Patent Publication Number: US-10316532-B1

Title: Liquid containment pool wall using polymer sheeting

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit of priority from U.S. Provisional Patent Application No. 62/521,042 of Bernard J. Kulkaski, filed Jun. 16, 2017, entitled LIQUID CONTAINMENT VESSEL COMPONENT OR POOL WALL USING POLYMER SHEETING the entirety of which is incorporated herein by reference. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH/DEVELOPMENT 
     Not Applicable 
     PARTIES TO A JOINT RESEARCH AGREEMENT 
     Not Applicable 
     REFERENCE TO SEQUENCE LISTING, TABLE OR COMPUTER PROGRAM 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     Prior Art 
     The following is a tabulation of the prior art revealed during a patent search that may be relevant: 
     
       
         
           
               
               
               
               
             
               
                   
               
               
                 Pat./application No. 
                 Kind Code 
                 Issue/Publication Date 
                 Patentee 
               
               
                   
               
             
            
               
                 RE29,936 
                 N/A 
                 Mar. 20, 1979 
                 Arp 
               
               
                 3,975,874 
                 N/A 
                 Aug. 24, 1976 
                 Witte et al. 
               
               
                 3,974,605 
                 N/A 
                 Aug. 17, 1976 
                 Beatty et al. 
               
               
                 4,027,442 
                 N/A 
                 Jun. 7, 1977 
                 Silverman 
               
               
                 4,047,340 
                 N/A 
                 Sep. 13, 1977 
                 Witte et al. 
               
               
                 4,048,773 
                 N/A 
                 Sep. 20, 1977 
                 Laven 
               
               
                 4,109,324 
                 N/A 
                 Aug. 29, 1978 
                 Cornelius 
               
               
                 4,118,809 
                 N/A 
                 Oct. 10, 1978 
                 Bertsch 
               
               
                 4,124,907 
                 N/A 
                 Nov. 14, 1978 
                 Laven 
               
               
                 4,177,614 
                 N/A 
                 Dec. 11, 1979 
                 Arp 
               
               
                 4,316,571 
                 N/A 
                 Feb. 23, 1982 
                 Corna et al. 
               
               
                 4,464,802 
                 N/A 
                 Aug. 14, 1984 
                 Glonek et al. 
               
               
                 4,566,141 
                 N/A 
                 Jan. 28, 1986 
                 Mahoney 
               
               
                 5,010,603 
                 N/A 
                 Apr. 30, 1991 
                 Hertzog 
               
               
                 5,791,099 
                 N/A 
                 Aug. 11, 1998 
                 Duffy 
               
               
                 5,815,853 
                 N/A 
                 Oct. 6, 1998 
                 Chase 
               
               
                 5,896,715 
                 N/A 
                 Apr. 27, 1999 
                 Maupas 
               
               
                 5,991,940 
                 N/A 
                 Nov. 30, 1999 
                 Fortier 
               
               
                 6,226,938 
                 B1 
                 May 8, 2001 
                 Hodak 
               
               
                 7,797,887 
                 B2 
                 Sep. 21, 2010 
                 Maupas 
               
               
                 8,702,030 
                 B1 
                 Apr. 22, 2014 
                 Gilham, Jr. 
               
               
                 8,850,773 
                 B2 
                 Oct. 7, 2014 
                 Cohen 
               
               
                   
               
            
           
         
       
     
