Field of the Invention

The invention pertains to materials that are permeable to water vapor and impermeable to water and air for use in applications where moisture transport is desired, but a gas or water barrier is required. Such

applications include building housewrap, building roofing membranes, building flashings, breathable apparel, and surgical barriers.

Background of the Invention Moisture transport membranes are used where it is desirable to transmit moisture but avoid gross air or liquid transport. For example, when used as housewrap, such membranes insulate a house from air drafts and protect wooden and drywall substructure from liquid water. Water vapor transport is desired to allow interior humidity to escape and protect the interior drywall, wood and insulation from water saturation. A high water transport rate allows interior moisture or equilibrated exterior moisture to leave the structure or "breath" so that it is not trapped in the wood, drywall and insulation, causing decay and mold buildup. The breathable membrane must also serve as weather protection against liquid water and air drafts.

Materials commonly used as housewrap include Tyvek (trademark) flash- spun high density polyethylene (HDPE), microporous membranes, nonwoven polypropylene (PP) and perforated polymer films. Tyvek flash-spun nonwoven has lightweight strength, high vapor transport and liquid hydrohead in one layer. Disadvantages of the product include high cost, tear propagation once a tear is introduced, and loss of

hydrophobicity when exposed to surfactant. Microporous membranes are cast or extruded films with inorganic filler and laminated thermally or extrusion laminated on substrates, and subjected to stretching. Perforated polymer film housewraps have microholes and offer low perm rating with high airflow. A disadvantage is that deterioration of the membrane results in perforation distortions and may allow water to penetrate.

Membranes are selected based on perm rating, mechanical strength (tear strength, including wet tear strength), air penetration resistance and hydrostatic head. Both woven and non-woven types of housewraps are commonly used in the construction of buildings. Non- woven housewraps typically have higher water vapor permeabilities than woven housewraps. The strength properties of woven housewraps are typically much higher than those of non- woven housewraps. Some housewraps are translucent, which assists in locating the studs and window and door openings. Non- woven based housewraps are not perforated because the process used in manufacturing the housewrap results in a structure that inherently allows water vapor to pass through the wrap. Most woven housewrap are microperforated, having tiny holes incorporated in the woven coated product.

There remains a need for an effective membrane material while avoiding one or more of the disadvantages of existing products.

Summary of the Invention

The invention provides a water- vapor permeable, water-impermeable and air-impermeable laminated material, comprising a fabric layer, a microporous film and an adhesive coating bonding the fabric layer and film together. The breathability (water vapor transmission rate) of the laminated sheet material is controlled by the fabric layer openings, the breathability of the microporous film, and the adhesive coat weight applied during manufacture.

According to one aspect of the invention, there is provided a water vapor- permeable, air-impermeable and water-impermeable laminated material having a selected water vapor transmission rate. The laminated material comprises a microporous film comprising a resin and a filler, a woven or non-woven fabric layer bonded to the microporous film, and an adhesive bonding the microporous film and the fabric layer together. The selected water vapor transmission rate of the laminated material is determined by a combination of the openings in the fabric layer, the water vapor transmission rate of the microporous film, and the coating weight of the adhesive. According to another aspect of the invention, there is provided a method of making a water vapor-permeable, air-impermeable and water- impermeable laminated material as aforesaid. Values are selected for the openings in the fabric layer, the water vapor transmission rate of the microporous film, and the coating weight of the adhesive, the values being selected to provide the selected water vapor transmission rate of the laminated material. A coating of adhesive is applied to one or both of the microporous film of the fabric, and the microporous film and the fabric are then bonded together by means of the adhesive. Further aspects of the invention and features of specific embodiments of the invention are described below. Detailed Description

In this patent application, reference to certain measured properties of the laminated sheet material or its components means measurement according to the following standard test methods: (1) water vapor transmission rate (WVTR) is measured in accordance with ASTM E-96; air resistance is measured in accordance with TAPPI-460; hydrostatic resistance is measured in accordance with AATCC-127; tensile strength is measured in accordance with ASTM D5034; and tear strength is measured in accordance with ASTM D4533. The breathable, laminated sheet material comprises a fabric layer, a microporous film and an adhesive. The fabric layer may be a woven or non- woven fabric, or combination of both, depending on the requirements of a particular application. These fabrics may be in the form of a film, natural or synthetic textile, woven scrim, non- woven and glass mat. The woven fabric may comprise one or more of a polyolefin, (e.g.

