GB1583587A

GB1583587A - Disposable absorbent structure

Info

Publication number: GB1583587A
Application number: GB37770/77A
Authority: GB
Original assignee: Procter and Gamble Co
Current assignee: Procter and Gamble Co
Priority date: 1976-09-10
Filing date: 1977-09-09
Publication date: 1981-01-28
Also published as: CA1124951A; ES230806Y; DK402577A; DE2740184A1; FI772676A; SE7710146L; BE858568A; NL7709924A; FR2364024A1; ES230806U; JPS5353458A; GR61589B

Description

(54) DISPOSABLE ABSORBENT STRUCTURE (71) We, THE PROCTER AND GAMBLE COMPANY, a Corporation organised and existing under the laws of the State of Ohio, United States of America, of 301 East Sixth Street, Cincinnati, Ohio 45202, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates generally to disposable absorbent structures and more particularly to such structures in the form of disposable diapers; Disposable, absorbent structures are intended to be discarded after being used once and provide substantial cost and convenience advantages when compared with their re-usable counterparts. For example, re-usable surgical sponges and dressings have to be sterilised after each use while similar disposable structures may simply be discarded. As a result of their cost and convenience advantages, disposable absorbent structures, generally, and disposable diapers in particular, have met with prodigious success in the market place. In the ensuing discussion, particular reference will be made to the field of disposable diapers since the present invention has particular application in this field. It should be understood, however, that the products of the present invention may be used broadly in the field of disposable absorbent structures.

As is well known, the three principal structural components of a disposable diaper are the topsheet, absorbent core and backing sheet. The backing sheet can comprise any of the various well known liquid impermeable materials such as polyethylene film and the absorbent core can comprise well known materials such as creped cellulose wadding, comminuted wood pulp or the like. The topsheet of the disposable diaper may be manufactured from a wide variety of materials and pursuant to a number of concepts. For example, the topsheet may be woven, nonwoven, hydrophobic, hydrophilic, fibrous, fabric, or perforated flexible plastic film. The above described components of a disposable diaper may be combined in any of the various manners well known in the art. One such method of combining the diaper components is described in detail in U.S. patent Re 26,151 to Duncan et al.

A great many variations are possible on the above described basic disposable diaper structure. U.S. patents nos: 3,730.184 and 3,837,343 for example, disclose a diaper construction in which the centre portion of the outer surface of a hydrophobic topsheet is treated with a surfactant to render selected portions of the outer surface hydrophilic.

The object of the relevant prior developments has generally been to produce a disposable diaper which will permit rapid penetration of the fluid through the topsheet into the absorbent layer and which will provide a dry outer surface in contact with the use. The rapidity with which liquid penetrates the topsheet isindicated by measuring the amount of surface run-off using a method to be described hereinafter while an indication of surface dryness may be determined by measuring the rewet characteristics of the topsheet using a method also to be described herein-after.

It is well known that the surface runoff characteristics of the diaper may be improved by making the outer surface of the topsheet hydrophilic. As indicated above. prior structures have achieved this result by various methods such as applying surfactant to the other surface of the topsheet. Surface dryness is improved however, by making the outer surface of the topsheet hydrophobic. The prior developments have sought to achieve a balance between good surface runoff characteristics and favourable surface dryness. but these developments lack the advantages of the present invention as will be explained.

The basic components of a conventional disposable absorbent structure are the topsheet, the absorbent core, and the impervious backing sheet. According to the present invention an additional component, a surfactant treated intermediate layer constituted by a discrete substrate or a surface layer of the absorbent core is interposed between the inner surface of the topsheet and the impervious backing layer. The surfactant treated intermediate layer improves the surface runoff characteristics for a wide variety of topsheets and in addition does not significantly degrade the ability of the topsheet to provide a dry outer surface in contact with the user, thus showing substantial advantage over the prior developments referred to above.

When the surfactant treated intermediate layer comprises a discrete substrate treated with surfactant, it is most effectively positioned at the interface between the topsheet and the absorbent core although it may also be positioned within the absorbent core or at the interface between the absorbent core and the impervious backing sheet.

In the alternative embodiment of the invention, when the surfactant treated intermediate layer is formed by surfactant treating a surface layer of the absorbent core, this surface layer may be on either face of the core.

Examples of disposable absorbent structures in accordance with the invention will now be described with reference to the accompanying drawings, in which: Figure I is a partially cut away perspective view of a disposable diaper having a surfactant treated intermediate layer; Figure 2 is a side elevation of the disposable diaper topsheet; Figures 3 to 5 are longitudinal sectional views of alternative forms of diaper.

Although the drawings illustrate only different forms of disposable diaper, it should be understood that the present invention is broadly applicable to the art of disposable absorbent structures, such as bandages, sanitary napkins and the like. The following description of a disposable diaper is intended to merely illustrate a preferred embodiment of the present invention.

