US3903889A

US3903889A - Disposable liquid absorbent products

Info

Publication number: US3903889A
Application number: US342162*A
Authority: US
Inventors: David Torr
Original assignee: First National Bank of Nevada
Current assignee: GOLDFARB KENNETH S; Colgate Palmolive Co
Priority date: 1973-02-16
Filing date: 1973-02-16
Publication date: 1975-09-09
Anticipated expiration: 1992-09-09

Abstract

An improved form of liquid absorbent product as, for example, a diaper is disclosed. There also is disclosed an improved liquid absorbent material composition.

Description

United States Patent Torr, deceased Sept. 9, I975 [54] DISPOSABLE LIQUID ABSORBENT $070,095 l2/l962 Torr 128/284 PRODUCTS 3,]2L427 2/]964 Mosier l28/284 3,528,421 9/1970 Vaillancourt ct 21].. .4 128/284 [75] Inventor: D vid Torr. ec late f Las 3.638.651 2 1972 Torr 128/284 Vegas, Nevv 3,66l,l54 5/1972 Torr [28/284 3 670,731 6 1972 H l 8 284 [73] Assignee: First National Bank of Nevada, armon 2 Executor oi the Estate of David L35 g Primary Examiner-Aldrich F. Medbery [22] Filed; 16, 1973 Attorney, Agent, or FirmWatson Leavenworth Kelton & Taggart [2]} Appl No: 342,162

U.S- i i. R [51] Int. Cl. A6lf 13/16 l {58] F'eld Search An improved form of liquid absorbent product as, for 128/296 290 R example, a diaper is disclosed. There also is disclosed an improved liquid absorbent material composition [56] References Cited UN'TED STATES PATENTS 11 Claims, 5 Drawing Figures 3.034922 5/]962 Boe .7 l28/284 PATENIEDSEP 91975 3.903.889

uggml IIIIII 1 DISPOSABLE LIQUID ABSORBENT PRODUCTS BACKGROUND OF THE INVENTION Various constructions of liquid-absorbent products such as disposable diapers, bed pads, hospital medical and surgical pads, sanitary napkins and like devices are known in the art. Generally, such disposable types of products include a body contacting layer of liquidpervious material, an outer layer which embodies liquid-impervious character therein, and an intermediate liquid-absorbent component which conveniently may be provided in the form of a particulate liquidabsorbent gel-forming material, which when wetted absorbs many times its own weight of liquid. ln association with the absorbent or gel-forming material there may be provided other components such as a core of fluffed fibrous pulp or a core of creped, laminated or single ply wadding. Whether the liquid-absorbent gelforming material is employed in conjunction with a fluffed pulp or a creped wadding core or not, there is a tendency for the liquid-absorbent gel-forming material particles to settle or shift in the product to an extent that when the product is wetted, a major quantity of the liquid is not absorbed by such material and in the case where a fluffed pulp or creped wadding core is used such liquid is absorbed by the fibers of the core so that the water-absorbent gel-forming material does not serve completely its intended function. As a consequence, if a pressure is applied to the product as, for example, by the weight of a baby's body in connection with the use of a diaper, such pressure can express or force the liquid back through the body contacting layer to the discomfort of the wearer thus producing the undesirable consequences sought to be avoided by using a liquid-absorbent gel-forming material in the product.

Also, known types of liquid-absorbent gel-forming materials are not fully satisfactory when embodied in disposable liquid-absorbent products since generally they form, when wetted, a substantially liquidus gel mass rather than a more desirable relatively dry gel.

Accordingly, it is desirable that the construction of liquid-absorbent products of the types described aforesaid be improved to locate more advantageously therein the liquid-absorbent gel-forming material, to optimally position same to effect maximum liquidabsorption by such material, and further to improve liquid-absorbent gel-forming material compositions by providing for their conversion into relatively dry gels upon wetting.

SUMMARY OF THE PRESENT INVENTION The present invention is concerned with improvements in the construction of liquid-absorbent products of the type which are disposable as, for example, by flushing in a toilet system. As used herein "products" includes diapers, bed pads, hospital medical and surgical pads and sheets, catamenial devices such as sanitary napkins or vaginal tampons, continuous filament material such as sutures, and products of similar description which are used for absorbing body liquids.

The present invention provides an improved form of liquid-absorbent product which can be made in various embodiments but which is characterized by the feature that the liquid-absorbent gelforming material used therein is optimally positioned or disposed in the product to insure maximum liquid-absorption thereby to overcome prior art product shortcomings of liquid return through the body contacting layer due to insufficient absorption by the liquid-absorbent material. Furthermore, improved compositions useful as the liquidabsorbent material are provided. While various embodiments of the invention are described herein in terms of disposable diaper construction, it will be understood that the invention is applicable in its broadest aspects to other types of liquid-absorbent products.

