US 3612055 A
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United States Patent Frederick Mesek  Inventors Downers Grove; Virginia L. Repke, Oak Forest, both oi Ill.  Appl. No. 6,864  Filed Jan. 29, 1970  Patented Oct. 12,1971  Assignee Johnson & Johnson Continuation-in-part of application Ser. No. 861,689, Sept. 29, 1969.
 DISPOSABLE DIAPER OR THE LIKE AND METHOD OF MANUFACTURE 21 Claims, 12 Drawing Figs.
 US. Cl 128/287  Int. Cl A6li 13/16  Field of Search 128/284, 286287, 290, 296
[5 6] References Cited UNITED STATES PATENTS 3,017,304 1/1962 Burgeni 128/290 R Primary Examiner-Charles F. Rosenbaum Attorneys-Harold L. Warner, Michael O. Tatlow and Robert L Minier ABSTRACT: A disposable multilayer diaper of high absorptive capacity is provided which comprises as a first layer, to be brought into contact with an infants skin, a porous, fibrous, nonwoven 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, loosely compacted cellulosic batt having greater wettability than that of the facing web. A third layer, integral with the second, is a paperlike, densified, highly compacted layer of the same cellulosic material as the second layer but of substantially smaller average pore size. The final layer is an impervious backing sheet adhered to the densified layer over a widely distributed area of adhesion.
PATENTEU nm 1 2 l97l SHEET 3 OF 3 DISPOSABLE DIAPER OR THE LIKE AND METHOD OF MANUFACTURE CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of our application Ser. No. 861,689, filed on Sept. 29, 1969.
BACKGROUND OF THE INVENTION years, many different disposable diapers have been proposed a 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 infant's skin and thereby avoid skin irritation and infection.
Another important criterion is lack of stiffness and ready conformability to the body of the infant for maximum comfort.
In one form of prior disposable diaper, creped cellulose wadding is used as the absorbent material, covered with a permeable paperlike facing material on the side to be brought into contact with the infant's skin and covered with an imper vious 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 paper's thickness away from the infants skin; In use, the weight of the infant presses the paperlike 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 foldedover 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 paperlike 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 reasonable 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 a discharge of urine;
b. handles the maximum flow rate of a discharge of urine;
c. rapidly draws (funnels) the urine away from the infant's skin, leaving a relatively dry layer in contact therewith; and
d. keeps the absorbed urine from wetting outer garments or bed clothes.
Specifically, these functions are accomplished by a multilayer diaper comprising, in order, a fibrous facing layer which is to be brought into contact with the infantfs skin, a layer of highly porous, loosely compacted cellulosic batt, a paperlike densified, highly compacted cellulosic fibrous layer integral with the loosely compacted batt and an impervious backing sheet adhered to the densified layer throughout the interface therebetween. The facing layer is of porous construction and its fibers have less wettability for water than the fibers of the loosely compacted batt, resulting in a tendency for liquid to flow from the facing web into the batt. The densified fibrous layer has a smaller average pore size than the loosely compacted batt, resulting in a tendency for liquid to flow from the batt into the densified layer.
The respective elements of the multilayer diaper cooperate in'that (I) liquid, such as urine, flowing into a small area on theouter surface of the facing layer'flows preferentially into the underlying batt rather than to other areas of the facing layer, thus tending to restrict wetting in the facing layer, to a smallarea and to move the liquid away from the infant's skin: (2) liquid flowing into a small area of the loosely compacted batt flows preferentially into theunderlying densified layer rather than to other areas of the batt, thus tending to restrict wetting in the batt to an area of moderate size and to move the liquid farther from the infant's skin; (3) liquid flowing into the densified layer tends to spread laterally because of its wicking action; (4) liquid which might pass through the densified layer during discharge (.when flow is rapid) is held back by the impervious backing sheet for sufficient time to permit absorption to take place; and (5) liquid in excess of the absorptive capacity of the densified layer is forced back by the impervious layer into the dry portion of the loosely compacted batt, thus utilizing' the. additional absorptive capacity therein.