As seen in Figure 1, a disposable diaper 10 basically comprises porous topsheet 12, absorbent core 14, impervious backing sheet 16 and surfactant treated intermediate layer 22. Topsheet 12 is superposed on absorbent core 14 and is fastened to the impervious backing sheet 16 in a manner well known in the disposable diaper art. Absorbent core 14 is of dimensions generally smaller than backing sheet 16 and is completely encased beween porous topsheet 12 and backing sheet 16. A more detailed description of how topsheet 12, absorbent core 14, and the impervious backing sheet 16 may be assembled into a disposable diaper is given in U.S. Patent Re 26,151 which is incorporated herein by reference.

Impervious backing sheet 16 is preferably a 0.001 to 0.002 inch (0.0025 to 0.0051 cm) thick polyethylene film, although other flexible fluid impervious materials may also be used.

Absorbent core 14 comprises absorbent layer 18 and envelope tissue 20. Absorbent layer 18 may be manufactured from a wide variety of the absorbent materials commonly used in absorbent structures, such as comminuted wood pulp generally referred to as airfelt. Other materials can also be used for absorbent layer 18 such as a multiplicity of plys of creped cellulose wadding or any equivalent material. In the preferred embodiment envelope tissue 20 is substantially coextensive with topsheet 12. Absorbent layer 18 is encased between envelope tissue 20 and impervious backing sheet 16 with envelope tissue 20 holding absorbent layer 18 in place and preventing lumping of absorbent layer 18. A preferred envelope tissue 20 has a basis weight of about 12 pounds/3,000 square feet and an air permeability of about 100 cubic feet per minute per square foot over a 0.5 inch water pressure drop.

Porous topsheet 12 has an outer surface 30 and an inner surface 31 (See Figure 3) and should be compliant, soft feeling, fluid permeable, and non-irritating to the user's skin. In addition, topsheet 12 has a capillary suction pressure lower than that of absorbent core 14.

Capillary suction pressure for a given article is the product of adhesion tension and specific surface area. Adhesion tension is defined as the product of the fluid's surface tension and the cosine of the contact angle the fluid makes with the article and may be measured using the methods detailed in the paper printed in the Journal of Colloid and Interface Science, Vol. 42, No. l, January 1973 entitled Dynamic Adhesion Tension Measurement which is incorporated herein by reference. The specific surface area of the article is the ratio of the solid surface area of the article available for wetting divided by the void volume of the article that the fluid can occupy. Capillary suction pressure for a porous article may be determined by the method described in the Textile Research Journal. Vol. 37(1967) pages 356-366 which is incorporated herein by reference.

Obviously, porous topsheet 12 may be manufactured from a wide variety of materials having a broad range of structural and physical characteristics. For example, topsheet 12 may be paper, rayon, polymeric, woven, nonwoven, fibrous, nonfibrous, hydrophobic or hydrophilic. A preferred topsheet 12 is shown in U.S. Patent 3,929,135 to Thompson which is incorporated herein by reference. As decribed therein, topsheet 12 is a low density polyethylene film having a thickness of from about 0.001 to about 0.002 inches (0.0025 to 0.0051 cm). The preferred topsheet 12 is formed to a thickness of about .015 inches (.038) with an array of tapered capillary structures 24,, each having a perforated apex 26 (See Figure 2).

In the preferred embodiment shown in Figure 1, intermediate layer 22 comprises a discrete substrate 28 which is treated with a surfactant. Substrate 28 may be any fluid pervious material which is flexible and compliant. Typically, the material used for envelope tissue 20 would also be used for su'bs"tra'te' '28. Thus, substrate 28 preferably has a basis weight of about 12 pounds/3,000 square feet and an air permeability of about 100 cubic feet per minute per square foot at a 0.5 inch water pressure drop.

In accordance with the present invention a great many surfactants may be used. A surfactant will increase the hydropbilicity of substrate 28 by increasing the adhesion tension of fluids contacting substrate 28 and will preferably be non-irritating to human skin. A nonionic surfactant such as an ethylene oxide/propylene oxide block condensation polymer having the general structure

and marketed under the Registered Trade Mark Pluronic L-92 by BASF Wyandotte Inc., Wyandotte, Michigan was used in the preferred embodiment. Many other cationic, anionic and nonionic surfactants are equally suitable such as sodium alkylaryl sulfonate manufactured by The Procter & Gamble Co., Cincinnati, Ohio under the Registered Trade Mark Orvus AB Granules or cetyl trimethyl ammonium bromide manufactured under the tradename Acetoquat CTAB by Aceto Chemical Co., Flushing, New York.

