Abstract:
Embodiments of the present invention generally relate to a non-slip roofing underlayment made using an extrusion lamination process with a desirable minimum substrate-to-substrate static coefficient of friction of at least 0.400, made using an extrusion lamination process. In one embodiment, a roofing underlayment is manufactured from the steps comprising providing a first layer of a woven thermoplastic material, extruding a second layer of thermoplastic material on the first layer, at a temperature between about 470 degrees and about 600 degrees Fahrenheit, and laminating a third layer of non-woven thermoplastic material on the second layer through a nip at a pressure between about 50 pounds per square inch and about 90 pounds per square inch.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of U.S. Provisional Application Ser. No. 60/803,294, entitled “Non-Slip Roofing Underlayment and Method,” filed May 26, 2006, the disclosure of which is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     Embodiments of the present invention generally relate to a roofing underlayment. More specifically, embodiments of the present invention relate to a non-slip roofing underlayment for use in roofing construction, and a method of manufacturing the same.  
         [0004]     2. Description of the Related Art  
         [0005]     Roofing structures typically comprise multiple layers of materials applied to the roof support structure. These layers may include a roofing underlayment affixed to the roof support structure, such as a weather-resistant membrane and the like. A roofing overlayment is generally placed over the underlayment such as shingles, tiles, metal roofing, and the like. Often, roofing underlayments are advertised as non-slip layers, designed to prevent workers applying the layer from slipping while walking on the layer.  
         [0006]     U.S. Pat. No. 6,308,482 entitled “Reinforced Roof Underlayment and Method of Making the Same,” issued to Strait, discloses a roofing underlayment made by an extrusion lamination process. The roofing underlayment in Strait achieves only a substrate-to-substrate static coefficient of friction, commonly referred to as “COF,” of 0.250-0.300. This range of low static COF is undesirable, whereas the efficacy of the underlayment may be detrimental when the COF is less than about 0.400. Other roofing underlayments with a COF equal to or greater than 0.400 are available. However, such underlayments are made using an adhesive lamination process and are generally not durable, whereas the adhesive may fail when exposed to wet and cold environments. Specifically, most adhesives typically break down when exposed to certain weather conditions, causing the laminated substrate layers of the underlayment to separate.  
         [0007]     Thus, an improved roofing underlayment having an advantageous COF, utilizing a reliable extrusion lamination process, is desired.  
       SUMMARY OF THE INVENTION  
       [0008]     Embodiments of the present invention generally relate to a non-slip roofing underlayment made using an extrusion lamination process with a desirable minimum substrate-to-substrate static COF. More specifically, embodiments of the present invention relate to non-slip roofing underlayment having a COF of at least 0.400, made using an extrusion lamination process.  
         [0009]     In one embodiment of the present invention, a method of manufacturing a roofing underlayment comprises the steps of providing a first layer of a woven thermoplastic material, extruding a second layer of thermoplastic material on the first layer, at a temperature between about 470 degrees and about 600 degrees Fahrenheit, and laminating a third layer of non-woven thermoplastic material on the second layer through a nip at a pressure between about 50 pounds per square inch and about 90 pounds per square inch.  
