INSULATED BREATHABLE FABRIC

Field of the Invention

The present invention is directed to insulated breathable fabrics, in particular insulated breathable laminates.

Background of the Invention

Breathable fabrics that allow transfer of water vapor, such as fabrics containing polytetraflouroethylene (PTFE) membranes, have become important in a wide number of applications. These applications include, for example, use in all- weather clothing, medical garments, and environmental protection suits. Breathable fabrics are particularly useful for garments that will be used in wet environments and for active pursuits where a user will produce significant amounts of perspiration. Under such circumstances a breathable garment with a PTFE membrane can provide an improved level of comfort for the wearer, while preventing excess moisture from penetrating into the interior of the garment.

In recent years numerous fabrics have been developed that are suitable for warm weather and are breathable. However, breathability can also be important in cold weather applications. Thus, a need exists for a breathable material for use in cold environments, in particular one having insulating and water resistant properties.

Summary of the Invention

The present invention is directed, in part, to a multilayer breathable fabric comprising a bicomponent membrane. The bicomponent membrane includes a porous scaffold material having a void volume of at least 60% and an interconnecting

microstructure, plus a resin composition applied to at least one surface of the scaffold material. The resin partially fills the voids sufficient to create adhesion of the resin to the scaffold material, but not such that all voids within the scaffold are filled. An insulating layer is placed in contact with the bicomponent membrane, and is secured to the bicomponent membrane by a discontinuous adhesive layer,

In some embodiments the porous scaffold material comprises polytetraflouroethylene (PTFE). In general the porous scaffold material is at least 10 microns thick, while it can be thicker or thinner in some implementations. The invention is also directed to a multi-layer fabric comprising a breathable membrane, the breathable membrane combining an expanded PTFE film partially impregnated with a resin material; and insulating layer in contact with the breathable membrane. Suitable resin materials include polyurethane.

The laminate can further include a woven or non- woven support layer, often a woven nylon support layer, wherein the breathable membrane is laminated to the woven nylon support layer. This layer can include non-wovens, tricot, stretch, plain weave, ripstop and other fabric designs.

The above summary of the present invention is not intended to describe each discussed embodiment of the present invention. This is the purpose of the figures and the detailed description that follow.

Detailed Description of the Invention

The present invention is directed, in part, to a fabric laminate containing at least two layers. The laminate includes a bicomponent breathable membrane and an insulating layer. In certain embodiments the insulating layer forms at least two interface zones across the laminate: a first interface zone wherein the insulating layer

is in adhesive contact with a resin material, such as polyurethane, and a second interface zone wherein the insulating layer is in non-adhesive contact with the bicomponent membrane.

In addition to providing good moisture vapor transfer, in typical implementations the laminate fabric will have a water column greater than 3 meters, generally more than 5 meters, desirably more than 7 meters, and preferably greater than 10 meters. However, in some implementations where water resistance need not be at a maximum, the water column can be significantly less than these numbers. Waterproofness is measured by the ability of the material to hold back a column of water over a defined period of time, typically using the test method of ISO 811.

In general the laminate fabric of the present invention has a high moisture vapor rate, usually in excess of 400 gm/m ² /24 hours, and preferably greater than 600 gm/m ² /24 hours, and may be in excess of 800 gm/ m ² /24 hours. Moisture vapor transmission rate is the measure of a fabric to pass water vapor through to the exterior of a garment while maintaining its waterproof characteristics. The test method utilized for these measurements is ASTM E96B.

Breathable Membrane

The invention is also directed to a multi-layer fabric comprising a breathable membrane, the breathable membrane typically combining an expanded PTFE film, which may or may not be partially impregnated with a resin material; and an insulating layer in contact with the breathable membrane. The resin material comprises, for example, polyurethane. The membrane can be made in accordance with the teachings of United States Patent Nos. 3,953,566; 4,187,390; and 4,194,041, incorporated herein by reference. The laminate also can contain a woven nylon layer,

wherein the breathable membrane is laminated to the woven nylon layer. In some embodiments the porous scaffold material is at least 5 microns thick. It is typically from 10 to 225 microns thick. In certain embodiments it is less than 50 microns thick.