The substrate 28 may be treated with surfactant in -any suitable manner such as by spraying surfactant onto substrate 28 or by dipping substrate 28 into a surfactant bath. As used in this application, the term "treating" also includes other methods of applying surfactant to substrate 28 such as by printing or extruding.

Substrate 28 is treated with surfactant in concentrations which depend upon the surface and the nature of the tdpsheet 12 chosen. For a given substrate 28 and topsheet 12 the amount and type of surfactant used must be sufficient to increase the adhesion tension of the fluid on substrate 28 such that the capillary suction pressure of substrate 28 is greater than the capillary suction pressure of topsheet 12. The larger the difference in capillary suction pressure between substrate 28 and topsheet 12 the greater the improvement in surface runoff characteristics of diaper 10. Substrate 28 may be more hydrophilic than absorbent core 14. In the preferred embodiment, a concentration of 0. 10 grams per square yard was used although concentrations between 10.0 and 0.001 grams per square yard were found to be acceptable.

In Figure 1, intermediate layer 22 is shown juxtaposed at the interface between absorbent core 14 and porous topsheet 12. Preferably, intermediate layer 22 is dimensioned to be substantially coextensive with absorbent core 14, but may be dimensioned so as to occupy a smaller region such as only the crotch area of diaper 10. Intermediate layer 22 may be held in place by being adhesively bonded to absorbent core 14 in a manner well known to one skilled in the art. A suitable adhesive is slowly soluble, if soluble at all. in water so as to obviate the possibility of having absorbent core 14 and intermediate layer 22 separate in use. An adhesive which is adequate is a latex-plasticized polyethylene adhesive such as that sold by United Shoe Machinery Corporation under the Registered Trade Mark Thermo Grip No. 307.

Since intermediate layer 22 is below the inner surface 30 of topsheet 12, intermediate layer 22 does not contact the user. Thus. the likelihood of irritation from the surfactant is lower with the present invention than with diapers having surfactant applied to outer surface 30. In addition. intermediate layer 22 greatly improves the ability of fluids to penetrate topsheet 12 as measured by a reduction in surface runoff. Absorbent structures exhibiting low surface runoff are desirable because such structures are less likely to leak fluid and will remove fluid from contact with the user faster. In addition intermediate layer 22 has substantially no effect on the surface dryness of a topsheet 12 having tapered capillary structures 24. Surface dryness is indicated by measuring the rewet of topsheet 12 and is a desirable characteristic because the drier the topsheet 12 the lower the possibility that diaper 1() will irritate the user's skin.

Surface runoff is determined at atmospheric pressure by placing a preweighed, 9-inch length of diaper 10 on a board inclined 10 degrees to the horizontal and dropping 25 milliliters of fluid on diaper 10 at a uniform rate for 3.5 seconds. The fluid used simulates the physical characteristics of urine and comprises 1% (by weight) of sodium chloride salt and 2.5 grams of a 10% solution (by weight) of an alky phenoxy polyethoxy ethanol such as that available under the Registered Trade Mark Triton X-100 as marketed by Rohm and Haas of Philadelphia, Pennsylvania per 3,500 millimeters of fluid. Diaper 10 is then reweighed and the percent fluid runoff is determined by the following formula:

weight of 25 ml weight of wet diaper Surface Runoff (%) =\of fluid j weight of dry diaper x 100 weight of 25 ml of fluid The rewet of topsheet 12 is determined by wetting a 4-inch square section of diaper 10 with a fluid simulating the physical characteristics of urine as described above. The amount of fluid used is 4.5 times the weight of the 4-inch square section diaper 10. An eight pound weight is applied to the 4-inch square section for 3 minutes thereby permitting the fluid to approach an equilibrium condition before a preweighed absorber is placed on topsheet 12 and the eight pound weight reapplied for an additional 2 minutes. The absorber is then reweighed and the weight of fluid absorbed by the absorber noted. Two 15 cm diameter sheets of Whatman (Registered Trade Mark) No. 4 filter paper manufactured by Whatman Inc. of Clifton, New Jersey were used successfully in the rewet tests conducted. The larger the amount of fluid absorbed by the filter paper the more likely topsheet 12 will present a wet outer surface 30 in contact with the user.

Improvements in the surface runoff characteristics of diaper 10 may be realized with intermediate layer 22 in locations other than those described above. Referring briefly to Figure 3, there is shown an alternative embodiment of the present invention wherein intermediate layer 22 is positioned within absorbent layer 18. It is also possible to position intermediate layer 22 at the interface between absorbent core 14 and backing sheet 16. The surface runoff improvements are not as great when intermediate layer 22 is not at the interface between absorbent core 14 and topsheet 12, but as seen in Table I the reduction in surface runoff is still significant when compared to diapers having no intermediate layer 22.