In the preferred embodiment of this invention, the facing layer is coextensive in dimension with the impervious backing sheet and there is no foldover 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 whichresult from direct contact between the plastic material and the skin.
I 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;
FIGS. 3 and 4 are partial cross sections similar to FIG. 2, illustrating alternate embodiments of the invention;
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 77;
FIGS. 8 and 9 are fragmentary perspective views, partially in cross section, of alternate embodiments of the invention with respect to the nature of the densified layer;
FIG. 10 is a simplified schematic view of the production line on which the diaper is made;
FIG. 11 is a schematic cross section of the diaper showing the manner in which urine absorption takes place; and
FIG. 12 is a graph having a series of curves, illustrating the advantageous high rate of liquid migration obtained by the use of composite batts having a densified layer.
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 water-absorbent 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 cotenninous 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 14 has a paperlike densified highly compacted lowermost fibrous layer 18 which is adhered to the impervious sheet by bead lines of adhesive 22 substantially throughout the interface therebetween. Marginal portions 16b and 12b are also ad hered to each other by bead lines 22.
In the preferred embodiment of the invention, moisture impervious sheet 12 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 0.0005.
Batt 14 is formed of loosely compacted short cellulose fibers, such as woodpulp 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 woodpulp 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 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 (TAPPl-T233SU64).
The paperlike densified layer 18 of batt 14 is formed by a slight moistening of one surface of the batt followed by the application of pressure thereto. The nature of the batt and of its densified layer and the method of producing the same are described in U.S. Pat. No. 3,017,304, dated Jan. 16, 1962.
The composite density of batt 14, including its densified layer 18, should be above about 0.07 g./cc., and preferably between about 0.10 and 0.15 g./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 woodpulp 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 percent to 25 percent by weight of textile length fibers, such as 1.5 denier rayon fibers uniformly cut to 1 -inch 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 US. Pat. application Ser. No. 729,784.
Facing layers suitable for use in this invention have fabric weights in the range of l to oz./yd. and densities less than 0.15 g./cc., generally in the range between 0.05 and 0.1 g./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 p.p.i. of width in the machine direction and at least 0.10 p.p.i. 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 among the above-described fibrous components of the diaper, such that the moisture is selectively drawn from the facing layer into the body of the batt and then from the body of the batt into the densified layer thereof.
The least wettable of the fibrous elements of the diaper of this invention 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 fibers of the layer, the contact angle approaching for fibers which are difficulty 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 unevenness 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.
The body of batt 14 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 wickability, or preferential absorptivity of the body of the batt for water is limited, however, by its low density which results in a large effective capillary radius for the capillaries between adjacent fibers.
The pressure causing a liquid to enter a cylindrical capillary is expressed by the equation:
P 2 cos /r where P is the capillary pressure,
is the surface tension of the liquid, is the liquid-fiber contact angle, and
r is the capillary radius.
With a given liquid, the pressure (capillary force) increases with the cosine of the liquid-fiber contact angle (reaching a maximum where the angle is zero), and decreases with narrower capillary radii so that narrower capillaries will draw liquid from wider ones.
The relative wickability between facing layer 16 and the body of batt 14 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 body of the batt, tending to provide greater wickability in the facing layer, but even then 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.
Densified fiber layer 18 of the batt provides the maximum capillary pressure because it combines the very low contact angle of the fibers of the batt with the high density (small capillary radius) of the densified fibers.
FIG. 11 illustrates the unique pattern of liquid absorption obtained in the diaper of this invention. When urine is 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, shown in FIG. 11 as shaded area 16w.
When the urine passes through'thefacing layer and comes into contact with the body of batt 14, itis preferentially absorbed into the body of the batt because of the enhanced wettability thereof. It spreads within the body of the b'att-to wet a larger, roughly circular zone therein, indicated by shaded area 14w.
Whenthe urine passes through the body of therbattinto contact with densified layer 18, it is strongly drawn therein because of its high density and is spread laterally through a much larger substantially circular zone (shown as shaded area 18w in FIG. 11 or to the edges of the batt,.de pending on the amount of urine passed.