In one embodiment of the invention, the disposable diaper is provided with a body contacting layer which can be of any suitable material having liquid-pervious character and which is of fine and soft texture to provide a reasonable measure of comfort to the wearer. Such layer could be a woven or a non-woven fabric and it could be of cotton, rayon, paper, synthetic materials etc. and could be of plural ply structure. The diaper also includes an outer layer of suitable material, e.g., one or more plys of tissue paper which has been waterproofed at one or both sides by applying thereto a suitable liquid repellent material, as for example, a stearate, silicone, wax, paraffin, a natural or synthetic resin etc. Intermediate the body contacting and outer layers there is provided a core of fluffed pulp material such as a core of fibrous cellulosic or other material. In accordance with the invention, a liquid-absorbent gel forming material composition as, for example, a modified guar gum in a particulate form thereof, is distributed throughout the fluffed pulp and is adhesively secured to the pulp fibers by means of a suitable tacky adhesive agent which possesses property of being permanently pliable so that it elastically maintains the positioning of absorbent material in the diaper, such adhesive agent being, e.g., a water soluble material such as a sugar or even a water repellent material such as a rosin, the adhesive serving to anchor the gel-forming material to the pulp fibers in a uniformly distributed pattern throughout the mass thereof, thereby to preclude migration of such material to the body contacting layer or outer layer component sides of the fluffed pulp core or to other such region of the diaper structure so as to limit or inhibit proper liquid absorption during use. Thus, the liquid-absorbent gel-forming material is elastically maintained in an optimum position in the diaper to insure that liquid entering the diaper structure through the body contacting layer is absorbed principally by the gel-forming material and not by the fibers of the pulp.

According to another embodiment of the invention, after the fluffed pulp core has been laid down on the outer layer of the diaper during manufacture of the same, the fluffed pulp is oversprayed with a tacky coating of said adhesive agent, following which the particulate, liquid-absorbent gel-forming material is sifted onto the fluffed pulp, the adhesive overspray functioning to anchor or position the gel-forming material in respect of the fluffed pulp core. For further enhancement of the positioning of the absorbent material, the underface or inner face surface of the body contacting layer, which in manufacturing is laid down on top of the fluffed pulp core, can be provided with a liquidpervious coating or film of the same tacky adhesive agent to further secure and position the liquidabsorbent gel-forming material in the diaper structure. If the adhesive agent is a water soluble material, the film thereof at the inner face surface of the body contacting layer will dissolve when the diaper is wetted and, accordingly liquid-pervious in relation to such adhesive film is intended to embrace a water soluble film. On the other hand, if the adhesive agent is water repellent, it would be made liquid-pervious in known manner, e.g., by perforations therein.

A further embodiment of the invention provides that in lieu of a fluffed pulp core, a core of one or more layers of creped paper wadding is embodied in the diaper structure, such core being oversprayed with a tacky film of the adhesive agent, following which the gelforming material is sifted onto the core, such material optionally then being further secured in the diaper structure by an adhesive agent film coating at the inner surface of the body contacting layer.

A still further form of the invention provides that the diaper may embody a core of plural layers of fluffed pulp with each fluffed pulp layer being separated from the others by an interposed tissue sheet, each fluffed pulp layer being oversprayed with a tacky adhesive agent prior to the sifting of the gel-forming material onto the same. The tissue separator sheet also may be coated with the tacky adhesive agent on the faces thereof which contact the fluffed pulp layers.

Still a further form of the diaper of the present invention provides that the fluffed pulp and/or creped wadding cores are not employed, so that the diaper structure could comprise the body contacting layer and outer layer with a film of liquid-absorbent gel-forming material embodying said adhesive agent disposed therebetween, the film optionally being loosely disposed between said layers or adhered to the inner face of the body contacting layer or the outer layer or both by means of the adhesive agent.

As adhesives, any water-soluble adhesive agent of character compatible with the absorbent material can be used, concentrated sugar base materials being particularly advantageous and including honey, corn syrup, dextrine, and the like. Other water soluble materials such as gelatinous substances and even pressure sensitive adhesives, if water soluble, can be used, Water repellent type materials also can be used as the adhesive agent, for example, the adhesive material can be rosin. If the adhesive agent is water repellent, it will be employed in such manner and association with the liquid-absorbent material so as to not inhibit access to the latter by the liquid entering the diaper as, for example. by establishing a barrier around the liquid-absorbent material. Various forms of adhesive materials of both water soluble and water repellent types will be described in greater detail later.