         [0010]     In another embodiment of the present invention, a roofing underlayment is manufactured from the steps comprising: providing a first layer of a woven thermoplastic material, extruding a second layer of thermoplastic material on the first layer, at a temperature between about 470 degrees and about 600 degrees Fahrenheit, and laminating a third layer of non-woven thermoplastic material on the second layer through a nip at a pressure between about 50 pounds per square inch and about 90 pounds per square inch. The roofing underlayment has a substrate-to-substrate static coefficient of friction is greater than about 0.400. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     So the manner in which the above recited features of the present invention can be understood in detail, a more particular description of embodiments of the present invention, briefly summarized above, may be had by reference to embodiments, several of which are illustrated in the appended drawings. It is to be noted, however, the appended drawings illustrate only typical embodiments of embodiments encompassed within the scope of the present invention, and, therefore, are not to be considered limiting, for the present invention may admit to other equally effective embodiments, wherein:  
         [0012]      FIG. 1  depicts a manufacturing system for making a non-slip roofing underlayment in accordance with one embodiment of the present invention;  
         [0013]      FIG. 2  illustrates a section of the manufacturing system of  FIG. 1 , in accordance with one embodiment of the present invention;  
         [0014]      FIG. 3  is an exploded perspective view of the layers of the non-slip roofing underlayment in accordance with one embodiment of the present invention; and  
         [0015]      FIG. 4  illustrates a method for making a non-slip roofing underlayment in accordance with one embodiment of the present invention 
     
    
       [0016]     The headings used herein are for organizational purposes only and are not meant to be used to limit the scope of the description or the claims. As used throughout this application, the word “may” is used in a permissive sense (i.e., meaning having the potential to), rather than the mandatory sense (i.e., meaning must). Similarly, the words “include”, “including”, and “includes” mean including but not limited to. To facilitate understanding, like reference numerals have been used, where possible, to designate like elements common to the figures.  
       DETAILED DESCRIPTION  
       [0017]      FIG. 1  depicts a system for manufacturing a roofing underlayment in accordance with one embodiment of the present invention. As shown in  FIG. 1 , a system  100  for making a non-slip roofing underlayment comprises an unwinding portion  101 , a pre-treatment portion  103 , an extrusion portion  105 , a lamination portion  107 , and a windup portion  109 . Use of extrusion lamination facilitates the use of thermoplastic material in the underlayment to improve the tensile strength and weather-resistance of the underlayment  
         [0018]     Several embodiments of the present invention comprise a single pass of unwinding a layer  102  of woven material, and conditioning the layer  102  for treatment using the unwinding portion  101  of the system  100 . In one embodiment, the woven material may be any thermoplastic, including, but not limited to, a polyolefin, e.g., polypropylene and polyethylene, any cloth material, and the like. In another embodiment, the woven thermoplastic is a 10×10 polypropylene. Optionally, the woven layer  102  enters the pretreatment portion  103  of system  100  where a surface of the woven layer  102  is pretreated to facilitate the acceptance of melted thermoplastic to be extruded upon the woven layer surface. In one embodiment, pre-treating the surface of the woven layer  102  comprises oxidizing the surface. In another embodiment, pre-treating the surface of the woven layer  102  comprises at least one of corona treatment, plasma treatment, flame treatment, chemical priming, and the like.  
         [0019]     After optional pretreatment, the woven layer  102  enters the extrusion portion  105  of system  100 . For further clarification, an expanded view of one embodiment of the extrusion lamination portion of system  100  is provided in  FIG. 2 , which is now described in conjunction with  FIG. 1 .  
         [0020]     As woven layer  102  enters the extruder portion  105 , a thermoplastic material  104 , is heated to a melting temperature. In one embodiment, the thermoplastic material is polypropylene, which is heated between about 470 and about 600 degrees Fahrenheit. In other embodiments, materials such as polyethylene, nylon, polyester, other engineered thermoplastics, or the like, may be utilized for the extrusion process. The molten thermoplastic  104  is extruded onto the woven layer  102  using one or more extruders  106 , as shown in  FIG. 2 , to produce a coated woven layer  108 . The coated woven layer  108  then enters the lamination portion  107  of the system  100 .  
         [0021]     As coated woven layer  108  enters the lamination portion  107 , a layer  110  of non-woven material is unwound and pulled into the lamination portion  107  of system  100 . In one embodiment, the non-woven material comprises polypropylene. In other embodiments of the present invention, materials such as polyethylene, cotton cloth, nylon, polyurethane, or the like, may be utilized. Both the coated woven layer  108  and the non-woven layer  110  are pulled into a nip  114  between two rollers  112 . In one embodiment, the nip pressure is set to a value between about 50 pounds per square inch (“psi”) and about 90 psi. The coated woven layer  108  and the non-woven layer  110  are laminated together to produce a non-slip roofing underlayment  116 .  
