Fabric (woven – knitted – or nonwoven textile or cloth – etc.) – Woven fabric – Including a foamed layer or component
Reexamination Certificate
1998-11-16
2001-05-22
Copenheaver, Blaine (Department: 1771)
Fabric (woven, knitted, or nonwoven textile or cloth, etc.)
Woven fabric
Including a foamed layer or component
C428S315900, C428S316600, C442S224000, C442S372000, C442S373000
Reexamination Certificate
active
06235662
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to flexible laminate composites which are especially suited for use for water resistant, but water vapor permeable textile materials, or apparel made from the materials.
BACKGROUND OF THE INVENTION
Materials for use for rainwear are known which have a layer of expanded microporous polytetrafluoroethylene (ePTFE) or porous polypropylene, see for example, Gore, et al., U.S. Pat. No. 4,194,041 or Henn, U.S. Pat. No. 4,969,998. Expanded microporous water-repellent polytetrafluoroethylene material described in Gore, U.S. Pat. No. 3,953,566 is especially well suited for this purpose. It is liquid water repelling, but allows water vapor, in the form of perspiration, to pass through. Polyurethanes and other polymers have been used for this purpose also. To confer good flexibility on the materials for use in the textile sector, the microporous layer should be made as thin as possible. However, a thinner membrane will generally mean a loss of performance, and thin coatings run the risk of decreasing water repellency.
U.S. Pat. No. 4,194,041 describes the use of an additional coating on microporous polymers which is based on a thin, air-impermeable coating composed of a polyetherpolyurethane or polyperfluorosulfonic acid that transports water vapor molecules by diffusion. The thin coating is employed to reduce transmission of surface active agents and contaminating substances through the polymers. Owing to the chemical structure of the polymer, the monolithic coating on the microporous structure exhibits a high transport of water molecules, (high permeability to water vapor) through the polymers material. This film should be applied as thinly as possible in order not to affect the flexibility, yet confer adequate protection on the composite. Furthermore, water vapor permeability deteriorates greatly in the case of thicker, monoithic films.
A type of composite membrane is known from U.S. Pat. No. 4,969,998. In this membrane the material of the inner layer has in part penetrated into the pores of the microporous outer layer. As the material for the microporous outer layer, microporous expanded polytetrafluoroethylene, is proposed. As for the inner layer a polyether-polythioether is proposed. The latter material up to a certain degree fills the pores of the microporcus layer, but is consistently tight, amorphous and nonporous. It is reported that this composite has moisture vapor transmission rates which are higher than the moisture vapor transmission rates of the laminate described first. However, when the composite was used as a textile laminate for rainwear it was found that under extreme athletic load and the associated heavy formation of perspiration, the latter cannot always be dissipated to the environment without residue. The liquid perspiration remaining on the inside of the clothing adversely affects the feeling of well-being and comfort of wearing.
SUMMARY OF THE INVENTION
It is a purpose of this invention to provide flexible liquid water resistant, water vapor permeable composites having a enhanced moisture vapor transmission rate.
The composite is:
(a) a layer of a microporous polymer that is water-vapor permeable and liquid water-resistant, said layer adhered to
(b) an air-impermeable polymer layer that is water-vapor permeable, wherein said layer (b) has adhered on the side opposite layer (a)
(c) a layer of a microporous polymer that is water-vapor permeable and hydrophilic.
The microporous polymer has voids throughout the internal structure which form an interconnected continuous air path from one side to another.
It has been found that when the composite containing layer (c) is used in a garment and this layer is innermost, the moisture vapor transmission rate is unexpectedly greater from the inside to the outside than the moisture vapor transmission rate of one of other three-layer composites, not containing a hydrophilic layer. This occurrence, which is surprising, may possibly be attributed to the fact that the moisture vapor transmission rate of the middle layer (b) increases in excess proportion when liquid water is present on the boundary surface. It may be that the microporous inner layer which has hydrophilic properties acts like a type of sponge and absorbs the perspiration which forms and distributes it over larger surface areas so that the individual water molecules on the boundary layer to the inner diffusion layer pass easily or in higher concentration into solution and thus migrate or diffuse more quickly to the outer side.
Microporous layer (c) can either be inherently hydrophilic or be rendered hydrophilic using known processes, for example using the process as is described in U.S. Pat. No. 5,209,850. Processes for rendering microporous polymers hydrophilic are described in two U.S. Pat. Nos. 5,352,511 and 5,354,587. DE-A 4243955 is also concerned with rendering initially water-repellent layers of fluoropolymers hydrophilic. Other treatment procedures are described below.
In a preferred aspect the microporous polymer layers are exemplified by a porous, expanded polytetrafluoroethylene (ePTFE) film.
DETAILED DESCRIPTION OF THE INVENTION
Definitions
By “flexible” is meant easily bent, i.e., pliable.
By “liquid water resistant” is meant that the material is waterproof at a water pressure of 13.8 kN/M
2
.
By “microporous” is meant a material has very small, microscopic voids throughout the internal structure which forms an interconnected continuous air path from one surface to the other.
By “air-impermeable” is meant that no airflow is observed for at least two minutes as determined by the Gurley test described below.
By “water vapor permeable” is meant an MVTR or at least 1000 g/m
2
per 24 hr, preferably 2000 g/m
2
per 24 hr.
By “hydrophilic” material is meant a porous material whose pores become filled with liquid water when subjected to liquid water without the application of pressure.
By “adhered” is meant layer to layer surface contact or impregnation, fully or partially, of layer (b) into the pores of layer (a), as well as adherence by use of an adhesive.
Suitable microporous polymers for layers (a) and (c) herein include fluoropolymers, e.g. polytetrafluoroethylene or polyvinylidene fluorides, polyolefins, e.g. polyethylene or polypropylene; polyamides; polyesters; polysulfone, poly(ethersulfone) and combinations thereof, polycarbonate, polyurethanes. To achieve flexibility, the layers should be thin.
If the microporous polymer of layer (c) is not naturally hydrophilic, it can be rendered hydrophilic by treating it. Materials that can be used to treat the microporous polymer to make it hydrophilic include: aqueous, alcoholic or aqueous/alcoholic solutions of a copolymer of tetrafluoroethylene and vinylacetate, polyacrylic acid and copolymers thereof, polyacrylamide and copolymers thereof, polyvinyl acetate (PVA), polystyrenesulfonate; polyethylene-, or propylene glycols (PEG, PPG), hydrophilic silicones; anionic, cationic, nonionic or amphoteric surface active agents or mixtures, and complexes of the above.
Treatment with hydrophilic material is accomplished by applying a liquid form of the material, e.g., a melt, or solution or latex dispersion of the material, as, e.g. by dipping, painting, spraying, roller-coating or brushing the liquid on the surface. Application is carried out until internal surfaces of the microporous structure are coated, but not until the pores are filled as that would destroy or severely lessen the water-vapor transmitting property of the layer. Thus, the presence of the hydrophilic material has little effect on the porosity; that is, the walls defining the voids in the microporous polymer preferably have only a very thin coating of the material. Application of the material can be achieved by varying the concentration, solids content of the solution or dispersion, and/or by varying the application temperature, or pressure.
The air-impermeable polymer layer (b) is combined with the polymer layers (a) and (c) by any one of several methods. The air-impermeable polymer can be applied in
Copenheaver Blaine
Lewis White Carol A.
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