Process for making a breathable absorbent article

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Reexamination Certificate

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Reexamination Certificate

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06447901

ABSTRACT:

The present invention provides a method of making a breathable absorbent article comprising a backsheet consisting essentially of a nonwoven material, in which positioning adhesive is applied directly to the backsheet by slot coating.
BACKGROUND OF THE INVENTION
Breathable absorbent articles, such as sanitary napkins and pantiliners, are those made with backsheets that are permeable to vapors, such as water vapor and air, and are impermeable to liquids. Such backsheets may be made of hydrophobic nonwoven materials, microporous films, or a variety of laminates. They provide the obvious advantage of improved comfort to the wearer. However, application of positioning adhesive, i.e., the adhesive applied to the garment-facing side of the backsheet to attach the absorbent article to the user's underwear, has proved to be a challenge. This is because positioning adhesives applied by typical coating methods tend to form a substantially continuous layer over the backsheet, impairing its vapor permeability and increasing subsequent transfer of the positioning adhesive to the user's underwear. This has limited the types of positioning adhesives and the methods by which they can be applied to breathable absorbent articles.
One sanitary napkin marketed in the United States and having a nonwoven backing is the Stayfree Classic, available from Personal Products Company. This sanitary napkin has a backsheet comprising a nonwoven material covering a plastic barrier. Positioning adhesive is applied to the nonwoven material in three, separated strips by slot coating. Slot coating is the continuous, direct coating of material onto a surface. During slot coating, the coating nozzle is in direct contact with the surface and a continuous stream of adhesive is extruded or pumped through the nozzle onto the receiving surface.
Positioning adhesive can also be applied to a nonwoven material by transfer coating. Positioning adhesive is coated onto a release paper and then transferred to the backsheet when the release paper is united with the absorbent article. However, even with this method subsequent transfer of the positioning adhesive to the wearer's underwear is a problem, especially since nonwoven materials are generally irregular and non-flat. Positioning adhesive, when transfer coated to the nonwoven material, remains only on the outer surfaces nonwoven material, failing to adhere to the entire surface of the nonwoven material. This leads to weak adhesive anchorage to the nonwoven material and subsequent delamination of the positioning adhesive. This is further exacerbated in absorbent articles that use vacuum formed and/or macerated pulp as the absorbent core, because the garment-facing surface of the absorbent article is macroscopically uneven and does not allow proper anchorage of positioning adhesive.
Applicant has now discovered that, unexpectedly, positioning adhesive may be directly applied to a backsheet consisting essentially of a nonwoven material by slot coating, such that the positioning adhesive forms a discontinuous layer on the nonwoven material, In this manner, both the breathability of the backsheet and the adherence of the backsheet to fabric substrates are maintained. A breathable absorbent article made according to the invention exhibits little or no positioning adhesive transfer to a user's undergarment or skin. The nonwoven backsheet has the appropriate properties to withstand direct application of positioning adhesive and offer a proper surface for receiving the positioning adhesive. An absorbent article made according to the invention also delivers better stability during use, due to reduced bunching.
SUMMARY OF THE INVENTION
The invention provides a method of making a breathable absorbent article comprising a cover, an absorbent core and a backsheet consisting essentially of a hydrophobic nonwoven material, which comprises applying positioning adhesive to the backsheet at a viscosity in the range of about 1000 to 1500 cps by slot coating.
The invention also provides a breathable absorbent article made by this method.
DETAILED DESCRIPTION OF THE INVENTION
The absorbent article may for example be a sanitary napkin, pantiliner, diaper, incontinence pad, interlabial article, or other similar product for absorbing exudates from the body, such as menses, urine, and feces. Preferably, the absorbent article is a sanitary napkin or a pantiliner. Such sanitary napkin or pantiliner may have an approximately rectangular, oval, dogbone, or peanut shape.
The absorbent article is made from a body-facing cover sheet, an absorbent core, a backsheet, and positioning adhesive. The absorbent article may comprise other known materials, layers, and additives, such as transfer layers, foam layers, net-like layers, fragrances, odor control agents, antimicrobial agents, medicaments, superabsorbents, and the like. The absorbent article may also comprise wings, tabs, or other lateral extensions as known in the art. The absorbent article can optionally be embossed with decorative designs using conventional techniques.
The absorbent core may comprise one or more layers of a variety of known absorbent materials, for example cellulose fibers, including wood pulp, regenerated cellulose fibers, and cotton fibers, polyethylene fibers, polypropylene fibers, polyester fibers, bicomponent fibers, acrylic fibers, polyvinyl alcohol fibers, peat moss and superabsorbent polymers. Combinations of these absorbent materials may be used as well. The absorbent core can be thermobonded, latex bonded, or a combination of the two, or bonded and densified in any other manner as desired.
The backsheet consists essentially of a nonwoven material. As used herein, “nonwoven material” means a fibrous, nonwoven web formed by entangling fibers of filaments, such as by spunbonding, carding or hydroentangling. A wide range of nonwoven materials are known, and any of these may be employed. Preferred nonwoven materials are made from synthetic monocomponent and/or multicomponent fibers, including polyethylene, polypropylene, polyester, and cellulose. More preferably, the nonwoven material comprising fibers selected from the group consisting of polyethylene, polypropylene, and combinations thereof.
The basis weight of the backsheet preferably ranges from about 25 to about 200 grams per square meter (gsm), more preferably from about 25 to about 60 gsm, most preferably from about 40 to 60 gsm. Generally, the backsheet has a width sufficient to cover the garment-facing side of the absorbent article. The backsheet may extend around the sides of the absorbent core in a C-shaped configuration with the portions of the backsheet that are adjacent its longitudinal edges extending upwardly from the garment-facing side toward the body-facing side of the absorbent article.
The absorbent article also comprises a liquid permeable cover formed from any fluid pervious material that is comfortable against the skin and that permits fluid to penetrate to the absorbent core. A variety of materials are known for this purpose, and any of these may be used. The cover should retain little or no fluid in its structure to provide a relatively dry surface next to the skin. The cover may comprise a nonwoven material. Alternatively, the cover may be formed from an apertured polymeric film. The thickness of the cover may vary from approximately 0.001 to 0.062 inch, depending on the material chosen. Generally, the liquid permeable cover is a single sheet of material having a width sufficient to cover the body-facing side of the absorbent article.
Positioning adhesive is applied to the garment-facing side of the backsheet, opposite the absorbent core. According to the invention, the positioning adhesive is applied by slot coating directly to the nonwoven material. The viscosity of the positioning adhesive during coating is in the range of about 1000 to 1500 cps, preferably from about 1000 to about 1200 cps. Typically, the positioning adhesive is applied at a temperature in the range of about 160 to 175° C. The basis weight of the positioning ad

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