In accordance with one aspect of the present invention there are provided breathable membranes formed from compositions having interpenetrating matrices in cured form, comprising: (a) a first polymer network characterized by nodes interconnected by fibrils, and optionally (b) a second polymer network comprising diorganosiloxy units. Component (a) can be any polymer capable of being stretched, drawn or expanded so as to obtain a microstructure characterized by nodes interconnected by very small fibrils. It is especially desirable that component (a) be polytetrafluoroethylene as taught by in the aforementioned U.S. patents. Polyethylene, polyamides, and polyesters are also known to exhibit a fibril structure upon being drawn or expanded.

Component (b) can be any curable silicone composition, however, it is preferred that an addition curable silicone composition be employed in the practice of the invention. Generally stated, addition curable silicone compositions comprise (1) a polydiorganosiloxane having alkenyl unsaturation, (2) an organohydrogenpolysiloxane crosslinking agent, and (3) a catalyst for promoting crosslinking of (1) and (2). Alkenyl-containing polydiorganosiloxanes typically employed in the practice of the present invention can have viscosities up to 100,000,000 centipoise or more at 25 ⁰ C, for example, in accordance with the teaching of U.S. Pat. No. 4,061,609 to Bobear. It has been found that excellent results are obtained when the viscosity of the alkenyl-containing polysiloxane is from about 500 centipoise to 50,000 centipoise at 25 ⁰ C, and especially when the viscosity is from about 3000 centipoise to 6000

centipoise at 25 ⁰ C.

Organohydrogenpolysiloxanes that can be utilized in the present invention may be linear or resinous and have viscosities of between about 25 centipoise and 10,000 centipoise at 25. ⁰ C, with the preferred range being from about 100 centipoise to about 1000 centipoise at ⁰ C.

The curing catalyst can be optionally be either an organic peroxide or a precious metal containing material. Suitable organic peroxides include dibenzoyl peroxide, bis-2,4-dichlorobenzoyl peroxide, di-t-butyl peroxide, 2,5-dimethyl-2,5-di- (t-butylperoxy) hexane, and dicumyl peroxide. Precious metal containing catalysts can be based on the metals rhodium, ruthenium, palladium, osmium, irridium and platinum. It is particularly preferred that a platinum metal complex be employed as the catalyst, for example, as taught by Ashby in U.S. Pat. Nos. 3,159,601 and 3,159,662, Lamoreaux in U.S. Pat. No. 3,220,970, Karstedt in U.S. Pat. No. 3,814,730, and Modic in U.S. Pat. No. 3,516,946. In an especially preferred embodiment, the addition curable silicone composition further includes a reinforcing organopolysiloxane resin of the type disclosed in U.S. Pat. No. 3,284,406 to Nelson or U.S. Pat. No. 3,436,366 to Modic. Briefly, such resins are copolymers of SiO ₂ units, (CH ₃ ) ₃ SiO units and (CH ₃ ) ₂ (CH ₂ =CH)SiO ₅ units, and SiO ₂ units, CH ₃ SiO units and (CH ₃ )(CH ₂ =CH)SiO units, respectively. Particularly preferred organopolysiloxane resins are MDQ resins having vinyl unsaturation on monofunctional siloxane units, difunctional siloxane units, or both. The use of such reinforcing organopolysiloxane resins is especially desirable when the viscosity of the alkenyl containing polydiorganosiloxane is less than about 5000 centipoise. It is also contemplated that there may be included any conventional extending

and/or reinforcing fillers. Fumed silica has been found to be particularly effective as reinforcing filler for the silicone component of the present invention.

In another particularly preferred embodiment of the present invention, the addition curable silicone composition also contains a silane or polysiloxane which functions both as an inhibitor and as an adhesion promoter. One such composition is described in U.S. Pat. No. 3,759,968 to Berger et al. as a maleate or fumarate functional silane or polysiloxane. Compositions effective only as an inhibitor are disclosed in U.S. Pat. Nos. 4,256,870 to Eckberg and 4,061,609 to Bobear. Other suitable inhibitors will be obvious to those skilled in the art. It is further contemplated that component (b) can be condensation curable silicone composition. Generally, condensation curable silicone compositions are available in either one or two packages and comprise (1) a polydiorganosiloxane having terminal hydrolyzable groups, e.g., hydroxyl or alkoxyl, and (2) a catalyst which promotes condensation curing. Such compositions are well known in the art, for example, as described in U.S. Pat. No. 3,888,815 to Bessmer et al.

