Abstract:
A water proof membrane containing high strength fibers bonded together with one or more urethanes is disclosed along with the methods of making including wet or dry laying the high strength fibers to form a web, applying an aqueous urethane medium to the web and drying the web and super calendaring the web, or the web can be formed by forming a web by any method from bicomponent core/sheath fibers, the sheath comprising one or more urethanes, followed by super calendaring.

Description:
[0001]     The present invention involves fibrous nonwoven mats or sheets having particular use as house wraps, packaging, exterior posters, covers, and other similar uses and methods for making these mats.  
       BACKGROUND  
       [0002]     House wraps are known. Perhaps the best known is a super-calendered, flash spun, high density polyethylene made by a process such as a process disclosed in U.S. Pat. No. 3,081,519. Others include film laminated woven polypropylene and polyethylene, film laminated spunbond polypropylene and cross-laminated perforated polyolefin films. At least some of these are used regularly as house wraps, but all have some disadvantages. The high density polyethylene suffers from water wicking due to its porosity and open areas around fasteners like nails, staples, etc. Also, high density polyethylene, having very little elasticity, do not grip the fasteners as desired. Film laminates suffer from delamination and to gross damage when the underlying woven polypropylene fibers are stretched even slightly out-of-plane or even slightly in the cross machine direction. Cross-laminated film remain subject to installation damage and require perforations to allow for water vapor transmission that weaken the structure further.  
       SUMMARY OF THE INVENTION  
       [0003]     The invention includes a membrane comprising dispersed, melt spun or spun lace fibers of a synthetic polymer and a polyurethane coating on the fibers bonding the fibers together. The fibers can be made from a high strength polymer or a high strength polymer mixture. A collected web of spun bond or spun lace fibers, or a web of wet or dry laid chopped high strength fibers is saturated with a polyurethane binder is then dried and the polyurethane cured followed by hot calendaring to transform the polyurethane into a matrix holding the fibers together. The membrane can also be comprised of spunbonded core/sheath fibers in which the sheath is a polyurethane and the core is a high strength synthetic polymer such as a nylon 6, nylon 66, polypropylene, polyethylene a polyester and many other high strength polymers.  
         [0004]     The spunbonded web of core/sheath fibers is then calendared to produce a polyurethane matrix bonding the high strength synthetic fibers together. While the membrane of the invention can comprise any ratio of high strength fibers to polyurethane, often the majority of the membrane is made up by the high strength fibers, typically the high strength fibers comprise about 51-90 wt. percent high strength fibers and about 10-49 wt. percent polyurethane matrix, more typically about 51-80 wt. percent high strength fibers and about 20-49 wt. percent polyurethane and most typically about 51-70 wt. percent high strength fibers and about 30-49 wt. percent polyurethane matrix.  
         [0005]     The membranes of the invention are a superior house wrap material because the elastomeric nature of the polyurethane forms a sealing relationship with nails, screws and staples that penetrate the mat in the process of building a structure, yet having a permeability to air that permits the membrane to breathe. The holes formed by the penetration of fasteners do not grow, even when subjected to reasonable stress. Membranes of the invention are also superior because they will not pass water through the holes in the membrane around the fasteners because the rubbery nature of the polyurethane matrix in the membrane seals against the penetrating portion of the fasteners. Membranes of the invention also have superior printability and better permanence of printing or dyeing due to being an ether polymer or containing an inhibitor addition, a colorant or a combination of these features.  
         [0006]     The membranes of the invention can also be used as a protective covers in the place of tarps, as water-proof packaging material and as water proof envelopes.  
         [0007]     Membranes of the invention are comprised of fibers of a synthetic polymer and a polyurethane coating on the fibers bonding the fibers together. The fibers can be made from a high strength polymer or a high strength polymer mixture. A collected web of spun bond fibers, spun lace fibers, or wet or dry laid chopped high strength fibers is saturated with a polyurethane emulsion, latex, solution or suspension binder and then dried, and the polyurethane cured, followed by hot calendaring to transform the polyurethane into a matrix bonding the fibers together.  
