CA1135454A - Sanitary napkin with two layer absorptive system - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A sanitary napkin having two compositionally distinct layers is provided. The bottom absorptive layer contains any of the conventional cellulosic materials such as wood pulp, while the top layer fea-tures a material which has relatively large capillaries and controlled fluid retention. The napkin includes a body contacting layer of fluid pervious material and a fluid impervious layer at the bottom.

Description

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FIELD OF THE INVENTIO~
The invention relates to a sanitary napkin and particularly a napkin having layers of different absorptive materials.
BACKGROUND OF THE INVENTION
There are several features which are desir-able in a sanitary napkin. The sanitary napkin must be comfortable, it must be highly absorbent, it must rapidly remove fluid from the surface adjacent the wearer and must be relatively inexpensive to produce.
Wood pulp fibers or other similar natural cellulosic fiber systems have long been used as the primary absorptive component of these napkins. Wood pulp fluff is soft, resilient, absorptive and inexpensive.
One of the dif~iculties in using wood pulp solely as an absorbent for menstrual fluid is that there is no preferential directional transfer so that -higher exudate concentration exists in regions closest to immediate con~act. The result is a wet pad surface which is conducive to early leakage. These transfer problems are accentuated as the pad becomes wetter.
Prior art has recognized these problems and has attempted to provide suitable composite absorptive systems utilizing wood pulp or the like as one of the absorptive layers. The other absorptive layer which is usually placed on the top has been chosen based upon the ., ~35~

theory that it is desirable to pass fluid as quickly through the surface of the top absorptive layer as possible. In some instances this is done by rendering the upper surface of the top absorptive layer "hydro-phobic" and/or by selective absorption of the more viscous parts of menstrual fluid in the top layer with, at least hypothetically, preventing the aqueous portion of the menstrual fluid from passing through to the fluff layer. It has also been theorized that absorptive systems utilizing two highly absorptive entities on successive layers would be particularly valuable.
An Example of composite absorbent systems, U. S. patent 3,371,667 discloses a highly porous resilient element designed to "entrap highly viscous mucoid and gelatinous constituents of the body fluids".
This patent teaches that the top layer so described would pass through the less viscous components, Suitable fibers contemplated are rayon which has been rendered rela,tively hydrophobic at the surface but treated with hydrophilic agents for the inner portion of the fibrous web.
Another representative composite napkin is described in U. S. patent 4,047,531 which has an outer fluff layer prepared from a thermomechanical pulp used in conjunction with a traditional fluff layer as an ~3S~

absorbent system. Again, the concept set foxth in this patent is the use of a "hydrophobic" fiber ln the uppermost layer.
There are other prior art composite absorptlve systems but they all seem to, in effect~ describe the use of a top layer which is at best less absorptive than the bottom layer and, may in fact, have little actual absorptive capabilities particularly as related to the aqueous components of the m~ënstrual fluid.
SUMMARY OF THE INVENTION
This invention provides an absorptive system for a sanitary napkin or the like having two layers with the layer closest to the body of the user passing fluid rapidly through the upper surface and still retaining overall absorptive capabilities while also wetting the bottom surface of a conventional cellulosic fi~rous matt.
It has been found that the composite absorp-tive systems can be substantially improved by utilizing a top layer which may function as an absorbent for all of the components of menstrual fluid by combining a high capacity with good fluid transfer properties.
Menstrual fluid, as it contacts the top absorp-tive layer of the composite sanitary napkin of this invention rapidly passes through the upper surface of the_layer and d perses rapidly radially as it passes ~s~

through the thickness of the first layer. During this passage a portion of all of the components of the fluid is retained.
The upper layer mus~ possess relatively large interfiber spaces for the upper layer to allow rapid fluid transfer. If extremely high fluid retention for the top layer is present, after the top layer is satu-rated, there will be fluid runoff between the top layer and the cellulosic fibrous layer abutting it with the resulting problems of side leakage. Also, there may be, in the case of a highly absorbent top layer, blockage of the capillaries in this layer as a result of the high level of absorption which would prevent at least a part of the flow from contacting the second absorptive layer.
It has now been found that a top layer having a capillary absorption composite value not greater than 0.5 and an equilibrium capacity not greater than 4.6 grams absorbed per grams of absorbent, in combination with a conventional cellulosic layer such as a wood pulp fiber, provides a highly effective absorptive system utilizing the absorptive capabilities of both layers with a high degree of efficiency without side leakage or surface puddling on the top of either absorp-tive layer.
This invention will be more readily understood with reference to the drawings in which FIG. 1 is a 545~
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perspective view and partial cross section of a typical sanitary napkin construction and FIGS. 2 and 3 are diagramatic representations of the tests utilized to characterize the top absorptive layer in the pad of the subject invention.
With reference to FIG. 1, a sanitary napkin N is depicted as having a fluid permeable outer wrap completely enclosing the remaining constituents of the napkin. A top absorptive layer 2~is located directly below the bottom upper face of the surrounding wrap.
The conventional wood pulp or similar absorbent layer 3 is located directly below the top absorptive layer and is disposed on top of a fluicl impermeable baffle 4.
The fluid impermeable baffle actually surrounds the sides of the bottom absorptive layer and may extend to cover part of the sides of the top absorptive layer.
This construction has the advantage of minimizing leakage from the sides of the pad. The pad is sealed at the forward and rearward edges 5 and 6 in any conven-tional manner such as adhesive sealing. Th~ sealing isindicated by the closely spaced line set inward from the edges at their respective ends. This particular pad is of the tabless variety and as shown partially in phantom lines, there is an adhesive peel strip which exposes bottom adhesive surface for attachment to undergarments.