Alternatively, the polysiloxane network can be prepared by the hydrolytic polycondensation of silanes having the general formula where each X is independently selected from the group consisting of hydrogen, alkyl radicals, hydroxyalkyl radicals, alkoxyalkyl radicals, and hydroxyalkoxyalkyl radicals, and Y is an alkyl radical, OX, where X is as previously defined, or an amino or substituted amino radical. The use of silanes having hydrolyzable groups to form a polysiloxane network of an interpenetrating polymer network is discussed in greater detail in U.S. Pat. No. 4,250,074 to Foscante et al.

The amount of curable silicone composition used in practicing the present invention can range from as little as about 1 part by weight per 100 parts by weight of

component (a) to as much as about 150 parts by weight per 100 parts by weight of component (a). A particularly preferred embodiment of the present invention utilizes from 1 to 50 parts by weight silicone per 100 parts by weight of component (a). Optimal results are obtained when from about 5 to about 35 parts by weight of silicone composition are used per 100 parts by weight of polytetrafluoroethylene. It should be noted that the translucency of the final product increases as the ratio of silicone composition to PTFE increases.

For ease of discussion, preparation of compositions having interpenetrating matrices in cured form will be described only with respect to polytetrafluoroethylene and addition curable silicone compositions. Those skilled in the art will appreciate that in order to prevent premature curing of the silicone composition the components must not all be combined until the time of use unless a suitable inhibitor is included (or moisture excluded in the case of condensation curable silicone compositions).

In a preferred embodiment of this invention a one component, addition curable silicone composition containing an amount of inhibitor effective to prevent curing below about 100 ⁰ C is dissolved in a suitable solvent, for example, kerosene or mineral spirits. The resulting solution is thereafter mixed with the polytetrafluoroethylene powder in a tumbler-type mixer suitable for mixing liquids with solids in order to incorporate the desired level of silicone into the PTFE. The semi-dry powder obtained is a mixture of PTFE, silicone composition and solvent which can be pressed into a cylindrical bar or other suitable shape.

The cylindrical bar is then extruded and calendered to provide a film of desired thickness. After the solvent is removed the film can be stretched to provide a film having a porous microstructure consisting of nodes and fibrils. Although expansion of the film can be carried out at temperatures ranging from room

temperature to about 325 ⁰ C, it is preferable that the temperature range from about 250 ⁰ C to about 300 ⁰ C so that the silicone composition cures during the stretching process.

If an inhibitor is not present to prevent premature curing of the silicone composition, it is desirable to prepare a mixture of PTFE and vinyl containing polydiorganosiloxane and a mixture of PTFE and organohydrogenpolysiloxane, either or both mixtures also containing a curing catalyst. At the time of use the powders are combined and the final product prepared as if an inhibitor were present.

Because of the presence of the silicone in the extruded PTFE film, stretching was easier as the silicone acted as an internal plasticizer. Consequently, it is not required that stretching be effected as fast as possible, and excellent results have been obtained with stretch rates of only 20% per second. Of course, this does not preclude stretching at rates of 1000% per second or more as taught by Gore in U.S. Pat. No. 3,953,566. Stretched films prepared in accordance with the present invention generally have thicknesses ranging from about 0.5 mils to about 10 mils. Quite surprisingly, however, the resultant materials had larger pore sizes than similar materials prepared solely from PTFE, yet they exhibit improved air permeability and improved resistance to liquid water permeability. It is also preferred that the expanded products be heated to above the lowest crystalline melting point of the PTFE so as to increase the amorphous content of the polymer, typically to 10% or more. Such amorphous regions within the crystalline structure appear to greatly inhibit slippage along the crystalline axis and thereby lock fibrils and nodes so that they resist slippage under stress. As a result, a surprising increase in strength is obtained.

Compositions prepared in accordance with the present invention find particular utility as filters, pump packing, insulation for electrical cables, and as laminates useful in the manufacture of breathable wearing apparel.

Insulating Layer

The insulating layer provides insulating, anti-static and other therapeutic attributes. The present invention provides an advantage by producing a waterproof or water-resistant fabric that also shows effective insulating properties. Suitable insulating layers include synthetics like Lite-Loft, Primaloft, Polarguard, Hollofil, Microloft, etc., all of which have good performance in wet conditions. They are also relatively easy to clean, resistant to mildew and rot, and quick drying.