         [0008]     Membranes of the invention can also be comprised of a web of core/sheath fibers in which the sheath is a polyurethane and the core is glass fibers, synthetic fibers of one or more high strength synthetic polymers such as a nylon 6, nylon 66, polypropylene, a polyester and many other high strength polymers or mixtures thereof, carbon fibers, ceramic fibers and amorphous silica fibers. It is known how to make a core/sheath fiber and the core/sheath fiber used in the present invention are made by extruding the high strength polymer or polymer mixture to form a core fiber followed closely by extruding the polyurethane sheath around the core fiber to produce the bicomponent, core/sheath, fiber. The spunbonded bicomponent fibers are collected on a collection belt in a known manner to form a web. The spunbonded web of core/sheath fibers is then calendared to produce a polyurethane matrix bonding the high strength synthetic fibers together. The core portion can be symmetrically located in the bicomponent fiber or can be off center. Normally, the sheath will completely surround the core, but it is sufficient if the sheath only partially surrounds the core, but the sheath should be in contact with at least 60 percent of the circumference of core, more typically at least about 80 percent and most typically at least about 90 percent of the circumference.  
         [0009]     In the invention the core is typically a strong, high melting point polymer or polymer mixture. By polymer mixture is meant a mixture of one or more polymers with or without other ingredients such as filler, colorant, UV discoloring inhibitor, hardening agent, catalyst, plasticizer or other functional ingredient. The core polymer can be one or more of a large number of polymers including polyamides, polypropylene, polyethylene, random copolymers of such polymers. Discoloring due to UV can be minimized or eliminated by ether or ester based polyurethane selection or by mixtures with controlled ratio of the two types of polyurethanes.  
         [0010]     In selecting the polyurethane for the sheath, and for the binder for the spun bond and spun lace fibers in the invention, when a binder is used, the following criteria is used to make the selection: 
        1) A high to the highest maximum water vapor transmission rate.     2) Good thermoplasticity to permit good hot super calandering.     3) Good elongation, toughness, and elasticity, to resist damage when stretched.     4) Swelling on contact with water to provide good seal around penetrating fasteners and to seal up tiny holes incurred in shipping, use, etc.        
 
         [0015]     Most typically ether based polyurethanes including Noveon, Inc.&#39;s ESTANE® 75AT3, 58245, 58315 and 54640 products are used in the invention, available from Noveon, Inc. of Cleveland, Ohio. Other ESTANE® ether based polyurethanes usable include 58881, 58300, 58,630, 58309, 58863 and 54640. Polyester based polyurethanes are also useable in the invention including Noveon&#39;s ESTANE® ETE 55DS3, 58149, ETE 60DS3, 58092 and 54610. Other suitable polyester based urethanes include Noveon&#39;s ESTANE® 58091, 58680, 58238, 5701, 58206, 58271, 58226 and 58277. Of course, like or similar urethane products from Noveon or from other suppliers are also usable in the invention.  
         [0016]     The core polymer can be one or more of a large number of polymers including polyamides, polypropylene, polyethylene, random copolymers of propylene and ethylene. The polyethylene can be of any type but most typically is linear low or high density polymer or copolymer.  
         [0017]     When the word “about” is used herein it is meant that the amount or condition it modifies can vary some beyond that stated so long as the advantages of the invention are realized. Practically, there is rarely the time or resources available to very precisely determine the limits of all the parameters of ones invention because to do would require an effort far greater than can be justified at the time the invention is being developed to a commercial reality. The skilled artisan understands this and expects that the disclosed results of the invention might extend, at least somewhat, beyond one or more of the limits disclosed. Later, having the benefit of the inventors disclosure and understanding the inventive concept, the objectives of the invention and embodiments disclosed, including the best mode known to the inventor, the inventor and others can, without inventive effort, explore beyond the limits disclosed using only ordinary skill to determine if the invention is realized beyond those limits, and when embodiments are found to be without any unexpected characteristics, those embodiments are within the meaning of the term about as used herein. It is not difficult for the artisan or others to determine whether such an embodiment is either as expected or, because of either a break in the continuity of results or one or more features that are significantly better than reported by the inventor, is surprising and thus an unobvious teaching leading to a further advance in the art. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]     Processes are known for making bicomponent fibers with having a core of one polymer surrounded by a sheath of a different polymer, often a lower melting point, binder polymer. These processes are illustrated in patents including U.S. Pat. Nos. 3,589,956 and 5,382,400, the disclosures of which are incorporated herein by reference. In these processes a first polymer or polymer mixture is extruded through a spinnerette to form a core fiber, cooled enough to permit the fiber to be pulled, and then a second, usually lower softening point polymer or polymer mixture is extruded into a sheath around the core fiber to produce a bicomponent fiber. The core portion can be symmetrically located in the bicomponent fiber or can be off center. Normally, the sheath will completely surround the core, but it is sufficient if the sheath only partially surrounds the core, but the sheath should be in contact with at least 60 percent of the circumference of core, more typically at least about 80 percent and most typically at least about 90 percent of the circumference.  
