FIELD OF THE INVENTION

The present invention relates to a nonwoven substrate treated with a particular surfactant for enhanced absorbent intake. The substrate of the present invention can be used in a variety of personal care articles comprising an absorbent component.

BACKGROUND OF THE INVENTION

Nonwoven materials have often been used in disposable, personal care articles to collect body fluids. Certain fluids, however, such as menses and runny BM (feces) have viscoelastic properties that present a challenge for many manufacturers when trying to capture the right level of absorbency without leakage. In addition to problems with leakage in some disposable, personal care articles, there are also hygienic issues that directly affect the user. Often the body fluid sits in direct contact with the user which makes for an unpleasant and unclean feel. Particularly with feminine hygiene products such as sanitary napkins, the unpleasant or unclean feeling may lead to poor perception in product performance and the inability to get maximum use from the product.

Often, polymeric nonwoven fabrics are employed in the construction of personal care products; however, most of these fabrics are normally hydrophobic and are water-repellant. Open-cell, polymeric foam materials have a cellular structure that is very resilient and soft and could be beneficial for use in personal care articles such as feminine hygiene products like sanitary napkins. A polyester, polyurethane open-cell foam that is hydrophobic would have the desirable resilience but would become suitable for application in a personal care article if the foam could be treated with a suitable surfactant to obtain the desired degree of hydrophilicity to make the foam wettable. The application of this wettable foam in the personal care article would be more beneficial to the wearer compared to a conventional nonwoven substrate. The challenge is to provide an article that promotes a dry, healthy environment at the material/skin interface.

Accordingly, there is a need to improve the hydrophilicity or wettability of a nonwoven substrate that is to be used in a personal care article that will not only improve absorbency but will also promote a dryer environment, particularly when the substrate used will not be in direct contact to the skin of a wearer.

SUMMARY OF THE INVENTION

The present invention relates to a hydrophobic, open-cell, polyurethane foam treated with from about 0.3% to about 3.0% of a nonionic surfactant to create a personal care absorbent article with enhanced intake properties. It is preferred that the nonionic surfactant of the present invention comprises at least an ethoxylated linear oleochemical alcohol or an ethoxylated acetylenic diol. The foam of the present invention provides enhanced absorbency characteristics that can be utilized in a number of personal care articles, especially feminine care pads.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention is set forth more particularly in the remainder of the specification, including reference to the accompanying figures, in which:

FIGURE 1 shows a cross-sectional SEM image at 20 times magnification of a polyurethane, hydrophobic foam of the present invention with an average cell size of 200 microns measured from scanning electron micrographs.

FIGURE 2 shows a cross-sectional SEM image at 20 times magnification of a polyurethane, hydrophobic foam of the present invention with an average cell size of 250 microns measured from scanning electron micrographs.

DETAILED DESCRIPTION OF THE INVENTION

While the specification concludes with the claims particularly pointing out and distinctly claiming the invention, it is believed that the present invention will be better understood from the following description.

All percentages, parts and ratios are based upon the total weight of the compositions of the present invention, unless otherwise specified. All such weights as they pertain to listed ingredients are based on the active level and, therefore; do not include solvents or by-products that may be included in commercially available materials, unless otherwise specified. The term "weight percent" may be denoted as "wt. %" herein. Except where specific examples of actual measured values are presented, numerical values referred to herein should be considered to be qualified by the word "about".

As used herein, "comprising" means that other steps and other ingredients which do not affect the end result can be added. This term encompasses the terms "consisting of and "consisting essentially of". The compositions and methods/processes of the present invention can comprise, consist of, and consist essentially of the essential elements and limitations of the invention described herein, as well as any of the additional or optional ingredients, components, steps, or limitations described herein.

As used herein, the phrase "absorbent article" generally refers to devices which absorb and contain body fluids, and more specifically, refers to devices which are placed against or near the skin to absorb and contain the various fluids discharged from the body and, in particular, viscoelastic fluids. Examples of absorbent articles include, but are not limited to, absorbent articles intended for personal wear, such as diapers; incontinence products; feminine hygiene products, such as feminine napkins, panty liners, tampons, and interlabial pads; other personal garments; and the like.

As used herein, "fouling" means the change in permeability of a fluid as it passes through a porous medium. More particularly, fouling is the reduction in permeability that occurs when components of a fluid pass through a porous medium and interact with the material structure, decreasing the inherent permeability of the porous material.

The term "hydrophilic", as used herein, refers to surfaces with water contact angles well below

90°.

The term "hydrophobic", as used herein, refers to the property of a surface to repel water with a water contact angle from about 90° to about 120°.

As used herein, "rewetting" refers to the amount of fluid that comes from the absorbent core back into and through the top layer, nonwoven surface. This may also be referred to as "flowback".

The use of any trademarks herein has been noted with CAPITALIZATION of the word wherever it appears to acknowledge and respect the proprietary nature held by the owners of the mark. The word is followed by the generic terminology only wherever it appears for the first time herein.

