Abstract:
An enhanced filtration multilayer laminated fabric ( 10 ) includes an air permeable, moisture-vapor-transmissive, polytetra-fluoroethylene (ePTFE) membrane central layer ( 12 ). This central layer ( 12 ) is sandwiched between a first pair of nonwoven textile layers ( 14, 16 ) and a second pair of woven textile layers ( 18, 20 ). The laminated fabric may also feature a fire resistant application. The top textile layer ( 18 ) may also include a permanent, highly breathable and highly durable electro-static discharge feature added to the inside of the layer by laying down a carbon based printed pattern on the inside of the layer. The filtration fabric ( 10 ) may be utilized to manufacture a wearable garment that is aesthetically pleasing and comfortable to wear in all weather conditions.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority from U.S. Provisional Patent Application No. 62/103,137 entitled “Respiratory Filtering Fabric And Garment Made Therefrom”, filed on Jan. 14, 2015 which is incorporated fully herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to filtration fabrics and more particularly, to a filtration fabric which has significant air permeability provided by an ePTFE layer in the center of the fabric, and which fabric may be utilized to manufacture a wearable garment that is aesthetically pleasing and comfortable to wear in all weather conditions, and can serve the additional function of filtering all types of harmful particulates from the air inhaled by the user. 
       BACKGROUND INFORMATION 
       [0003]    Respirators and masks are generally used to prevent aspiration of airborne particulates. Airborne particulates may include smoke caused by a fire or explosion; smoke and gunpowder pollutants from gunfire; blowing sand such as in the desert; and even contaminants from open sewage pits, as are often found in third-world countries or war-torn regions. Although respirators and masks are the most common solution, many individuals do not feel comfortable wearing them, and indeed, feel out of place wearing a respirator, or even a mask. Further, because of the cumbersome nature of traditional respirators, in practice many people resort to pulling a t-shirt or handkerchief up over their face to act as a crude filter when they find themselves in dusty or smoky situations. 
         [0004]    Current respiratory materials provide reasonably good air permeability initially. However, these materials quickly become “clogged” with contaminants as the process of “capturing” the contaminants also reduces the size of the pores through which the air travels through the respiratory materials. This in turn decreases the air flow and increases the force necessary to draw in enough oxygen, essentially making it more and more difficult to breathe. In addition, these masks or respirators are generally not fire retardant, nor are they waterproof or Electro-Static Discharge (ESD) resistant. This is particularly problematic in cold regions where any moisture in the mask will freeze, again causing clogging of the respiratory materials, and essentially making the mask unusable. 
         [0005]    The current invention allows for not only good particulate release during exhalation, but because all areas of the garment are capable of filtration, it can be rotated if necessary to a clean, unused area (in scarf form). The garment is also completely unaffected by moisture 
         [0006]    Accordingly, what is needed is a fabric that serves as an air filtration material and provides significant air permeability without becoming clogged with particulates or moisture and which fabric can be utilized in the making of aesthetically pleasing clothing items such as scarfs, balaclavas, shemaghs, masks, face shields and the like. 
       SUMMARY 
       [0007]    In accordance with an exemplary embodiment of this invention, the present invention provides for a multilayer fabric which provides air filtration. The multilayer fabric is composed of several layers of different materials. The multiple layers include a central film or membrane of expanded polytetrafluoroethylene (ePTFE) or other similar hydrophobic material having good air permeability and moisture-venting properties. This central layer is sandwiched between a first pair of textile layers. These three layers are then in turn sandwiched between a second pair of textile layers. In this arrangement, the ePTFE membrane is effectively sandwiched between two (2) layers on each side of the membrane creating a five (5) layer laminate or composite. 
         [0008]    Textiles suitable for the first pair of textile layers include spun bond or nonwoven fabric. These layers are ultrasonically point bonded on opposite sides of the central ePTFE membrane. These layers serve to protect the PTFE membrane from damage, and allow space for the membrane to breathe. They also provide a solid anchor point for the adhesive lamination of the outer fabric layers. 
