US 3381688 A
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May 7, 1968 wBT'rEO AREA sqcm.
D. SATAS ABSORBENT PADS WITH SILICA GEL LAYER FOR USE AS SURGICAL RECEPTACLES Filed Aug. 12, 1963 INVENTOR.
United States Patent 3,381,688 ABSORBENT PADS WITH SiLlCA GEL LAYER FUR USE AS SURGICAL RECEPTACLES Donates Satas, Palatine, llll., assignor to The Kendall Company, Boston, Mass, a corporation of Massachusetts Filed Aug. 12, E63, Ser. No. 301,417 7 Claims. (Cl. 128-296) This invention relates to absorbent articles and, more particularly, to absorbent dressings including sanitary napkins.
An absorbent dressing for collection of liquid exudates of the body is usually composed of an over-sized pad of absorbent fibrous materials. The cross-sectional area of the pad taken in a plane of the pad parallel to the surface of the pad placed toward the body over the exudation site is normally greater than the area of the drainage opening. The overlapping portions of the pad help to keep the exudation site and the area immediately adjacent thereto clean from external contamination. In the case of a wound dressing the pad also may serve as a cushion to lessen or prevent the effect of impact or pressure at the wound site.
The main path of flow of the fluid in the pad is generally perpendicularly from the surface of the pad directly over the discharge opening toward the exterior surface of the pad. The fluid taken up by the pad normally does not distribute itself laterally to any substantial extent from the region of the pad over the discharge site. This is particularly a characteristic of pads in which the main body portion of absorbent material is a mass of loosely associated short absorbent fibers, such as cotton fibers and comminuted wood pulp commonly known as fluif. The result is a column of saturated absorbent material extending from the body side of the pad to the external side of thepad in the pad region located substantially over the discharge site.
In heavy drainage cases the fluid strikes through the external side of the pad .and may spot or stain -clothing or bedding. Furthermore, the absorbent material in this column may become overly saturated with the discharge fluid to give a wet, soggy feeling to the wearer of the pad.
The ineflicient utilization of the absorbent capacity of the absorbent material of pads and the like and premature strike-through have been long standing problems which have received considerable attention particularly by those in the wound dressing and sanitary napkin fields. Impermeable coverings on the exterior surface of the pads have been suggested to eliminate the disadvantages from strike-through. This, however, reduces the air permeability of the pad. The placement of impermeable sheeting within the body of absorbent material, for example in a plane substantially parallel to the body side of the pad and preferably near the exterior surface of the pad, is also objectionable. In addition to reducing the breathability of the pad, the sheeting also is an absolute barrier to the utilization of the absorptive capacity of the material beyond the sheeting. The impermeable sheeting, whether positioned on the exterior surface of the pad or within the body portion of the pad, blocks the aforedescribed perpendicular channeling of the fluid, and forces the fluid to gradually move laterally and longitudinally from the wet column, forming what maybe described as a generally expanding column of wet fibers. The fluid is not drawn from the column to the adjacent portions of the absorbent material in the pad.
Another approach to the solution of the problems of premature strike-through and inefficient utilization of the absorbent material is the use of permeable sheeting impregnated with fluid repelling agents. The body fluid is repelled from the permeable sheeting, located either at or near the exterior surface of the pad. Since water is a constituent of fluid exudates of the body, these agents generally belong to the class of hydrophobic materials. In the case of dressings where sterility is a necessity, such as in wound dressing and maternity pads, the zone of the fluid directional control created by the hydrophobic materials must be substantially stable to exposure to temperatures and pressures at least equal to that employed in normal sterilization systems.
An object of this invention is a fluid absorbent article constructed to provide improved utilization of the absorbent material in the article. Included within the objects of this invention are fluid absorbent articles providing improved utilization of absorbent material thereof after exposure to elevated temperatures and pressures, particularly such absorbent articles as wound dressings and sanitary napkins sterilized under sterilizing autoclaving conditions. A further object of this invention is a fluid absorbent pad constructed to direct fluid laterally and longitudinally away from the site of fluid intake in the pad. Essentially, this invention is directed to the absorbent material component of the article constructed with a fluid directional control zone within, or on the external surface of, the absorbent material making up the body portion of the article. The fluid directional control zone comprises highly wettable finely divided particulate matter thinly distributed on a suitable carrier therefor. The carrier preferably is air permeable and a fluid absorbent material. Particularly advantageous, the carrier for the colloidal silica deposit may consist of the same material as the absorbent material forming the body of the article. As will be shown hereinafter in a preferred form of an absorbent dressing, the fluid is drawn from the accumulation thereof in the absorbent material in the region over the site of the fluid intake and directed laterally and longitudinally away therefrom. The fluid spreads along the zone and then diffuses to the adjacent absorbent material which may be to both sides thereof when the zone is located within the body of the absorbent material. As will also be shown, the rate of capillary flow of the fluid in the zone is greater than the rate of capillary flow of the fluid in the main body portion of the absorbent article.