The present invention also provides an improved liquid-absorbent gel-forming material composition which, in contrast with known compositions of such material type, when wetted form a relatively dry gel mass as distinguished from a relatively liquidus form of gel mass. Particular compositions of water-absorbent gelforming material of improved character will be described in greater detail later in the description.

The invention, accordingly, comprises the diaper construction possessing the features, properties and re lation of elements which will be exemplified in the devices as well as the absorbent material composition hereinafter described and the scope of the present invention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects of the invention will be in part obvious and will in part appear from the following detailed description taken in conjunction with the accompanying drawings, wherein like reference numerals identify like parts throughout and in which:

FIG. I is a longitudinal sectional view through one form of diaper made in accordance with the present invention in which a core of fluffed pulp is disposed intermediate the body contacting and outer layers of the diaper, the fluffed pulp having adhered thereto by means of a suitable tacky adhesive agent, particles of a liquidabsorbent gel-forming material.

FIG. 2 is a longitudinal sectional view of another form of diaper in which the fluffed pulp core has been oversprayed with the tacky adhesive agent before the liquidabsorbent gel-forming material is sifted onto the fluffed pulp, with the inner face of the body contacting layer also carrying a film of the tacky adhesive for further securing or positioning the absorbent material within the diaper structure.

FIG. 3 is a longitudinal sectional view of another form of diaper in which plural creped wadding layers are employed therein in lieu of fluffed pulp as a bulking material.

FIG. 4 is a longitudinal sectional view of a diaper in which the fluffed pulp is provided in two or more layers thereof with each layer being separated from the others by means of a tissue sheet.

FIG. 5 is a longitudinal sectional view through a further form of diaper made in accordance with the present invention in which no bulking layer, such as fluffed pulp or creped wadding is used but rather the diaper is comprised of the body contacting and outer layers with a film of the liquid-absorbent gel-forming material in which is embodied an adhesive agent being disposed therebetween.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention, as indicated earlier, is applicable to the construction of a disposable type liquidabsorbent product and inclusive of disposable diapers, bed pads, catamenial devices, continuous filaments such as sutures and the like, although particular embodiments of the invention will be described at greater length herein in terms of its applicability to disposable diaper construction.

Referring now to FIG. 1, there is depicted a diaper 10 which includes a body contacting layer, which body contacting layer can be comprised of plural-ply components as, for example, an outermost fabric sheet 12 such as a non-woven cellulosic material sheet or other material type which possesses soft texture and accordingly, are advantageous for contact with the skin. Succeeding plys of tissue, e.g.,

paper tissue sheets

14 and 16 make up the remaining components of the body contacting layer. Together the three sheets l2, l4 and I6 possess the structural strength, including wet strength properties, suitable for the intended purpose and they also have the property of being liquidpervious to permit body liquid to pass through the skin contacting layer for the purpose to be described in greater detail shortly. The diaper I0 also includes an outer layer which, is comprised of plural plys of components of suitable material such as tissue paper sheets I8, 20 and 22, the outer face of tissue sheet 22 being coated with a suitable material, such as a stearate, a silicone, a wax, paraffin or like material which will render the outer layer liquid-impervious. The purpose of making the outer layer liquid-impervious is well-known by those skilled in the art. e.g., it traps liquid within the diaper, thus preventing leakage and facilitate absorption. The liquid-impervious coating 24 also could be applied to the inner face of sheet 18 or at the interface of

sheets

18 and 20 or at the interface of

sheets

20 and 22 with equal facility.

One of the advantages of using a fluid-impervious coating of the materials aforementioned is the convenience with which the material coating can break up into segments when the user tears the diaper into pieces preliminary to disposal by flushing same in a toilet water system. Certain other types of fluid-impervious material. as for example polyethylene, are less advantageous to use because such material must be first removed from a diaper as a single sheet thereof and be disposed separately and differently than the remainder of the diaper.

