Fabric (woven – knitted – or nonwoven textile or cloth – etc.) – Nonwoven fabric – Including an additional nonwoven fabric
Reexamination Certificate
1999-10-19
2002-06-25
Morris, Terrel (Department: 1771)
Fabric (woven, knitted, or nonwoven textile or cloth, etc.)
Nonwoven fabric
Including an additional nonwoven fabric
C442S076000, C442S327000, C442S334000, C442S335000, C442S337000, C442S381000, C442S392000, C442S394000, C442S395000, C442S396000, C428S397000, C604S358000, C604S367000, C604S370000, C156S305000, C156S321000, C156S322000
Reexamination Certificate
active
06410465
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a moisture vapor permeable, substantially liquid impermeable composite sheet structure useful in apparel, surgical drapes, sterile wraps, packaging materials, protective covers, construction materials, and personal care absorbent articles such as diapers and sanitary napkins. More particularly, the invention is directed to a thin moisture vapor permeable film and a multiple layer fibrous substrate that combine to form a composite sheet that is durable, strong, and flexible, that acts as a barrier to liquids, bacteria, viruses and odors, and yet is also highly permeable to moisture vapor.
BACKGROUND OF THE INVENTION
Various woven and nonwoven sheet materials used in making medical drapes, medical gowns and absorbent articles, such as diapers and sanitary napkins, must be comfortable, soft, pliable and substantially liquid impermeable. The sheet materials used in medical apparel and absorbent articles function to contain the discharged materials and/or to isolate these materials from the body of the wearer or from the wearer's garments and bed clothing. As used herein, the term “absorbent article” refers to devices which absorb and contain body exudates, and, more specifically, refers to devices which are placed against or in proximity to the body of the wearer to absorb and contain the various exudates discharged from the body. Absorbent articles include disposable diapers, incontinence briefs, incontinence undergarments, incontinence pads, feminine hygiene garments, training pants, pull-on garments, and the like.
An ideal sheet material for use in medical apparel and absorbent articles will exhibit a high moisture vapor transmission rate that will reduce the build up of heat and humidity inside garments and articles made from the material. The ideal sheet material will also exhibit excellent barrier properties so as to prevent the passage or seepage of fluids, and will even prevent the passage of bacteria and viruses. The ideal material must also be strong enough so that it does not rip or delaminate under normal usage conditions regardless of whether the material is dry or wet. Where the sheet material is to be used in apparel, it is also important that the material be flexible, soft and drapable. Finally, where the sheet material is to be used in medical apparel, it is important that the sheet not generate fiber lint that might contaminate a medical environment.
PCT Publication No. WO 97/45259, which is hereby incorporated by reference, discloses a breathable composite sheet material comprised of a moisture vapor permeable thermoplastic film adhered to a fibrous substrate. The breathable thermoplastic film is primarily comprised of a polymer material selected from the group of block copolyether esters, block copolyether amides and polyurethanes. The fibrous substrate is a nonwoven sheet made primarily of a polymer fibers that are not compatible with the film, such as a polyolefin fibers. The film is adhered to the fibrous substrate by extruding a layer of the molten film-forming polymer directly onto the fibrous substrate and then mechanically engaging the film and the fibers of the substrate, as for example by pressing the molten film into the fibrous substrate in a nip formed between two rolls.
U.S. Pat. No. 5,445,874 discloses a waterproof, blood-proof and virus-proof laminate material suitable for use in protective apparel. The laminate is comprised of a moisture vapor permeable film adhered to a woven or nonwoven fabric. The preferred film is a thermoplastic polyester elastomer. The disclosed fabrics include nonwoven fabrics of polyester, nylon and polypropylene. U.S. Pat. No. 5,445,874 discloses that the film can be laminated to the fabric by powder adhesive lamination, hot melt lamination, or wet adhesive lamination.
Adhesive lamination, thermal lamination and extrusion coating methods have all been used to produce composite sheets of a fibrous nonwoven substrate and a moisture vapor permeable, substantially liquid impermeable film. It has been possible to make such composite sheets with good barrier properties so long as the moisture vapor permeable film is relatively thick (i.e., >25 microns). However, it has been difficult to make such composite sheets with thinner films without sacrificing important barrier properties. Very thin moisture vapor permeable films are desirable in a composite sheet because thinner films facilitate greater flux of moisture vapor through the composite sheet and because thinner films use less of the film material and are accordingly less expensive to produce.
Adhesive lamination is carried out in a post film formation step. For adhesive lamination to be feasible, the moisture vapor permeable film must have enough tensile strength and tear strength so that the film can be formed, wound onto a roll, and later unwound and handled during the adhesive lamination process. It is difficult to handle moisture vapor permeable films less than 25 microns (1 mil) in thickness during the adhesive lamination process without tearing the film or introducing defects into the film.
Thermal lamination of moisture vapor permeable films less than 25 microns thick has similarly resulted in composite sheet materials with inadequate barrier properties. When composite sheets are made by thermally laminating a thin film to a fibrous substrate, the thin film handling problems associated with adhesive lamination, as described above, are encountered. In addition, to carry out a thermal lamination, the film must be subjected to elevated temperatures and pressures so as to soften the film and force it into mechanical engagement with the fibrous substrate. Generally, the peel strength between the film and the fibrous substrate increases with increasing lamination temperatures and increasing nip pressures. Unfortunately, when moisture vapor permeable films with a thickness of less than 25 microns are subjected to the increased temperatures and pressures needed to obtain adequate peel strength in the composite sheet, small holes develop in the film such that the composite sheet does not exhibit the fluid barrier properties desired in a composite sheet for use in absorbent articles or medical apparel. These defects can result from non-uniform temperatures throughout the web during bonding or from high nip pressures.
A composite sheet with excellent tensile and peel strength, that does not emit loose fibers, can be produced using a carded web of staple fiber that is powder bonded with an adhesive that is compatible with the fibers of the web. The composite sheet is produced by extrusion coating the powder-bonded web with a molten thin film that is also compatible with the fibers of the web and the powder adhesive. “Compatibility” of thermoplastic materials is an art-recognized term that refers, generally, to the degree to which the thermoplastic materials are miscible with each other and/or interact with each other. “Incompatible” materials, as used herein, means materials that are substantially immiscible with each other or do not interact with each other. Incompatible materials do not wet or adhere well to each other, even when heated. As used herein, “compatible” materials are materials that are not “incompatible” with each other, as defined above. For purposes of this application, a fiber is deemed to be compatible with a synthetic adhesive or with another polymer if the adhesive or other polymer is miscible with material that comprises the majority of the fiber and if the adhesive or other polymer readily wets the fiber or if the adhesive or polymer can adhere well to the fiber.
A composite sheet, made from a powder-bonded web that has been extrusion coated with a film of a thermoplastic polymer compatible with the fibers of the web and the solidified powder adhesive, exhibits good tensile strength and low linting because the solidified powder adhesive binds all of the fibers in the web into a strong matrix. These sheets exhibit excellent peel strength because the film readily adheres to the compatible adhesive a
Lim Hyun Sung
Ostapchenko George Joseph
E. I. du Pont de Nemours and Company
Morris Terrel
Ruddock Ula C.
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