CA1124951A

CA1124951A - Disposable absorbent structure having a surfactant treated intermediate layer

Info

Publication number: CA1124951A
Application number: CA286,438A
Authority: CA
Inventors: John D. Roberts; Raymond L. Bendure
Original assignee: Procter and Gamble Co
Current assignee: Procter and Gamble Co
Priority date: 1976-09-10
Filing date: 1977-09-09
Publication date: 1982-06-08
Also published as: ES230806U; DK402577A; BE858568A; FI772676A; ES230806Y; FR2364024A1; JPS5353458A; DE2740184A1; GB1583587A; NL7709924A; GR61589B; SE7710146L

Abstract

DISPOSABLE ABSORBENT STRUCTURE
HAVING A SURFACTANT TREATED
INTERMEDIATE LAYER
J. David Roberts and Raymond L. Bendure A B S T R A C T
A disposable absorbent structure having a surfactant treated intermediate layer beneath the outer surface of the topsheet. The surfactant treated intermediate layer may be either a discrete substrate treated with surfactant or it may be a component of the disposable absorbent structure, such as the absorbent core, which is treated with surfactant.
The disposable absorbent device has improved fluid penetration characteristics without a significant degradation in surface dryness for a wide range of topsheet materials and constructions.

Description

BACKGROUND OF THE INVENTION
1. Field of the Invention This invention relates generally to disposable absorbent devices and more particularly to disposable diaPers.
1S Still more particularly this invention relates to disposable diapers.havln~ a surfactant treated intermediate layer which has improved surface runoff characteristics without a significant degradation in surface dryness for a broad range of topsheet materials and constructions.

2. Description of the Prior Art Disposable, absorbent structures are intended to be used once before being discarded ana provide substantial cost and convenience advantages when compared with their reusable counterparts. For example, reusable surgical sponges and dressings have to be sterilized a~ter each use while similar disposable structures may simply be discarded.
As a result of their cost and convenience advantages, disposable l~Z~9~;~
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 art of disposable diapers slnce the present invention has particular application to the diaper art. 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 in the diaper art, 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 liquid impermeable materials well known in the art such as polyethylene film and the absorbent core of disposable absorbent structures lS can comprise well-knawn materials such as creped cellulose wadding, comminuted wood pulp, or the like. The topsheet o 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 diape 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 The prior art teaches a great many variations on the above described basic disposable diaper structure.
United States Patents 3,730,184 and 3,837,343 to Mesek, for example, teach a diaper construction in which the center portion of the outer surface of a hydrophobic topsheet is treated with a surfactant to render selected portions of the outer surface hydrophilic. In addition, each of the patents to Mesek teach the addition of a densified layer in the absorbent core to improve wicking of the fluid which enters the absorbent layer. This latter structure is the subject of U.S. Patent 3,612,055 to Mese~ et al. and is described in detail therein. U.S. Patent 3,838,692 to Levesque describes a variation in diaper structure in which the topsheet is of a hydrophobic nature and is treated with a wetting agent on the outer surface to render it hydrophilic at discrete spaced apart points. Another variation in conventional diaper construction is described in U.S. Patent 3,934,588 to Mesek et al. in which the outer surface of the facing layer is provided with areas of preferential liquid flow surrohnded by areas of increased water repellency. The areas of preferential liquid flow are formed by thinning selected areas of the topsheet.
The object of the relevant prior art 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 user. The rapidity with which liquid penetrates the topsheet is indicated by measuring the amount of surface runoff 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 hereinafter.
It is well known in the prior art that the surface runoff characteristlcs of a diaper may be improved by making the outer surface of the topsheet hydrophilic. As indicated above, prior art struc.ures have achieved this result by various methods such as applying surfactant to the outer surface of the topsheet. Surface dryness is improved, however, by making the outer surface of the topsheet hydrophobic.
The prior art developments have sought to achieve a balance between good surface runoff characteristics and favorable ~.1 Z4951 surface dryness, but the prior art lacks the aspects of the present invention in which improvement in the surface runoff characteristics can be obtained without a significant sacri-fice in the surface dryness of the topsheet for a wide range of topsheet materials and constructions.
It is therefore an object of the present invention to provide a disposable absorbent structure having rapid fluid penetration through a variety of topsheets without significant degradation in surface dryness.
An additional object of the present invention is to provide a disposable absorbent structure having a sur-factant treated intermediate layer.
A further object of the present invention is to provide a disposable absorbent structure having no surfact-ant on the outer surface of the topsheet.
These and other objects and advantages of the present invention will be readily apparent from the following description and claims taken in connection with the attached drawing to which they relate.
SUMMARY OF THE INVENTION
The principal components of a conventional dis-posable 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, is interposed below the outer surface of the topsheet. 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.
In one embodiment of the invention, the surfactant treated intermediate layer comprises a discrete substrate / `

s.s~ .
.