The diaper also includes a core or intermediate layer of fluffed pulp of cellulosic fibers, the fibers 26 of which have been beaten in known manner in a hammer mill to produce a threedimensional mass which provides a desirable quality of bulk to the diaper structure. In accordance with the invention, a liquid-absorbent gel-forming material 28 preferably in particulate form, is distributed throughout the fluffed pulp mass, the particles of the gelling material being secured to the pulp fibers by means of a tacky adhesive agent having the property of permanent pliability to elastically maintain the material 28 in fixed disposition in the diaper structure. As used herein, the property of permanent pliability of the adhesive agent is intended to mean that the adhesive is of an essential non-drying character and remains flexible throughout the intended life span of the disposable product in which it is employed and does not assume any character of brittleness which in turn would cause a stiffening of the structure of the product and/or the absorbent material therein. The absorbent material 28 can be provided in various forms, an example being any of the materials enumerated in detail in US. Pat. No. 3,070,095. guar gum being particularly advantageous for this purpose because upon being wetted it can absorb up to times or more of its own weight in liquid. More desirably. the liquid-absorbent gel-forming material is provided in the novel composition thereof to be described later herein.

For the purpose of adhering the absorbent material particles to the fluffed pulp fibers, various adhesive agents can be used. Such agent can be a water soluble material, e.g.. corn syrup solids, honey, dextrine. pressure sensitive adhesive material etc. Water repellent materials also could be used as the adhesive agent, as for example, rosin. The essential requirement is that the adhesive agent, whether water soluble or water repellent, should possess the property of being permanently pliable and not subject to rigidizing into a brittle film of the adhesive after a certain period of time. The advantage of adhesively securing the particles 28 throughout the three-dimensional mass of particle fibers 26 is that the particles cannot then migrate toward the tissue sheet 18, tissue sheet 16. or such other region in the diaper where the accumulated mass would not function to the degree intended for absorbing liquid.

In making the diaper [0. the outer layer materials can be laid down one on top of the other. following which the fluffed pulp core 26 is laid down on top of the outer layer sheet 18. A mixture of absorbent material and adhesive agent can then be sifted onto the fluffed pulp to effect adhesion of the absorbent material particles to the fluffed pulp fibers. Following laying down of the fluffed pulp layer and impregnation of the same with the absorbent material tacky-adhesive mixture. the skin contacting layer components l2, l4 and 16 are laid down on top of the fluffed pulp. The diaper layers are then secured as a unitary structure in known manner as. for example, by employing a suitable heat-seal connection around marginal portions of the expanse of the diaper structure.

FIG. 2 shows another form of diaper 40 which has skin contacting and outer layers of the same construction as those of diaper 10. However. the fluffed pulp layer 42, during the formation of the diaper, is first given an overspray of the tacky adhesive agent 44 to form a film thereof on the fluffed pulp mass. There is then sifted or otherwise distributed onto the adhesive film, particulate form absorbent material 46 which becomes secured to the tacky adhesive film 44. Following the deposition of the absorbent material 56, there optionally but not essentially, may be employed a further overspray of the tacky adhesive as a liquid-pervious film 48 on top of the absorbent material. The body contacting

ply components

12, 14 and 16 can then be overlaid on the tacky adhesive film 48 and tissue sheet 16 becomes adhesively connected to the particulate absorbent layer 46 by action of the adhesive film 48. The advantage of this form of construction is that it provides an optimized anchorage or positioning of the liquidabsorbent gel-forming material in the diaper structure. If the adhesive agent is a water soluble material, the adhesive film 48 will dissolve upon entry of the liquid through the liquid-pervious body contacting layer. On the other hand, if the adhesive agent is a water repellent material, the film 48 would be rendered liquidpervious in known manner prior to or at the time it is laid down, as for example, by needle piercing the film.

FIG. 3 depicts a further form of diaper construction 60 which employs one or more creped wadding layers in place of fluffed pulp. Thus, the diaper can have creped wadding layers 62 and 72, each of which is separated by the tacky adhesive films 64, 68 and a layer of liquid-absorbent gel-forming material 66. Additionally. an overspray of tacky adhesive 74 can be applied to the upper creped layer 72 and a second layer of liquidabsorbent gel-forming material 76 can be laid between the tacky layer 74 and a further tacky adhesive layer 78, the latter in turn being secured with tissue sheet 16 in the manner shown. In such construction, if the adhesive agent were a water repellent material, at least each of

adhesive films

78, 74 and 68 would be made or rendered liquid-pervious.

FIG. 4 shows an embodiment 80 of diaper in which the diaper employs fluffed pulp for bulking purposes. with the fluffed pulp being provided in two or more lay ers such as at 82 and 94 with the respective layers each being provided with an overspray film of

tacky adhesive

84 and 96, as well as particulate liquid-absorbent gel-forming

material layers

86 and 98. The two fluffed pulp layers are further separated by an adhesive layer 88 and a layer of tissue paper 92, with the diaper further having a tacky adhesive film 102 at the underface of the skin contacting layer. As with diaper 60,

adhesive films

102, 96 and 89, if such were of a water repellent material would be rendered liquid-pervious.

