Abstract:
A construction system is based on a plurality of interlocking panels, each panel formed of a non-woven, needle-punched, thermo-mechanically compacted fabric, each panel having dual density gradients, a first density gradient extending from the first outer surface to the center of panel and a second density gradient extending from the center of the panel to the outer surface, wherein less dense sections of each panel provide acoustic and thermal insulating properties and more dense sections of each panel provide strength and load-bearing properties.

Description:
[0001]    The present application claims the benefit of prior U.S. Ser. No. 61/191,947, filed Sep. 12, 2008. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention is directed to a construction system employing non-woven, polymer fiber-based panels. More specifically, the present invention is directed to a construction system employing resilient, light-weight panels formed from recycled materials. 
       BACKGROUND OF THE INVENTION 
       [0003]    In the US most residential and low- to mid-rise commercial buildings are made by framing, also known as stick construction. This is a building technique based around structural members, usually called studs, which provide a stable frame to which interior and exterior wall coverings are attached, and then covered by a roof comprising horizontal joists or sloping rafters covered by various sheathing materials. 
         [0004]    Recently, the US Department of Housing and Urban Development and the National Association of Home Builders has been urging the construction industry to develop and design panelized systems. Thus, manufacturers are reinventing the process of home construction using assembly line automation and prefabricated panels made from a wide variety of materials. The installed panels form a structural envelope that eliminates the need for conventional framing, provides integral insulation, and can be assembled swiftly by less skilled laborers. 
         [0005]    Newer panelized systems incorporate a variety of materials such as light gauge steel, aluminum, concrete, and fiberglass. 
         [0006]    Most of the new panelized systems provide improved insulation, specifically improved air tightness and thermal performance, as compared to traditional stick construction. Conventional wood framing creates a structure where a minor thermal bridge occurs at each vertical stud and gaps can exist between insulation batts and stud surfaces that allow air leaks. Conversely, panel systems offer a dense, uniform and continuous air barrier with few thermal bridges and little opportunity for internal convection. 
         [0007]    Further, industrialization of the construction process is also an advantage for panel manufacturers. Typically, panels can be produced in an automated factory environment, using computer controlled equipment that transfers panel-cutting instructions directly from digital CAD (computer aided design) drawings. The resulting components can be precisely engineered and are easy to inspect for quality control. Once the panels are shipped to the jobsite, they can be quickly assembled, speeding the onsite construction schedule and allowing homes to be placed under roof more quickly. 
         [0008]    Recently developed panelized systems take many forms. The most widely used panels are made from an expanded polystyrene core adhered to oriented strand board (OSB) or plywood skins. The foam alone has little strength, but when bonded to the plywood, it acts as a bridge, or web, to augment structural capacity and resist buckling. Known as structural insulated panels, these panels function quite well but the available geometry is that of a flat panel only and they tend to be quite heavy. Although for certain end-use applications these panels function quite well, the only available geometry is that of a flat panel and the panels are extremely heavy. 
       SUMMARY OF THE INVENTION 
       [0009]    Accordingly, the present invention is directed to a construction system based on a plurality of interlocking panels, where each panel is formed of a non-woven, needle-punched, thermo-mechanically compacted fabric, each panel has a first outer surface and an opposed second outer surface, and each panel has dual density gradients, a first density gradient extending from the first outer surface to the center of panel and a second density gradient extending from the center of the panel to the outer surface, such that less dense sections of each panel provide acoustic and thermal insulating properties and more dense sections of each panel provide strength and load-bearing properties. Preferably, the fibers of the non-woven fabric comprises are formed of at least one polymer selected from polyolefins, polyesters, PET and copolymers thereof, PBT, polyamides, aramids, cotton, flax, and hemp. Optionally, at least one of the first outer surface and the second outer surface further includes a coating selected from the group consisting of polyolefins, polyesters, PET and copolymers thereof, PBT, polyamides, and aramids. 
         [0010]    In a preferred embodiment at least some of the panels contain a piezoelectric material in fiber or film form to render the panel capable of sensing and responding to at least one form of environmental stimulation such as sound waves, other pressure waves, and temperature. 
         [0011]    It is also within the scope of the present invention that at least some of the fibers of the non-woven fabric have co-linear channels that extend along the fiber length for improved thermal and acoustic insulation and moisture transport. 
         [0012]    In one embodiment the dual density gradient of at least some of the panels is formed by the panel comprising two thinner panels sandwiched together wherein the sandwiched panels are of at least two differing densities, thereby providing the density gradient. 
         [0013]    Further, the panels can be cut or formed into shapes that allow direct construction of non-traditionally shaped buildings such as orthogonal, angular, and dome-like buildings. 