         [0009]    Textiles suitable for the second pair of textile layers include woven fabric such as aramid jersey knit layers. These layers are hot-melt adhesively bonded to opposite sides of the first pair of spun bound fabric textile layers. The design of the multilayer fabric allows for selection of a wide variety of other face fabrics to be used. For example, fleece or wool fabrics for cold weather use, or self-cooling hydrophilic printed fabrics (Omnifreeze) for hot weather use. The fabrics can also be printed with an ESD grid prior to lamination to allow use of the garment in spark sensitive environments. 
         [0010]    The multilayer fabric may be plasma treated for oleophobic and hydrophobic properties. This treatment allows the garment to repel water and resist contamination by oily substances, and allows for easy cleaning in the field. The garment will not absorb water and thus will maintain adequate air flow, even in heavy precipitation. The multilayer fabric may also include a conductive layer printed on an inside surface of a woven fabric layer. 
         [0011]    Various embodiments of the multilayer fabric include the manufacture of garments such as scarves, balaclavas, shemaghs, masks, face shields, the upper portion of an extended turtleneck shirt, neck gaiters, face panels, and mouth covers and the like. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    These and other features and advantages of the present invention will be better understood by reading the following detailed description, taken together with the drawings wherein: 
           [0013]      FIG. 1  is a cross-sectional view of an embodiment of the filtration fabric according to the present invention having a central ePTFE layer and multiple external layers. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0014]    The invention features a multilayer laminated fabric that is made into a garment. As a fashion forward textile, the laminated fabric of the present invention may be used to manufacture scarves, balaclavas, shemaghs, masks, face shields, the upper portion, at least, of an extended turtleneck shirt, and the like. Any article of clothing, article designed and configured to be worn over the face (mouth and/or nose) of the user) or the like made from the fabric disclosed herein can be utilized in warm weather conditions or cold weather conditions, such as for skiing, snow shoeing, snowboarding, cross-country skiing, and the like. 
         [0015]    Additional features of the invention include: exhibiting a high air permeability (greater than 15 and preferably greater than 20 CFM); self-cleaning in that exhaling will dislodge any trapped particulates from the fabric since the mechanism of filtration uses a gradient—the outer fabric layer provides coarse filtration, the spun-bond layer provides a finer filtration, and any fine particles that do reach the PTFE membrane layer are stopped on the surface of the membrane. Upon exhalation, the particles are easily released from the structure; waterproof; and can be made to be fire retardant and antistatic so that when the fabric is used in a military application around explosive ordinance, there is no risk of unintended explosion. 
         [0016]    As shown in the enclosed drawing, the invention is, in the preferred embodiment, a five layer structure forming a filtration fabric  10 . In order to be used to manufacture scarves, balaclavas, shemaghs, masks, face shields, the upper portion, at least, of an extended turtleneck shirt and the like, this fabric may comprise a sheet of any predetermined length, width and form, which may later be incorporated into a final product. Alternatively, the filtration fabric may be cut and sewn to fit a specific desired design as a final product with a desire to minimize stitch holes that could allow particulate to come through. 
         [0017]    In one embodiment, the fabric  10  includes at least five layers, wherein the central layer  12  is an expanded ePTFE (polytetrafluoroethylene) membrane  12 . The membrane  12  has air permeability from about 20 to about 30 cfm and pore size of about 1.5-3.0 microns. An exemplary membrane  12  is TG4 available from TTG, Inc. which has an approximate air permeability of 24 cfm and an approximate pore size of 2.0 microns. 
         [0018]    Due to the nature and structure of the ePTFE membrane  12 , during use, any particulates that are drawn through the outer fabric layers towards the central ePTFE membrane are prevented from passing into the membrane  12 . Therefore, instead of becoming filtered by being trapped or lodged within the interstices of the membrane  12 , these filtered particulates remain solely on the outer surface of the membrane  12 . Thus, the membrane  12  and outer fabric layers can be cleared of any filtered particulates by simply exhaling. Alternatively, particulates may be removed by applying some airflow in a direction opposite that from which the air originally flowed relative to the membrane  12 , or the garment (such as a scarf for example only) can be shifted to a allow breathing to occur through a new, unused area of the garment 
         [0019]    The ePTFE membrane  12  is an interior expanded polytetrafluoroethylene (ePTFE) layer with hydrophobic, good air permeability, and moisture-vapor-transmission properties. The expansion of polytetrafluoroethylene opens billions of microscopic pores in the ePTFE membrane  12  to enhance air permeability and water vapor transmission rate. 
