US 3768480 A
Description (OCR text may contain errors)
United States Patent [1 1 Mesek et al.
[ Oct. 30, 1973 DISPOSABLE DIAPER 1nventors:Fredei-ick 1 Mesek, '7 In Grove; Virginia L. Repke, Oak Forest, both of III.
 Assignee: Johnson & Johnson, New
 Filed: June 7, 1972  Appl. No.: 260,557
Primary ExaminerCharles F. Rosenbaum 1 Attorney-Michael Q. Tatlow et al.
 ABSTRACT A disposable multi-layer diaper of high absorptive capacity and improved feel is provided which comprises as a first layer, to be brought into contact with an infantskin, a porous, fibrous, nonwoven bonded facing web of controlled wettability made of short cellulosic fibers and long fibers at a given overall concentration. The outer face of the facing layer is characterized by a blend of long and short fibers, with the concentration of long fibers being in excess of the overall concentration, while the inner face of the facing layer is also characterized by a blend of long and short fibers, with the concentration of short fibers being in excess of the overall concentration. The outer face of the facing layer has a sufficient amount of long fibers to give the diaper improved feel and wearing characteristics. The concentration of short cellulosic fibers gradually, and preferably substantially uniformly, increases from the outer face to the inner face of the facing layer to provide a gradually increasing degree of wettability for preferentially drawing the urine away from the outer face, through the facing layer and into a second layer, in juxtaposition to the facing layer. The second layer is a highly porous, loosely compacted completely cellulosic batt having greater wettability than that of the facing web. A third layer, integral with the second, is a paper-like, densified, highly compacted layer of the same cellulosic material as the second layer but of substantially smaller average pore size and which is selectively thickened in certain areas. The final layer is an impervious backing sheet adhered to the densified layer over a widely distributed area of adhesion.
10 Claims, 4 Drawing Figures DISPOSABLE DIAPER BACKGROUND OF THE INVENTION Disposable diapers have met with increased commercial acceptance in recent years primarily because of their convenience, as opposed to cloth diapers, which need to be laundered once soiled. Many different constructions have been proposed and used, and some have met with widespread commercial success in spite of certain inadequacies in functional properties.
One of the most serious prior art problems has been the inability to provide a suitable construction that would keep moisture away from the surface of the diaper which comes into contact with the infants skin and thereby avoid skin irritation and infection. Commonly assigned Mesek et al.'U.S. Pat. No. 3,612,055 discloses several diaper constructions that function extremely well in keeping moisture away from an infants skin, while at the same time handling a full volume discharge of urine.
These functions are accomplished by a multi-layer diaper comprising, in order, a fibrous facing layer in the form of a substantially homogeneous blend of short and long fibers which is to be brought into contact with the infants skin, a layer of highly porous, loosely compacted cellulosic batt, a paper-like 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 preferentially from the batt into the underlying densified layer rather than to other areas of the batt, thus tending to restrict wetting in the batt to an area of moderate size. Liquid flowing into the densified layer tends to spread laterally because of its wicking action and 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. Liquid in excessjof 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.
Since facing layers in diapers of the type disclosed in the above-mentioned patent have substantially the same amount of short cellulosic fibers adjacent the outer face thereof as adjacent the inner face, there is essentially no wettability difference within'the facing layer itself, with the result that the diaper is dependent, at least to some degree, upon the increased wettability of the fibrous batt to retain urine away from the outer surface of the facing layer.