On occasions when a substantial amount of urine has been voided, the densified layer becomes saturated and excess urine, aided by the presence of impervious sheet'l2 and'its adherence to the densified layer in a discontinuous pattern substantially throughout the interface therebetween, flows into the previously dry portions of the body of the batt, and finally into the previously dry portions of the facing layer. It is to be noted, however, that such flow from a saturated densified layer 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.
The densified layer of the batt, for the reasons explained above, creates a high capillary pressure which tends to move liquid away rapidly from the area of the original'wetting. However, the speed of liquid migration is limited in the densified layer because of the resistance provided by its small capillaries. The composite batt used in this invention, with its densified layer in intimate contact with absorbent material of lesser density, provides improved speed of liquid migration over either the densified layer alone, or the umcompressed layer alone. I v I FIG. 12 illustrates the improved speed of liquid migration obtained by the combined action of the densified layer and the uncompressed layer, as compared to the rates of liquid migration in theseparate layers. In FIG. 12, the length of liquid migration (in a horizontal direction) is plotted against the time for such migration for the densified layer, for the uncompressed layer (labeled as fluff) and for the 'combinationof the two. It will be seen that it takes about 9 seconds for liquid to migrate ,5 centimeters when both layers cooperate, as contrasted with about 12 seconds for the fluff alone, and about seconds for the dense layer alone. If the length of liquid migration were plotted against the square-root of time, rather than against time, the curves of FIG. 12 would be approximately straight lines. J
While it is not desired to be bound by any particular theory of operation, it is believed that the improvement in speed of liquid migration obtained by the cooperation of the dense and uncompressed layers of the batts used in thisinvention results from the proximity of the two layers-and the fact that just ad.- jacent to the high capillary pressure generated by the dense layer are the large capillaries of the uncompressed layer which can move larger quantities of the liquid with relatively little flow resistance. I v
There is also cooperation between the densified layer of the batt and impervious sheet 12 to which it is adhered. A voiding of urine usually takes place within a short time, and the rate of 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 and in spite of the relatively high rate of absorption obtainable for the reasons specified above. The impervious sheet serves to hold the urine and keepit from wetting the bed clothes or outer clothing so that the absorptive portions of the diaper can have the time to function, In addition, the'impervious sheet serves as an anchor to stabilize the fluff portion of the batt against migration of the loosely compacted fibers, since the impervious sheet is adhered to the densified layer integral with the fluff portion of the batt, over a widely distributed area.
' 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 theinfant when the diaper is pinned in place.
Another advantage of the FIG. 3 embodiment is derived from the fact that the folding-over of thefacing layer compresses it at the inner surface of the fold andstretches 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, theurine will tendto be held in the densified 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 coterminous 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 portionof the upper surface of the diaper (asshown in FIGS. 2 and 3) which is covered with any plastic material, and no plastic material comes into direct contact with the infant's 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 batts disposed between facing'layer l6 and the impervious sheet 12, batt 14 with its densified layer 18, similar to that of FIG. 2, and a second, larger batt 20 with its own densified layer 22, similar to the other one. The overall effect is to provide a stepped cross section as shown in FIG. 4.
When an infants weight rests on the stepped construction of FIG. 4, there isa tendency for the uncompressed absorbent material of batts l4 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 and, for the reasons explained above, greater wickability of the more highly compressed center portion as compared to the less compressed marginal portions. g
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.
The diaper of this invention is normally packaged and sold in a folded condition. FIG. 6 illustrates the diaper of FIG. I 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 margins 12b 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 12c. This subassembly 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 layer of the double fold. In the preferred embodiment, each double fold at the edge of the diaper comprises approximately one-third of the resulting transverse 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 infant's 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.
In the embodiments discussed above, densified layer 18 is a continuous layer covering one entire face of batt 14. However, the densified layer may, if desired, be a widely distributed discontinuous layer, as shown in FIGS. 8 and 9, in which the diapers are shown in fragmentary form and in perspective, with the impervious sheet upward and with a portion of the sheet removed to show the structure of the densified layer.