         [0020]    The entire finished laminate may be treated to be both oleo-phobic and hydrophobic. 
         [0021]    Frozen moisture or condensation is the primary cause of the clogging that occurs to facial masks when used in colder climates. In a preferred embodiment, the filtration fabric of this invention allows for sufficient water repellency even in colder weather so the risk of clogging from frozen condensation is minimized. 
         [0022]    The ePTFE membrane  12  is, in the preferred embodiment, ultrasonically point-bonded between two layers  14  and  16  of about twenty weight (GSM) polyester spun bound or nonwoven material. An exemplary material for layers  14  and  16  is available from Bondex. This material has air permeability of about 300 to about 500 cfm. 
         [0023]    As shown in the figure, the first pair of textile layers  14  and  16  are preferably identical to one another and serve to protect the ePTFE membrane layer  12  from damage and provide a stronger anchor point for the ePTFE membrane layer  12  to the outside layers  18  and  20  of the fabric. Most importantly, however, these layers  14  and  16  allow the maintenance of maximum air flow.  10 . The “peel” strength of the fabric structure configured according to the teachings of the present invention increased from about 0.5 lbs/in to 2 lbs/in when comparing the three layer knit-membrane-knit to the knit-sb-membrane-sb knit composite of the invention, but the most important reasons for the layers are membrane durability and to maintain the air flow and allow flexibility of outer fabric selection. 
         [0024]    The ultrasonic point bonding between the two layers  14  and  16  and the ePTFE layer  12  is performed with enough bonding sites to sufficiently adhere or bond the layers together while not significantly interfering with the air flow. Thus, this process maximizes the air flow from the outside of the fabric into and through the ePTFE layer. An exemplary ultrasonic point-bonding converter is Beckmann Converting in Amsterdam N.Y. An exemplary pattern is the “BC” pattern with the number of bonding sites per square inch is about 8 to about 10. 
         [0025]    Finally, outer layers  18  and  20  are adhered to the spun bond layers  14  and  16  using a hot-melt adhesive pattern. The outside layers  18  and  20  are typically a woven, fleece or knit fabric, such as an aramid Jersey knit SD 1883 produced by SSM Industries with air permeability of about 250 to 400 cfm and inherent flame resistant properties. 
         [0026]    This hot-melt adhesive pattern bonding is also designed to provide sufficient bonding while not significantly interfering with the airflow into and through the fabric. An exemplary hot-melt adhesive pattern bonding method is roto-gravure lamination. It is to be recognized that the volume of adhesive per square inch of fabric may also vary appropriately when associated with corners, stress points, and the like. 
         [0027]    The entire assembled composite fabric will be treated with a durable water repellent treatment using a plasma treatment method that does not affect the air permeability of the structure of the fabric  10 . In one embodiment a method of plasma treatment includes applying a permanent water and oil repellent treatment on the molecular level throughout the depth of the laminate. An exemplary plasma treatment method is available from P2i in Oxfordshire UK. While causing minimal change to the airflow, this plasma treatment still treats all of the surfaces of all of the layers in situ. Such treatment will also greatly help maintain maximum airflow because the fabric components will no longer be absorbent at all) Such treatment technology may also be utilized to provide not only water repellent properties but also oil repellent properties as well. 
         [0028]    Many objects that are handled by humans are explosive in nature or may be damaged by an electrical discharge and their handling must eliminate or at least significantly reduce the possibility of an Electro-Static Discharge (ESD) that might cause the explosive device to explode or render the electronic device inoperative. For example, there is the potential that clothing items of the type mentioned herein may become exposed to a buildup of static electricity, which creates a risk that the clothing item will support an electrical charge and result in a dangerous environment for the equipment or object being handled (electronic or software, ordinance, etc.) and the persons operating the equipment. Therefore, it is preferred that the clothing item made from the fabric disclosed herein exhibit electro-static dissipating properties. 
