Wettable article

Details Wettable article Wettable article

1999-03-25

2002-06-11

Ruhl, Dennis (Department: 3761)

Surgery

Means and methods for collecting body fluids or waste material

Absorbent pad for external or internal application and...

C427S002310, C427S180000, C427S202000, C427S414000

Reexamination Certificate

active

06403858

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to an article, such as a film or a fibrous web.
Polymers are used extensively to make a variety of products which include blown and cast films, extruded sheets, injection molded articles, foams, blow molded articles, extruded pipe, monofilaments, and nonwoven webs. Some of such polymers, such as polyolefins, are naturally hydrophobic, and for many uses this property is either a positive attribute or at least not a disadvantage.
There are a number of uses for polymers, however, where their hydrophobic nature either limits their usefulness or requires some effort to modify the surface characteristics of the articles made therefrom. By way of example, polyolefins, such as polyethylene and polypropylene, are used to manufacture polymeric fabrics which are employed in the construction of such disposable absorbent articles as diapers; incontinent care products; feminine care products, such as sanitary napkins and tampons; filter elements; wipes; surgical gowns and drapes; protective pads; wound dressings, such as bandages; and the like. Such polymeric fabrics often are nonwoven webs prepared by, for example, such processes as meltblowing, coforming, and spunbonding. Frequently, such polymeric fabrics need to be wettable by water. Wettability can be obtained by spraying or otherwise coating (i.e., surface treating or topically treating) the fabric with a surfactant solution during or after its formation, and then drying the web.
Some of the more common topically applied surfactants are nonionic surfactants, such as polyethoxylated octylphenols and condensation products of propylene oxide with propylene glycol, by way of illustration only. These surfactants are effective in rendering normally hydrophobic polymeric fabrics wettable. However, the surfactant is readily removed from the fabric, often after only a single exposure to an aqueous liquid.
Substantial efforts have been directed to increasing the durability of surfactants which are topically applied to a polymeric fabric. Such efforts include the following, by way of illustration:
(1) use of a composition which includes water, a primary surfactant, and a cosurfactant which is functional to wet the fabric with the composition and which provides for substantially uniform distribution of the primary surfactant onto the polymeric fabric;
(2) use of a surfactant, with or without a nonionic cosurfactant, which is the reaction product of an acid anhydride derivative, such as a substituted succinic anhydride, with a polyhydroxy compound, such as sorbitol, a polyethylene glycol, triethanolamine, a polyhydroxyamine, certain primary and secondary amines, and certain unsaturated aliphatic sulfo compounds;
(3) use of a surfactant, with or without a nonionic cosurfactant, which is the reaction product of certain unsaturated aliphatic sulfo compounds with the reaction product of an acid anhydride derivative, such as a substituted succinic anhydride, with a polyamine having at least one NH group capable of addition to a double bond;
(4) use of a surfactant mixture which includes an ester-acid, ester salt, or a mixture thereof, and an amidic-acid, amidic salt, or mixture thereof, with or without a nonionic cosurfactant; and
(5) use of a surfactant mixture which includes a sorbitol succinate surfactant, such as an ethoxylated amino sorbitol succinate salt or an alkenyl succinate anhydride ethoxylated fatty amine salt, and a cowetting aid which can be, for example, a silicone polyether or a primary or secondary alcohol having up to about 8 carbon atoms.
In addition to water wettability, many absorbent, i.e., porous, products are concerned with, at least to some degree, the rate at which the aqueous liquid penetrates the porous product. For example, when the porous product is a nonwoven web or other fibrous material, the liquid must penetrate between the fibers of the web. A porous substrate in which an aqueous liquid penetrates at a rapid rate will be more effective in absorbing large volumes of liquid delivered over a short period of time, and, as a consequence, more effective in preventing or minimizing leakage. Furthermore, a porous substrate which quickly absorbs liquid will allow other components of an absorbent product to more effectively move liquid away from the locus of liquid insult to the remainder of the absorbent product. Therefore, more of the absorbent product will be available for absorption of the liquid.
It is known that the rate of penetration of a liquid into a porous substrate is directly proportional to the surface tension of the liquid and the cosine of the contact angle that the liquid makes with the surface of the substrate (see, e.g., A. W. Adamson, Chapter XIII, “Wetting, Flotation, and Detergency” in “Physical Chemistry of Surfaces,” Fifth Edition, John Wiley & Sons, New York, 1990, pp. 495-496). Lowering the surface tension of the liquid, therefore, has an adverse effect. On the rate of liquid penetration. That is, when the surface tension of the liquid is decreased, the driving force of liquid penetration also is decreased. The cosine of the contact angle, on the other hand, is at a maximum value of 1 when the contact angle is zero. As the contact angle increases, the cosine decreases, approaching zero as the contact angle approaches 90°.
The methods of making a polymeric substrate wettable as described above all involve reducing the surface tension of the liquid to a value which is approximately the same as or lower than the surface free energy of the substrate to be wetted by the liquid. Such methods also lower the contact angle. However, as already noted, lowering both the surface tension of the liquid and the contact angle is counterproductive with respect to the rate of liquid penetration. Thus, there is a need for materials which are wettable and exhibit a rapid uptake of liquid.
SUMMARY OF THE INVENTION
The present invention addresses some of the difficulties and problems discussed above by providing a wettable article which also has a rapid rate of liquid penetration. Wettability and rapid liquid penetration properties are achieved by minimizing the reduction in the surface tension of an aqueous liquid coming in contact with the article while maintaining a small contact angle that the liquid makes with the surface of the article.
Accordingly, the present invention provides a wettable article consisting of an article with a hydrophobic surface having a coating which includes a surface free energy modifier and a surface-active agent. The hydrophobic surface may be composed of a hydrophobic polymer. The surface free energy modifier has a surface free energy greater than that of the surface of the article, but less than the surface tension of an aqueous liquid to which the wettable article may be exposed, and desirably is present in an amount sufficient to substantially cover the surface of the article. The surface-active agent is present in an amount effective to lower the surface tension of the liquid to a value which is greater than the surface free energy of the surface of the article and equal to or less than the surface free energy of the surface free energy modifier.
The article may be, by way of example only, a film or a fibrous sheet. The fibrous sheet may be a woven or nonwoven web.
The hydrophobic polymer may be, by way of example, a polyolefin. Typical polyolefins are polyethylene and polypropylene. Also by way of example, the surface free energy modifier may be a protein and the surface-active agent may be a polyethoxylated alkylphenol.
The present invention also provides a method of preparing a wettable article. The method involves forming an article by melt extrusion, at least a portion of which is formed from a polymeric composition which includes a hydrophobic polymer and a surface-active agent adapted to migrate to a surface of the article; and coating the surface of the article with a surface free energy modifier.
By way of example, the surface free energy modifier may have a surface free energy greater than that of the surface of the ar

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