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The pad illustrated in FIG. 1 in its cur-rently preferred embodiment, utilizes an outer fluid permeable wrapper of spunbonded polypropylene as described in U. S. Patent No. 3,886,942 and a presently preferred baffle material is 0.6 mil polypropylene.
The bottom absorbent layer presently preferred is wood pulp fluff and the upper absorbent l~yer is chosen based upon an evaluation set ~orth in the table below and cost factors.
It is to be understood that the embodiment depicted in ~IG. 1 is merely representative of a particular configuration which may be chosen and the inventive concept is not to be limited to that configuration. For example, a sandwich type of napkin can be made in which the fluid permeable top layer only extends to the edge of the pad and the fluid impermeable bottom sheet or baffle is affixed directly to the fluid pervious top layer completely around the periphery of the pad.
The capillary absorption composite value is obtained by the capillary absorption composite test.
This test is performed as follows: first, the material to be tested is produced on web forming equipment which for purposes of comparison is set to form a web having a basis weight of 34 grams per square foot. The material is die cut to produce a three inch diameter circle. A
similar die cut wood pulp fluff three inch diameter disc ~35i~

is also cut by the same means and placed under -the experimental absorbent material for testing. The testing apparatus is depicted in FIG. 2.
The testing apparatus consists of a variable rate syringe pump and means for maintaining constant temperature and pressure on the sample. The fluid utilized for testing is bovine blood-which has its hematocrit i.e. red blood cell level adjusted to a level of 20 percent of weight of t~e solution. The blood is fed by the pump 11 past a magnetic stirrer 12 through a syringe ejector 13 and into intake tube 14.
Intake tube 14 leads into a hollow walled heat exchanger 15 which, as shown in partial cross section, rests upon a supporting block B which in turn rests upon the sample pads 19. A colostomy bag 10 is located beneath the samples and sits upon a support 1~3. The colostomy bag is fluidly connected with a constant temperature bath 23 through colostomy intake tube 21 via pump P. As shown in the drawings, pump P also provides the heat exchanger 15 with a temperature control water flow through water intake tube 20. Stand pipe 22 is also connected to the colostomy bag by pressure tube 24. The stand pipe in conjunction with the constant temperature bath 23 controls both temperature and pressure. The sample is maintained at a constant temperature of 37 C. which is body temperature by means of the constant temperature bath-generated fluid flow into the heat exchanger 15 ~3SgLS~

through line tube 20 (with the fluid exiting from the heat exchanger jacket through exit conduit 16) and also through the flow through tube 21 into the colostomy bag 17. The pressure is maintained at 75 centimeters of water and the flow of the modified bovine blood is maintained for 90 minutes at a flow rate of 2 milli-llters per hour. The capillary absorption composite value is calculated after the test is completed. The value is a ratio of the surface area of the stain from the bovine blood of the upper surface of the absorbent top layer with the stain area on the lower surface of the bottom layer absorbent. The lower the value the greater the amount of Z-direction passage of the fluid and spread of the fluid along the bottom surface of the absorbent material. It should be stressed that the value calculated is not one reflective solely of capillarity or the size of the capillaries. If this was to be the desired test then there would be only a measure of the time it took to pass the bulk of the fluid through from one surface to the other. By measuring the actual radial spread or dispersal of the fluid along the bottom surface and by comparing this value with the spread on the top, an indication of capillarity in conjunction with absorption is obtained.
The second method utilized for characterizing the upper absorptive layer in the pad of the subject 9 _ ~L~L3S~

