Abstract:
A roofing product used in commercial built-up roofs includes a roll roofing sheet having a backing film adhered to one side thereof, the backing film being miscible with an adherent substance when the roofing sheet is unrolled and applied to a roof using the adherent substance. Prior to the unrolling of the roofing sheet, the backing film inhibits the transfer of material to an opposite side of the roofing sheet.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to roofing materials, and, more specifically, to a roll roofing sheet especially adapted for installation on flat and low-pitch roofing structures. 
       BACKGROUND OF THE INVENTION 
       [0002]    Over the years, various types of roofing materials and roofing systems have been developed and used to meet the demands of commercial and residential buildings with varying roof pitches ranging from flat to steeply pitched. Each type of material (e.g., stone, ceramic, wood, metal, rubber and asphalt/bitumen) has benefits and limitations in performing its intended function. 
         [0003]    Asphalt roofing has wide popularity and can be made in many forms and compositions to provide it with different desirable properties, depending upon the application. For example, it may be reinforced using different fabric mat materials, such as fiberglass, polyester or other natural and synthetic materials. The asphalt may be modified by incorporating other compositions, such as styrene-butadiene-styrene (SBS) or atactic polypropylene (APP). Asphalt roofing material may be made in a variety of forms including shingles of various shapes and sizes, as well as continuous sheets of roofing material commonly referred to as “roll roofing sheets.” 
         [0004]    Modified bitumen membranes (i.e., asphalt mixed with chemical modifiers) were developed in Europe during the late 1960&#39;s for roofing applications and found a market in the United States in the 1980&#39;s. These products are an important part of the roofing industry, in that they are necessary components of built-up roofing (“BUR”), which is the preferred roofing type for commercial buildings. The membranes are provided in rolls as roll roofing sheets with a size and weight permitting manual handling, whereby they can be rolled out over an area of the roof that is to be covered. 
         [0005]    During installation, a waterproof base roll roofing sheet is spread over a roof deck. The base roll roofing sheet may be covered by one or more intermediate waterproof roll roofing sheets secured to each other by, for instance, melted hot-mopped asphalt. The uppermost roll roofing sheet is typically called the cap sheet. 
         [0006]    In some parts of the country (e.g., in California and other southwestern states), state or local regulations require that the exposed portions of all cap sheets meet certain minimum standards for reflectivity, typically those standards which fall under the Energy Star® criteria. The standards may be met by providing the cap sheet with a white reflective coating that is applied to the cap sheet at the factory, as is described in co-pending, co-owned U.S. Patent Publication Nos. 2005/0257875, 2005/0261407, and 2005/0261409, which are incorporated herein by reference. When the cap sheet comes off the production line, the side which has been coated white (i.e., the “front” or “top”) meets, or exceeds, the Energy Star® reflectivity criteria. Typically, however, the opposite side of the cap sheet (i.e., the “back” or “bottom” side) is still somewhat tacky, and partially transfers to the front side, diminishing the reflectivity of the front side when the cap sheet is rolled for shipment and/or storage. It is common to coat the non-reflective side of the cap sheet with sand or talc to prevent the cap sheet from sticking to the machinery used in the manufacturing process, as well as for preventing transfer of material between the front and back sides when rolled. Sand or talc from the back side of the membrane degrades the reflective surface, with the degree of degradation increasing in direct proportion to the amount of time that the membrane is stored in its rolled configuration. 
         [0007]    The reflective coating may be further degraded during installation of the cap sheet. Most commonly, the cap sheet will be installed by a two-person team using hot asphalt (i.e., “the hot mop” process). The asphalt is heated in kettles at the work site to temperatures of about 350° C. to about 450° C. One person spreads the molten asphalt onto the membrane to be covered and the other person rolls the cap sheet over the asphalt. The hot asphalt fuses adjacent layers. When the cap sheet membrane is unrolled, sand or talc remains loosely adhered to the reflective surface, where it presents a slipping hazard to the workers. The act of brushing the sand or talc off the top of the cap sheet for collection and removal further degrades the reflective surface. If the sand or talc were to be left on the cap sheet, it would interfere with the reflectivity of the cap sheet and promote weathering of the reflective surface. In the foregoing circumstances, it remains an objective to maximally preserve the reflectivity of the cap sheet without burdensome changes in the methods used to produce or install the membrane. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention overcomes the disadvantages and shortcomings of the prior art discussed above by providing a roofing product which includes a roll roofing sheet having a backing film adhered to one side thereof. When the roofing sheet is in the form of a roll, the backing film inhibits the transfer of material to an opposite side of the roll roofing sheet. When the roofing sheet is unrolled and applied to a roof using an adherent substance, the backing film is miscible with the adherent substance. By way of example, the backing film can be made from a combination of a low density polypropylene (LDPP) and ethylene-vinyl acetate (EVA). The proportion of LDPP to EVA can range from 20%-80% LDPP to 20%-80% EVA with a preferred ratio of about 60% EVA to 40% LDPP. 
