Fabric (woven – knitted – or nonwoven textile or cloth – etc.) – Coated or impregnated woven – knit – or nonwoven fabric which... – Coating or impregnation specified as porous or permeable to...
Reexamination Certificate
1997-12-03
2001-02-13
Raimund, Christopher (Department: 1771)
Fabric (woven, knitted, or nonwoven textile or cloth, etc.)
Coated or impregnated woven, knit, or nonwoven fabric which...
Coating or impregnation specified as porous or permeable to...
C442S394000, C442S395000, C442S396000, C442S370000, C442S372000
Reexamination Certificate
active
06187696
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 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, yet is also highly permeable to moisture vapor.
BACKGROUND OF THE INVENTION
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. Manufacturing and use requirements for such products often demand that the sheet material also be strong and durable. 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. 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. Finally, the ideal material must be strong enough so that it does not rip or delaminate under normal usage conditions regardless of whether the material is dry or wet.
It is known that the exterior of the sheet material used in medical apparel and absorbent articles can comprise a flexible, fluid and vapor impervious cover to prevent fluids from passing through garments and articles made from the sheet material. These outer covers are often constructed from fluid and vapor impervious films such as polyethylene. While these films do an admirable job of containing liquids, they are not pleasing to the touch and they do not readily pass moisture vapor, which makes garments and articles made with such films uncomfortable and irritating to the wearer.
Certain polymeric films have been made more acceptable for apparel and personal care applications by creating micropores in the films to make breathable (i.e., moisture vapor permeable) microporous films. In microporous films, moisture is transported through the films by way of small gaps or holes in the film. One notable microporous film composite is made from polytetrafluoroethylene that is adhered to a textile material with an adhesive, as disclosed in British Patent Application No. 2,024,100. Microporous films adhesively bonded to textile substrates have been used in a variety of apparel products, including absorbent articles, as disclosed in PCT Patent Publication Nos. WO 95/16562 and WO 96/39031.
Laminates of a microporous film and a fibrous textile substrate have a number of disadvantages, including that such laminates permit some seepage of fluids when used as the backsheet in an absorbent article. For example, when microporous film laminates are used as the backsheet of a disposable diaper, the backsheet may permit the transmission of some urine through the pores in the backsheet when an infant wearing the diaper sits down. Liquid seepage through microporous film laminates is especially likely to occur when the microporous laminate is exposed to a fluid with a low surface tension, as for example when urine in a diaper is exposed to surfactants within the diaper itself. In addition, liquid seepage worsens as moisture vapor transmission increases. This is a result of an increase in pore size or in the actual number of pores.
When fluids seep through the pores of a microporous film, bacteria, viruses, and other microbes can pass through the film along with the fluids. Likewise, the passage of fluids through laminates made with microporous films, whether the fluids are liquid or gaseous, also increases the odors that emanate from such laminates. Microbial adsorbents have been added to some microporous films in an attempt to capture microbes passing through such films, as disclosed in PCT Patent Publication No. WO 96/39031. However, it is difficult to distribute microbial adsorbents throughout a microporous film in a manner that will adsorb all microbes seeping through the holes in the film. Likewise, microbial adsorbents are unlikely to prevent the passage of odors through the pores in a microporous film.
Moisture vapor permeable films comprised of polyether block copolymers, like the film disclosed in U.S. Pat. No. 4,493,870, have an advantage in apparel and personal care applications because such films are non-porous and therefore substantially impermeable to fluids, but they permit the passage of moisture vapor. U.S. Pat. Nos. 4,725,481; 5,422,172; and 5,445,874 disclose that moisture vapor permeable polyether block copolymer films can be attached to a variety of fibrous substrates including polyester, polypropylene and nylon. Bonding methods used to join the polyether block copolymer films to the fibrous substrates include adhesive lamination, thermal lamination and extrusion coating. Adhesive lamination and thermal lamination are generally carried out in a two step process whereby the film is first formed and is subsequently laminated to the fibrous substrate. With extrusion coating, a melted film is extruded directly onto a fibrous substrate and then passed through a nip while the film is still hot in order to press the film into engagement with the fiber network of the fibrous sheet.
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 not been possible 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 significantly 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 structure, tensile strength and tear strength such that the film can be formed, wound onto a roll, and later unwound and handled during the adhesive lamination process. It is extremely difficult to handle moisture vapor permeable films less than 25 microns (1 mil) in thickness during the adhesive lamination process without introducing holes into the film. Thus, when adhesive lamination has been used to attempt to make composite sheets with thinner films, the composite sheets have not exhibited the fluid barrier properties (e.g., hydrostatic head, dynamic fluid transmission) desirable for a composite sheet designed for use in absorbent articles or medical apparel.
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 ext
Curro John Joseph
LaVon Gary Dean
Lim Hyun Sung
McKenna J. Michael
Ostapchenko George Joseph
E. I. Du Pont de Nemours and Company
Raimund Christopher
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