Table I shows the percentage reduction in surface runoff for a diaper 10 having an intermediate layer 22 treated with 1.0 grams/square yard of an ethylene oxide/propylene oxide block condensation polymer (Pluronic L-92 as described above) and having a tapered capillary topsheet.

TABLE I Surface Runoff Rewet Position of (% reduction in (gms)

intermediate surface runoff layer 22 of diaper having hw/intermediate w/out inter- no intermediate layer mediate layer layer 22) Topsheet/ absorbent core 76 0.06/0.05 interface Within absorbent 47 0.()5/().05 core Absorbent core/ backing sheet 5() 0.07A).05 interface TABLE III

Surfactant Surface Runoff Rewet (0.01 gm/sq.yd. applied (% Reduction in Surface (gms) Topsheet to envelope tissue runoff of diaper having with without (material/construction) no surfactant) surfactant surfactant Polyethylene/Embossed Ethylene oxide/propylene Capillary film oxide block condensation 72 0.04/0.05 polymer (Pluronic L-92) Polyester/Spun bonded fabric Ethylene oxide/propylene (e.g. as marketed by oxide block condensation E.l. DuPont de Nemours polymer (Pluronic L-92) 89 2.3/2.6 & Co. under the Registered trade mark Remary Rayon staple /carded fibers and /nonwoven an acrylate /fabric Sodium alkylaryl latex binder/ sulfonate 41 2.8/2.5 (e.g. as manufactured (Orvus AB Granules) by Kendall Corp. and designated 6211) When compared to a diaper 10 having surfactant applied to the outer surface 30 of the topsheet 12, a diaper in accordance with the present invention exhibits improved surface runoff characteristics for a broader range of topsheet 12 materials and constructions and has the additional advantage of preventing the user from contacting the surfactant. A diaper 10 having a tapered capillary topsheet 12 and an envelope tissue 22 (see Figure 4) treated with 0.001 grams/square yard of an ethylene oxide/propylene oxide block condensation polymer (Pluronic L-92) showed approximately a 70 percent reduction in surface runoff compared to a diaper having the same surfactant and concentration applied to the outer surface 30 of topsheet 12.

The preferred embodiment heretobefore given has specifically referred to the disposable diaper art. It will be obvious to one skilled in the art of disposable absorbent structures that the present invention may be used otherwise than as described. In particular, other disposable absorbent structures such as bandages and surgical dressings are contemplated.

Claims

WHAT WE CLAIM IS:

1. A disposable diaper comprising an absorbent core, a porous topsheet superposed on the absorbent core, an impervious backing sheet joined to the porous topsheet so as to encase the absorbent core between the two sheets and a surfactant treated intermediate layer constituted by a discrete substrate or a surface layer of the absorbent core and disposed between the inner surface of the topsheet and the impervious backing sheet.

2. A disposable absorbent structure comprising an absorbent core, a porous topsheet superposed on the absorbent core, an impervious backing sheet joined to the pordus topsheet so as to encase the absorbent core between the two sheets and a surfactant treated intermediate layer constituted by a discrete substrate or a surface layer of the absorbent core disposed between the inner surface of the topsheet and the impervious backing sheet.

3. A structure according to claim 1 or claim 2 wherein the surfactant is a nonionic ethylene oxide/propylene oxide block condensation polymer.

4. A structure according to claim 3 wherein the concentration of surfactant is from 10 to 0.001 gram/square yard of treated intermediate layer.

5. A structure according to any one of the preceding claims wherein the discrete substrate is a flexible, liquid-pervious sheet.

6. A structure according to claim 5 wherein the liquid-pervious sheet is tissue paper having a basis weight of from 12 to 14 pounds per 3,000 square feet and having an air permeability of about 100 cubic feet per minute per square foot.

7. A structure according to claim 5 or claim 6 wherein the liquid-pervious sheet is interposed between the porous topsheet and the absorbent core.

8. A structure according to claim 5 or claim 6 wherein the liquid-pervious sheet is interposed between the absorbent core and the impervious backing sheet.

9. A structure according to claim 5 or 6 wherein the liquid-perviotis sheet is disposed within the absorbent core.

10. A structure according to any one of the preceding claims wherein the absorbent core comprises an envelope tissue forming at least part of the discrete substrate and an absorbent layer encased between the envelope tissue and the impervious backing sheet.

11.' A structure according to claim 10 wherein the porous topsheet is provided with tapered capillaries.

12. A structure according to any one of the preceding claims wherein the absorbent core comprises an envelope tissue and an absorbent layer encased between the envelope tissue and the impervious backing layer. the intermediate layer comprising a surface portion of the absorbent layer.

13. A disposable diaper according to claim 1, substantially as described and as illustrated with reference to any one of Figures 1, 3, 4 and 5 of the accompanying drawings.