Webs that can be used as a facing layer in diapers as disclosed in the above-mentioned patent can be formed by an air laying technique. Recent improvements have been made in such techniques, such as for example, the improvements disclosed and claimed in commonly assigned, copending Ruffo et al. application Ser. No. 108,546 filed Jan. 21, 1971, the disclosure of which is hereby incorporated herein by this reference. Briefly, one of the air laying techniques disclosed therein includes the steps of feeding fibers of two different types to separate fiber opening means at a given feed rate to provide the subseqently formed web with a given overall concentration of the different type fibers, individualizing fibers from said separate fiber sources, suspending the fibers from each source in separate gaseous streams, impelling the gaseous streams at least initially toward one another and combining said streams to form a single combined carrier stream wherein the fibers from each gaseous stream intermix with one another with the total gas to total fiber volume ratio being at least 12,000zl in the combined gaseous carrier stream, and condensing the entrained and individualized fibers from said combined stream to form a random nonwoven web. At gas to fiber volume ratios above 12,000:l the fibers in the individual streams are spaced sufficiently from one another that if streams are brought together at an angle without substantial diminution in the velosity of the streams, fibers in each stream can cross over the oncoming fibers to form a nonwoven product wherein the product is characterized by having a concentration of at least one fiber type on one face of the product in excess of the overall concentration and a concentration of at least one different fiber type on the other face of the product in excess of the overall concentration, with a transition zone between the faces such that the concentration of each fiber type gradually diminishes away from the face having the maximum concentration for that fiber type to the opposite face.
SUMMARY OF THE INVENTION In accordance with this invention, a diaper is provided which retains all of the advantageous functional characteristics of the diapers disclosed in the abovementioned patent, while at the same time providing at no increase in cost, (1) improved feel and resultant increased comfort to the infant, and (2) a gradually increasing wettability gradient within the facing layer to promote flow of urine through the facing layer and into the batt, thereby a relative dry surface in contact with the infants skin.
These improved functions are accomplished in a multi-layer diaper which includes in order (1) a waterimpervious backing sheet, (2) an intermediate layer comprised entirely of short cellulosic fibers that are loosely compacted throughout a major portion of the batt and which are densified at one side of the batt to provide an integral paper-like skin adjacent the backing sheet, and (3) a facing layer that is formed of long or textile length fibers and short cellulosic fibers, with the greatest concentration of long fibers being adjacent the outer face of the facing layer, and with the concentration of short cellulosic fibers gradually increasing from the outer face to the inner face adjacent the batt. It is the concentration of long fibers adjacent the outer surface of the facing layer that gives the diaper improved feel and which results in greater comfort to the infant. The concentration of long fibers at the outer surface also effectively prevents, or at least minimizes, any tendency of the short cellulosic fibers to dust from the facing layer, while at the same time strengthening the outer portion of the facing layer.
The short cellulosic fibers are at maximum concentration at the inner face of the facing layer, and the concentration of short cellulosic fibers most preferably substantially uniformly increases in concentration from the outer face of the facing layer to the inner face thereof. Because the individual short cellulosic fibers are more wettable than the individual long fibers, there is a gradual increase in wettability throughout the cross-sectional thickness of the facing layer that is substantially directly proportional to the concentration of the short cellulosic fibers. As noted above, the wettability gradient within the facing layer itself promotes, or enhances, passage of urine through the facing layer and into the even more wettable, unbonded loosely compacted, cellulosic fibrous portion of the batt layer. The facing layer may be formed in accordance with the teachings in the above-mentioned Ruffo et al. application. By using this process, any unground or compacted pulp particles are confined to the interior of the diaper.
BRIEF DESCRIPTION OF THE DRAWINGS OF FIG. 1 is a perspective view, with certain portions broken away, of an open unfolded diaper in accordance with this invention;
FIG. 2 is an enlarged partial cross section of the diaper of FIG. 1, taken generally along line 2-2;
FIG. 3 is a perspective view on a reduced scale of the diaper in its configuration after being put on an infant; and
FIG. 4 is a simplified schematic view of the production line on which the diaper is made.
DETAILED DESCRIPTION While this invention is susceptible of embodiment in many different forms, there is shown in the drawings and will herein be described in detail a preferred embodiment of the invention, with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the embodiment illustrated. The scope of the invention will be pointed out in the appended claims.
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 14 has a continuous paper-like densified highly compacted lowermost fibrous layer 18 that includes spaced, parallel thickened densified portions 19 in the form of parallel lines that extend completely through the cross-sectional thickness of the batt. Densified layer 18 is adhered to the impervious sheet by bead lines of adhesive 22 substantially throughout the inter face therebetween. Marginal portions 16b and 12b are also adhered to each other by bead lines 22.
