Nonwoven fabrics have been used for a wide variety of applications for at least fifty years. Nonwoven fabrics are textile-like materials produced directly from a web of fibers so as to eliminate the many time consuming steps involved in converting staple length fibers into woven or knitted goods. In one method of making a nonwoven fabric, a web of fibers is produced, e.g. by carding or air laying techniques, and the fibrous web is then strengthened by the application thereto of a polymeric binding agent. In another method of making a nonwoven, the fibrous web is subjected to fluid forces which serve to entangle the fibers, thus providing strength to the finished material. Nonwoven fabrics are inherently porous structures, i.e. they comprise openings or pores allowing for the passage of fluids such as air and water or aqueous solutions. In addition, nonwoven fabrics may be tailored so as to have good softness, drapeability, and tactile impression. Owing to their desirable characteristics, nonwovens have been employed as facing materials for absorbent products such as disposable diapers, sanitary napkins, incontinent devices, wound dressings and the like.
More recently, efforts have been made to produce porous or liquid-permeable facing materials for absorbent products by using plastic films as the starting materials. For example, it is known to produce an apertured plastic film by placing a heated thermoplastic sheet material on a patterned perforated surface and applying a vacuum thereto. The vacuum pulls the softened sheet material through the perforations, thereby causing the film to rupture and form apertures.
U.S. Pat. No. 3,929,135 to Thompson et al discloses perforated topsheet materials for absorptive devices such as sanitary napkins, incontinent pads, bandages and the like. These topsheet materials are constructed from liquid impervious materials such as low density polyethylene and comprise a plurality of tapered capillaries each of which has a base opening in the plane of the top sheet and an apex opening which is remote from the plane of the top sheet. The tapered capillaries disclosed by Thompson et al. are preferably provided in the form of a frustum of a conical surface and have an angle of taper of from about 10.degree. to 60.degree..
U.S. Pat. No. 4,324,276 to Mullane discloses an apertured formed film having a caliper of less than about 0.030 inch (0.075 cm), an open area of at least 35% and a plurality of apertures at least 75% of which have an equivalent hydraulic diameter (EHD) of at least 0.025 inch (0.064 cm). The apertured formed film disclosed by Mullane et al. is useful as a topsheet for disposable absorbent products of the type mentioned above.
U.S. Pat. No. 4,839,216 to Curro et al. discloses a debossed and perforated plastic material produced by providing a starting film on a perforated forming surface and applying an unconstrained liquid stream to the upper surface of the starting film. The liquid stream has sufficient force and mass flux to cause the film to be deformed toward the forming surface, such that the material acquires a substantial three-dimensional conformation, and to cause perforations to be created therein.
European Patent Application 0 304 617 in the name of Kao Corporation discloses a covering sheet for a sanitary article. The covering sheet comprises an opaque, hydrophobic film having land portions and recesses, said recesses being formed to have a bottom portion and side walls. The side walls have a slanting part which is provided with an opening such that the slanting part is not covered by the land portion. This patent states that the opening is always exposed to sight when it is looked down at.
U.S. Pat. No. 4,690,679 discloses an apertured film comprising a first layer of a first polymeric film and a second layer of a second polymeric film. Apertured films wherein the apertures have average equivalent circular diameters ranging from about 0.010 inches (0.0254 cm) to about 0.030 inches (0.0762 cm) are disclosed as being useful as covering materials for absorbent products.
Other patents relating to apertured films and methods and apparatus for making the same include U.S. Pat. No. 3,632,269 to Doviak et al. and U.S. Pat. No. 4,381,326 to Kelley.