In FIG. 8, the densified layer is in the form of parallel, narrow densified strips 18s running lengthwise of the diaper and separated by narrow undensified strips. In FIG. 9, the densified layer is in the form of a rectangular grillwork 18g of densified material encompassing a plurality of small areas of undensified material. Densified layers of the forms shown in FIGS. 8 and 9 are made in the same manner as the continuous densified layers described above, except that the compression is applied by embossed rollers, as described in the aforementioned US. Pat. No. 3,017,304.
Suitable fibrous structures for making the pads or batts 14 used in this invention are made from short cellulosic fibers obtained by the grinding or comminution of compacted woodpulp fibers 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 body of 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 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 dense, compacted, paperlike layer of skin is prepared by moistening a surface of the cellulosic batt with a fine spray of water, and then subjecting the moistened batt to pressure. The formation of the densified skin on the cellulosic batt is believed to be due to the formation of strong hydrogen bonds between contacting moistened fibers, similar to the bonds between the fibers in paper. By the proper selection of the amount of moisture applied to the surface of the batt and by the proper selection of degree of compression imposed, the properties of the densified skin may be varied as desired. The thickness, density, strength, and other characteristics of the densified skin will depend upon the uniformity by which the moisture is applied, the depth to which it penetrates, and the degree to which the fibers are compressed. For example, by
finely spraying about 0.0015 cc. of water per square centimeter of web surface and then exposing the web to a pressure of about 40 p.s.i., a suitable densified, coherent paperlike skin 18 is obtained on the surface of the web which has been moistened.
The short fibers used in making batts 14 of this invention are generally entirely fibers of woodpulp 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 diaper of this invention, in each of the embodiments discussed above, may be assembled in equipment such as that schematically shown in FIG. 10. A roll of compacted woodpulp 41 is provided to feed a source of short cellulosic fibers to grinding mill 42 from which a stream of fibers is blown onto belt 43 as a layer 44 weighing between about 2 and about 10 03./yd.. The pulpboard normally has a moisture content of 5 to 10 weight percent, but if it is lower (as from prolonged exposure to a dry atmosphere) the pulpboard is slightly moistened before grinding in mill 42 to bring its moisture content within the desired range.
Mill 42 grinds the pulpboard into individual short fibers. 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 body of batt 14 provides islands of increased tenacity for holding liquid. When an infant's 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.
The airblown layer is passed under compacting roll 46 from which it emerges with enough integrity to sustain itself as a web without the support of belt 43. The web then passes through a pair of calender rolls 47 for further compression and then under nozzle 48 which deposits a fine spray of moisture on the upper surface of the web. The moistened web then passes between another set of calender rolls 49 which exert heavy pressure on it to form a skin 51 on its upper surface.
The amount of moisture applied to the web may vary suitably from about 0.0005 to about 0.03 cc. of water per square centimeter of web surface, depending on the thickness of the web and the thickness of the paperlike densified skin desired, with lesser amounts of moisture being used for thinner webs and very thin, papery skins and greater amounts for thicker webs and skins of greater thickness.
The amount of pressure applied by rolls 49 may vary from abut 5 to about or more p.s.i., with the commercially preferable range being from about 10 to about 50 p.s.i. In a typical embodiment, the web is sprayed with about 0.0015 cc. of water per square centimeter of web surface and subjected to a pressure of about 40 p.s.i. to obtain a densified, coherent papery skin on the surface of the web which has been moistened.
In the absorbent web and in the batts cut therefrom, there are weak hydrogen bonds in the body of the batt providing sufficient strength to maintain the integrity of the batt in ordinary handling, and there are strong hydrogen bonds in the densified layer or skin to increase the cohesive strength of the composite. After the skin is formed, the absorbent web comes into contact with a web of facing material 52 and is supported thereby while being cut by cutter 53 into individual batts 14. The facing material (previously prepared as described below) is fed from roll 54.
Polyethylene film 12 is fed to the assembly from roll 56, lines of adhesive being applied from applicator 57. As described above, the adhesive is applied as parallel lines or beads between the impervious sheet and the densified layer of the batt (or the facing layer in the marginal portion of the 'diaper). Adhesive may, if desired, be applied as a continuous layer between the polyethylene and the batt, but such application tends to provide excessive stiffness. 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 sheet and the batt is required and no portion of the polyethylene should be more than about 2 inches from a point of adhesion. In the absence 'of such close overall adhesion, the polyethylene film may be separated from the densified layer to create substantial spaces in which uncontrollably large amounts of free liquid urine can accumulate.