In the preferred embodiment of the invention, moisture impervious sheet l2 is formed of polyethylene having a thickness of approximately 0.001 inch. 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 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, staple length fibers or textile length fibers which are longer than about one-fourth inch in length, and generally are between about A 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 (TAPPI- T233 SU64).
The paper-like 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 US. Pat. No. 3,017,304, dated Ian. 16, 1962. The thickened densified portions 19 are formed by further compression of batt 14 while it is still moist, as will hereinafter appear.
The composite density of batt 14, including its densified layer 18, should be above about 0.07 gm./cc. and preferably between about 0.10 and 0.15 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, on an overall basis, is made of a given concentration of fibers consisting predominantly of short cellulosic fibers such as wood pulp fibers or cotton linters, in amounts of about 50 to about 98 percent, the balance being textile length fibers such as rayon, polyester, cellulose acetate, nylon, etc. 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 since low cost is a factor which is of substantial importance, it is desired to use as large an amount of short cellulosic fibers as is consistent with strength requirements.
Facing layer 16 is preferably formed by an air laying process, such as for example, the process disclosed in the above-mentioned Ruffo et al application, to produce a web having opposed outer and inner major faces 15 and 17, respectively, with face 15 being characterized by a concentration of staple length fibers in excess of the overall concentration, and with face 17 being characterized by a concentration of short cellulosic fibers in excess of the overall concentration. The term faces, as used herein, means that portion of the facing layer which extends inwardly from one outer major surface to approximately one-fourth of the total corsssectional thickness of the facing layer. The transition zone between the opposed faces 15 and 17 is characterized by a decreasing concentration of the respective fiber type from the face at which it predominates to the opposite face of the product. Face 15 preferably is comprised of a greater amount by weight of textile length fibers and a lesser amount by weight of short cellulosic fibers (as compared with the overall concentration of these fibers) interspersed and blended therewith; with face 17 preferably being comprised of a greater amount by weight of short cellulosic fibers and a lesser amount by weight of textile length fibers (as compared to the overall concentration of these fibers) interspersed and blended therewith.
The overall concentration of textile length fibers within facing layer 16 may vary from about 2 to about 50 percent, preferably from about to about 40 percent. The textile length fibers may, for example, be 1.5 denier rayon fibers uniformly cut to 1% inches in length, although the present invention is not limited to any specific textile length fiber or concentration thereof. For example, in facing layers with the overall concentration of textile length fibers being from about 10 to about 40 percent by weight,it has been found that the concentration of textile length fibers at face is about 5 to percent by weight higher than the overall concentration. In a specific embodiment of facing layer l6,which had an overall composition of about percent by weight rayon fibers and about 75 percent by weight short cellulosic fibers, the concentration of rayon fibers at face 15 was approximately -40 percent, and the textile length fibers were substantially uniformly blended with 65-60 percent of short cellulosic fibers. In this last-mentioned facing layer embodiment, approximately 5-10 percent of rayon fibers were present at face 17, and were in uniform admixture with about 95-90 percent of short cellulosic fibers.
Facing layers suitable for use in this invention have fabric weights in the range of 1 to 5 oz/ydF, and most preferably within the range of 1.75 to about 2.75 oz./yd. The present invention also contemplates that fabric having an even lower fabric weight may be provided. After formation, the web is treated with a bonding agent, such as a self-cross-linking acrylic emulsion, and the facing web is treated with a wetting agent to partially conteract the water repellency of the bonding agent and bring the facing layer to the desired degree of wettability. One bonding agent which has been employed with considerable success is a latex of polyethylacrylate copolymer containing small amounts of acrylonitrile and a cross-linking monomer sold under the trademark HYCAR 2600 X 120. The bonding agent should preferably be of the low viscosity type with a viscosity less than 5centipoises. 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 TRI- TON GR-S. A non-ionic surfactant may also be used, and a polyoxyethylene sorbitan monolaurate sold under the trademark TWEEN 20 has been found to be particularly useful. In a typical application, the binder suspension is controlled to give the fabric a dry solds 1 add on in the range of from about 4% to 9 percent based on the fabric weight, of which from about 0.15 to about 0.30 percent is the amount of surfactant. In facing layers having an extremely low percentage of textile length fibers, such as in facing layers approaching 2 percent textile length fibers, the binder amount would be toward the high side of the above-mentioned range. It will be understood that the above-mentioned surfactants moderate and reduce the water repellency which may be imparted to the short and long fibers of thP 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.
