Hydrophobic Sheet With Hydrophilic Passages

Abstract

Sheet material, suitable for use as a diaper liner or the like, which is of a generally hydrophobic nature but includes hydrophilic passages in the product to permit liquid to be transmitted through the product.

Description

This invention relates to hydrophobic sheets. More particularly, this invention relates to hydrophobic material having hydrophilic passages therein.

Inasmuch as the present invention has particular application to the art of diaper liners, particular reference will be made thereto -- it being understood that the products of the present invention will find other uses in various fields as described hereinafter.

Diaper liners are used for the purpose of providing an intermediate substrate between the lower body area of a baby or infant and an actual absorbent layer or diaper per se, for the purpose of preventing or reducing soiling of the diapers by solid body discharge. As such, diaper liners must be capable of permitting fluids to pass through the liner to be absorbed by the absorbent diaper, and conversely, retain the solid discharges. One type of diaper liner commercially used is based on a substrate or layer of material which is highly liquid permeable, and is of a hydrophilic nature having a porosity such that it reduces diaper soiling by preventing the passage of solid particulate matter through it. This type of liner more or less acts as a "filter," in that it is essentially of a structure for optimum filtering efficiency of the solid particulate matter. However, due to the fine porosity and hydrophilicity of such types of diaper liners, it is evident that the major proportion of the liner per se will remain wet and in contact with the skin of the wearer's body. This should preferably be avoided, as it could lead to skin irritation.

A further type of liner known in the prior art comprises a substrate of a hydrophobic nature -- for example, such liners are constructed of hydrophobic synthetic fibers which may either be inherently hydrophobic or alternately, fibers which have been rendered hydrophobic in nature (as in the case of cellulose fibers which are conventionally rendered hydrophobic by chemical treatment to alter their properties). While possessing several advantageous features in its own right, such diaper liners have several disadvantages including, for example, that in order to assure the passage of liquids through the hydrophobic sheet to an underlying absorbent diaper, the porosity of the hydrophobic sheet has to be sufficiently coarse to allow "strike through" (or otherwise the surface tension of saline body liquids could prevent or reduce penetration of the liquid through the liner). This coarse porosity inherently results in a lower soiling resistance (i.e., the filtering availability or capacity of the liner). Still further, depending on the water-retentivity characteristics of the underlying absorbent diaper, secondary "strike through" from a saturated absorbent diaper back to the skin of the infant's body (through the diaper liner) occurs, even at points removed or spaced from the zone of liquid impact.

Accordingly, there is a need today for a product suitable for use as a diaper liner or diaper facing, which overcomes the disadvantages of the prior art products. Applicant has now developed such a product in accordance with this invention, which not only overcomes the prior art disadvantages with such products, but at the same time, provides several advantageous features in its own right.

More particularly, in accordance with this invention, there is provided a product overcoming the disadvantages of the prior art and comprising a sheet of flexible material having opposed major surfaces, said sheet having a porosity fine enough to reduce substantially the passage of particulate matter therethrough. The product, as a diaper liner, has in a most preferred form a major proportion of at least one surface of said sheet being of a hydrophobic nature, and a minor proportion of said one surface being of a hydrophilic nature, said hydrophilic proportion of said sheet comprising in the most preferred form, spaced-apart areas of hydrophilic passages extending inwardly from said surface of said sheet.

In accordance with a further aspect of this invention, there is provided a method of preparing the abovedescribed products, which method according to one aspect, includes the steps of providing a length of flexible sheet material having a pair of opposed major surfaces, at least one surface being of a hydrophilic nature, the material being selected so that it has a fine enough porosity to prevent the passage of particulate matter therethrough, treating the hydrophilic surface of said material so as to render at least said one surface hydrophobic in nature, and subsequently treating the hydrophobically rendered hydrophilic material at spaced-apart points to provide spaced-apart hydrophilic passages extending inwardly of said hydrophobic surface of said sheet.

In accordance with an alternate embodiment of the present invention, the above products may be produced by the steps which include providing a length of flexible sheet material having a pair of opposed major surfaces, the length of sheet material being generally hydrophobic or having at least one major surface thereof which is hyrophobic in nature, said material having a fine enough porosity to prevent the passage of particulate matter therethrough, and treating said material, or at least said major surface which is hydrophobic in nature, at spaced-apart points to provide spaced-apart hydrophilic passages extending inwardly of said major surface of said sheet material.