Referring to the drawings: FIG. 1 is a cross-sectional View of a wound dressing taken along a line parallel to a longitudinal edge of thedressing;
FIG. 2 is a digram of an apparatus for measurement of fluid absorption in pads of absorbent material;
FIG. 3 shows the relationship between the amount of the colloidal silica at the control zone and fluid spreading at the zone; and
FIG. 4 compares the rates of capillary flow of treated and untreated absorbent material.
The numeral 1 designates a Wound dressing comprising an absorbent pad 2 of fibrous material. The absorbent fibrous pad is encased in a covering 3, for example a smooth, perforated film united to the surface of the pad to provide a nonadherent dressing as taught in US. Patent 2,923,298.
The numeral 4 generally designates the fluid directional control zone comprising colloidal silica 5 distributed on and carried by absorbent fibers of the pad 2 in or along the surface of a plane located within the body of the pad, as illustrated, and substantially coextensive with the pad. A pad of this structure may be prepared by spraying a silica sol upon the surface of a mass of absorbent fibrous material in the manner described below and then laying another mass of the same absorbent fibrous material on the sprayed surface. If the thickness of this mass of fibers is the same as that of the first mass, the sprayed surface fibers are in a plane located substantially medially between the bottom and top surfaces of the pad (as viewed in FIG. 1) and either of these surfaces may be placed toward the body portion to be covered by the dressing. If the plane of the control zone is located substantially nearer to one surface of the dressing than the other, or on one surface of the pad, it may be desirable to appropriately mark the dressing to indicate that the surface furthest from the control zone is the body side of the dressing.
The dressing as shown in FIG. 1 is shown with the lower surface as the body side of the dressing. The group of arrows pointing upwardly in the pad indicates the path of fluid flow from a wound directly under the central portion of the dressing. Upon reaching the control zone the fluid is directed longitudinally and laterally from the vertical column of saturated fibers. The liquid path at this zone is indicated by the arrows pointing to the left and right of the vertical group of arrows in the drav ing. As more fluid is drawn along this zone adjacent fibers wick olf fluid into the untreated body of fibers. This is indicated by the arrows bearing downwardly from the control zone. The fluid gradually diffuses into the absorbent material above the zone as the intake of fluid from the wound site continues. Thus, the absorptive capacity of the absorbent fibers 2 located in regions removed from the wound site and even at the edges of the pad is utilized.
As illustrated in FIG. 1, the zone of improved capillarity may be considered as an integral part of the absorbent material of the pad. The advantages in the construction of the articles of the invention in this manner are obvious. The directional control zone, however, need not be integral with the absorbent material. Alternatively, a separate permeable sheet may be impregnated with the colloidal silica and then placed on the exterior of a pad of the absorbent material or positioned within the body of the pad in a plane substantially parallel to the body side of the pad and coextensive therewith as explained above.
As used herein the term colloidal silica is intended to mean that form of silica which is deposited from an aqueous silica sol on an appropriate substrate and evaporation of the liquid medium therefrom. It is not necessary to heat the deposit to remove water of hydration from the silica. The term silica sol describes colloidal dispersions of silica in liquid media, usually in aqueous media. The colloidal silica consists of the various hydrated forms of silicon dioxide corresponding to the several empirical formulas proposed for these various forms of silica wherein one or more, or fractions of molecules of water are shown associated with one molecule of silicon dioxide (SiO The size of the dispersed silica particles in the sols may range from 1 millimicron to 1 micron. Silica sols preferred for use in the manufacture of articles of this invention are those in which the particle size is no greater than about 250 millimicrons and which averages from about to 35 millimicrons. These silica particles are further characterized by having very high surface area, generally within the range of 100 to 500 square meters per gram of silica.