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 percent and approaching zero in the optimum embodiment, as described in detail in the above-mentioned patent. 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 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.
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. When the urine passes through the facing layer and comes into contact with the body of batt 14, it is preferentially absorbed into the body of the batt because of the enhanced wettability thereof. It spreads within the body of the batt to wet a roughly circular zone therein that is slightly larger than the wetted zone in facing layer 16. When the urine passes through the body of the batt it initially contacts one or more of the thickened densified lines 19 and the urine is strongly drawn into the densified layer 18 because of its high density and is spread laterally through a much larger zone, or to the edges of the batt, depending on the amount of urine passed. the urine is transported rapidly along lines 19, more rapidly than it is transported transversely across the densified bridging portions between lines, with the result that the roughly circular zone in the initially wetted loosely compacted portion of the batt is distorted into a roughly oval zone in the densified portion of the batt.
The urine is transported relatively rapidly in all directions of the densified layer 18 because the densified layer is continuous over one face of the absorbent panel. However, the thickened portions 19 provide for an increased volumetric flow rate in the longitudinal direction to rapidly move a larger volume toward the ends of the absorbent structure. The bridging portions provided by the portions of the densified layer between the thickened portions rapidly transport the liquid away from the initially wetted area of the densified layer and into contact with previously unwetted thickened portions, with the result that liquid is rapidly drawn away from the initially wetted area and transported both longitudinally and transversely into substantially all portions of the densified layer.
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 12 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 thickened densified portions provide for an increased crosssectional area in the absorbent panel, as compared to a densified layer of uniform thickness or a plurality of spaced densified zones, with th greater cross-sectional area providing a capacity to a sorb an increased volume of urine. Thus, with the structure of the present invention more urine can be stored in the densified layer, and the tendency for urine to flow back into the batt or into the facing layer is resisted.
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 uncompressed layer alone.
It is to be noted that the facing layer as assembled into the diaper is coterminous with the impervious sheet and there is no folding over of the impervious sheet to envelope any edgeof fibrous material. Thus there is no portion of the upper surface of the diaper 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 made such plastic-toskin contact unnecessary.
The diaper of this invention is normally packaged and sold in a folded condition as described in the abovementioned patent. Briefly, 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. 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 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 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, 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. 3. In one form of the invention, as illustrated in FIG. 3, 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. The facing sheets are removed to expose the adhesive surfaces when the diaper is applied to the infant, as in the configuration shown in FIG. 4, and the free ends of the adhesive tabs are secured to opposite corners of the diaper.
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 wood pulp fibers or cotton linters. The batts are initially formed by air blowing the 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 dense compacted paper-like layer or 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 unformity 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 lbs./in. a suitable densified, coherent paper-like skin 18 is obtained on the surface of the web which has been moistened. The thickened densified portions 19 may be obtained by subjecting the web to additional pressure, as by the use of an embossing roll, while the web is still moist, and the additional pressure is preferably several times higher than the pressure that is applied to form the densified layer 18.