In applying the adhesive film in each of FIGS. 24 diaper forms, such films can be applied in any convenient manner such as a spray, or as a solution deposited by a transfer roll or such other manner as suits the intended purpose.

An exemplary adhesive particularly suited for use in connection with the diaper construction of the present invention is a water-soluble adhesive comprising of corn syrup. The corn syrup adhesive should be employed in such form that its water content is minimal, in order to reduce its hydration effect on the diapers absorbent composition, Accordingly, one particularly useful adhesive is a concentrated commercially avaiL able syrup having 82% solids (the remaining l8% of the adhesive being water which appears to be effectively bound within the syrup).

Because such concentrated syrups are extremely viscous and susceptible to drying into a non-tacky form, their direct incursion within the present diaper construction is difficult; it has therefore been discovered that they should be applied in diluted form. In order to avoid the deleterious effect which an aqueous diluent would have on the absorbents, the diluent should preferably be non-aqueous and should preferably comprise an organic compound in which the present adhesive dissolves.

With exemplary reference to the aforementioned corn syrup, it has been discovered that alcohols in particular. glycerol, polyvinylglycol and the like are well suited as diluent-solvent to implement the incorporation of adhesives into diapers. These diluent-solvents should be employed in an amount sufficient only to reduce the viscosity of the absorbent to a convenient level. Thus, the aforementioned concentrated corn syrup should, for example, normally be diluted with at least about 20% by weight of alcohol, based on the weight of syrup. More usually, dilution with from about 30% to 50% by weight of solvent is preferred. The degree of dilution is not, however, critical and appropriate solvents and ranges for each of the present adhesives would be readily apparent to those of ordinary skill in the art upon reading this description.

When the adhesive of this invention is employed with the fluffed pulp embodiment depicted in FIGS. 1, 2 and 4, it is preferred to incorporate from about 10% to about 25% by weight of adhesive solids per weight of fluffed pulp. Again, the amounts of adhesive are not critical, however, and one of ordinary skill in the art would readily perceive from the foregoing preferred values, the broadest ranges of adhesive proportion which would be operable in accordance with the pres ent invention.

FIG. 5 shows still another form of diaper 120 in which neither fluffed pulp nor creped wadding layers are employed. The diaper has skin contacting and outer layers as described before, between which is disposed a film 122 of the liquid absorbent gel-forming material having the tacky adhesive agent embodied therewith. The advantage of this construction is that the diaper can be made of very much reduced thickness to provide wearer comfort, while at the same time retain its liquidabsorption characteristics. The film 122 can have the adhesive agent embodied therein as by mixing same with the absorbent material where the adhesive is a water soluble type. In this manner the adhesive agent can be employed to secure the absorbent material film 122 to either or both of

tissue sheets

16 and 18 by ap plying moisture coating to the surfaces of such sheets or to the absorbent material film during the diaper manufacturing process. On the other hand, if a water repellent adhesive is embodied with the absorbent material film 122, the same, for example, can be applied at the surfaces of the film in various manners to facilitate securement of the film to the

paper tissue sheets

16, 18 so as not to present a barrier to the passage of liquid through the body contacting layer to the absorbent material film 122 when the diaper is in use.

It will be apparent that the diaper structures of the foregoing described embodiments as well as other types of disposable products can be made with certain variation from the constructions disclosed. For example, the diaper instead of having a fluffed pulp or creped wadding layer may employ a tissue paper core in association with the absorbent material. The essential requirement is that the absorbent material be fixedly positioned in the diaper by employing the adhesive agent to secure the absorbent material to the tissue paper sheet used in place of the fluffed pulp and/or creped wadding. Further, such adhesive agent should have the character of being permanently pliable as discussed earlier.

As used herein liquid" is intended to mean an aqueous liquid. for example, urine.

The invention further provides a superior absorbent composition for use in the absorbent products already described. Such desirable objective has been achieved through the discovery of an additive which will convert the normally liquidus or syrup'like and sticky gels produced pursuant to hydration of the water soluble absorbents of the prior art into a film dry gel.

Water soluble absorbents which may be improved by this discovery include proteins such as albumin and polysaccarides such as galactomannans, pectins, algins, starches, and natural gums. These and additional applicable absorbents are recognized in the art as a useful class and may further be identified in terms of their common ability to assililate at least ten times their weight of water, aso as to produce hydrate bearing ste rically unhindered OH radicals.

For the sake of clarity, this discovery will be further described in terms of an exemplary absorbent guar gum, which is a species of galactornarman. Such exem plification should not, however, be construed as limiting the scope of this discovery, as it will be clear to those skilled in the art that all known absorbents which produce hydrate exhibiting complexable OH groups will also benefit therefrom.

