Diaper insert

[57] ABSTRACT

A disposable diaper insert for a disposable or nondisposable diaper comprised of, in combination, at least one absorbent pad disposed between a liquid impermeable topsheet and a liquid impermeable bottom sheet, each of said sheets being formed from a hydrophobic material such as a thermoplastic film and each of said films being characterized by a plurality of valvular apertures or openings therein and a system of dimples disposed across the surface thereof.

Claims, 7 Drawing Figures

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.PATENTED JUN 3 1975

3,886,941

SHEET

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PATENTED J’J 3 1975

3,886,941

SHEET

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F I G. 5

3,886,941

PATENTED JU« 3 ¹⁹⁷⁵

SHEET

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3,886,941

DIAPER INSERT

The present invention relates to diapers and more particularly to disposable inserts for disposable or nondisposable diapers which are adapted to provide improved absorbency, and which can be used once and thrown away. In a more specific aspect, the disposable diaper inserts of the present invention are utilized in conjunction with disposable or non-disposable diapers whereby only the disposable diaper insert is discarded after soilage, thereby permitting future use of the diaper.

Disposable diapers have been known in the art for a number of years, and are now gaining widespread acceptance by consumers, both in private homes and in hospitals and institutions. Their present success is achieved in part by the elimination of the necessity of storing, washing and folding the disposable diaper as is the case with the conventional cotton woven diapers.

To compete with the conventional product, the cost of the disposable diaper must be relatively low and it should be similar to a cloth diaper with regard to absorbency, softness, bulk and conformability.

In both types of diapers, premature removal from the infant adds considerably to the consumer’s problem as reflected either by the increased labor effort required to clean conventional diapers or by the expense of replacing the disposable diaper. This premature removal can be motivated by a variety of factors but is mainly attributable to the effect of partial saturation of the diaper. Thus when an infant partially wets a diaper, the mother or the consumer is prone to immediately replace the diaper due to her associating wetness with “diaper rash,” odor, discomfort and other such characteristics.

Attempts to ameliorate the problems by utilizing diaper aids, e.g., disposable absorbent diaper inserts, or “booster pads,” have not been entirely satisfactory for a variety of reasons. Merely as illustrative, the conventional diaper aids suffer from one or more of the following disadvantages:

a. They do not possess sufficient absorptive capacity;

b. They are uncomfortable to the user; and

c. They suffer from poor liquid retention properties after absorption.

It will of course be understood that the terms “diaper aids,” “booster pads” and “diaper inserts” are susceptible to various interpretations and meanings. As used herein, however, it is intended that these terms designate absorbent material or products to be used in conjunction with conventional diapers (as contrasted to their being part of the structure of the diaper) in order to provide additional advantages such as improved absorbency and reduced leakage from the diaper.

It is therefore an object of the present invention to provide an insert for diapers which can be utilized in conjunction with a conventional diaper so as to provide added absorbency and which can be easily removed from the diaper, after soilage, and discarded permitting future use of the diaper.

Another object of the present invention is to provide a diaper insert for disposable diapers which enables the diaper to be utilized for relatively longer periods of time thereby providing increased economical operation.

Another object is to provide a diaper insert for diapers which have a high degree of liquid retention.

A still further object is to provide a diaper insert for disposable diapers having a high degree of initial absorption or wicking properties.

These and other objects will become apparent from the description of the invention taken in conjunction with the accompanying drawings in which:

FIG. 1 is a perspective view of the diaper insert made in accordance with the present invention with some portions opened up to reveal other portions and certain details of construction.

FIG. 2 is a section taken along the line 2—2 of FIG. 1.

FIG. 3 is an enlarged fragmentary cross-section of FIG. 2 showing a section of the diaper insert during unsaturation.

FIG. 4 is a view similar to FIG. 3 except that the diaper insert is saturated with liquid.

FIG. 5 is a plan view, partially cut away of a diaper insert according to a further, but less preferred embodiment of the present invention.