The colloidal silica should be deposited essentially as a surface layer on the appropriate carrier. Spray application of a silica sol upon the fibers at the surface of air laid wood pulp pads and nonwoven cotton fabric pads is suitable as a method by which to deposit the highly wettable colloidal silica particles on the very surface of and/or in these fibers with a minimum of penetration into the depths of the pad. Penetration to fibers beyond the surface of the pad reduces the spreading efficiency of the control zone. Thus, the most effective form of the control zone in accordance with this invention is essentially a surface treated with and containing the highly fluid wettable particles.
The deposited silica is not a continuous layer; the deposit does not span the interstices between the fibers at the sprayed surface to form a physical barrier to fluid taken up in the pad from the fluid discharge site. Substantial spreading of fluid at the zone can be obtained with surprisingly small amounts of deposited colloidal silica, provided that the silica is relatively uniformly distributed throughout the zone surface. The colloidal silica is uniformly distributed if substantially all of the fibers at the surface contain some portion of the total amount of silica deposited. The silica should not be spot deposited in clusters of coalesced particles since this reduces spreading elficiency of the zone. It is unnecessary to load the surface of the fibers with a build-up of deposited particles or internally load the fibers with colloidal silica. Loading of the fibers at the surface of the control zone also results in decreased spreading efficiency.
The effect of the amount of deposit and the concentration of colloidal silica in the spray medium on spreading is shown in FIG. 3. The data represented in the graph of FIG. 3 was obtained by testing pads constructed in accordance with this invention using the apparatus of FIG. 2. The pads tested were prepared by spraying various amounts of 1%, 5% and 10% silica sols on one side of sheets of nonwoven cotton fibers. The sheets were of the type commonly known as nonwoven fabrics in which intermingled, unspun fibers are frictionally interlocked by means of kinks, twists, bends and curls in the fibers to form a coherent article in sheet form.
The silica sols for spraying were prepared by diluting an aqueous sol containing about silica particles colloidally dispersed in water. The particles were discrete substantially uniform spheres of silica having an average particle diameter of approximately 15 millimicrons. The surface area of the particles was about 210 square meters per gram silica. To this aqueous sol were added appropriate amounts of water to obtain the sols for spraying containing 1%, 5% and 10% silica. The sols were sprayed on the surface of the sheets by means of an atomizer of the type Well known for use in spraying cleaning liquids on glass. Only the sides of the sheets exposed to the spray were wetted. The fibers at the other sides of the sheets were dry. The sheets were permitted to air dry after the spray treatment at ordinary room temperatures. The amounts of the silica deposits on the sheets were calculated from the amounts of the sols sprayed thereon.
Samples of the treated and dried sheets were tested on the apparatus shown in FIG. 2. This apparatus consists of an open liquid reservoir 6, containing colored water 7, connected to a supply tube 8 for delivery of water from the reservoir to the sample platform 9. Centrally located in the top surface of the platform 9 is a well 10 connected by a channel 11 to the supply tube 8. A tube 12 is connected to the supply tube 8. Both the well 10 and the connecting opening in tube 3 for the tube 12 are located in the same horizontal plane. The flow of water from the reservoir 6 to the supply tube 8, the channel 11, the well 10 and tube 12 is controlled by the stopcocks 13 and 14 located in tube 8 above and below tube 12, respectively.
Prior to placing the sample 15 upon the platform 9 for testing the colored water 7 is permitted to flow into and fill the well 10 (level with the top surface of platform 9), the channel 11, the tube 8 and tube 12. The surface of the platform 9 surrounding the well 10 is dry. The tube 12 may be calibrated for measuring the water removed from the apparatus during the test. This is a measurement of the amount of fluid absorbed in the test sample.
The stopcock 13 is closed when the test sample 15 is placed upon the platform 9 and remains closed during the test. The test sample 15, i.e., the absorbent pad, is positioned on the platform 9 so that the opening of the well 10 is under the middle portion of the pad.
The test samples were placed with the untreated side of the fabric resting upon the platform 9. The path of the liquid flow in each case was upwardly with little lateral spreading from that portion of the sheet directly over the opening of the well until the treated surface was reached. The liquid then spread laterally in the manner previously described. In each case the area of the treated surface wetted with the colored Water was greater than the area of the fluid intake on the bottom untreated surface of the sheets. The differences in these areas were measured and plotted against the amounts of colloidal silica deposited for each of the silica sol sprays, as shown in FIG. 3.