         [0029]    An additional feature of the invention is therefore to impart a cost effective and durable electrical conductive or electro-static dissipative (ESD) performance to the fabric/clothing item using one or more methods. In a first method, a screen printing technology prints on a portion of the clothing item with an electrically conductive ink. The print lay-down of ink is critical to conductivity performance and in the case of the overall concept of the present invention, preventing loss of air permeability of the fabric. 
         [0030]    In this first embodiment for providing ESD protection, the printing of a conductive grid (such as utilizing silver ink, for example) may be provided on an inner surface of the outer knit layers  18 ,  20 , where this inner surface is facing the spun bound layers  14 ,  16 . This process serves to make the fabric static dissipative, or Electro-Static Discharge (ESD) resistant. Thus, the fabric&#39;s use around explosives and ordinances will be allowed. 
         [0031]    In a preferred implementation of this first embodiment of ESD protection of the present invention, an inner surface of at least one of the outer layers  18 ,  20  of the second pair of textile layers is treated with a printed carbon treatment. The surface can be entirely treated or more preferably, partially treated, such as with a pattern. The placement of the carbon on the inner surface of the outer pair of textile layers  18 ,  20  is superior to the prior art usage of carbon on an upper surface of the outer layer of the cover, because the carbon on the upper surface is subject to breakage and degradation due to UV solar breakdown. 
         [0032]    To ensure protection of the conductive print and long term function, the print is applied ONLY to the inside of at least one of the outer textile layers. Because the print/ink is a water based polyurethane compound with a durable carbon particle component, when the ink is applied to the fabric, there is no significant loss in air permeability. If the print were to be applied to the ePTFE membrane, the very small pore sizes (1.5-3 microns) of the ePTFE membrane would be filled with the ink, blocking a substantial portion of but not all air flow. When the carbon print is applied to the inside of one or more of the outer textile layers, the print adheres to the large yarn fibers and as a result in the woven fabric blocks very little air flow. Openings in the face fabric are order of magnitude 500× larger than those of the ePTFE membrane. 
         [0033]    Thus with the ePTFE membrane portion of the item controlling the overall air permeability of the laminate, the conductive ink must be printed on the textile fabric and not on the ePTFE membrane. Effective coverage to attain to meet static dissipation requirements is based upon the level of carbon in the ink and the surface area printed on to the fabric. Trials done to date that provide optimum discharge used a 15-20% print lay down in a diamond shape pattern with approximately 1.5-2.0 mm lines over a 1.0-1.5 square centimeter area. 
         [0034]    One compelling aspect of this feature of the invention is that even though the printed ink is located on the inside of the laminate, the porous nature of the various materials and laminate layers used allow volume electrical conductivity through the fabric/layers and thus allow static dissipation through the fabric. Static dissipation or static decay test method Federal Standard 191A and 4046 and NFPA-99 challenges the conductive material to provide decay of 5000 volts in less than 0.5 seconds usually less than 0.1 seconds. 
         [0035]    Further testing has shown that the ESD printing on the inside of the laminate does not significantly impact air permeability performance of the membrane and thus does not impact or reduce the level of relative humidity transported through the laminate. A material with ESD printing as described by this feature of the invention can still maintain greater than 1% relative humidity transfer/square foot of surface area/per minute. 
         [0036]    In another embodiment for providing Electro-static dissipation, the fabric material may be produced with ESD yarns or fibers (such as carbon fibers) in or as part of the outer layers  18 ,  20  which provides static dissipative or electrostatic discharge (ESD) or anti-static characteristics. 
         [0037]    The present invention is not intended to be limited to a device or method which must satisfy one or more of any stated or implied objects or features of the invention and should not be limited to the preferred, exemplary, or primary embodiment(s) described herein. Modifications and substitutions by one of ordinary skill in the art are considered to be within the scope of the present invention, which is not to be limited except by the allowed claims and their legal equivalents.