The insulating material can include, for example, material disclosed in U.S. Patent No. 4,992,327, incorporated herein by reference. Such insulating layers can include synthetic fiber thermal insulator material in the form of a cohesive fiber structure, which structure comprises an assemblage of: (a) from 70 to 95 weight percent of synthetic polymeric microfibers having a diameter of from 3 to 12 microns; and (b) from 5 to 30 weight percent of synthetic polymeric macro fibers having a diameter of 12 to 50 microns, characterized in that at least some of the fibers are bonded at their contact points, the bonding being such that the density of the resultant structure is within the range 3 to 16 kg/m , the thermal insulating properties of the bonded assemblage being equal to or not substantially less than the thermal insulating properties of a comparable unbonded assemblage.

Microfibers and macrofϊbers for use in inslulating layer of the present invention may be manufactured from polyester, nylon, rayon, acetate, acrylic, modacrylic, polyolefins, spandex, polyaramids, polyimides, fluorocarbons,

polybenzimidazols, polyvinylalcohols, polydiacetylenes, polyetherketones, polyimidazols, and phenylene sulphide polymers such as those commercially available under the trade name RYTON. In general it is preferred that the microfibers are drawn following extrusion to impart tensile modulus of at least 63 g/dtex (70 g/den). The bonding may be effected between at least some of the macrofibers to form a supporting structure for the microfibers, or may be between both macrofibers and some of the microfibers at their various contact points. The macrofibers may be selected from the same material and may be either the same as the microfibers or different. In one advantageous embodiment of the invention microfibers are formed from polyethylene terephthalate and the macrofibers are selected from the polyethylene terephthalate or a polyaramid, such, for example, as that commercially available under the trademark "Kevlar".

The macrofibers can be monofibers, i.e., fibers having a substantially uniform structure or may be multi-component fibers having a moiety to facilitate macrofiber to macrofiber bonding. The macrofiber may be a fiber mixture in which at least 10% by weight comprises macrofibers of a lower melting point thermoplastic material to assist the macrofiber to macrofiber bonding. In a further embodiment of the invention the macrofibers may be a fiber mixture comprising multi-component macrofibers and a monocomponent macrofiber capable of bonding one with the other.

In another embodiment of the present invention the macro component fiber may be a mix or blend of macrofibers having different properties, for example, a macro fiber mix may comprise two or more different fibers such as a polyester fiber to give the desired bonding and a "Kevlar" fiber to give stiffness. The proportion of stiffening fiber to bonding fiber may be varied to provide different properties subject

to the requirement that the proportion of bondable fibers is sufficient for the macrofiber structure to provide an open support for the microfibers as hereinafter described.

Some materials, such as, for example, polyphenylene sulphide fibers, aromatic polyamides of the type commercially available under the trade name "APYIEL", and polyimide fibers such as those manufactured by Lenzing AG of Austria, exhibit flame retardant properties or are nonflammable. Such materials can, therefore, confer improved flame or fire resistant properties on manufactured products containing the materials in accordance with the present invention. In certain embodiments the insulating material can include a batt having high filling power and bulk under load comprising crimped hollow polyester filaments. Critical ranges for the percent void, denier, crimp frequency, and crimp index are defined for the fibers which interact to provide batts having higher bulk under load than would be expected by virtue of the voids alone when compared with the bulk of solid fibers, such as taught by U.S. Patent No. 3,772,137, incorporated herein by reference.

Hollow filaments used in the practice of the present invention are optionally characterized as having a round cross-section with a hole centrally located in the filament and forming a hollow core extending throughout the length of the filament. The percent "void content" of the hollow filament is the percent of the filament cross section that is hollow or, alternatively, it is 100 times the ratio of the cross-sectional area of the hollow core to the cross-sectional area of the entire filament. The fibers of this invention have a void content of about 13 percent to about 25 percent.

Applications for the material include shoe and boot liners, mittens, gloves, hats, coats, trousers, waders, protective coveralls, medical gowns and drapes.

particular implementations, those skilled in the art will recognize that many changes may be made hereto without departing from the spirit and scope of the present invention.