The present invention relates to an improved absorbent substrate that can be utilized in or as a variety of personal care products, particularly disposable absorbent articles, and more specifically, feminine hygiene products including feminine napkins, panty liners and interlabial pads. Personal care products of the present invention include, but are not limited to, feminine hygiene products like sanitary wipes and menses absorbing devices (e.g., sanitary napkins and tampons), infant and child care products such as disposable diapers, absorbent underpants, and training pants, wound dressings such as bandages, incontinence products, products for wiping and absorbing oils, and the like.

Specifically, the present invention relates to a hydrophobic, open-cell, polyurethane foam treated with from about 0.3% to about 3.0% of a nonionic surfactant, said nonionic surfactant comprising at least an ethoxylated linear oleochemical alcohol such as an alkylphenol ethoxylate, such as LUTENSOL® A65N, commercially available from BASF, or an ethoxylated acetylenic diol such as SURFYNOL® 465, commercially available from Air Products, Allentown, Pennsylvania, to treat the foam and arrive at the present invention. Not only is the present invention particular about the type of surfactant but has also discovered the particular add-on concentration level that should be used to enhance the intake of body fluids, particularly menses, into the foam. Thus, the foam of the present invention is treated with a nonionic surfactant at a concentration of about 0.3%, about 0.8%, about 1.6%, about 2.0% or about 3.0%. The concentration levels are critical to the ability for the foam to become hydrophilic in order to provide the intake function desired by the foam.

The present invention provides an advantage in that it employs the appropriate surfactant at the optimal concentration level to provide a foam that was contrary to the known characteristics that are typical of a hydrophobic foam and provides surprisingly advantageous results that were never before realized. The significance and advantage of the present invention versus previous foams is that the foam of the present invention provides a more durable and flexible absorbent material that has enhanced performance capabilities. The foam absorbent minimizes mismatch in deformational characteristics between the intake layer (IL) and body-side liner (BSL), thus reducing air gaps and resistance to flow.

As shown in table 1 below, common surfactants were used on the foam with comparative results founded by the present invention. In fact, the table identifies surfactants (by trade name) that are not nonionic and with characteristics that are inherent or could likely be predicted in a hydrophobic foam, i.e., they do not alter the wettability or cause the foam to be hydrophilic and thus did not have the functioning properties desired of being able to intake body fluids, specifically menses. The table shows and compares the results of LUTENSOL® A65N, STANDAPOL® 215, an anionic surfactant sodium lauryl sulfate, commercially available from BASF, SILASTOL® 207, a hydrophilic finish, commercially available from Schill and Seilacher, and SILASTOL® 163, an anionic surfactant dioctyl sodium sulfosuccinate, commercially available from Schill and Seilacher. As the results show, LUTENSOL® A65N was the only chemical found to have the effect needed to provide the improved substrate as desired to reach the presently claimed invention. The combination of the foam, concentration and particular surfactant have been discovered that provides an absorbent foam which, can be used as an absorbent personal care product or as an enhanced intake layer in a personal care absorbent garment.

Surfactant Add-on Wettability 1 ^st Intake 2 ^nd Intake Rewet (g) level time (sec) time (sec)

%

LUTENSOL® A65N

0.3 wettable 43 18 2.6

0.8 wettable 24 16 2.4

1.6 wettable 22 17 2.5

2.0 wettable 8 14 1.7

3.0 wettable 7 12 2.0

STANDAPOL® 215

0.1 Not wettable — — — 0.3 Not wettable — — —

1.0 Not wettable — — —

SILASTOL® 207

0.5 Not wettable — — —

1.0 Not wettable — — —

1.3 Not wettable — — —

1.6 Not wettable — — —

SILASTOL® 163

0.6 Not wettable — — —

0.7 Not wettable — — —

0.9 Not wettable — — —

1.4 Not wettable — — —

1.9 Not wettable — — —

2.0 Not wettable — — —

The foam of the present invention provides an enhanced intake and rewet performance by selectively finding the appropriate surfactant type and add-on level that would provide the novel attributes desired. The foam of the present invention is particular to that which is an open-cell or porous, polyester polyurethane, hydrophobic foam. Such foam can be made by the reaction of a polyester polyol with a toluene diisocyanate. As shown in FIGS. 1 and 2, the average cell size of the foam will be from about 100 microns, from about 150 microns or from about 200 microns mm to about 250 microns, 300 microns, or from about 350 microns and the thickness of the foam will be about 1.0 mm, about 1.5 mm, or about 2.0 mm. Although various basis weights can be used, it is recommended that the basis weight of the foam be about 45 gsm, about 50 gsm or about 55 gsm with a density of about 0.02 g/cc, about 0.03 g/cc or about 0.05 g/cc and an average pore size of about 200 microns, about 250 microns or about 300 microns.