treated with surfactant. In this embodiment the intermediate layer is most effectively positioned at the interface bet-.~een the topsheet and the absorbent core although it may also he positioned within the absorbent core or at the interface between the absorbent core and the impervious backing sheet.
In an alternative embodiment of the invention, the surfactant treated intermediate layer is form~d by surEactant treating one of the principal components of the disposable diapar below the outer surface 0c the topsheet. Thus, either the inner surface of the topsheet, or the absorbent core may be treated with sur~actant.

The term "disjunctively disposed" when used herein to describe a particular positioning of the surfactant treated intermediate layer indicates that said inter-mediate layer is an element separate and distinct fromthe diaper topsheet.

l~Z49Sl BRIEF DESCRIPTION OF THE DRAWING
Figure 1 is a partially cut away perspectlve view of a disposable diaper having a surfactant treated inter-mediate layer.
Figure 2 is a side elevation of the disposable diaper topsheet.
Figures 3 through 5 are longitudinal section views-of alternative embodiments of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to Figure 1, there is shown a pre-ferred embodiment of the present invention as it would be used in a 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 dis-posable diaper is intended to merely illustrate a preferred embodiment of the present invention.
As seen in Figure l, disposable diaper 10 basical-ly comprises porous topsheet 12, absorbent core 14, imperv-ious backing sheet 16, and surfactant treated intermediatelayer 22. Topsheet 12 is superposed on absorbent core 14 and is l~Z4951 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 between 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.
Impervious backing sheet 16 is preferably a 0.001 to - 10 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 rnaterials 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 imper-vious 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 feel-ing, fluid permeable, and non-irritating to the user's skin.
In addition, topsheet 12 has a capillary suction pressure 11~4~5il 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. 1, January 1973 entitled Dynamic Adhesion Tension Measurement. 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.
Obviously, porous topsheet 12 may be manufactured from a wide variety of materials having a broad range of struc-tural and physical characteristics. For example, topsheet 12 may be paper, rayon, polymeric, woven, nonwoven, fibrous, nonfibrous, hydrophobic or hydrophilic. A preferred top-sheet 12 is shown in U.S. Patent 3,929,135 to Thompson.
As described therein, topsheet 12 is a low density poly-ethylene 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 cm) with an array of tapered capillary structures 24, each having a perforated apex 26 (See Figure 2).

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1~2~5~1 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 substrate 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 hydrophilicity of substrate 28 by increasing the ad-hesion 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 2 2 )8 (CH2 ~ C~ ~ )46 ~ (cH2cH2o)8H

- 7a -

3~1 and marketed under the trademark Pluroni ~ 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 trademark Orvus~ AB
Granules or cetyl trimethyl ammonium bromide manufactured under the trademark 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 sub-strate 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 concentra-tions which depend upon the surface and the nature of the topsheet 12 chosen. For a given substrate 28 and top-sheet 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 ofsubstrate 28 is greater than the capillary suction pressure of topsheet 12. The larger the difference in capillary suction pressure between ~2~5~

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 polyethlene adhesive such as that sold by United Shoe Machinery Corp~ration and identified as Thermo Grip No. 307.
Since intermediate layer 22 is below outer surface 30 of topsheet 12, intermediate layer 22 does not contact the user. ~hus, the liklihood 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 _ g ._ ~124~1 tapered capillary structures 24. Surface dryness is indicated by measuring the rewet of topsheet 12 and is a desirable characteristic because the drier topsheet 12 the lower the possibility diaper 10 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 milli-liters of fluid on diaper 10 at a uniform rate for 3.5 sec-onds. 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 Trito ~ 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:

Surface Runoff (%) =~weight of 25 ml~ ~weight of wet diaper-~
~of fluid ~weight of dry diaper ~ 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 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 i~ 951 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/s~uare yard of an ethylene oxide/
propylene oxide block condensation polymer (Pluronic L-92 as described above) and having a tapered capillary topsheet.
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4~9~ii TABT,~. I

Surface Runoff Rewet Position of(o6 reduction in (gms) intermediatesurface runoff , layer 22of diaper having w/intermediate w/out inter-no intennediate layer mediate layer layer 22) Topsheet absorbent 76 0.06/O.OS
core interface ~ithin absorbent 47 0.05/0.05 core .