         [0009]    The adherent substance can be either hot asphalt or an adhesive/solvent mixture. When the adherent substance is hot asphalt, the backing film melts and merges with the hot asphalt. When the adherent substance is an adhesive/solvent mixture, the backing film dissolves into the adhesive/solvent mixture. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    For a more complete understanding of the present invention, reference is made to the accompanying drawings, in which: 
           [0011]      FIG. 1  is a schematic view of a built-up roof constructed using a cap sheet in accordance with the present invention; 
           [0012]      FIG. 2  is a vertical cross-section of the cap sheet shown schematically in  FIG. 1 ; 
           [0013]      FIG. 3  is a procedure flow diagram of a process for manufacturing a roll roofing cap sheet in accordance with the present invention; and 
           [0014]      FIG. 4  is a schematic diagram of an apparatus for applying and adhering a backing film to the cap sheet shown schematically in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    As shown in  FIG. 1 , in a typical BUR installation  10 , a structural deck  12  is covered by a waterproof base roll roofing sheet  14 . The base roll roofing sheet  14  may be covered by one or more intermediate waterproof roll roofing sheets  16 . The uppermost roll roofing sheet in a BUR is cap sheet  18 . The roll roofing sheets  14 ,  16 ,  18  may be secured to each other by melted hot-mopped asphalt  20 , or by using a torch to fuse the membranes. 
         [0016]    With reference to  FIG. 2 , the cap sheet  18  is in the form of a layered modified bitumen membrane. More particularly, the cap sheet  18  includes a fiberglass or polyester reinforcing mat  22 , which is sandwiched between and bonded to a top layer  24  and a bottom layer  26 . Numerous granules  28  are embedded in the top layer  24 . The granules  28  are produced, for example, from crushed stone, ceramic or other hard, finely divided materials and each one is coated with a reflective coating  30 . A backing film  32  is adhered to the bottom layer  26 . 
         [0017]    The top layer  24  and the bottom layer  26  are formed from modified bitumen, such as SBS or APP. At present, about 60% of modified bitumen roll roofing sheets used in the roofing industry are based on atactic polypropylene modified bitumen (“APP membranes”). Styrene-butadiene-styrene modified bitumen membranes (“SBS membranes”) account for substantially all of the remainder of commercial roofing applications. The SBS membranes are generally more rubbery and easier to handle than the APP membranes, and have lower melting points. It is strongly preferred that SBS membranes be used for the top layer  24  and the bottom layer  26 , rather than APP membranes. However, the fabrication process and layered roll roofing sheets discussed herein with respect to SBS membranes can be applied, with a few obvious modifications, to APP membranes, or other membranes based on modified bitumen. 
         [0018]    The backing film  32  is made from a combination of a low density polypropylene (LDPP) and ethylene-vinyl acetate (EVA). The proportion of LDPP to EVA can range from 20%-80% LDPP to 20%-80% EVA with a preferred ratio of about 60% EVA to 40% LDPP. The backing film  32  could be made from other polymeric materials, such as linear low density films like PET (polyethyleneterephthalate) films, vinyl films, or a combination of low density and high density films, including, but not limited to PET, HDPE, HDPP, LDPP, LDPE, and EVA, as is known in the art. The objective in selecting a material or a combination of materials is to give the backing film  32  an overall melting point of approximately that of the hot-mopped BUR asphalt  20  (see  FIG. 1 ), which is preferably about 105° C. This allows the backing film  32  to melt and mix with the melted BUR asphalt  20  upon contact, solidifying in union with the BUR asphalt  20  as both cool below their respective melting points to thereby form a solid bond merged interface joining the two layers. The backing film  32  comes in a sheet that is preferably about 40.25 inches wide with a tolerance range of about 39.75 inches to about 42 inches. The backing film  32  has a thickness of preferably about 0.45 mils with a tolerance range of about 0.3 mil to about 1.0 mil. The backing film  32  can be obtained pre-made from a manufacturer such as Pliant Corporation of Schaumberg, Ill., USA which can be found at the web site www.pliantcorp.com. 