         [0019]     In the invention the core is typically a strong, high melting point polymer or polymer mixture. By polymer mixture is meant a mixture of one or more polymers with or without other ingredients such as filler, colorant, hardening agent, catalyst, plasticizer or other functional ingredient. The core polymer can be one or more of a large number of polymers including polyamides, polypropylene, polyethylene, random copolymers of a binder for the spun bond and spun lace fibers in the invention, the following criteria, is used to make the selection: 
        1) A high to the highest maximum water vapor transmission rate.     2) Good thermoplasticity to permit good hot super calandering.     3) Good elongation, toughness, and elasticity, to resist damage when stretched.     4) Swelling on contact with water to provide good seal around penetrating fasteners and to seal up tiny holes incurred in shipping, use, etc.        
 
         [0024]     Most typically ether based polyurethanes including Noveon, Inc.&#39;s ESTANE® 75AT3, 58245, 58315 and 54640 products are used in the invention, available from Noveon, Inc. of Cleveland, Ohio are used. Other ESTANE® ether based polyurethanes usable include 58881, 58300, 58,630, 58309, 58863 and 54640. Polyester based polyurethanes are also useable in the invention including Noveon&#39;s ESTANE® ETE 55DS3, 58149, ETE 60DS3, 58092 and 54610. Other suitable polyester based urethanes include Noveon&#39;s ESTANE® 58091, 58680, 58238, 5701, 58206, 58271, 58226 and 58277. Of course, like or similar urethane products from Noveon or from other suppliers are also usable in the invention. Also, the same type of urethane compounds, in the form of an aqueous emulsion, latex, solution or suspension is used to saturate webs of chopped fibers of a high strength, high melting polymer or polymer mixture(s), such as nylon and other polymers described above.  
         [0025]     The bicomponent fibers can either be spunbond or melt blown into a random pattern mat or web on a collection belt, or formed into a tow of fibers that is chopped into discrete lengths, opened wet or dry and then formed into a fibrous nonwoven mat in either a wet process or a dry laid process.  
         [0026]     Dry forming processes like those disclosed in U.S. Pat. Nos. 4,012,553, 4,054,713 and 5,382,148, the disclosures being herein incorporated by reference, can be used to form the webs from chopped fiber. The nonwoven webs can also be formed from chopped fibers of high strength, high melting point polymer or polymer mixture dispersed in an aqueous dispersion formed from processes like those disclosed in U.S. Pat. Nos. 4,112,174 and 3,766,003, the disclosures of which are hereby incorporated herein by reference. Webs useful in the present invention can also be formed from conventional high strength polymer or polymer mixture fibers including polyamides, polypropylene, polyethylene and others using any of these processes. Regardless of how the webs of high strength chopped fibers of polymer(s) or polymer mixtures, or chopped bicomponent fibers, are formed, aqueous urethane binder is applied to the web by spraying, dip and squeeze, roll over roll, or with a curtain coater in known manner and the web of fibers is then run through an oven to remove any water present in the web and to soften the sheath on the bicomponent fibers sufficiently to bond the fibers together where the fibers cross one another. The web is then cooled to solidify the sheath, or is run through a hot calander to densify the bonded web and to produce the membrane of the invention.  
         [0027]     The hot calendar, super calendar, is well known being a series of polished, closely stacked, metal rollers, and referred to in U.S. Pat. No. 5,405,821. The temperature is controlled to be high enough to plasticize and masticate the urethane(s), but not so high that the high strength fibers are damaged.  
         [0028]     Several most typical embodiments of the invention have been set forth above, but having the benefit of this disclosure; many other modifications will be obvious to the ordinary artisan. All such embodiments not showing unexpected results naturally are enabled by, and are a result of, the invention and are intended to be included in the scope of the following claims.