BRIEF DESCRIPTION OF THE DRAWINGS
For a more complete understanding of the present invention, reference is made to the accompanying drawings, in which:
FIG. 1 is a schematic view of a built-up roof constructed using a cap sheet in accordance with the present invention;
FIG. 2 is a vertical cross-section of the cap sheet shown schematically in FIG. 1;
FIG. 3 is a procedure flow diagram of a process for manufacturing a roll roofing cap sheet in accordance with the present invention; and
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
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.
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.
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.
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.
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.
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.
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.
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.
Patent Application
20080081152