     The present design relates to a liquid storage vessel or pool that uses a rigid polymeric material to provide an environmentally friendly, easily installable, corrosion proof containment wall having high tensile strength, burst strength, and creep resistance. 
     Liquid containment vessels or reservoirs such as out-of-ground swimming pools, water storage tanks, fish growing vessels and other similar containers are typically comprised of a structural frame, a flexible membrane liner and a rigid containment wall. Large quantities of water held in a tank place immense hydrostatic pressure on the containment vessel. Consequently, round or oval liquid containment walls lined with sheets of metal are typically used to distribute these pressures more evenly. 
     Pool containment walls are commonly manufactured using steel or aluminum sheet metal as discussed in U.S. Pat. No. 4,316,571 issued to Coma et al. and U.S. Pat. No. 4,566,141 issued to Mahoney. There has been a recent trend in the residential swimming pool market where salt is used to generate the chlorine required to sanitize a pool. This method leads to a high level of corrosion and deterioration of metallic pool components. While steel offers great strength, it corrodes quickly in fresh and salt water environments even when painted or galvanized. The slightest dent or scratch in the coating material will lead to eventual failure of the containment wall if left uncorrected. 
     Aluminum has also served as a desirable wall material due to its lighter weight and considerable tensile strength. This metal has a protective oxide layer, but even thick aluminum will corrode over time especially in salt water settings. Limestone, which is found in many soils and landscaping products, will also accelerate the corrosion process if it comes in contact with an aluminum containment vessel. Resin may be added to the steel or aluminum sheet metal to slow the corrosion process; but again, any scrapes, holes, dents or other damage to the wall surface will result in material failure if left uncorrected. 
     Many inventors have attempted to solve the corrosion problem by offering non-corrosive pre-fabricated foam or plastic panels that are assembled on-site and secured with interlocking geometries and various mechanical fasteners. (See e.g. U.S. Pat. No. 4,109,324 issued to Cornelius; U.S. Pat. No. 4,118,809 issued to Bertsch; U.S. Pat. No. 4,124,907 issued to Laven; and U.S. Pat. No. 4,177,614 issued to Arp.) A liner is then inserted into the pool cavity to retain a watertight seal and transfer the hydrostatic pressure to the pool wall, relying solely on the tensile strength of that wall to prevent the lower strength waterproof membrane from rupturing. The problem with these designs is that any rip or tear in the pool liner will result in a leak and may end in a catastrophic failure of the pool panels. The more seams and mechanical fasteners required to create the pool wall, the higher the likelihood of failure. Additionally, these plastics are susceptible to creep, and the panels are prone deflection and stretching over time while placed under load. 
     Other inventors have suggested spraying foam directly on an aluminum or steel pool wall to create a hardened surface that is impervious to corrosion (See U.S. Pat. No. 4,027,442 issued to Silverman.) This design requires an ultraviolet coating to prevent the sun from degrading the material. A compromised foam layer would be difficult to remove and would likely require the complete replacement of the costly pool wall. 
     In recent years, some swimming pool manufacturers have introduced a flexible waterproof member that serves as the containment wall, requiring no structural frame or liner. See U.S. Pat. No. 5,815,853 issued to Chase. The Chase patent claims a self-standing semi-rigid structure that relies on a polypropylene wall laminated to a flexible polypropylene mesh. The patent claims the lack of frame as an advantage; however, this design is of lower quality and strength and subject to stretching. The thin nature of the wall makes it susceptible to punctures and the lack of a frame limits the feasible pool depth. The increased creep in this material can be expected to create extensive distension of the pool wall over time and eventual failure. Any significant force applied to the vertical axis of the pool wall is likely to result in a failure or collapse of the pool wall. 
     BRIEF SUMMARY OF THE INVENTION 