In greater detail, the products of the present invention as described above, can be characterized as having a sufficiently fine porosity such that, in the case of diaper liners used in conjunction with diapers, the passage of solid particulate matter through the product forming the diaper liner to the diaper per se, is reduced or prevented, so as to reduce or prevent diaper soiling by the solid particulate matter, while also, the repellency of the product is normally augmented. Still further, at the same time, the products of this invention possess the property of passing body liquids through the hydrophilic passages so that they may be absorbed by an underlying absorbent diaper or absorbent substrate. In this manner, such products as in the case of diaper liners, and due to the characteristics of the product, prevent secondary strike-through (except at the hydrophilic passages) and substantially reduce skin irritation which could otherwise be caused by body fluids remaining in contact with a wet diaper liner and the skin.

The products of the present invention, when used as diaper liners, have a major proportion of at least one surface thereof which is hydrophobic in nature, and conversely, a minor proportion of said one surface which has hydrophilic passageways extending inwardly of that surface. To this end, the hydrophilic passageways are in the form of spaced-apart passages, preferably as outlined hereinafter. These passages permit the transmission of liquids through the material into the absorbent substrate. In the case of diaper liners, the hydrophilic passages may extend only over a selected area of the total area of the material -- that is in the area of the diaper liner where the body discharges occur. Thus, for example, only a central area of the material which is intended for use as a diaper liner may be provided with the spaced-apart hydrophilic passages, so that when the diaper liner is used, it will be positioned with respect to, e.g., a diaper, such that the area with the hydrophilic passages will be located in the required place when in use.

In the area where the hydrophilic passages are located, they are most preferably of a type wherein the spacedapart passages have intervening areas of a hydrophobic nature. In this respect, the geometrical surface configuration of the hydrophilic passages may vary as desired, ranging from spacedapart "dots" to geometrical configurations such as circles, parallelograms, lines, etc. Still further, the surface area of each individual hydrophilic passage may vary considerably, depending on the intended use of the product; in general, the total cumulative area of all hydrophilic passages may amount to 1 percent to about 90 percent of the total area of the material; for most diaper liner applications, the total cumulative hydrophilic surface area may be in the order of from about 5 to about 40 percent, desirably about 10 percent to 35 percent, which has been found to impart sufficient and most desirable properties. As indicated previously, most of the hydrophilic passages will be located in a given area -- e.g., the central area of a diaper liner and hence, for diaper liners, the above preferred total hydrophilic cumulative area will be located in said central area, with intervening hydrophobic areas between the hydrophilic areas. However, if desired, a single hydrophilic area, of any suitable shape, may be employed to form a large hydrophilic passage with an area within the above ranges. If desired, the hydrophilic area may be centrally located, and preferably surrounded by the hydrophobic portion of the material.

In one preferred embodiment, the total product is hydrophobic throughout, and between the opposed major surfaces thereof except for the hydrophilic passages extending therethrough between the opposed surfaces. In an alternate embodiment and for preferred applications as described hereinafter, the material may have the property of being hydrophobic on one surface thereof with the hydrophobic characteristics extending inwardly of said surface but not through to the opposed major surface, and with the spaced-apart hydrophilic areas on the hydrophobic surface defining passages extending from the hydrophobic surface into operative relationship with an absorbent portion, to permit the passage of liquids from the hydrophobic to the absorbent portion.

The material forming the products of the present invention may be any suitable material having the desired and required characteristics for the products for any intended use. Thus, in the case of diaper liners, the material must be one which is flexible, and non-harmful or non-irritating to the body when placed in use. A particularly preferred material from which the diaper liner products are derived are conventional commercially available non-woven materials of wood fibers or the like, which may include synthetic fibers (such as rayon fibers). However, other types of sheet materials such as woven materials, paper or paper-like material, etc., may also be used depending on the intended purpose of the products of the present invention. Without being limiting, the products of the present invention may be derived from materials which are initially hydrophobic or hydrophilic. In turn, such materials, may be derived from or include fibers such as pulp fibers, cotton linters, synthetic fibers such as cellulose acetate fibers, vinyl chloride, vinyl acetate (e.g., the product marketed under the trade mark "VINYON"), polyamides, viscose staple rayon, rayon or other regenerated cellulose fibers such as cellulose acetate or cellulose triacetate, acrylic fibers, polyester fibers, polyolefin fibers such as polypropylene fibers, and natural fibers such as wool and silk fibers, protein fibers such as those products marketed under the trade mark "VICARA," combinations of the above fibers, etc.