Absorbent .
core 50 0.07/0.05 backing sheet interface , ~1~4~5~
Substrate 28 may, in some absorbent structures, comprise other components of diaper 10 which are treated with surfactant. Figure 4 illustrates an alternative embodime~t of the present invention in which intermediate layer 22 comprises envelope tissue 20 which is treated with surfactant.
In addition, as shown in Figure 5, intermediate layer 22 can comprise a portion of absorbent layer 13 which is treated with surfactant. Further, intermediate layer 22 can comprise the inner surface 31 of topsheet 12 which as in the example-s given above is treated with surfactant.
Table II shows the percent reduction in surface runoff exhibited by a diaper 10 having a tapered capillary topsheet 12 and having various components of diaper 10 treated with 0.001 grams/square yard of an ethylene oxide/propylene oxide block condensation polymer (Pluronic L-92 as described above).

~2~51 .

T~BLE II

Surface runoff Rewet (~ reduction in (gms) Dia~er surface runoff component of diaper not ~with without treated with treated with ~surfactant surfactant surfactant surfactant) .

Inner surface 39 0.06/0.05 0 of topsheet Envelope 72 0.04/0.05 tissue Absorbent.
layer 36 0.05/0.05 . .

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. . .

: - 14 -.: .

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The present invention has improved surface runoff characteristics without a degradat:ion in the rewet character-istics for a broad range of topsheet materials and construc-tions. These improvements are evident from Table III which shows the percent reduction in surface runoff for a diaper 10 having topsheets of varying materials and constructions.

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~ en compared to diaper 10 having surfactant ap~lied to the outer surface 30 of the topsheet 12, 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 capillar~
topsheet 12 and an envelope tissue 22 (see Figure ~) 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 heretofore 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. In addition, many modifications of the above described invention may be used and it is not intended to - hereby limit the present invention to the particular embodiments shown or described.
What is claimed:

Claims

1. A disposable diaper comprising:
an absorbent core;
a porous topsheet superposed on said absorbent core, said porous topsheet having an outer surface facing outwardly of said absorbent core and having an inner surface facing said absorbent core;
an impervious backing sheet joined to said porous topsheet and encasing said absorbent core between said backing sheet and said topsheet; and a surfactant treated intermediate layer disjunctively disposed between said inner surface of said topsheet and said impervious backing sheet.

2. A disposable absorbent structure comprising:
an absorbent core;
a porous topsheet superposed on said absorbent core, said porous topsheet having an outer surface facing outwardly of said absorbent core and having an inner surface facing said absorbent core;
an impervious backing sheet joined to said porous topsheet and encasing said absorbent core between said impervious backing sheet and said topsheet; and a surfactant treated intermediate layer dis-junctively disposed between said inner surface of said topsheet and said impervious backing sheet.

3. The disposable absorbent structure of Claim 2 wherein said surfactant treated intermediate layer comprises a substrate treated with a surfactant.

4. The structure of Claim 3 wherein the surfactant is a nonionic ethylene oxide/propylene oxide block condensation polymer.

5. The disposable absorbent structure of Claim 4 wherein the concentration of said surfactant is from about 10 to about 0.001 gram/square yard of treated substrate.

6. The disposable absorbent structure of Claim 3 wherein said substrate is a discrete flexible fluid pervious sheet.

7. A disposable absorbent structure of Claim 6 wherein said fluid pervious sheet is tissue paper having a basis weight of from about 12 to about 14 pounds per 3,000 square feet and having an air permeability of about 100 cubic feet per minute per square foot.

8. The disposable absorbent structure of Claim 6 wherein said fluid pervious sheet is juxtaposed between said porous topsheet and said absorbent core.

9. The disposable absorbent structure of Claim 6 wherein said fluid pervious sheet is juxtaposed between said absorbent core and said impervious backing sheet.

10. The disposable absorbent structure of Claim 6 wherein said fluid pervious sheet is disposed within said absorbent core.

11. The disposable absorbent structure of Claim 3 wherein said absorbent core comprises an absorbent layer and an envelope tissue; said absorbent layer being encased between said envelope tissue and said impervious backing sheet; said substrate comprising said envelope tissue.

12. The disposable absorbent structure of Claim 11 wherein said porous topsheet is provided with tapered capillaries.

13. The disposable absorbent structure of Claim 3 wherein said absorbent core comprises an absorbent layer and an envelope tissue; said absorbent layer being encased between said envelope tissue and said impervious backing layer; said substrate comprising a portion of said absorbent layer.