     The present design addresses the problems discussed above by offering a lightweight, easily transported, simply installed liquid containment wall that may be made of recycled materials. The rigid polymeric sheet material used in this wall offers creep resistance, high tensile strength, increased burst strength and superior chemical resistance. It may be used alone, it may be layered or it may be used in combination with foils, meshes or other similar materials depending on the application and strength required. 
     Polymers are chemicals made of repeating units of carbon and hydrogen that create “chains.” The strength of these polymers can be increased by “orienting” the chains within the material. In this process the polymer chains may be aligned in the direction of the load or in multiple directions. This increases the tensile strength and creep resistance of the material; larger loads can be transferred to these oriented chains as opposed to polymer materials that have not been oriented. 
     Thermoplastic polymers offer a light weight, high strength material that is resistant to both chemicals and creep and provides excellent thermal insulation which is desirable in heated pool applications. These materials may be made of recycled or virgin polyethylene, polypropylene, and polystyrene among other commonly used plastics. The orienting or stretching of polymers is well known in the art; the chains in these thermoplastic materials can be oriented by subjecting the polymer to strain while in a softened state. The preferred method involves reheating thermoplastic material to a specified temperature and then mechanically drawing an extrudate in either film, sheet, or fiber form as it exits the die and prior to solidification. The thermoplastic orientation can be adjusted to suit the load that will be applied, working much like the plurality of metal bands encircling a wine barrel; however, these bands or chains are embedded within the material itself. 
     Pool containment walls are generally constructed of steel or aluminum. The present design suggests the use of an oriented polymer such as polyethylene terephthalate (PET). Material creep may be reduced by selectively orienting the chains or by increasing the thickness of the plastic. Multiple layers of material will also offer increased strength, toughness and creep resistance. A material such as PET is impervious to corrosion and offers an economical and readily available material as it is often made from recycled plastics. 
     The polymer pool wall may be constructed of a single sheet or alternatively by arranging multiple smaller strips of oriented polymer and fusing them to form a sheet of the desired size. Ideally, these sheets are manufactured in coils allowing the user to achieve the desired wall thickness by unwinding the material and placing it along the pool base in concentric rings. Installing the pool wall in this way eliminates exposed seams and reduces the likelihood of leaks and failure. 
     A substantially oval or round standard support structure will be used in most applications. These support structures are typically constructed of a plurality of connected members that encase the pool wall, providing additional reinforcement and strength. Laminates or films may be added to the containment wall to address applications requiring increased burst strength, weather resistance, impact resistance, tear resistance, or aesthetic improvement. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  provides a perspective view of a standard liquid containment vessel. 
         FIG. 2  provides a perspective view of the polymer pool wall in a coiled form that has been made from multiple strips of material. 
         FIG. 3A  provides a perspective view of a plurality of oriented polymer strips encircling the exterior surface of the containment wall to provide reinforcement. 
         FIG. 3B  provides a perspective view of a multiple layers of oriented polymer strips encircling the exterior surface of the containment wall on a bias to provide reinforcement. 
         FIG. 4A  provides a top view of the coiled polymer sheeting. 
         FIG. 4B  provides a perspective view of a spiral installation of the polymer sheeting on the pool base 
         FIG. 5A  provides a side view of the lamination process 
         FIG. 5B  provides a side view of the final laminated product 
         FIG. 6A  is a side view of a pressure or impact point on a non-oriented polymer sheet 
         FIG. 6B  is a side view of a pressure or impact point on an oriented and laminated polymer sheet 
         FIG. 7  provides a perspective view of the corrugation process 
     