invention is controlled capacity. By the term con-trolled capacity is meant that the absorptive layer has some absorptlve capacity but of a limited amount.
As mentioned previously, it is desired that the second absorptive layer contributes substantially to the absorption process and in order to accomplish this desideratum, it is necessary to carefully control the absorptive capacity of the uppermost layer. The value of absorptive capacity is determined by the capillary sorption apparatus depicted at FIG. 3. The test will be explained with reference to the component parts of the apparatus described therein. Generally this par-ticular test can be summed up as an analysis which determines the relationship between pore volume and capillary pressure during absorpti.on of a particular system. The apparatus utilized fc>r conducting this test includes a filter funnel 35 including a flat ground PYREX filter disk 40 of medium porosity. The filter disk is three inches in diameter and the sample prepared is described for the previous test and cut to the three inch diameter configuration is placed upon the filter disk. Tubing 33 connects the funnel to a length of capillary glass tubing which lies in a fixed horizontal position. The fluid reservoir 30 is connected to the capillary tube 31 by a three-way stopcock 32. Interposed between the capillary tube and the stopcock is a drain 36. The capillary tube ~35~

is calibrated either internally or by utilization of a meter stick so that the volume fluid per centimeter of tubing can be calculated. The reservoir 30 is filled with a commercially available research fluid called Isoton~. This fluid has a pH of 7.4 and the surface tension was adjusted to 54 dynes. After filling the reservoir, an uninterrupted column of liquid extends from the lower face of the filter plate into the capil-lary tube. A porous Teflon weight~of approximately 210 grams is placed on top of the sample as it rests on the sample plate and a cover is placed over the filter funnel to prevent fluid loss. The filter funnel 35 is mounted on a graduated meter stick 34 and the funnel is raised to a position of 60 centimeters with the stopcock closed.
; The stopcock is then opened to allow the free flow of fluid from the specimen tested to the capillary tube.
The system is then allowed to equilibrate with equili-bration depending upon the particular choice of absorptive pad tested. The cell is then lowered at predetermined intervals allowing equilibrium at each until the total void volume of the sample has been filled i.e. at 0 cm. At this point the sample has gone from a state of dryness to one of complete satu~ation.
For purposes of the particular test, the absorptive value chosen is the amount of fluid retained per gram of absorbent at 30 centimeters height on the desorption cycle.

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A series of absorbent materials were tested according to the test procedures described above and the results set out in Table I.
Table I
MATERIALS CHARACTERIZATION
Capacity Top/Bottom Capillary Basis Wt.StainTension Material g/ft~2Ratio~g/g@30cm) Body Wadding 34g/ft21.07 1.54 (20 plys) Wood Pulp Fluff 32g/ft2 .77 4.6 Polyester 3.0 32g/ft2 .06 .6 Denier ABSORBIT 3.3 33~7g/ft2.13 2.8 Denier ABSORBIT 1.5 33g/ft2 .78 3.0 Denier Rayon 1.5 Denier 32g/ft2 1.14 1.4 Rayon 3.0 Denier 32g/ft .28 1.5 Polyester/Rayon 32g/ft2 .05 4 80/20 Blend 3.0 Denier BUCKEYE CLD 34g/ft2 .12 7.58 AQUALON 34g/ft2 .10 7.79 Thermo Mechanical 34g/ft2 1.39 3.40 (Australian TMP) (Pinus Radiata) ~3~i~5~

The pulp referred to as thermo-mechanical on the table is an example of the material described in U. S. patent 4,047,531 set forth previously in the disclosure as prior art.
AQUALON is a trademark of Hercules Incorporated and is a material noted for its highly absorbent or so-called superabsorbent characteristics. The composi-tion is of carboxymethylated cotton linters.
BUCKEYE CLD is a trademark of Procter & Gamble and is also a so-called superabsorbent material and con~
sists of carboxymethylated wood pulp fibers.
ABSORBIT is a trademark of American Enka, Division of Akzona and is an alloyed cellulose fiber containing an alkali metal salt or ammonium salt of a copolymer or terpolymer of acrylic acid and/or meth-acrylic acid.
It should be noted that denier seems to have a substantial effect on performance of the particular material chosen. Note that the higher denier ABSORBIT
and the higher denier rayon samples meet the criteria for the test but the lower denier ABSORBIT and rayon samples do not. It is apparent, therefore, that in order to satisfy the particular test parameters which definè the subject inventionj factors other than the choice of absorbent material play a role.

Claims (3)

WHAT IS CLAIMED IS:

1. A flexible, soft sanitary napkin comprising in combination:
a) a fluid permeable upper layer;
b) a first absorbent layer of a relatively thin, highly absorbent material of large capillaries, said absorbent material having a capillarity absorp-tion composite value not greater than 0.5 and a capacity not greater than 4.6 gm. absorbed/gm. absorbent;
c) a second layer of conventional cellu-losic absorbent material positioned under said first layer; and d) a fluid impermeable baffle.

2. The bandage of Claim 1 in which the top layer is from 5 to 80% by weight of the total absorbent material.

3. The bandage of Claim 1 in which the top layer is from 15 to 60% by weight of the total absorbent material.