It is desirable that the foam is imparted with a durable hydrophilic treatment so that the foam can be used as an absorbent product, as a disposable, absorbent personal care product or within disposable, absorbent personal care and non-personal care products. The term "durable" as used herein with reference to a coating of the foam means that the coated porous foam remains wettable after multiple exposure to an aqueous medium, such as water, saline, urine, and other body fluids.

The hydrophilicity of the coating on the substrate may vary and can be varied in a controlled manner across at least one dimension of the porous foam. For example, a coated porous foam may have a central region of higher hydrophilicity which extends, for example, along the length of the substrate, with regions of lower hydrophilicity on both sides of the central region. Thus, the hydrophilicity of such a substrate would vary in a controlled manner across the width thereof. The method for preparing a treated porous foam of the present invention involves providing a porous, hydrophobic polymer substrate and exposing at least a portion of the foam to a non-ionic surfactant. The treatment composition may further include other components, such as wetting agents, emulsifiers, lubricants, anti-stats, skin care ingredients, anti-oxidants, vitamins, botanical extracts, scents, odor control agents, color, anti-microbials, and the like. Exemplary methods of treating the foam of the present invention with the non-ionic surfactant may be by spray coating, "dip and squeeze", foaming, or the like. Such methods that can be used to treat the foam of the present invention are described in detail in USP 7,018,945 to Yahiaoui et al.

The "dip and squeeze" method is the preferred method of the present invention as it showed more success in rendering the foam uniformly hydrophilic as compared to other methods that could be employed. While other methods can be used, the present invention found the results to be inconsistent with significant variation in the uniformity of the treatment. Additionally, the "dip and squeeze" method is able to uniformly treat the foam by forcing the large volume of air out of the hydrophobic foam structure and replaces the air volume entirely by the aqueous surfactant solution. The excess surfactant fluid is then removed by squeezing the foam after it is removed from the solution bath thereby leaving a thin surfactant film on all surfaces of the foam. After drying the foam, the surfactant is left on the surface making it wettable.

EXAMPLES

The following examples further describe and demonstrate embodiments within the scope of the present invention. The examples are given solely for the purpose of illustration and are not to be construed as limitations of the present invention, as many variations thereof are possible without departing from the spirit and scope of the invention. EXAMPLE 1

A nonionic surfactant LUTENSOL® A65N was applied to the open-cell polyester polyurethane substrate at various concentration levels using the "dip and squeeze" method in which the polyurethane foam is completely submerged into a bath of the aqueous nonionic surfactant solution with a concentration level of 3.0%. Pressure is applied onto the foam web while it is still submerged followed by a squeezing of excess surfactant solution while the foam substrate is taken out of the surfactant solution bath. The foam substrate was then dried. The concentration of the surfactant on the foam after drying was 2.0%. The "dip and squeeze" treatment, as described, are for open-cell polyester polyurethane foams but could also apply to polyether polyurethane foam as well as other hydrophobic foam substrates such as polyolefin foams. EXAMPLE 2

The wettability, fluid intake time and fluid rewet properties of the foam was measured using a menses simulant that was made of swine blood diluted to a hematocrit level of 30% by volume, with sheared, thick egg white added to mimic the mucin component of menses. This simulant is available from Cocalico Biologicals, Inc. of Reamstown, Pennsylvania. The wettability of the foam was screened by placing a drop of menses simulant on the surface of the foam and measuring the time taken for the drop to be taken into the foam structure. Drop intake time of less than 10 seconds was considered to be wettable and further intake measurements were done by simulating an absorbent composite. To test the effectiveness of the treatment in making the foam hydrophilic an absorbent composite was simulated by placing a nonwoven sheet on top of the foam followed by an absorbent airlaid under the foam. The intake properties were measured using the flat intake test method STM00205 and the rewet properties were measured by STM00371 (Details on patents disclosing these methods to be provided). Menses simulant was used as the fluid for the test and 7 ml of fluid in total was insulted; the first insult being 2 ml followed by a trickle of 3 ml and another insult of 2 ml. The time taken for the fluid to be absorbed was recorded as the intake time for the two insults. A blotter paper was placed on the structure and a pressure of 0.5 psi was applied and the fluid transferred from the system to the blotter paper was identified as the amount of fluid rewet.

The dimensions and values disclosed herein are not to be understood as being strictly limited to the exact numerical values recited. Instead, unless otherwise specified, each such dimension is intended to mean both the recited value and a functionally equivalent range surrounding that value. For example, a dimension disclosed as "40 mm" is intended to mean "about 40 mm".

All documents cited in the Detailed Description of the Invention are, in relevant part, incorporated herein by reference; the citation of any document is not to be construed as an admission that it is prior art with respect to the present invention. To the extent that any meaning or definition of a term in this written document conflicts with any meaning or definition of the term in a document incorporated by reference, the meaning or definition assigned to the term in this written document shall govern.

While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.