polyethylene and polypropylene), polyester, polyamide, polyethylene terephthalate (PET), nylon, glass mat, and combinations thereof. The woven fabric comprises machine-direction and cross-direction tapes which may be made by a sheet extrusion process and followed by slitting, stretching, orientation and annealing of tapes. The woven fabric has sufficient openings to achieve the finished product target breathability. A weaving pattern in the range of 2x2 to 12x12 may be used.

In other embodiments, the fabric layer is a non- woven fabric comprising randomly laid spun-bonded fibers. The fibers may be polyolefin, including polyethylene and polypropylene, and polyester. The fibrous fabrics can be used autonomously or in combination with one another using a tie layer to laminate the fabrics. The microporous film comprises a blend of polymer resin and inorganic filler. Suitable resins include polyolefins (e.g. PE, PP), nylon, and blends thereof. Suitable fillers include mineral fillers such as calcium carbonate, talc, magnesium carbonate, and blends thereof. The film may comprise in the range of 40% to 80% by weight of filler. The microporous film may be made by a cast or blown extrusion process and stretched in the machine direction, the cross direction or both directions, to achieve the required breathability, for example, a WVTR in the range of 350 to 1,050 g/m ² /day. Representative weights for the microporous film are 25 to 150 g/m ² .

Adhesive is used for bonding the microporous film and the fabric layer together. Suitable adhesives include hot melt (e.g. pressure-sensitive hot melt), thermoplastic and acrylic based adhesives. The adhesive may be applied with various spray patterns, using a slot die or a variety of nozzles. Representative adhesive weights are in the range of 2 to 25 grams per square meter.

The breathable laminated material has a WVTR in the range of 35 to 700 g/m ² /day, alternatively greater than 600 g/m ² /day. The air resistance may be greater than 1,000 sec/100 cc. The hydrostatic resistance may be at least 250 cm. The material may have a tensile strength of 20 to 90 pounds/inch (3.51 to 15.80 kN/m), and a tear strength of 8 to 70 lbs (1.4 to 12.3 kN/m). Representative product weights are in the range of 47 to 325 g/m ² . The WVTR of the laminated finished sheet product is controlled by a combination of the fabric layer openings, the microporous film

breathability, and the adhesive coat weight used to laminate the layers. For embodiments in which the fabric layer is a woven, the openings are a function of weaving pattern and tape width. For embodiments in which the fabric layer is a non- woven, the openings are a function of the density of the fabric. In some embodiments, the fabric layer or the microporous film or the adhesive coating will be the substantially limiting factor in determining the WVTR of the laminated material, i.e., where the breathability of two of the components far exceeds the breathability of the third component. For example, where the fabric layer is a woven scrim with significant openings between the tapes, and the adhesive coating weight is low, the WVTR of the laminated material is substantially determined by the WVTR of the microporous coating, with some effect from the adhesive and virtually none from the scrim.

The laminated sheet material is substantially impermeable to air and to liquid water, that is, sufficiently impermeable for practical purposes for its intended applications, e.g. as housewrap, roofing membranes, building flashings, breathable apparel and surgical barriers. Reference in this specification to impermeability does not mean that absolute

impermeability is required. Example

A laminated sheet material according to the invention comprises a microporous film having a weight of 20 grams per square meter, an 8 x 8 woven scrim having a weight of 50 grams per square meter comprising tapes 3.1 mm in width, laminated together with an adhesive having a weight of 5 grams per square meter. The laminated material has a WVTR of 20 metric perms. In the example, the WVTR of the laminated material is substantially dictated by the WVTR of the microporous film. As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible in the practice of this invention without departing from the scope thereof. Accordingly, the scope of the invention is to be construed in accordance with the following claims.