    
    
     REFERENCE NUMERALS 
     
         
         
           
               5  Containment Wall 
               10  Support Frame 
               15  Hydrostatic Pressure 
               20  Vessel Base 
               25  Oriented Polymer Sheeting 
               30  Laminate Material 
               35  Adhesive 
               40  Laminating Pressure Rolls 
               45  Finished Laminated Material 
               50  Corrugating Rolls 
               55  Finished Corrugated Material 
               60  Coiled Material for Installation 
               65  Exposed Seam 
               70  Pressure or Impact Point 
               75  Waterproof Liner 
               80  Oriented Polymer Reinforcing Bands 
           
         
       
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to  FIG. 1 , a typical pool or liquid containment vessel is comprised of a containment wall  5  reinforced by a support frame  10  and resting on a vessel base  20 . A water-retaining liner or membrane (not shown) may be placed over the containment wall  5  and vessel base  20  to create a water tight barrier. 
     Liquid within the containment vessel exerts hydrostatic pressure  15  on the containment wall  5  as shown in  FIG. 1 ; this pressure increases proportionally with the depth from the water surface. Pressure applied from motion within the pool such as diving, wave action and hydraulic shock can exceed the static water column pressure by several orders of magnitude. Consequently, the containment wall  5  must be made of a material having sufficient tensile strength, burst strength and creep resistance to accommodate these forces. 
     The preferred embodiment is comprised of a containment wall  5  constructed from at least one sheet of rigid oriented polymer 25 such as PET. The plurality of chains within the material may be oriented axially or biaxially through conventional manufacturing means. The oriented polymer should be mechanically drawn at a draw ratio between 2:1 and 6:1 to achieve the material properties required for this application. The direction of orientation may also be adjusted to achieve a material with the desired burst strength, creep resistance, tensile strength, and toughness. Thickness of the polymer sheet may also be modified to improve these material properties. 
     In another embodiment, single or multiple sheets or layers of non-oriented polymer pool wall may be used provided that the material has the requisite thickness, layering or positioning to withstand at least 1.25 times the static water column pressure exerted on a liquid containment vessel having a sixty inch depth. 
     The containment wall  5  may alternatively may be formed by arranging multiple smaller strips of oriented polymer 25 and fusing them to each other or to one or more plies of polymer to form a sheet of the desired size as shown in  FIG. 2 . These materials may be fused by any common manufacturing method such as sonic or laser welding. 
     In another embodiment, the containment wall  5  may be comprised of multiple smaller strips of oriented polymer 25 that are woven together to form a sheet of material. 
     In yet another embodiment, one or more oriented polymer reinforcing bands  80  may be added to the containment wall  5  as shown in  FIGS. 3A and 3B . These bands may encircle the exterior of the containment wall  5  much like hoops on a barrel to increase the strength of the containment vessel. Alternatively, the bands  80  may be affixed to the interior of the containment wall  5 . The bands  80  may be secured to the containment wall  5  by any number of means including but not limited to plastic welding techniques, adhesive application or the use of mechanical fasteners. 
     The bands  80 , if used, will ideally be placed substantially parallel to one another and they may, but need not be, placed such that they are substantially parallel to the ground as shown in  FIG. 3A . Multiple layers of banding may be used as shown in  FIG. 3B  and oriented in different directions. The bands  80  may also be woven together to further enhance their reinforcing strength. The spacing and widths of the bands  80  may vary based on the strength requirements for the particular application. The cross-sectional profile of the band may take any one of a number of shapes including but not limited to rectangular or bell-shaped profiles. It should be noted that the use of bands  80  may eliminate the need for a support frame  10  in applications requiring minimal strength provided that the material properties of the oriented polymer sheeting  25  and bands  80  are suited to the forces that will be exerted on the liquid containment vessel. 
     Referring now to  FIGS. 4A and 4B , the containment wall  5  is ideally manufactured in rolls or coils, allowing for easy installation. The containment wall  5  is unwound from the coil  60  and one or more overlapping sheets are placed the vessel base  20  to construct the containment wall  5 . Concentric layering of containment wall  5  material will further strengthen the wall, offering increased impact resistance, creep resistance and durability. Because the seams are not exposed there are fewer points of failure in the containment wall  5 . The single exposed seam  65  will be located on the exterior of the concentric layers. This seam may be fastened by any method or means that fixes the pool wall in a secure position. 
     Polymeric sheet material may be used alone or in combination with a secondary sheet material create the containment wall  5  to enhance UV resistance, creep resistance, impact resistance and tensile strength. Additionally, decorative coatings, ink, paint, varnish or printed webbing may be applied to enhance the appearance and durability of the pool wall. The polymeric sheet material may be laminated or affixed to one or more layers of metallic foil, mesh, or plastic. Adhesive  35  may be introduced between the polymeric sheet material  25  and the laminate material  30  and be routed through pressure rolls  40  to create a finished laminate material  45  as shown in  FIGS. 5A and 5B . The addition of one or more of these layers will increase the tensile strength and impact resistance of the pool wall. Similar means may be used to adhere multiple layers of polymer sheeting to enhance the strength of the containment wall  5 . 
     Mesh, if used, may be woven or non-woven and made out of any suitable material such as stainless steel, fiberglass, polymers, basalt fiber or carbon fiber. Laminated sheets of this nature are known to enhance material properties and will protect the containment wall  5  from tearing, ruptures, bursting and collapse. See  FIG. 6A  illustrating a pressure or impact point  70  penetrating a polymer sheet  75 .  FIG. 6B  depicts oriented polymer sheeting  25  having impact resistant sufficient to prevent the pressure or impact point  70  from piercing the laminate material  30 . 
     Polymer or laminated polymer sheets may be corrugated using corrugating rolls  50  having a wave-like, square-edge, semi-circular or similar alternating shape, provided that such corrugations do not create an accordion effect on the material. See  FIG. 7 . Corrugations are commonly used in steel and are known for increasing the compressive strength of the base sheet material. Corrugations will similarly increase the tensile strength of polymer and laminated polymer sheets and will provide dimension to the sheet thickness, increasing its stiffness and allowing for easier installation. Ideally the corrugations in the material will be uniform and evenly spaced, allowing concentric layers of the pool wall to lock into one another. In addition, impact resistance will increase, the likelihood of warpage will decrease and a more durable containment wall will result in a corrugated containment wall  55 . 
     The polymeric sheet material used to create the containment wall  5  can be made using any one of a number of known plastic materials having sufficient strength to withstand at least 1.25 times the static water column pressure exerted on a liquid containment vessel having a sixty inch depth. The properties of PET make it a suitable plastic for use in this application. Because it is often made of recycled plastics, it is readily available, economical, and environmentally friendly; however, it should be recognized that a number of plastic materials may be used. 
     While the above description contains many specifics, these should be considered exemplifications of one or more embodiments rather than limitations on the scope of the invention. As previously discussed, many variations are possible and the scope of the invention should not be restricted by the examples illustrated herein.