It has been discovered that the addition of certain compounds to ordinary guar gum will produce a modi fied guar which will absorb up to at least 20 times its weight of water to produce a relatively dry, non-sticky. and inert gel. as opposed to the somewhat syrup-like and sticky gel which is normally formed incident to the hydration of pure guar gum.

The essential additive required for the formation of the modified guar gum composition is borate anion which is utilized in an amount sufficient to complex the gel formed from the hydration of guar gum alone. Where present. the borate anion will successfully convert the normally liquidus or syrup-like and sticky guar hydrate into a firm and dry mass having substantially improved characteristics for use in the previously described absorbent products as well as absorbent prod nets of other constructions which employ or use an absorbent material as a component.

Apparently, the borate anion of this embodiment operates by complexing with the OH units of separate molecules and agglomerates of an absorbent such as hydrated guar gum so as to form cross links therebetween, thus stabilizing the hydrated guar into the desired firm gel. Unfortunately, this cross-linkage takes place at an almost instantaneous rate, where there exists in combination, free borate anion, water, and guar gum. Accordingly, it has been necessary to determine a means of regulating the formation of cross-linkages, because once such cross-linkages have bound the hydrated guar gum into a firm gel, the gel operates to form a water impenetrable barrier. Such barriers may impede the flow of liquid into the absorbent product and thereby limit the utility of products having an ab sorbent layer in substantial thickness.

It has been determined that one means of retarding the transformation of hydrated guar gum into a firm gel is to introduce the borate anion into the absorbent product in the form of an essentially water insoluble borate-release agent. So introduced, free borate anion will be released to the absorbent system only slowly, as determined by the solubility coefficient of its insoluble form, and only after the aqueous liquid sought to be ab sorbed by the product has entered the product itself.

Accordingly, one means by which the requisite slow release of borate anion may be accomplished is through the addition, in an amount of from about 3% to about 10% of guar (based on the weight of borate anion), of a borate salt having a solubility in water of less than 0.1% at 25C., preferably less than about 0.05%. The release from such a compound an example of which would be zinc borate would be regulated by its own solubility coefficient, so as slowly to yield borate anion at a rate which would allow optimal penetration of the liquid sought to be absorbed, while still allowing the firm gellation of guar gum. This rate dependency occurs because it is the solublization of borate ion which is the limiting factor for the formation of a firm gel, due to the essentially instantaneous nature of the reactions or guar hydration and guar hydrate cross-linkage.

Accordingly, the minimum solubility coefficient of an essentially insoluble borate such as zinc borate requires that, upon introduction of an liquid into the absorbent pad, only a small concentration of free borate anion will be available to cross-link the almost instantaneously formed guar gum hydrates. Consequently, even though some firm gel is produced by the available free borate anion, insufficient cross-linkage to produce a liquidimpervious barrier will occur. As the liquid is in troduced and penetrates into the pad, however, addi tional free borate anion is released from the insoluble borate due to the removal of the original free borate anion from the equilibrium system as a cross-linking complex for guar gum hydrate. Thus, within a matter of from about 5 to about minutes, sufficient borate anion is solubilized from the original borate-release agent so as to cross link substantially all available guar gum hydrate.

The foregoing reaction for the production of a crosslinked guar hydrate or for other suitable absorbents, as well as the stability of the resultant firm gel, are both highly dependent upon the pH of the reaction environ ment. Only at a pH of from about 7.0 to 7.4, and optimally at about 7.1, does the requisite cross-linking of the hydrated gel through the borate anion occur. Moreover, this cross-linking reaction is reversible. Consequently, it is necessary that, during use, the product be maintained within the aforementioned pH range.

It has therefore been discovered that it is convenient to further modify the aforementioned admixture of naturally occurring guar gum and an insoluble boraterelease agent through the inclusion of an additive which will maintain the pH of the system during and after the introduction of the aqueous liquid sought to be absorbed within the pH range conducive to the formation ofa firm gel. It has been determined that the achievement of an appropriate pH may best be obtained through the addition of an amount of any amine sufficient to maintain the system comprising guar gum, an insoluble borate-release agent, and the liquid sought to be absorbed, within a pH of from about 7.0 to 7.4.