FIG. 6 is a plan view of a diaper insert wherein the absorbent material has a contoured configuration.

FIG. 7 is a plan view of a conventional diaper showing the diaper insert in position on the diaper.

In its broad aspect, the disposable diaper insert of the present invention is comprised of, in combination, at least one absorbent pad disposed between a liquid impermeable topsheet and a liquid impermeable bottom sheet, each of said sheets being formed from a hydrophobic material such as a thermoplastic film and each of said films being characterized by a plurality of valvular apertures or openings therein and a system of dimples disposed across the surface thereof.

Referring in detail to FIG. 1 there is shown a disposable diaper insert, generally designated 10, comprising a rectangular absorbent pad 12 substantially centrally located and sandwiched between a thin, flexible bottom sheet 14 of liquid impermeable material, and a thin flexible topsheet 16 also of a normally liquid impermeable material. Bottom sheet 14 and topsheet 16 have a plurality of slits 18 and a system of dimples 22 therein which slits and dimples will be described in greater detail hereinafter.

Bottom sheet 14 and topsheet 16 are of approximately equal size and are of a length and width slightly greater than the corresponding dimensions of absorbent pad 12. The edges of bottom sheet 14 and topsheet 16 are sealed to each other around the entire periphery of the insert 10 and just outside the outermost edges of absorbent pad 12. The sealing can be accomplished by any convenient means, such as the use of an adhesive, but heat sealing is preferred and is indicated by heat seal 20 around the periphery of the insert.

The absorbent pad 12 can be a plurality of layers of absorbent tissue paper or wadding stacked to the desired thickness. The wadding layers need not be adhered to each other but, since it has been common practice to adhesively, mechanically, or otherwise secure the layers to each other to maintain the relative position of the layers and the shape of the absorbent pad, such can also be done in the insert of the present invention. The wadding can be stacked to form a pad of any desired thickness and hence absorbency can be controlled for any particular use.

Absorbent materials other than tissue and wadding will of course be useful in the insert construction of the present invention. For example, absorbent non-woven

3,886,941 pads can be fabricated to any desired thickness and substituted for the absorbent pads described above. One such absorbent pad which has been used extensively in disposable diapers is a wood pulp product commonly known as wood fluff and is prepared in the 5 same manner as a non-woven fabric. Thus such type absorbent pad is also useful as the absorbent pads of the inserts of the present invention.

The only criteria for utility in the present invention are that the material be absorbent, be capable of being 10 fabricated in the form of a pad, be compatible with the waste products with which it will come in contact and be non-irritating to the skin.

Various natural and synthetic polymeric materials are themselves absorbent or can be made absorbent 15 and will therefore be useful as, or in combination with, the absorbent pad of the present invention. One group of polymers which are particularly preferred are insoluble hydrophilic homopolymers and copolymers which form a gel upon absorption of water. These materials 20 offer the obvious advantage of holding tenaciously to liquid and preventing the release of liquid from the absorbent article and leaking or wetting skin or clothing with which the absorbent article is in contact.

In practice, the materials which have been found par- ²⁵ticularly useful are insoluble hydrophilic polymers prepared from the following starting materials: poly (alkylene oxides), e.g. poly(ethylene oxide), polyvinyl alcohol, polyvinylmethyl ether, copolymers of maleic anhydride and ethylene, copolymers of maleic anahydride ³⁰and vinylmethyl ether, polyelectrolytes, etc.

Insoluble hydrophilic polymers, sometimes referred to as “hydrogels,” are especially useful in the present invention because they possess the ability to consume very large amounts of water in the order of 25 to 100 ³⁵times their dry weight.

The term “insoluble” or “insolubilization” as employed in relation to these polymers is intended to define the formation of a gel which does not flow and does not expel water under the pressures encountered in the use of products described above.

The insolubilization can be effected by a wide variety of methods and includes, but is not limited to, ionizing and nonionizing radiation and chemical cross-linking through covalent and ionic bonding.