After the facing material and polyethylene are brought into contact with opposite faces of the absorbent batts, the assembly is subjected to compression by rolls 58 and 59 to shape the diaper assembly, and the individual diapers are cut off by cutter 61.
If desired, adhesive applicator 57 may be omitted and adhesion between the polyethylene layer and the fibrous layers may be achieved by heat-sealing, employing a suitable sealing element in the production line.
The facing layer, as described above, contains between 75 percent and 98 percent by weight of short fibers, not exceed ing about one-fourth inch in length. The average short fibers are from about one-sixteenth to about three-sixteenths-inchin 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 g./cc. to about 0.025 g./cc. measured by ASTM Method D-l777 at 0.16 p.s.i.
Facing layers having weights between about 1 and about oz./yd. are generally suitable for use in this invention. One particular facing layer which has been used with satisfaction is composed of approximately percent textile length fibers such as uniformly cut 1% 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 Hycar 2600x120. The bonding agent should preferably be of the low viscosity type with'a viscosity less than 5 centipoises. 23
To avoid excessive water repellency, a surfactant, preferably an anionic surfactant, is included in the binder suspensiomA typical surfactant which has been found to be suitable is the ionic sulfonated alkylester sold under'the trademark Triton GR-S. I
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 3 l0-320 R, where it is dried and the resin binder cured. The resultant material has a density of 0.05 to 0.07 g./cc., and a drystrength of about 1.4 p.p.i. of width in the cross direction. The wet strengths are about'0.9 p.p.i, of width in the machine direction and about 0.5 p.p.i. of width in the cross direction.
The bonding agent in the facing layer tends to provide the layer with greater dimensional stability than the body of the batt which contains no bonding agent. When the diaper is wet with urine and the infants weight is on aportion thereof, both the facing layer and the body of the batt will be compressed under the weight, but the body of the batt is more subject to compression because it contains no bonding agent. This increased compaction in the body of the batt enhances the margin of wickabili'ty 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 togetherwith 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 fibercontaining facing material is adequate in most instances.
In all embodiments of the invention, the adherence of the impervious layer to the densified layer, 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 paperlike densified cellulosic layer effects a dimensional stabilization of the densified layer against transverse movement and thereby brings about a stabilization of the loosely compacted fiber fluff portion of the batt layer since the paperlike densified layer is integral with the fluff portion of the batt, and
holding forces are transmitted from the dimensionally stable impervious layer through the widely distributed adhesive, to the densified layer, and thence to the fluff.
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:
l. A multilayer 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, loosely compacted, cellulosic fibrous batt in face-to-face juxtaposition to said facing layer and having greater wettability to water than said facing layer, (3) a paperlike, densified compacted cellulosic fibrous layer of relatively high wettability and relatively high fluid'retentivity integral with said loosely compacted batt on the face thereof opposite the face in juxtaposition to said facing layer, and (4) a water-impervious backing sheet adhered to said densified layer.
2. 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.
3. The diaper of claim 1 wherein the fiber content of said facing layercomprises 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 fibershaving a fiber length between about one-half and about 2% inches.
4. The diaper of claim 1 wherein'the fibers of said 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.
5. The diaper of claim 1 wherein said batt and said backing sheet are adhered to each other by an adhesive discontinuously distributed over the entire interface between them.
6. A multilayer diaper comprising (1) 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 onehalf 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, cellulosic fibrous batt in face-toface juxtaposition to said facing layer and having greater wettability to water than said facing layer, (3) a paperlike, densified, compacted cellulosic fibrous layer of relatively high wettability and relatively high fluid retentivity integral with said loosely compacted batt on the face thereof opposite the face in juxtaposition to said facing layer, and (4) a water-impervious backing sheet adhered to said densified 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.
7. 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.