The short fibers used in making batt 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 diaper of this invention may be assembled in equipment such as that schematically shown in FIG. 4. A roll of compacted wood pulp 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 oz./yd. the air blown 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 at, 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 paper-like densified skin desired, with lesser amounts of moisture being used for thinner webs and very thin, paper skins and greater amounts for thicker webs and skins of greater thickness.
the amount of pressure applied by rolls 49 may vary from about to about 100 or more lbs./in. with the commercially preferable range being from about 10 to about 50 lbs./in. 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 10 lbs. lin f teasers a densi fi ed, asherem pa ery skin of uniform thickness on the surface of the web which has been moistened. The amount of moisture is selected so that the web is still moist following formation of the skin 51. the web then passes between an embossing roll 52 and a back up roll 53 for formation of the thickened densified portions 19. Roll 52 has a plurality of axially spaced, circumferentially extending riblike projections 54 that bear upon the previously formed ,skin 51, and because of the residual moisture in the web and the increased pressure applied by projections 54, thickened densified portions 19 are produced.
The pressure applied by the projections 54 on the embossing roll also produces recesses or air gaps 20 (FIG. 2) in alignment with thickened portions 19. As is evident from FIG. 2, the unthickened portions of the densified layer 18 merge with the loosely compacted batt 14 at a generally planar interface 21, and the thickened densified portions extend beyond interface 21 and into the loosely compacted batt 18 to give the absorbent panel a three dimensional strengthening effect.
After the skin and the thickened portions are formed, the absorbent web comes into contact with a web of facing material 55 and is supported thereby while being cut by cutter 56 into individual batts l4. Polyethylene film 12 is fed to the assembly from roll 58, lines of adhesive being applied from applicator 59. 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 60 and 61 to shape the diaper assembly, and the individual diapers are cut off by cutter 62.
If desired, adhesive applicator 59 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, is preferably formed in accordance with the process disclosed in the above-mentioned Ruffo et al application. The facing layer has an overall concentration of from about between 50 and 98 percent by weight of shortfibers, not exceeding about one-fourth inch in length. The average short fibers are from about one-sixteenth to about three-sixteenths inch in length. The facing layer is prepared by first feeding a supply of short cellulosic fibers and a supply of textile length fibers 71 to a fiber opening and mixing apparatus 72, which take the form of two individual rotating lickerins as described in the above-mentioned Ruffo et al application. The fibers 70 and 71 are fed to the opening means 72 at a desired rate to provide a web 73 with a desired overall fiber concentration, and apparatus 73, in addition to opening the fiber source and individualizing the fibers, also suspends the fibers from each source in separate gaseous streams which are impelled toward one another and combined to form a single carrier stream wherein the fibers from each separate stream cross over one another to form the facing layer as described above.
The volume ratio of gas to fiber in each of the separate gaseous streams depends on the type and length of fibers. Thus, for example, for most commercially available shorter type fibers usable in the facing layer of the present invention, larger volume ratios may be employed as compared to the use of staple or longer length fibers where higher volume ratios are desirably employed. With shorter fibers, the volume ratio of gas to fiber in the separate gaseous stream is at least l2,000:l to l5,000:l and up to 275,00011. With the longer or textile length fibers, the volume ratio of gas to fiber in the separate gaseous stream preferably has a minimum of from about l5,000:1 to l8,000:l and up to 275,000:1 (desirably between 100,000:l to 275,000:). The minimum gas to fiber volume ratio in the combined stream depends to some extent on the overall concentration of short and long fibers, and preferably will be equal to or above the minimum ratios set forth above. With gas to fiber volume ratios of between about 12,0002] to about 275,000:1 in the combined stream, highly uniform webs (see the definition in the Ruffo et al application) can be produced at a high production rate up to 550 feet per minute, or greater. As noted above, the transition in fiber concentration from face 15 to face 17, and vice versa, is substantially uniform. The term substantially uniform, as used herein, is intended to mean that at any point between the opposed faces there is substantially no clear cut or distinct line of demarcation between the fibers of the fabric, when the fabric is viewed in cross section.
The web 73 emerging from apparatus 72 may be carried by a conveyor 74 to a bonding station when it is through bonded by a bonding agent of the type described above from source 75. the web is then dried by passing around drying drums 76, and then passes upwardly, as shown schematically in FIG. 4, where it is bonded to the remainder of the diaper structure.