A particularly preferred hydrogen for use in the articles of this invention is comprised of at least one hydrophilic polymer of the formula

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which has been cross-linked and wherein Ri and R₂ are selected from the group consisting of hydrogen, alkyl radicals and alkyl substituted aryl radicals, and wherein R3-R₆ are selected from the group consisting of hydrogen, methyl, phenyl and vinyl radicals, and n is greater ₆₅than one.

The hydrogels are polymeric compounds containing at least one of the structural units shown below:

<td></td><td> R1 f — c</td><td> *2 _____c__o</td>

<td></td><td> c .......</td><td> t H H ------C ----o</td>

<td></td><td> t r₃</td><td> r₄</td>

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wherein R,-R₄ are selected from the group consisting of hydrogen, methyl, phenyl and vinyl radicals.

These hydrophilic polymers may include carbon-tocarbon cross-linking between straight chain carbon atoms and the carbon atoms of branch chain methyl groups and in addition a very minor and insignificant number of bonds may include two oxygen atoms linking the carbon atoms.

The polymeric gel compounds may contain crosslinking bonds present as intermolecular bonds (e.g. between two different molecules) and intramolecular bonds (e.g. between carbon atoms of the same molecule), and combinations of intra and intermolecular cross-linking bonds.

The hydrogels can be used in the diaper constructions of the present invention either in the form of thin transparent sheets disposed between or in place of wadding layers of the absorbent pad or can be embedded in the fibers of the absorbent pad as a powder or in shredded form. The manner in which the materials are incorporated into the pad is not critical since it is merely necessary to have the polymers come in contact with the liquid which penetrates the topsheet of the absorbent article.

The materials used in the fabrication of the topsheet and bottom sheet of the diaper insert of the present invention are also not limited to any particular chemical composition since it is their physical properties rather than their chemical properties which are important in the articles of the invention. These materials should, of course, be thin, flexible, self-supporting, and substantially water impermeable sheets or films. Preferably

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The slits can be formed according to the methods described in U.S. Pat. No. 3,762,255 issued October 2, 1973 and entitled “Method and Apparatus for Piercing Thin Sheet Material”. Briefly, there is disclosed therein 5 a method and apparatus for piercing thin sheet material, such as plastic film, wherein the sheet material is passed between a piercing member having a plurality of independently resilient protrusions extending therefrom and a backing member having a retiform exterior 10 surface. The piercing member or backup member is moved relative to the other member, thereby causing the resilient protrusions to follow the retiform surface and selectively pierce the film. The piercing member can be a metal comb, a wire brush or a metal strip hav15 ing a plurality of substantially parallel slits extending from one edge thereof in the direction of the opposite edge defining the resilient protrusions. The backing member can be a wire screen, a perforated metal sheet, an engraved metal roll or an endless belt which is 20 driven longitudinally with respect to the piercing member.

The depressed areas 22 (dimples) are distributed across the surface of the topsheet and bottom sheet in the manner shown in FIGS. 1—4. Thus, it will be seen 25 that the bottom sheet 14 and topsheet 16 contain a plurality of dimples arranged in staggered parallel rows along the surface of the bottom sheet and topsheet (FIG. 1) and which extend beyond the plane of the bottom sheet and topsheet (FIGS. 2 and 3). The configura³⁰ tion of these dimples can be circular, eliptical, rectangular, diamond shaped, and the like, the important criteria being that they be formed in a manner such that there is substantially no breaking or cutting of the topsheet during or after fabrication.

³⁵ The full advantages of the present invention are not achieved if, during fabrication of the dimples, the bottom sheet or topsheet is broken, cut, or melted to an extent which would hinder the controlled passage of liquid to the absorbent pad (which as explained previ⁴⁰ ously, is the function of the valvular openings). It will be evident that if cutting or breaking of either sheet occurs during fabrication of the dimples, that the liquid will pass through these cuts or breaks when the absorbent pad is unsaturated and once the absorbent pad is ⁴⁵ saturated or even partially saturated, that these entry points will also serve as points or sites through which the liquid exudes back through the topsheet in contact with, for example, a baby’s skin.