8. The diaper of claim 7 wherein said density is between about 0.05 and about 0.1 grams per cubic centimeter.
9. The diaper of claim 1 wherein said batt, together with its compacted layer, has a composite density between about 0.07 and about 0.2 grams per cubic centimeter.
10. The diaper of claim 1 wherein said densified, highly compacted layer is a continuous layer covering the entire surface of said batt which is opposite the surface in juxtaposition to said facing layer.
11. The diaper of claim 1 wherein said densified, highly compacted layer is a discontinuous layer widely distributed over the entire surface of said batt which is opposite the surface in juxtaposition to said facing web.
12. The diaper of claim 11 wherein said discontinuous, densified, highly compacted layer is in the form of parallel narrow densified strips separated by narrow undensified strips.
13. The diaper of claim 11 wherein said discontinuous densified, highly compacted layer is in the form of a grillwork of densified material encompassing a plurality of small areas of undensified material.
14. The diaper of claim 2 wherein said facing layer has a double thickness at its side marginal portions.
15. The diaper of claim 2 wherein a second batt, wider than said first-named batt, and narrower than said backing sheet, is provided between said first-named batt and said backing sheet to provide a stepped construction in said diaper with maximum thickness in its center portion.
16. The diaper of claim 6 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.
17. The diaper of claim 6 wherein the individual fibers in said cellulosic batt have liquid-fiber contact angles with respect to water not greater than about 15.
18. 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 percent to about 10 percent of the weight of the loosely compacted batt.
19. A multilayer diaper comprising l a porous facing layer in the form of a water-wettable bonded web of fibers, at least some of which are long fibers, (2) a highly porous, loosely compacted, cellulosic fibrous batt in face-to-face juxtaposition to said facing layer and having greater wettability to water than said facing layer, (3) a paperlike, densified compacted cellulosic fibrous layer of relatively high wettability and relatively high fluid retentivity integral with said loosely compacted batt on the face thereof opposite the face in juxtaposition to said facing layer, and (4) a water-impervious backing sheet adhered to said densified layer.
20. The method of manufacturing a diaper which comprises moistening a surface of highly porous, loosely compacted layer of short cellulosic fibers and thereafter subjecting said layer to com ression to form a densified skin on said surface and to provi e a composite absorbent batt, applying a water repellent bonding agent and a surfactant to a fibrous layer comprising a uniform mixture of short and long fibers and drying said last-named layer to provide a facing layer, sandwiching said composite absorbent batt between said facing layer and a water impervious backing sheet with the densified skin of said batt in face-to-face juxtaposition to said backing sheet and applying an adhesive to at least one surface of the interface between said densified layer and said backing sheet as a discontinuous layer thereon prior to bringing said densified layer and said backing sheet into said face-to-face juxtaposition.
21. The diaper of claim 1 wherein said water-impervious backing sheet is heat-sealed to said densified layer.
Patent NO 3: 55
Inventor(s) Dated October 12,1971
Frederick}; Mesek and Virginia L, Regke It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
r. In Column 3, line 26, "2 inches in length" should read .1
----2 1/2 inches in length----.
In Column 3, line 53, '1 inch length" should rea.d--l 1/2 inch length---. In Column 3, line 63, "l to 5 oz./yd." should read----- 1 to 5 oz./yd. In Column 3, line 66, "1.5 oz./yd. should read----l.5 oz./yd. In Column line 19, "90" should read--9O In Column line 20, "90" should read----90--. In Column a, line 30, "30" and "60" should read----30a.nd 6o----. In Column h, line 33, "ho" and "60" should read---- l0a.nd 60----. In Column line 38, "15" should rssd----l5----. In Column 0, line #6, "P 2 cos/r" should reed----P=2\fcos O---.
In Column line &9, "is the surface tension of the liquid" should read---- V'ie the surface tension of the liquid----.
In Column h, line 50, "is the liquid-fiber contact angle" should read----9 is the liquid-fiber contact angle--.
In Column 8, line 18, "O3./yd? should read ----oz./ d?
Signed and sealed this 6th day of June 1972.
EDWARD M.FLETCHER,JR. Attssting Officer ROBERT GO'I'TSCHALK Commissioner of Patents