A particularly efficacious amine for the foregoing purpose is 2-amino, 2-methyl, l, 3-propanediol. This amine is a solid, and consequently presents no problem, during storage of the absorbent product prior to use, through the introduction of any liquid thereto. Liquid amines, for example triethanol amine, may also be employed in the present invention. Where such liquid amines are utilized, however, it is preferred that they be stabilized by the further inclusion ofan essentially inert carrier, for example a magnesium or calcium silicate, so as to minimize the presence of free liquids in the absorbent pad. Where such carriers are employed, it is suggested that they be present in an amount of from about 50 to about by weight of the liquid amine.

As was previously indicated, the amount of amine which should be included within the absorbent composition may vary depending upon the intended use of the absorbent product itself. In many instances, the liquid sought to be absorbed will already be of a pH within the range of from about 7.0 to 7.4, and consequently no such amine would be required. Under other circumstances, however, the pH of the aqueous liquid sought to be absorbed would not fall within the aforementioned range, and in such case, stabilizers such as the p hivines should be added to the absorbent compt non 1r amounts up to about 25% based on dry ab sorbent, and are readily calculatable by those of ordinary skill in the art.

An example of an embodiment in which a pH stabilizer should be included within the absorbent composi tion is one in which the absorbent product is intended to be used as a diaper. The normal pH of infant urine falls within the range of from about 6.5 to about 7.0. Accordingly, the inclusion of an amine such as 2 amino, Z-methyl, 1,3-propanediol in an amount of from about 5 to about 25% by weight of dry guar gum will insure the desired formation of a firm cross-linked guar gum hydrate.

This invention additionally includes the discovery that the physical form in which a modified absorbent (that is a composition comprising an absorbent such as guar gum, a borate-release agent and, optionally, a pH stabilizer) is incorporated into an absorbent product, may directly affect the efficiency with which the absor bent product assimilates the liquid sought to be absorbed. As has been previously stated, the modified guar gum of this invention produce, upon addition of liquid, a firm gel which may block the penetration of additional liquid into the pad. Because of this propensity of the preferred modified absorbents to form liq- .......-la. H... ha-mwwm-a mmmm... *0... 1.....- a...

uid-impervious barriers, it has been discovered that the selection of unusually coarse grinds will facilitate the complete absorption of the liquids for which the present products were intended.

In the prior art, powdered guar capable of passing through a 140 mesh Tyler screen has ordinarily been employed in absorbent products. Where such fine pow der is used in conjunction with the present boratcrelease agents as a modified guar gum, however, it has been discovered that impenetrable barriers of firm gel may be produced even before all the available liquid has entered the absorbent product.

Accordingly, this invention offers the additional improvement that such impenetrable barriers may be avoided through the use of coarse particles or agglomerates of absorbent such as guar gum in the absorbent composition. By coarse, it is intended that the absorbent particle sizes should be comprised in a proportion wherein at least 50% of the particles are of a size between 60 and 100 mesh Tyler screen, more preferably, at least 70% should be of a size between about 60 and 100 mesh.

Where the particles of guar gum in the present absorbent composition are within the foregoing size ranges, the resultant porosity of the absorbent composition greatly facilitates the penetration of the liquid sought to be absorbed through such composition. Moreover, the larger particles of such guar gurn are less quickly susceptible to hydration and subsequently crosslinkage into a firm gel. Consequently, the slight retardation of firm gel formation resultant from such large particles also operates to permit more uniform penetration of the liquid sought to be absorbed throughout the absorbent product and thus improves the efficiency with which such liquids are absorbed.

A further feature of the present invention provides an improved form of securement means therefor when used, especially for use in a diaper. It is known to provide pressure sensitive tape components at two corners of the four corners of a disposable diaper structure with the tape components being secured in part at the outer surface of the outer layer, the remaining lengths of such tape components when the diaper is in folded packed condition are folded inwardly in adhesive securement against surface portions of the body contacting layer which have been treated with a release agent. When the diaper is unfolded from its packaged condition for use, the said remaining lengths of the tapes are peeled from the release coated surfaces, the diaper wrapped about a baby's body, and the tape segment remaining lengths secured at the other two corners of the structure at the outer surface of the outer layer, such tapes thus func tioning in place of conventional pin fasteners. ln accordance with the present invention, two corner inner surfaces of the diaper, that is, the inner surface of the body contacting layer inner surface at the other two corners of the diaper structure are provided with a release agent coating. Thus, when the diaper is folded for packaging, the prcssure sensitive adhesive surfaces overlay the release coating surfaces to prevent any consequen tial adhesion between such opposed corner surfaces. After the diaper has been fitted on a baby, the inner surface corners carrying the pressure sensitive adhesive are overlapped with the opposite corners of the diaper structure but at the outer layer surface and adhesive securement effected.