For these reasons and furthermore in view of the ease and simplicity of fabrication, I have found that the preferred form of the dimple is circular as shown in FIGS. 1-4.

The dimples can be formed in the bottom sheet and topsheet in a variety of ways. The easiest and therefore ⁵⁵ the most preferred method involves the use of a roller equipped with heating means and having a number of spikes or probes extending therefrom across the width of the roller and around its circumference. The spikes, pins, or probes, which have smooth, rounded end points, can be spaced as desired on the roller in order to provide the desired number of dimples to the diaper insert. The dimples are provided on the diaper insert preferably after the valvular openings, and this opera₆₅ tion can be effected by passing the diaper insert containing the valvular openings in contact with the heated roller. In this technique, the diaper insert is supported on a resilient back-up member, such as an endless con5 they are thermoplastic films which are capable of being heat sealed to each other.

The bottom sheet and topsheet can be an olefinic or vinyl film. Merely as illustrative, polyethylene of a thickness of from about 0.4 to about 1.5 mils can be employed. This type of film has previously been used extensively in disposable diapers and commonly has had an embossed design in its surface to simulate the appearance and hand of cloth. These manufacturing techniques will also find use in the diaper inserts of the present invention.

Any film which is useful as a bottom sheet will also be useful as a topsheet for the disposable absorbent insert of the invention. It is preferable, however, to use a film for the bottom sheet and topsheet which resembles cloth more closely in feel and appearance. One film which has been found particularly useful is ethylene-ethyl acrylate film. This copolymer is cloth-like, softer and stronger after slitting than polyethylene film. The film should have a thickness of from about 0.4 to about 2.0 mils with about 1.0 to 1.5 mils being preferred.

As described above, the bottom sheet and topsheet are made from a substantially liquid impermeable material and must be provided with valvular openings to be effective as the diaper insert of the present invention.

The term “valvular” as used throughout the specification and in the claims is intended to refer to apertures in the bottom sheet and topsheet which are capable of opening to permit passage of liquid under certain circumstances and reclosing to retard passage of liquid under certain other circumstances. When open, the valvular openings should have the ability to pass at least 20 milliliters of liquid within 10 seconds when an area of about 20 square inches is wetted. These openings may be of two basic types, substantially straight slits and punctures.

The slits useful in the present invention must be substantially straight since, if they are curved, V-shaped or of any other configuration, they will form flaps in the surface of the film which are too easily opened and tend to remain open. Such slits, while permitting sufficient passage of liquid in the direction of the absorbent pad, do not act to substantially reduce backflow of liquid,’which is the primary object of the present invention. This disadvantage is also present if holes are formed in the film by removing pieces of film material as opposed to puncturing the film without removal of film material. The film is thereby left open to the uncontrolled passage of liquid in both directions.

FIG. 1 shows a preferred arrangement of slits. The slits 18 are arranged in longitudinal rows in a manner such that each row constitutes a longitudinal array of substantially parallel straight slits each angularly disposed with respect to the longitudinal axis of the row. Adjacent rows are similarly disposed except that the slits are arranged in a manner such that the end points of each slit lie in a line substantially between the end points of corresponding slits in the adjacent alternate rows. The slits should each be from about 0.030 to about 0.25 inch in length. Preferably there are from about 30 to about 150 slits per square inch, each of such slits being from about 0.07 to about 0.2 inch in length. The most preferred film contains about 81 slits per square inch, each about 0.1 inch in length.

