Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Composite having voids in a component
Reexamination Certificate
2000-06-13
2001-07-17
Pezzuto, Helen L. (Department: 1713)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Composite having voids in a component
C428S315500, C428S319300, C428S422000, C428S423100, C428S523000, C442S077000, C442S088000
Reexamination Certificate
active
06261678
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. Nos. 4,194,041 or Henn, 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, this monolithic coating on the microporous structure exhibits a high transport of water molecules, (high permeability to water vapor) through the polymeric 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, monolithic films.
Other coatings for microporous materials are described in the art. For example, EP 0581168 (Mitsubishi) describes the use of fluorinated alkyl methacrylate and fluorinated alkyl acrylate for polyolefin membranes. The substances are physically bound to the polymer matrix and contain a crosslinking monomer. The substance is applied in the form of a solution usually in fluorinated solvents. After coating, the solvent is removed. The situation is similar with a process for treating polymers with solutions of amorphous fluoropolymers (WO 92/10532).
Solutions of fluorine-containing polymers are also involved in a patent for coating ePTFE with Teflon AF (EP 0561875). WO 91/01791 (Gelman Sciences Technology; EP 0561277 (Millipore)/U.S. Pat. No. 5,217,802 propose treating a porous membrane with a fluorine-containing monomer and a crosslinker. The treatment is followed by polymerization. Perfluoropolyethers in conjunction with ePTFE for use as water-repellent finish are mentioned in WO 92/21715.
For improved water repellency performance, oleophobicized and hydrophobicized textile substrates sprayed with fluorocarbon emulsions are mentioned in EP 0594154.
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 microporous 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 improved resistance to contaminants, especially to oil contaminants. The increased oleophobicity enhances the usefulness of the composites in garments and in separation applications.
It is another purpose of the invention to provide composites of enhanced moisture vapor transmission rate.
The composites of the invention are flexible, liquid water resistant, oleophobic, water-vapor permeable composites.
In its simplest and first embodiment, the composite is:
(a) a layer of a microporous polymer that is water-vapor permeable, oleophobic, and which is liquid water-resistant, said layer adhered to
(b) an air-impermeable polymer layer that is water-vapor permeable.
The microporous polymer has voids throughout the internal structure which form an interconnected continuous air path from one side to another.
In one embodiment, the composite of the invention is composed of solely layers (a) and (b) as defined above.
In another second embodiment, a third layer, layer (c), of a microporous polymer can be present on the other side of the air-impermeable polymer layer. Layer (c) is also water vapor permeable. It can be made of the same polymer as used in layer (a) or it can be a different polymer. Preferably it is the same.
In a preferred aspect the microporous polymer layers are exemplified by a porous, expanded polytetrafluoroethylene (ePTFE) film.
In one instance in this second embodiment, membrane (c) may be hydrophobic. In another instance it may also be oleophobic. In another instance it may be made oleophobic. In still another instance it is hydrophilic.
Layer (a) is made oleophobic by treating it with an oleophobic polymer, such as, for example, a polymer that has recurring pendant fluorinated side chains. A trifluoromethyl group will be at the end of the recurring pendant alkyl-perfluoroalkyl groups which depend from the polymer backbone. Especially useful are polymers with an acrylate or methacrylate polymer backbone. In one aspect, the microporous film consists of ePTFE which is coated with a material that has perfluoroalkyl groups CF
3
—(CF
2
)
n
—, where n is ≧0, append from the polymer backbone.
In this latter instance, i.e., when layer (c) is hydrophilic, it has been found that when the composite containing this layer 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 the other three-layer composites of the invention. 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 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.
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 “oleophobic” is meant a material has an oil resistance of 1 or more.
By “microporous” is meant a material has very small, microsco
Buerger Wolfgang
Steffl Rudolf
von Fragstein Rainer
Zehnder Wolfgang
Lewis White Carol A.
Pezzuto Helen L.
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