         [0014]    Furthermore, the present invention is directed to a construction method which includes the steps of providing a plurality of interlocking panels, each panel having a first outer surface and an opposed second outer surface, each panel made by the process which includes the steps of forming a non-woven fabric from individual fibers, needle-punching the non-woven fabric in order to further entangle the fibers, and thermo-mechanically compacting the needle-punched, non-woven fabric, each panel having dual density gradients, a first density gradient extending from the first outer surface to the center of the panel and a second density gradient extending from the center of the panel to the second outer surface, wherein less dense sections of each panel provide acoustic and thermal insulating properties and more dense sections of each panel provide strength and load-bearing properties, and assembling a low-rise building by interlocking the panels. 
         [0015]    Preferably, the non-woven fabric is formed of fibers derived from at least one polymer selected from polyolefins, polyesters, PET and copolymers thereof, PBT, polyamides, aramids, cotton, flax, and hemp. 
         [0016]    In a preferred embodiment the non-woven fabric is formed of thermoplastic fibers and the construction method further includes the step of forming raceways within the interlocked panels with a hot bar, the hot bar having a temperature exceeding the melting temperature of the thermoplastic fibers, the raceways providing means for running utility lines and plumbing throughout the building. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0017]    In accordance with the present invention a construction system is provided which employs non-woven, polymer fiber-based panels, which are, preferably formed from recycled materials. Thus,  FIG. 1  illustrates one particular preferred embodiment in which panel A is formed to be slidably interlocked with panel B. That is, the panels A and B possess a tongue and groove arrangement such that in use, when interlocked, there is transmission of load across the joints formed by the tongue and groove configuration of the interlocking panels, thereby substantially eliminating differential deflection between adjoining panel edges. 
         [0018]    Because these panels are textiles, they can be integrated with advanced materials in order to achieve desired design characteristics resulting in, essentially, an “intelligent” building. For example, embedding piezoelectric fibers into the non-woven fabric of the panel can result in a stiffening of the panel construction or actuate a shape memory function. Optical fibers can provide for illumination sensing and control. Phase change materials can provide thermal management capabilities, although even without such the present panels possess thermal insulations properties approaching and, depending on density, exceeding that of conventional fiberglass insulation. Capillary channeled fibers can provide acoustic insulation. Kevlar® or similar fibers can render the present panels bullet-proof. Further, when formed from preferred thermoplastic materials such as recycled PET the present construction panels have been found to be more fire resistant than traditional stick construction, as PET is essentially self-extinguishing. 
         [0019]    Optionally, the present panels may be reinforced with any of a variety of materials including fiberglass or even steel. Further, films providing specific functions such as moisture or gas barriers, or even decorative finishes, may be laminated to one or both surfaces of the panels. 
         [0020]    In a less preferred embodiment, the present panels may serve as the core layer of an insulated panel having plywood or OSB outer layers. 
         [0021]    The present panels have a dual density gradient, preferably with a high density on the side that will form the exterior surface (providing stiffness and moisture barrier properties) and a low density on the side that will form the interior surface (providing thermal and acoustic insulation), although other arrangements of the density gradients are also within the scope of the present invention. For example, each panel may include areas of high density on each surface sandwiching an area of low density in the middle. Alternatively, each panel may be formed of alternating layers of differing densities. The differing layers may be formed individually and laminated together or, more preferably, they may be formed during the thermo-mechanical compaction step of the manufacturing process, as is discussed in greater detail below. 
         [0022]    Thus, in a most preferred embodiment, fibers are spun from resin pellets derived from a recycled material such as PET (polyethylene terephthalate) from plastic bottles. The fibers are then formed into one or more non-woven web layers. The webs then are needle-punched to interconnect the webs or to further entangle the fabric fibers. An exemplary needle-punching machine  70  is shown in  FIG. 2 . The machine includes a web feeding mechanism  72 , a needle beam  74  with a needle board and needles, a stripper plate  76 , a bed plate  78 , and a fabric take-up mechanism  80 . The fiber web, sometimes carried or reinforced by a scrim or other fabric, is guided between the metal bed and the stripper plates, which have openings corresponding to the arrangement of needles in the needle board. During the down stroke of the needle beam each barb carries groups of fibers, corresponding in number to the number of needles and the number of barb per needle, into subsequent web layers a distance corresponding to the penetration depth. During the upstroke of the needle beam  74 , the fibers are released from the barbs and interlocking is established. At the end of the upstroke, the fabric is advanced by the take-up mechanism and the cycle is repeated. Needle density is typically determined by the distance advanced and the number of penetrations per stroke. 
         [0023]    It is preferred that the needles used have from one to three barbs (although 6, 9 or even more barbs may be used), and that the needle not penetrate completely through the layers of the webs, but instead penetrate to a depth within about one or two millimeters of the underlying surface of the lowermost web layer. Avoiding full penetration of the needles can reduce the probability of connecting pores from one surface of the non-woven fabric to the other. 
         [0024]    Thereafter, the needle-punched non-woven fabric is thermo-mechanically compacted. This is the process step which sets the physical properties of the panel and renders the web rigid and capable of use in load bearing applications. 
         [0025]    A variety of low density sample panels were produced by the above-described method. Property test results are set forth in Table 1, below. 
         [0000]    
       