3,886,941 veyor belt, or a resilient back-up roller. The depth of the dimple can be controlled by limiting the depth to which the probes depress the film. If desired, portions of the topsheet and bottom sheet may be retained in their untreated (without the dimples) condition. This can be accomplished, for example, along a strip about 1 inch wide near the periphery of the bottom sheet and topsheet. Since each sheet or film is thermoplastic, the amount of heat and pressure applied to the areas to be treated should be strictly controlled in order to avoid substantially puncturing the material. As a general rule, the amount of heat required should be enough to soften the film, and the amount of pressure should be sufficient to plastically distort the film to the general contour of the probe. It will, of course, be understood that the correct heat and pressure conditions will depend (among other variables) upon the residence time of the treated absorbent pad, i.e., the length of time the sheet is in contact with the roller; the thickness of the absorbent pad, etc. The correct conditions, however, can be easily ascertained by one skilled in the art and hence no further detailed description of the conditions appears necessary.

Referring specifically to FIGS. 3 and 4, it will be seen that the dimples 22 extend beyond the plane of the bottom sheet 14 and top sheet 16 a short distance, and that the absorbent material 12α, immediately below (or above) each dimple, is in a compressed state. At the site where a dimple is formed over a portion of the slit 18, it will be seen that the slit is opened to a much greater degree than corresponding slits situated remote from the dimples 22. However, because of the placement of the dimples, the slits disposed between corresponding dimples are opened to a greater extent than would be the case if no dimples were present. This is attributed to the fact that the pressure exerted on the surface of the topsheet and bottom sheet by the dimples causes the slits to open slightly under the influence of the stretching of the sheet. Portions of the compressed absorbent pad are associated with these opened slits, and because of this association, wicking is achieved at a degree never heretofore achieved. As a matter of fact, in most cases, wicking is instantaneous. As the liquid is transferred to the absorbent pad 12, the absorbent pad absorbs the liquid throughout its entire area until either partial or full saturation. As will be seen in FIG. 4, (which depicts a saturated absorbent pad), the compressed material 12α has expanded and urges the dimples 22 outward, closer to the plane of the bottom sheet and topsheet respectively. This action serves to close the previously opened slits, thereby trapping the bulk of the liquid in the absorbent pad.

Thus, advantageously, according to the present invention, maximum wicking and absorption is achieved during the critical period when flooding, (such as by urination and the like) is experienced, whereas transfer of the liquid from the absorbent pad back through the same slit opening is substantially reduced by virtue of the combination of the valvular action of the slit and the dimple.

The dimples can be arranged on the absorbent article in a variety of patterns. Thus, the overall design effect can be diamond shaped, curvilinear, herringbone and the like. The preferred design configuration is a system of substantially straight staggered, parallel rows along the surface of the topsheet. The number of dimples per square inch of absorbent pad area can be varied over a relatively wide range.

The advantages and wicking characteristics of the dimple-slit combination are fully described in the copending application of Theodore Fredrick Kozak entitled “Disposable Absorbent Articles”, Ser. No. 312,131, filed on Dec. 4, 1972 and assigned to a common assignee. The range of slit size, dimple size and frequency of each are fully disclosed thereunder. The principal difference between the absorbent article disclosed thereunder and the instant diaper inserts is that in the diaper insert, both sides, i.e. top and bottom sheets, are slitted and dimpled thereby permitting rapid absorption on both sides of the diaper insert. Thus, as disclosed and demonstrated in said copending application, improvements have been noted utilizing as little as one dimple (having a diameter of 0.05 inch) per square inch of absorbent pad. Good results are obtained when as many as 100 dimples (0.05 inch diameter) per square inch of absorbent pad area are utilized. It will of course be understood that the number of dimples per square inch of absorbent pad area depends on the dimple size. As a general rule, the total area occupied by dimples should not exceed more than 20 per cent of the area of the absorbent material. Excellent results are achieved when the total dimple area is from 4 to 12 per cent of the area of the absorbent material. Preferably there are from about three to about 25 dimples (0.10 inch diameter) per square inch of absorbent material area, and most preferably from about six to about 15 per square inch of absorbent pad area.

