diaper of claim 17 wherein the individual fibers in said cellulosic batt have liquid-fiber contact angles with respect to water not greater than about 15.
2E. The diaper of claim 17 wherein said discontinuously distributed adhesive is in the form of parallel lines running lengthwise on said backing sheet.
22. A multi-layer diaper comprising l) a porous facing layer in the form of a water-wettable bonded web of mixed long and short fibers, of which from about 75 to about 98 weight percent are short fibers having a fiber length less than one-fourth inch and from about 2 to about 25 weight percent are long fibers having a fiber length between about one-half and about 2% inches, said fibers. being bonded together by a water-repellent bonding agent and coated with a surfactant, (2) a first highly porous, loosely compacted batt of short cellulosic fibers in face-to-face juxtaposition to said facing layer, having greater wettability to water than said facing layer and having substantially no density gradient in the thickness dimension when in an unfolded state, (3) a second highly porous, loosely compacted batt of short cellulosic fibers in contact with said first highly porous batt on the side thereof opposite said facing layer, and (4) a water-impervious backing sheet adhered directly to said second highly porous batt on the face thereof opposite said first highly porous batt by an adhesive discontinuously distributed over the entire interface between them, said backing sheet and facing layer being substantially rectangular and substantially coextensive, said second batt being substantially rectangular, narrower than said backing sheet and facing layer and centrally disposed with respect thereto and said first batt being substantially rectangular, narrower than said second batt and centrally disposed with respect thereto to provide a step-wise construction and to provide marginal portions of said diaper in which said backing sheet and said facing layer are in direct contact with each other.
23. A multi-layer diaper comprising l a porous facing layer in the form of a water-wettable bonded web of mixed long and short fibers, of which from about 75 to about 98 weight percent are short fibers having a fiber length less than one-fourth inch and from about 2 to about 25 weight percent are long fibers having a fiber length between about one-half and about 2% inches,
side thereof opposite said facing layer, and (4) a waterimpervious backing sheet adhered directly to said crimped cellulose wadding layer on the face thereof 0pposite said highly porous batt by an adhesive discontinuously distributed over the entire interface between them, said backing sheet and facing layer being substantially rectangular and substantially coextensive and said batt and wadding layer being substantially rectangular, narrower than said backing sheet and facing layer and centrally disposed with respect thereto to provide marginal portions of said diaper in which said backing sheet and said facing layer are in direct contact with each other.
24. The diaper of claim 23 wherein said wadding layer is disposed on said diaper so that the ridges of its crepe run in the longitudinal direction of the diaper.
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|U.S. Classification||604/365, 604/389, 604/380, 604/375, 604/370|
|Cooperative Classification||A61F13/535, A61F13/49406|
|European Classification||A61F13/535, A61F13/494A|