         
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
             
             
               
                   
                   
               
               
                   
                 Test Method 
                 Sample 
               
             
          
           
               
                 Property Tested 
                 ASTM 
                 Units 
                 1500 
                 2000 
                 2800 
               
               
                   
               
             
          
           
               
                 Density 
                 D 1622-03 
                 pcf 
                 3.81 
                 4.96 
                 7.97 
               
               
                 Thickness 
                   
                 inches 
                 0.956 
                 0.947 
                 0.935 
               
               
                 Nail Pull Resistance Method A 
                 C473-06a 
                 lbf @ max load 
                 52.0 
                 80.1 
                 205.4 
               
               
                 Mini-Wall Racking 
                   
                 max load (lbf) 
                 257.60 
                 433.50 
                 862.00 
               
               
                 Thermal Resistance (75° F.) 
                 C 518-04 
               
               
                 K-Factor 
                   
                 Btu*in/h*ft2*° F. 
                 0.2513 
                 0.2435 
                 0.2429 
               
               
                 R-Value 
                   
                 ° F.*ft2*h/Btu 
                 3.803 
                 3.888 
                 3.850 
               
               
                 R/inch (actual) 
                   
                 ° F.*ft2*h/Btu*in 
                 3.979 
                 4.106 
                 4.118 
               
               
                   
               
             
          
         
       
     
         [0026]    From these early tests it is clear that the present inventive panels can achieve an insulation R-value close to that of current fiber glass: at an R/inch value of 4, a 3 inch thick panel in accordance with the present invention would achieve an R-value of 12, where a 3 inch sample of fiberglass insulation is typically R-13. The present panels would, of course be heavier than fiberglass, but would provide structural integrity, which fiberglass does not provide. 
         [0027]    Although the present invention has been described in connection with the preferred embodiments, it is to be understood that modifications and variations may be utilized without departing from the principles and scope of the invention, as those skilled in the art will readily understand. Accordingly, such modifications may be practiced within the scope of the following claims. Moreover, Applicant hereby discloses all subranges of all ranges disclosed herein. These subranges are also useful in carrying out the present invention.