The particular physical shape of the sheet material of the products of the present invention is not critical, and will of course vary according to the intended use of such products. Conventionally, products such as diaper liners are of a generally rectangular shape measuring about nine inches by thirteen inches or larger. Likewise, the thickness of the material of the present invention is not critical, but for most applications like diaper liners, the thickness is normally kept to a minimum weight for economic reasons.

Although reference in the above description has been generally made to sheet material functioning as a separate entity and capable of reducing or preventing the passage of solid particulate matter therethrough but permitting the passage of liquids, within the scope of this invention it is also contemplated that such a product may in fact form a separate layer or layers of a composite multi-layered product -- or still further, form an integral part of a total product as an outer portion thereof. Thus, for example, it may be desirable in certain instances to employ the products of the present invention in a multi-layered product, and to this end, the additional layers of such a multi-layered product may have different functional purposes for any intended or given application. Thus, the products of the present invention may form an outer covering layer adhesively or otherwise secured to one or more inner layers or cores of absorbent material, etc. for certain applications.

The porosity of the products of the present invention is such that the material is capable of substantially preventing the passage of solid particulate matter and at the same time, remain hydrophobic in nature to liquids (except of course at the hydrophilic passages). To this end, the generally hydrophobic products with the hydrophilic passages should have a porosity, as calculated on the basis of the permeability of the product to water under a pressure head of 60 cm. of water, above about 1 cc/sq. cm/sec. and up to about 200 cc/sq. cm/sec., or higher, preferably above 50-75 cc/sq. cm/sec. Products having the above preferred ranges have been found to perform very satisfactorily where such materials are used as diaper liners. To this end, the materials for the products of this invention will be chosen accordingly, depending on the requirements for any given application.

The above products may be obtained by the methods previously briefly outlined. In greater detail, and in both embodiments of such methods, the starting materials are initially chosen to have the desired porosity factor as described above; such starting materials being in any desired form -- e.g., sheet form of either a continuous length or individual precut lengths. In the case of a normally hydrophilic starting material, one or both opposed major surfaces, or still further, the toal hydrophilic material is treated to render the same substantially hydrophobic in nature. For this purpose, and depending on the type of material employed, the treatment is preferably of a chemical nature wherein a liquid repellent composition is applied to the material in an amount sufficient to provide the hydrophobic characteristics on one, or both of the opposed major surfaces, or throughout the material. Thus, for example, liquid repellent compositions in a liquid form may be employed to provide the liquid repellency or hydrophobic characteristics by saturation or other equivalent techniques as required. In this first or initial step of forming the products when starting with a hydrophilic material, the type of liquid repellent composition employed may be any suitable composition which imparts the desired properties to the material. However, depending on the intended use of the end products, the type of composition and active ingredients therein will have to be chosen to provide any additional characteristics required; by way of example, such treating compositions may be chosen from those which do not impart stiffness (i.e., the material remains sufficiently flexible), it should be non-toxic and non-irritating in the case of diaper liners, etc.

Typical of the compositions which may be used for the purpose of rendering the material liquid repellent are such compositions or products marketed under the trade marks "PHOBOTEX FTC," "PHOBOTEX FTA," "PARAMUL DC--1," "PARAMUL DC--2," "PARAMUL 115," as well as silicone compositions, fluorine derivative compositions such as those marketed under the trade mark "SCOTCHGARD FC--208," repellent rubber or latex compositions, repellent plastic or resinous compositions such as vinyl polymers and copolymer-based compositions, various types of wax derivatives or waxes, as well as such products marketed under the trade marks "QUILON," "AQUAPEL EMULSION 360 XC," "KROMYLL-S," "ARIDEX," liquid repellent "AEROTEX" compositions, "ZELAN," etc.

The liquid repellent treating composition may be in any form suitable for application to the hydrophilic material, for example, it may be a gaseous composition, liquid composition or a powder. In gas phase treating compositions, the compositions are normally impregnated into the material by exposing the material to the gas for a sufficient period of time to permit the gaseous composition to permeate the material, whereafter it is permitted to set and cure. In the case of compositions in powder form, they may be applied to the hydrophilic material by any suitable means, whereafter they may be set and cured according to conventional procedures. In the case of liquid compositions, as previously mentioned, the hydrophilic material may be treated by a saturation technique, or alternately by a spray or like technique. Again, following evaporation of any carrier, the liquid repellent is permitted to set and cure as required. In all cases, the setting or curing of the liquid repellent may vary according to the type of composition.