In FIG. 3, curve A is a plot of the data obtained with samples sprayed with various amounts of the 1% silica sol. Curve B is based on samples sprayed with various amounts of the 5% silica sol and curve C is based on samples sprayed with various amounts of the 10% silica sol. The data of FIG. 3 show that the spreading efficiency of the control zone is related to the amount of silica deposited, the concentration of the silica colloidal particles in the spray droplets, the uniformity in distribution of the deposits on the fibers at the zone, and the depth of the zone containing the colloidal silica. FIG. 3 shows that finer sprays should be used in the spray application of the more concentrated sols. Better distribution is possible with a greater number of droplets of smaller size to deposit the same amount of colloidal silica. Substantial improvement in fluid directional control and spreading is possible with relatively small amounts of colloidal silica spray deposited from dilute sols. However, the spraying conditions must be carefully controlled since the relatively large amounts of water tends to cause penetration beyond the surface of the zone, resulting in a decrease in spreading efficiency, as indicated by the negative slopes of curves A and B in FIG. 3. Generally, a deposit of colloidal silica on the fibers at the surface of the control zone in an amount of from about 5 to 60 grams per square meter of surface will suflice to provide substantial spreading of fluid to absorbent material located in portions of the pad not directly over the fluid intake site.
The absorbent pads of this invention are capable of absorbing greater quantities of fluid without strikethrough to the exterior of the pad. Several pads were prepared by spraying colloidal silica onto the surface of one side of non-woven fabric sheets as described above. Each sheet was then folded upon itself with the treated surface of the sheet within the pad of the folded sheets. The pads thus had a layer of colloidal silica in the center plane thereof. The pads were tested on the apparatus shown in FIG. 2, measuring the volume of liquid absorbed by the pads. Control pads, not treated with colloidal silica, but otherwise identically made, were also tested. Strike-through occurred in the control pad upon absorption of 5 cc. of colored water. At 5 cc. absorption in the case of the treated samples, the water rose only to the central portion of the pad and began to spread laterally and longitudinally away from the region over the fluid intake site. Upon absorption of cc. of colored water in the control pads, the area of strike-through was approximately the same as the area of the fluid intake site. There was no strike-through at 20 cc. of absorption in the case of the treated pads; the colored water had spread extensively along the treated surface in the center of the pads. The exterior surface of the treated pads were dry. In the case of the untreated pads the fibers in the area directly over the fluid intake site and at the exterior surface thereof were saturated with the liquid. Similar results were observed in the case of pads made from loosely packed wood pulp. Samples of treated pads were steam sterilized in an autoclave. The effectiveness of the control zone after sterilization on spreading the fluid was substantially the same as in the case of the non-sterilized pads. The autoclaving conditions were the same as those normally employed in hospital autoclaves for sterilization.
The rates of capillary flow of a liquid in the treated and untreated fibrous pads is shown in FIG. 4. Strips of non-woven cotton fabric were impregnated with a dilute solution of silica sol and dried. The lower portions of the treated strips and untreated strips were immersed in water and the rate of capillary rise was observed, similar to the method described in the Industrial and Engineering Chemistry, Analytical Edition, volume 6 at pages -90 (1934). Plotting the rate of liquid rise in the strips in cm./min. against the reciprocal of the rise in cm. give the straight lines T and U. The line T is based upon the data observed for the treated samples and the line U on the data of the untreated samples. As shown in FIG. 4, the colloidal silica was effective in substantially increasing the rate of capillary flow in the fibrous strips. The dotted line extensions of lines T and U intercept the ordinate at substantially the same point. According to the equation represents the intercept value, the intercept is a function of the size and distribution of spaces available for capillary flow in fibrous media and of the physical properties of the liquid. Since the liquid and fibrous media were constant, it appears that the colloidal silica deposit in the treated sample did not adversely effect the number of and size of spaces available for capillary flow in the fibrous strip. Accordingly, the use of wettable finely divided particles of colloidal size and having large surface area of from to 500 square meters per gram may be effectively employed in accordance with this invention to directionally control the flow of fluids in absorbent materials. In the foregoing equation 11,, is the height of the liquid at time t; g the acceleration due to gravity, r the radius of capillary, 'y the surface tension, p the density, and '21 viscosity of the liquid and 0 is the wetting angle.
