Fabric (woven – knitted – or nonwoven textile or cloth – etc.) – Nonwoven fabric – Nonwoven fabric with a preformed polymeric film or sheet
Reexamination Certificate
1998-11-25
2004-01-13
Juska, Cheryl A. (Department: 1771)
Fabric (woven, knitted, or nonwoven textile or cloth, etc.)
Nonwoven fabric
Nonwoven fabric with a preformed polymeric film or sheet
C442S395000, C442S398000, C442S399000
Reexamination Certificate
active
06677258
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 moisture vapor permeable film and fibrous substrate that combine to form a composite sheet that is durable, strong, and flexible, that acts as a barrier to liquids, bacteria and odors, yet is also highly permeable to moisture vapor. The invention is also directed to an absorbent article having a backsheet made of the aforementioned composite sheet of the invention.
BACKGROUND OF THE INVENTION
Sheet materials used in making medical drapes, medical gowns and absorbent articles, such as diapers and sanitary napkins, must be both comfortable and substantially liquid impermeable. Manufacturing and use requirements for such products often demand that the sheet material also be strong and durable.
Infants and other incontinent individuals wear absorbent articles to receive and contain urine and other body exudates. Absorbent articles function both to contain the discharged materials and to isolate these materials from the body of the wearer and from the wearer's garments and bed clothing. Disposable absorbent articles having many different basic designs are known to the art. It is also known that the exterior of absorbent articles can be covered with a flexible, fluid and vapor impervious sheet to prevent any absorbed fluid from passing through the article and soiling adjacent articles such as clothing, bedding and the like. These outer covers, generally referred to as backsheets, are often constructed from fluid and vapor impervious films such as polyethylene.
While plastic 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 made with plastic films uncomfortable and irritating to the skin. Plastic films have been made more acceptable for apparel and personal care applications by creating micropores in the films to make breathable 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 their manufacture requires a separate adhesive bonding step after the film is made, and that such laminates permit some seepage of fluids when used as the backsheet in an absorbent article. For example, when such microporous film laminates are used as a 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.
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 medical 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. No. 4,725,481 suggests that such films may be attached to a textile fabric by adhesive bonding or melt bonding. However, the cost of making such films and then bonding the films to fibrous textile substrates has been high relative to microporous film laminates. In addition, known moisture vapor permeable films like the films disclosed in U.S. Pat. Nos. 4,725,481 and 5,445,874 do not readily adhere to many common nonwoven substrate materials, such as polyolefin-based nonwoven materials, without the application of a separate adhesive.
PCT Patent Publication No. WO 95/16746 (assigned to E. I. duPont de Nemours & Company (hereinafter “DuPont”)) discloses a composition of a polyether block copolymer combined with a less costly thermoplastic homopolymer so as to make an overall film that is less costly, more heat sealable and more adherable to itself and other substrate materials. However, PCT Patent Publication No. WO 95/16746 does not disclose strong and durable composite sheets of thin breathable films that have been extruded directly onto fibrous substrates, nor does it disclose a method for making such composite sheets.
There is a need for a sheet material that acts as a barrier to fluids, yet is also highly permeable to moisture vapor. There is also a need for a sheet material that readily transmits moisture vapor, but significantly deters the passage of bacteria and odors associated with such fluids. There is a further need for such a moisture vapor permeable, fluid impermeable composite sheet material that is also durable, strong, and flexible enough to be used in absorbent articles, and can be produced in an economical fashion, i.e., without the use of adhesives to join the layers of the composite sheet in a separate step. Finally, there is a need for an absorbent article that incorporates such a moisture vapor permeable composite sheet in the article's backsheet, leg cuffs, waistshields, or other features.
SUMMARY OF THE INVENTION
The invention provides a moisture vapor permeable, substantially liquid impermeable composite sheet material comprising a fibrous substrate and a moisture vapor permeable thermoplastic film layer. The fibrous substrate is comprised of at least 50% by weight polyolefin polymer fibers. The moisture vapor permeable thermoplastic film layer is melt bonded directly to one side of said fibrous substrate. The composite sheet exhibits a peel strength of at least 0.1 N/cm, a dynamic fluid transmission of less than about 0.75 g/m
2
when subjected to an impact energy of about 2400 joules/m
2
, and a moisture vapor transmission rate, according to the desiccant method, of at least 200 g/m
2
/24 hr, preferably at least 1500 g/m
2
/24 hr.
Preferably the film layer of the composite sheet has an average thickness of less than 50 microns and is comprised of at least 50% by weight of polymer selected from the group of block copolyether esters, block copolyether amides, polyurethanes, and combinations thereof. It is further preferred that the film layer be melt bonded to the substrate in the absence of an adhesive between the film layer and the substrate. The more preferred composite sheet has a peel strength of at least 0.15 N/cm, a film thickness of less than 30 microns, and a moisture vapor transmission rate, according to the dessicant method, of at least 2500 g/m
2
/24 hr, and a dynamic fluid transmission of less than about 0.5 g/m
2
when subjected to an impact energy of abo
Carroll Nora Liu
Curro John Joseph
Lavon Gary Dean
Lim Hyun Sung
Mc Kenna J. Michael
E. I. du Pont de Nemours and Company
Juska Cheryl A.
Pratt Christopher C.
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