Normally, for most applications, only a minimum amount of liquid repellent composition is applied to the hydrophilic materials for economic reasons and to avoid any subsequent complications due to excess repellents being present in the treated material. In this respect, a total amount of repellent applied to the material will, of course, vary depending on the type of repellent, the amount of material to be treated, etc., and hence wide limits will obviously be used for different compositions.

Upon obtaining a normally hydrophobic surface or product using a hydrophilic starting material, or alternately starting with a hydrophobic material, and according to both aspects of the method of this invention, the hydrophobic material is then treated to provide spaced-apart hydrophilic passages therein. To this end, the treatment may either be of a chemical, electrical or thermal nature -- the choice of which will depend on the type of material and in the case where a liquid repellent has been used, the type of liquid repellent employed to render the normally hydrophilic starting material hydrophobic. By way of example, the hydrophobic material may be provided with hydrophilic passages by treating spaced-apart selected areas with a chemical composition capable of nullifying the hydrophobic properties of such material whereby the treated areas thus form hydrophilic passages, or in the case of normally hydrophilic starting material, revert back to a hydrophilic nature. Typical of the treating compositions which may accomplish this are compositions functioning as a wetting composition -- such compositions being, e.g., those products marketed under the trade marks "TRITON GR--5," surfactants such as "AEROSOL OT," "HYAMINE 1622," "DUPONOL-EP," "COMPOUND TL," "HIGH FOAM BASE B," "STANDOPOL WAQ," etc., as well as other chemicals which can function to coat the fibers and provide the hydrophilic passages.

Again, as mentioned above with respect to the liquid repellent composition, the wetting agent composition will likewise have to be selected depending on the characteristics desired in the end product -- e.g., the wetting agent employed may have to be one which is capable of being sterilized, is non-toxic, etc. Likewise, as outlined above, the concentration of the wetting agent in the treating composition, and the amount required to provide hydrophilic passageways, will vary depending on the type of composition, its effectiveness, etc. Various techniques can be employed for applying the treating composition to the hydrophobic material -- for example, predetermined amounts of the wetting agent compositions may be applied to at least one major surface of the material (or to both opposed major surfaces) in a pattern conforming generally to the configuration of the spaced-apart hydrophilic passages desired in the products. Thus, for example, the wetting agent compositions may be applied in the form of "dots," a pattern of lines, intersecting or otherwise, etc.

Whatever type of treatment is employed to treat the hydrophobic material and provide hydrophilic passages therein, it should be chosen and selected such that the porosity of the material is not destroyed or deleteriously affected during treatment, in order to maintain the desirable characteristics of the product.

Following both the treatment to render the normally hydrophilic material hydrophobic (when employed), and the treatment used to provide hydrophilic passages in the resulting hydrophobic material, when employing chemical treatment compositions which otherwise moisten or wet the product entirely or partially, drying of the product is carried out as an intermediate step. The drying step may be carried out by any suitable treatment, ranging from exposure to the atmosphere for a sufficient period of time to permit the evaporation of the solvents or the like, or by subjecting the treated material to elevated temperatures (but not at a temperature sufficient to destroy the treating agents or impart undesirable properties to the material per se).

Following production of the sheet materials, if not pre-cut to a desired shape or size before treatment, they may be subsequently passed to further processing stages to carry this out - or in the alternative to combine the sheet materials with additional layers.

Tests carried out on the products of the present invention, in the case of diaper liners, have demonstrated that the products substantially prevent soiling of underlying absorbent diapers by preventing the passage of particulate solid matter through to the underlying diaper, and at the same time, permitting the passage of liquid body discharges through the products into the absorbent diaper. At the same time, products of the present invention provide a substantial reduction in the area of a wearer's body in contact with wet or moistened materials, thereby reducing substantially the possibility of skin irritation. Still further, the above-described method permits the production of such products in a very economical and feasible manner.

In addition to use as diaper liners, products of the present invention may be used for various other industrial applications or consumer products - for example, such products may be used individually or in combination with substrate layers of, e.g. an absorbent nature for underpads or the like, surgical dressings, sanitary napkins, etc. de

Having thus generally described the invention, reference will now be made to the following Examples, illustrating preferred embodiments only.