Clinical tests of maternity pads constructed in accordance with this invention having the control zone located substantially in the center of the pad and in the plane substantially parallel to the body side of the pads showed that the maternity pads of this invention spotted through to a substantially lesser extent than untreated, commercially available maternity pads. The absorbent material of both the treated pads and the untreated pads was airlaid wood pulp (fluff). The treated pads were covered with a porous sheet of Skintex. The untreated pads were covered with 4-ply absorbent wadding. Only about of the treated pads showed strike-through. Strike-through occurred in 36% of the untreated maternity pads. In the case of the untreated pads, spreading occurred on the surface of the absorbent wadding at the exterior of the pad only. In the absence of this cover of wadding there would have been substantially no spreading. In the case of the treated pads, the exudate spread along the silica treated surface in the manner described with respect to FIG. 1 and prevented strike-through except in instances of heavy drainage.
The invention claimed is:
1. An absorbent article comprising a mass of fluid absorbent material and a fluid directional control zone having a surface thereof contiguous with absorbent material of said mass, said surface of the control zone comprising a material carrying finely divided particles of a size from about 5 millimicrons to 1 micron having a surface area of from 100 to 500 square meters per gram of said particles and wettable by fluid to be absorbed by said absorbent material, said particles being substantially uniformly distributed throughout the surface area of said zone in an amount to provide a rate of capillary flow of fluid along the surface of said zone greater than the 7 rate of capillary flow of fluid in the mass of said absorbent material.
2. An absorbent article comprising a mass of fluid absorbent material and a fluid directional control zone having a surface thereof contiguous with absorbent material of said mass, said control zone being located in a plane of said mass in the path of fluid flow in the absorbent material from a fluid intake site and substantially parallel to a plane passing through the site of the fluid intake at a surface of said mass, said surface of the control zone comprising a material carrying finely divided particles of a size from about to 35 millimicrons having a surface area of from about 100 to 500 square meters per gram of said particles and wettable by fluid to be absorbed by said absorbent material, said particles being substantially uniformly distributed through the surface area of said zone in an amount of from about 5 to 60 grams thereof per square meter of said surface of the control zone whereby the rate of capillary flow of fluid along the surface of said zone is greater than the rate of capillary flow of fluid in the mass of said absorbent material.
3. An absorbent article in accordance with claim 2 wherein said particles are inorganic particles and the material comprising the surface of said control zone and carrying said particles is a fluid absorbent fibrous material.
4. An absorbent article comprising a mass of fluid absorbent material and a fluid directional control zone having a surface thereof contiguous with absorbent material of said mass, said control zone being located in a plane of said mass in the path of fluid flow in the absorbent material from a fluid intake site and substantially parallel to a plane passing through the site of the fluid intake at a surface of said mass, said surface of the control zone comprising fluid absorbent fibers carrying colloidal silica having a particle size of from about 5 millimicrons to 1 micron and a surface area of about 100 to 500 square meters per gram of silica particles, said silica particles being substantially uniformly distributed on the fibers of said zone in an amount to provide a rate of capillary flow of fluid along the fibers of said zone greater than the rate of capillary flow of fluid in the mass of said absorbent material.
5. An absorbent article in accordance with claim 4 wherein the size of said silica particles average from about 5 to rnillirnicrons.
6. An absorbent article in accordance with claim 5 wherein the amount of said colloidal silica carried by said fibers is from about 5 to 60 grams per square meter of said surface of the control zone.
7. An absorbent article in accordance with claim 4 wherein said colloidal silica particles are present in an amount of from 5 to 60 grams thereof per square meter of said surface of the control zone.
References Cited UNITED STATES PATENTS 2,230,903 2/1941 Ostenberg 128296 2,690,415 9/1954 Shuler 128290 2,923,298 2/1960 Dockstader et al. 128-296 2,992,644 7/1961 Plantinga et al 128-156 3,081,154 3/1963 Acker et al. 252-449 3,146,076 8/1964 Talvenheirno 252l RICHARD A. GAUDET, Primary Examiner.
CHARLES E. ROSENBAUM, Examiner.