As a general rule, dimple size can be in the range of about 0.025 to about 0.250 inch diameter. From the standpoint of functional and aesthetic qualities, it is preferred that the dimple size range from about 0.075 to about 0.150 inch diameter.

In still another, but less preferred embodiment, the dimples are associated with the diaper insert depicted in FIG. 5 wherein the slits 18 are shown as being in straight parallel relation.

The fabrication of the diaper insert may be accomplished by a variety of techniques. In a preferred technique, a thin film of thermoplastic material such as an ethylene ethyl acrylate film of the desired thickness is slit according to the procedure described previously. After the slitting operation, the assembly of the diaper insert, more or less, follows conventional methods of fabrication. The topsheet and bottom sheet are cut to approximately the same dimensions which are equal to the desired size of the final diaper insert. The size can be varied according to the desired use, for example, in rectangular form the diaper insert can have a width of 4-6 inches and a length of 10-18 inches.

The topsheet and bottom sheet are juxtaposed one on the other with the absorbent pad sandwiched therebetween in approximately the center of the sheets. The absorbent pad should be of a length and width slightly smaller than the topsheet and bottom sheet to permit sealing of the topsheet to the backing sheet around their periphery. An overhang of about one-half inch on each side should be sufficient. Sealing can conveniently be accomplished by heat sealing the edges. The heat sealing might also be used to simultaneously accomplish a cutting of the edges to trim excess sheet material from the diaper and yield a diaper structure which is neat in its appearance.

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If desired, the absorbent pad may be of hour glass configuration (contoured). In this case, and for ease of fabrication, only the absorbent pad is of hourglass configuration. The bottom sheet and topsheet can be rectangular so as to facilitate the heat sealing of the edges.

Thus, referring to FIG. 6, where like parts are designated by like reference numerals, it will be seen that the absorbent pad 12 is of hourglass configuration, and is sandwiched between bottom sheet 14 and topsheet 16. It will be noted that the bottom sheet and topsheet are substantially rectangular whereas the absorbent pad 12 is of hourglass configuration. This design is merely for ease of fabrication since it will be obvious that the topsheet and bottom sheet can also be of substantially hourglass configuration, corresponding to the shape of absorbent pad 12.

The diaper insert of the instant invention can be utilized in conjunction with conventional diapers of the disposable or non-disposable type. The insert is normally positioned in the center of the diaper as shown in FIG. 7, the diaper insert 10 is positioned on diaper 24 on the side which would normally be in contact with a baby’s skin. The diaper 24 shown in FIG. 7 is of the disposable type having a “wing” fold design. This type of fold permits the use of the diaper insert without any securing means since the insert can be held in position by the edges formed by the wing fold. In other type designs, it may be necessary to include attachment means such as tape fasteners and the like in order to prevent migration of the insert during operation. These type of securement means are well known in the art and hence no detailed description appears necessary.

When in position on the diaper, the structure of the insert permits the rapid absorption of liquid through the topsheet. However, when excessive flooding occurs, some of the liquid may flow around the insert between the bottom sheet of the insert and the absorbing surface of the conventional diaper. Since the bottom sheet of the insert is also capable of absorbing liquid as explained previously, some of the liquid will be absorbed into the insert via the bottom sheet thereby minimizing the flow of excess liquid into the diaper.

Surprisingly, it has been found that the combination of the diaper insert and the diaper results in the diaper insert and diaper totally absorbing a disproportionately higher urine load than if the absorbent contained in the diaper insert were added to the diaper absorbent and made an integral part of the diaper. In other words, the degree of total absorbing is greater when the diaper insert and diaper are utilized as described herein as contrasted to using the diaper without the diaper insert but containing the combined amount of absorbent material of the basic diaper and diaper insert.

The slit-dimple construction causes the liquid to be readily absorbed and retained by the insert in the manner previously set forth. Thus when the insert becomes saturated or even partially saturated, the consumer need only replace the insert leaving the basic diaper ready for future use. This of course represents a savings in time and labor and is also highly desirable from a practical economical standpoint.