It will be understood by those skilled in the art that variations and modifications of the specific embodiments described above may be employed without de-' parting from the scope of the invention as defined in the appended claims.
what is claimed is:
l. A multi-layer diaper comprising: a porous facing layer in the form of a nonwoven web formed of staple length fibers and short cellulosic fibers at an overall concentration of staple length fibers from about 25 to about 55 percent by weight and an overall concentration of short fibers from about 45 to about 98 percent by weight, said web having an outer major face characterized by a concentration of staple length fibers in excess of said overall concentration and an inner major face characterized by a concentration of short cellulosic fibers in excess of said overall concentration; a highly porous, loosely compacted, cellulosic fibrous batt in face-to-face juxtaposition with the inner face of said facing layer; and a water-impervious backing sheet adhered to the outer surface of said batt.
2. A diaper as set forth in claim 1 wherein said staple length fibers are rayon fibers.
3. A diaper as set forth in claim 1 wherein said staple length fibers are polyester fibers.
4. A diaper as set forth in claim 1 wherein said staple length fibers are present at an overall concentration from about to about 40 percent by weight and are present at said outer major face in a concentration of from about 5 to 20 percent by weight higher than said overall concentration.
5. A multi-layer diaper comprising: a porous facing layer in the form of a nonwoven web formed of staple length fibers and short cellulosic fibers at an overall concentration of staple length fibers from about 2 to about 55 percent by weight and an overall concentration of short fibers from about 45 to about 98 percent by weight, said web having an outer major face characterized by a concentration of staple length fibers in excess of said overall concentration and an inner major face characterized by a concentration of short cellulosic fibers in excess of said overall concentration, the intermediate portion of said web between said faces being characterized by a transition whereby the concentration of said staple length fibers gradually decreases from said outer major face to said inner major face and the concentration of said short cellulosic fibers gradually decreases from said inner major face to said outer major face; a highly porous, loosely compacted, cellulosic fibrous batt in face-to-face juxtaposition with the inner face of said facing layer; and a water-impervious backing sheet adhered to the outer surface of said batt.
6. A diaper as set forth in claim 5 wherein said staple length fibers are present at an overall concentration from about 10 to about 40 percent by weight and are present at said outer major face in a concentration of from about 5 to 20 percent by weight higher than said overall concentration.
7. A diaper as set forth in claim 6 wherein the transition of each type of fibers between said faces is substantially uniform.
8. A diaper as set forth in claim 5 wherein said staple length fibers are rayon fibers.
9. A diaper as set forth in claim 5 wherein said staple length fibers are polyester fibers.
10. A multi-layer diaper comprising: a porous facing layer in the form of a nonwoven web formed of staple length fibers and short cellulosic fibers at an overall concentration of staple length fibers from about 2 to about 55 percent by weight and an overall concentration of short fibers from about 45 to about 98 percent by weight, said web having an outer major face characterized by a blend of staple length fibers and short cellulosic fibers with the concentration of staple length fibers being in excess of said overall concentration, and said web having an inner major face characterized by a blend of short cellulosic fibers and staple length fibers with the concentration of short cellulosic fibers being in excess of said overall concentration, the intermediate portion of said web between said faces being characterized by a transition whereby the concentration of said staple length fibers gradually decreases from said outer major face to said inner major face and the concentration of said short cellulosic fibers gradually decreases from said inner major face to said outer major face; a highly porous, loosely compacted, cellulosic fibrous batt in face-to-face juxtaposition with the inner face of said facing layer; and a water-impervious backing sheet adhered to the outer surface of said batt.
W105? UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,7 Dated October 30,1973
Inventor(s) Frederick Mesek and Virginia Repke It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
Column line 62, "cores" should read cross Column 6, line 1, "thP" should read the Column 9, line 11, "paper skins" should read papery skins Column 10, line 2, "275,ooo:)"- should read 275,oo0;1).---.
Column ll, me 7, "25" should read 2% Signed and sealed this 16th, day of April 1972 (SEAL) Attest:
EDWARD I'LFLETGHERJR. MARSHALL DANN Attesting Officer Commissioner of" Patents