EXAMPLE 1

A length of hydrophilic non-woven fabric of cellulosic fibers, and having a weight of from 300 to 600 grains/square yard, and of a generally rectangular shape grains/square yard, and of a generally rectangular shape suitable for use as a diaper liner was provided. A liquid repellent composition was formulated based on the product marketed under the trade mark "KROMYL-S" in a solvent (water) at a concentration of 1 percent active. The above-described non-woven material was impregnated to a wet pick-up of 250 percent. The treated material was then subjected to a drying step at 140.degree.C. to permit evaporation of the solvent. After testing, it was found that the material was substantially hydrophobic throughout.

The thus-obtained hydrophobic non-woven fabric material was then treated in spaced-apart areas with a solution of a wetting agent composition. This latter composition was formulated based on the product marketed under the trade mark "TRITON GR--5," the composition having a concentration of 0.5 percent by weight. The composition was applied to one major surface of the hydrophobic material in an area which, in actual use for a diaper liner, would be that area normally susceptible to liquid body discharge. In this embodiment, the wetting agent composition was applied to form a pattern of "dots" which were spaced-apart a distance of approximately 5 mm, the diameter of the "dots" being in the order of from about 1 to about 2 mm. The total area of the hydrophilic passages thus formed in the material amounted to approximately 10 percent of the total surface area of the non-woven fabric. Following application of the wetting agent, the material was permitted to dry and subsequently tested as described hereinafter.

Products formed according to the above procedure were tested for use as diaper liners, in which the products of the present invention were interposed between a conventional absorbent diaper and an infant's body. When in use, it was found that liquid discharges from the body which occurred readily passed through the hydrophilic passages of the diaper liner into the absorbent diaper per se; but on the other hand the particulate matter of solid body discharges did not pass through the liner to any extent. Thus, the diaper liner of the present invention prevented soiling of the underlying absorbent diaper by its properties.

EXAMPLE 2

A product according to the present invention similar to that described above was prepared. In this case, the product was tested by pouring a 1 percent sodium chloride aqueous solution onto the product. It was observed that all of the fluid passed through the spaced-apart hydrophilic channels or passages created by the hydrophilic dots and no strike-through occurred from the balance of the product. Still further, where the underlying absorbent was not totally saturated, strike-through would not occur even through the hydrophilic passages. Conversely, even when the underlying absorbent diaper was saturated, no strike-through in the area that did not have the hydrophilic passages was found, whereas this would have been the case with coarse porosity hydrophobic liners.

EXAMPLE 3

The products of this Example illustrate a further form of this invention, in which there is provided but a single large area of a hydrophilic nature surrounded by a hydrophobic area.

In one form, a hydrophobic non-woven fabric similar to that of Example 1, was treated with a solution of a wetting agent composition as described in that Example. In that case, the solution was applied to an eliptically shaped area of the material, generally centrally located of the material. The total area of the hydrophobic material which was treated was approximately 20 percent of the surface area of the material, thereby forming an eliptically shaped hydrophilic passage in the otherwise hydrophobic material. The product was then tested as a diaper liner and was found to perform satisfactorily, in that liquid discharges readily passed through the eliptically shaped hydrophilic central portion of the diaper liner, while particulate matter was retained by the liner.

A similar product to that described above was prepared, but in this case, the material used was hydrophobic in nature. Thereafter, by treating the material in the above described manner with the wetting agent, and again forming a single eliptically shaped hydrophilic passageway generally centrally located in the sheet material, which was approximately 20% of the total area of the material, the product when used as a diaper liner was found to have the advantageous properties described above.

From the above Examples, it will be evident that the products of this invention provide many advantageous features over conventional products. It will be understood that various modifications can be made to the above-described embodiments without dparting from the spirit and scope of the invention.

Claims

I claim:

1. A disposable, liquid permeable, diaper liner product comprising a length of a nonwoven fabric having opposed major surfaces, said nonwoven fabric having a sufficiently fine porosity to prevent the passage of particulate matter therethrough, a major proportion of at least one surface of said fabric being of a hydrophobic nature and the minor proportion of said one surface being of a hydrophilic nature, said proportion of said fabric of a hydrophilic nature comprising discrete, spaced apart hydrophilic areas said areas extending between said opposed surfaces of the nonwoven fabric.

2. The product of claim 1 wherein said product is incorporated as part of a further structure with said product forming the outer layer of said structure.