         [0022]     The underlayment  116  is then cured and cooled. In one embodiment, the curing process occurs as the molten resin of the underlayment  116  is cooled by a combination of chill rolls under pressure. The cooling is sufficient to bring the resin of the underlayment  116  from a molten to a rigid state with sufficient physical bonding to hold the structure in place.  
         [0023]     The underlayment  116  then enters a winding portion  109  where it is wound into a cylindrical coil and ready for shipment. Additionally, the underlayment  116  may be tested to determine whether the associated substrate-to-substrate static COF is about 0.400. The substrate-to-substrate static COF provides an efficient method of measuring friction over other measurement methods, such as substrate-to-substrate kinetic COF and substrate-to-steel kinetic and static COFs because the substrate-to-substrate static COF fluctuates more as the parameters associated with making a non-slip roofing underlayment change, as compared to other frictional measurements.  
         [0024]     In some embodiments, to further strengthen roofing underlayment  116 , the underlayment  116  may run through one or more additional passes of system  100  and laminated to one or more additional layers of woven thermoplastic  102  in the lamination section  107 . Thus, the resulting roofing underlayment may be customized with additional layers to meet various roofing needs.  
         [0025]      FIG. 3  is an exploded perspective view of the individual layers of an underlayment  116 , in accordance with one embodiment of the present invention. Specifically, at least one layer  102  of interwoven strands of polypropylene with melted polypropylene  104  extruded onto the woven layer  102 , to create coated woven layer  108 , is laminated to at least one layer  110  of non-woven polypropylene to produce roofing underlayment  116 .  
         [0026]      FIG. 4  illustrates steps in a process flow describing one exemplary embodiment of the present invention. The steps need not be performed in the sequence illustrated, and some of the steps may be performed substantially simultaneously. As described in  FIG. 4 , upon starting method  400  at step  402 , a woven layer  102  of thermoplastic is unwound from a wrapped cylindrical roll and runs through a single pass on a primary process line to be pretreated, in step  404 . Pretreatment of the woven layer  102  may include oxidizing a top surface of the woven layer  102  to facilitate the upcoming extrusion and lamination processes. One example of such a woven thermoplastic material is a 10×10 per square inch woven pattern of polypropylene.  
         [0027]     Once the woven layer  102  is pretreated, in step  406 , the woven layer  102  enters an extruder  106  where molten thermoplastic  104 , such as molten 2 mil polypropylene, is extruded through a die onto the woven layer  102  at a melting temperature of about 535 degrees Fahrenheit, to produce a coated woven layer  108 . In step  408 , the coated woven layer  108  is pulled into a nip  114  of two rollers  112 , wherein the pressure of the nip is set to about 80 psi.  
         [0028]     As shown in step  410 , a layer  110  of non-woven thermoplastic, such as, for example, 1 ounce spun-bonded non-woven polypropylene, is unwound and runs on an auxiliary line into the nip  114  at a time substantially simultaneous to the coated woven layer  108  entering the nip  114 . In the nip, the pressure exerted upon the coated woven layer  108  and the non-woven layer  110  laminates the two layers together to create an underlayment  116 , as shown in step  412 .  
         [0029]     Once laminated, the resulting underlayment  116  is cured and cooled in step  414  and is tested to determine that the substrate-to-substrate static COF is about 0.400. The underlayment  116  then is ready for use and the process ends at step  416 .  
         [0030]     Although the exemplary embodiment described in  FIG. 4  depicts a single pass of one layer of woven thermoplastic  102  and one layer of non-woven thermoplastic  110  laminated together using an extruded coating  104  of melted thermoplastic to produce underlayment  116 , the process in  FIG. 4  may be repeated for multiple passes to further strengthen the roofing underlayment. For example, underlayment  116  may be run through an additional pass to coat the exposed woven side of the underlayment  116  with extruded melted polypropylene at 535 degrees Fahrenheit, followed by lamination to another layer of woven polypropylene at a nip pressure of 80 psi.  
         [0031]     While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. Specifically, embodiments of the present invention are further scalable to allow for additional clients and servers, as particular applications may require.