         [0019]    The cap sheet  18  of  FIG. 2  can be conventionally fabricated in a sequence of steps on a roofing machine, such as the one shown diagrammatically in  FIG. 3 . With continuing reference to  FIG. 3 , fiberglass or polyester mat material  34  is provided to mat unwinder stand and splicer apparatus  36 , which produces a continuous woven mat or felt  38 , thereby forming a fibrous reinforcement for the roofing material to be produced. Simultaneously, asphalt  40 , modifying polymers  42 , and optional mineral stabilizers  44  are added to a mixing tank  46  from which liquefied modified asphalt  48  issues and which is directed to impregnation vat  50 . The impregnation vat  50  receives the continuous mat  38 , which is dipped into the liquefied modified asphalt  48  in the vat  50 , thereby producing an asphalt impregnated mat  54 . At the granule application station  56 , granules  58  are distributed onto the asphalt impregnated mat  54  producing a granule-faced roofing material  60 . The granules  58  will embed into the surface of the asphalt impregnated mat  54  due to the temperature of the asphalt and its softened state at high temperatures. The granule-faced roofing material  60  is then fed through water cooling trays  62  to lower the temperature of the asphalt for further processing and to lock the applied granules  58  onto the surface of the mat  54 . After leaving the water cooling tray  62 , the roofing material  64  has a backing film  66  applied at a backing applicator station  68  to be discussed hereinbelow with reference to  FIG. 4 . The roofing material  64  is then further cooled and dried by air knives and/or cooling fans  70 . After its accumulation on a finish looper (accumulator)  72 , the roofing material  64  is fed to a roll winder/cutter  74  to produce the finished roofing material  76  in the form of roll roofing which is then placed in storage  78 . 
         [0020]    With reference to  FIGS. 3 and 4 , the backing film  66  is applied to the mat  54  at the backing applicator station  68  using a two-roll mill apparatus  80 , which includes a film roller  82  and a tension roller  84  acting in conjunction with conveyor rollers  86  of the roofing machine shown diagrammatically in  FIG. 3 . The backing film  66  is un-rolled from the film roller  82  onto the mat  54  in the opposite direction of movement (see arrow) of the mat  54  as the mat  54  is rolled over the conveyer rollers  86 . The tension roller  84  pushes the backing film  66  onto the surface of the mat  54 . The backing film  66  sticks naturally to the mat  54  since the material of the mat is still hot at this point in the manufacturing process. The tension roller  84  thus guides the backing film  66  over and onto the entire surface area of the mat  54 . 
         [0021]    The present invention is adapted for other techniques for constructing built-up roofs. For instance, bitumen layers and a cap sheet can be adhered together with adhesives mixed with solvents (combined aromatic and aliphatic), instead of with melted asphalt. The composition of the backing film remains the same as when melted hot-mopped asphalt is used. However, instead of melting and merging with the hot asphalt, the backing film dissolves into the adhesive/solvent mixture, thereby forming a mechanical bond between the uppermost bitumen layer and the cap sheet. The solvent present in the adhesive/solvent mixture can be either aromatic or aliphatic. In one preferred embodiment, the solvent constitutes about 15%-25% by weight of the adhesive/solvent mixture. The adhesive can be any traditional asphaltic adhesive as is known in the art, provided it can be applied to the backing film at a temperature which starts at 45° C. and rises. 
         [0022]    This invention has been described with reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as defined in the appended claims. For instance, the present invention can be used in other types of roofing, such as APP, SBS, and SEBS modified roofing membranes. These and other variations and modifications are included in the present invention as defined in the appended claims.