What is claimed is:

1. In a multi-layer, disposable absorbent product such as a disposable diaper, sanitary napkin, or the like,

a liquid-pervious body contacting layer,

an outer material layer, said outer material layer being characterized by being liquidimpervious, and

a dry liquid-absorbent organic material disposed between said body-contacting and outer layers in substantially fixed relationship therewith,

there also being a core of at least one layer of a bulking material disposed between said bodycontacting and outer layers, there being a film of a water-repellent adhesive agent overlaying said bulking material layer at the side thereof remote from said outer layer, said absorbent organic material being overlayingly adhered to said film, there being a second liquid-pervious film of said adhesive agent overlaying said absorbent organic material.

2. The disposable absorbent product of claim 1 in which said layer of bulking material is a layer of fluffed cellulosic fibers.

3. The disposable absorbent product of claim 1 in which said layer of bulking material is a layer of creped paper wadding.

4. in a multi-layered disposable absorbent product such as a disposable diaper, sanitary napkin or the like comprising:

a liquid-pervious body contacting layer;

an outer material layer, said outer material layer being characterized by being liquid-impervious; and

a dry liquid-absorbent organic material disposed between said body contacting and outer layers;

the improvement which comprises a borate-release agent admixed with said absorbent organic material, said borate-release agent being in a borate compound having a solubility in water of less than about 0.1% at 25C.

5. The disposable absorbent product of claim 4, wherein said borate-release agent is zinc borate.

6. The disposable absorbent product of claim 5, wherein said absorbent organic material is selected from the group consisting of water soluble proteins and polysaccharides which, upon absorption of at least l0 parts by weight of water, are characterized by the pres ence of sterically unhindered OH radicals.

7. The disposable absorbent product of claim 6, wherein said absorbent organic material is naturally occurring guar gum.

8. The disposable absorbent product of claim 4, in which said absorbent material additionally contains a pH stabilizer in sufficient amount to maintain the pH of the absorbent product within the range of from about 7.0 to 7.4.

9. The disposable absorbent product of claim 8, wherein said pH stabilizer is an amine, present in an amount up to about 25% by weight of absorbent.

10. The disposable absorbent product of claim 4, wherein said absorbent organic material is in particulate form, the particles thereof being sized so that at least 50% thereof are between 60 and 100 mesh Tyler.

11. The disposable absorbent product of claim It), wherein at least of said particles are of a size between about 60 and mesh Tyler.

Claims

1. IN A MULT-LAYER, DISPOSABLE ABSORBENT PRODUCT SUCH AS A DISPOSABLE DIAPER, SANITARY NAPKIN, OR THE LIKE, A LIQUID-PERVIOUS BODY CONTACTING LAYER, AN OUTER MATERIAL LAYER, SAID OUTER MATERIAL LAYER BEING CHARACTERIZED BY BEING LIQUID-IMPERVIOUS, AND A DRY LIQUID-ABSORBENT ORGANIC MATERIAL DISPOSED BETWEEN SAID BODY-CONTACTING AND OUTER LAYERS IN SUBSTANTIALLY FIXED RELATIONSHIP THEREWITH, THERE ALSO BEING A CORE OF AT LEAST ONE LAYER OF A BULKING MATERIAL DISPOSED BETWEEN SAID BODY-CONTACTING AND OUTER LAYERS, THERE BEING A FILM OF A WATER-REPELLENT ADHESIVE AGENT OVERLAYING SAID BULKING MATERIAL LAYER AT THE SIDE THEREOF REMOTE FROM SAID OUTER LAYER SAID ABSORBENT ORGANIC MATERIAL BEING OVERLAYINGLY ADHERED TO SAID FILM, THERE BEING A SECOND LIQUID-PERVIOUS FILM OF SAID ADHESIVE AGENT OVERLAYING SAID ABSORBENT ORGANIC MATERIAL

4. In a multi-layered disposable absorbent product such as a disposable diaper, sanitary napkin or the like comprising: a liquid-pervious body contacting layer; an outer material layer, said outer material layer being characterized by being liquid-impervious; and a dry liquid-absorbent organic material disposed between said body contacting and outer layers; the improvement which comprises a borate-release agent admixed with said absorbent organic material, said borate-release agent being in a borate compound having a solubility in water of less than about 0.1% at 25*C.

6. The disposable absorbent product of claim 5, wherein said absorbent organic material is selected from the group consisting of water soluble proteins and polysaccharides which, upon absorption of at least 10 parts by weight of water, are characterized by the presence of sterically unhindered OH radicals.

11. The disposable absorbent product of claim 10, wherein at least 70% of said particles are of a size between about 60 and 100 mesh Tyler.