Patent Application
20050210802
1. Field of the Invention
This invention relates to a single ply roofing membrane having a top layer and a bottom layer for covering industrial and commercial flat and pitched roofs. More particularly, the invention relates to a single ply reinforced roofing membrane in which the bottom layer is embossed to improve roll blocking without sacrificing the heat seaming performance of the roofing membrane.
2. Reported Developments
Single ply roofing membranes to cover flat and pitched roofs are known in the art of commercial roofing membranes. Some membranes comprise bottom and top polyolefin-based sheets with a fiber reinforcement scrim sandwiched between the sheets. To promote adhesion between the scrim and the polyolefin sheets, a highly flowable, functional-polyolefin is incorporated into one or both sheets as disclosed in U.S. Pat. No. 6,544,909.
Other membranes of the prior art consist of materials based on atactic polypropylene (APP) modified bitumen. Still other membranes consist primarily of materials based on styrene-butadiene-styrene (SBS) modified bitumen. Attachment of these membranes to underlying roof decks are accomplished with adhesives and/or screws. To adhere one membrane to another membrane to render the roof covering waterproof, the selvage edge of one membrane is overlapped with the selvage edge of the next membrane. A torch is then used to soften the membranes at their overlapped portions to achieve a seam sufficient to withstand weather conditions.
U.S. Pat. No. 6,134,856 discloses a roll roof membrane , and a method for its preparation, which obviates the use of a torch to achieve a seam between the overlapped portions of the membranes. The roof membrane comprises a support sheet having bonded on the top and bottom surfaces thereof layers comprising APP modified bitumen, a first selvage edge disposed in the top APP modified bitumen layer along one side of the membrane, a second selvage edge disposed in the bottom APP modified bitumen layer along the opposite side of the membrane, and wherein each of the selvage edges have a series of embossed ridges and valleys adopted to accept adhesives, the valleys extending substantially through the APP modified bitumen layers to the support sheet.
The method of preparing the roll roof membrane includes the steps of: a roll of support sheet is unwound and passed through an accumulator; the unwound sheet is dip coated by immersion in a coating vat containing molten compounded APP, asphalt, and one or more fillers and fire retardants; while the coatings are in a molten state, the selvage edges on opposite sides and opposite surfaces of the membrane are contacted with top side embosser and bottom side embosser; the APP modified bitumen layers are cooled and solidified by floating the membrane in a water bath and the membrane is wound into a roll. A suitable liquid parting agent, such as a coconut oil, can be added to the bottom surface of the membrane to reduce the tendency for the membrane to stick during winding and subsequent handling.
We have observed that roll blocking tends to occur with single ply membranes of the prior art. As the membranes are produced, they are wound into rolls, stored in roll configurations and delivered to the site of installation. Since the membrane is smooth, portions thereof tend to stick and adhere to each other thereby hindering the unwinding process. Embossment of selvage edges on opposite sides and opposite surfaces of the membrane does not appear to solve the roll blocking problem: while the embossed portions of the membrane easily unwind, the remaining portions constituting the majority of the surface area tend to stick and adhere to each other.
We have now discovered that the roll blocking problem can be greatly reduced by the complete embossment of the bottom layer of the single ply membrane.
In accordance with the present invention, there is provided a single ply roofing membrane for covering industrial and commercial flat and pitched roofs. The single ply roofing membrane comprises: a bottom layer and a top layer wherein the layers are permanently bound together, and the bottom layer is embossed with various patterns to increase the surface area of the membrane.
In a preferred embodiment of the present invention the single ply roofing membrane comprises: a top layer of a polyolefin, a bottom layer of a polyolefin, and a fibrous reinforcing scrim sandwiched between the top and bottom layers wherein the bottom layer is embossed with various patterns. Suitable polyolefins are polymers including polyethylene, polypropylene, terpolymers of ethylene, propylene and diene monomers, ethylene-propylene copolymers, ethylene-butane copolymers, ethylene-hexane copolymers, ethylene-octane copolymers, propylene-C4-8 alpha olefin copolymers, and metallocene polyolefins. In order to improve adhesion between top and bottom layers and the reinforcing scrim, a small amount, preferably about 0.5-20% w/w, and more preferably about 1-10% w/w, and most preferably about 1-5% w/w of a highly-flowable, functional polyolefin is incorporated into one or both polyolefin layers. A maleic anhydride-modified polyolefin (CK Witco), an epoxy-modified polyethylene (Elf Atochem) and methacrylate terpolymers thereof (Elf Atochem) are preferred. The thickness of the membrane preferably ranges from 0.1 to 5 mm (4 to 200 mils), and more preferably from 0.6 to 2.5 mm (25 to 100 mils).
The fibrous reinforcing scrim is preferably of fiberglass and/or polyester. However, woven or non-woven fabrics may also be used. The tenacity of the scrim can range from about 100 to 3000 denier, preferably 500 to 1500, and most preferably 1000 denier. Preferred support scrims have a tensile strength greater than about 14 KN per meter (80 pounds force per inch).
The bottom layer of the single ply roofing membrane is embossed with various patterns which includes: a polyhedron with a polygonal base and triangular faces meeting in a common vertex, such as a pyramidal base; a cone configuration having a circular or ellipsoidal configurations; and random pattern configurations. The depth of the embossments can be about 0.01 to 2 mm (0.4 to 80 mils), preferably 0.025 to 0.5 mm (1 to 20 mils), and most preferably 0.05 to 0.25 mm (2 to 10 mils).
The invention being described is with reference to the preferred embodiments described in the Summary of the Invention with respect to the top and bottom layers and the scrim sandwiched between the layers. However, the invention also finds utility with other scrims or support sheets made of papers and film. In the description that follows like numerals denote like components.
In addition to the random patterns shown in
In preparing the single ply roofing membrane conventional equipment and methods are used which are well known in the prior art. Such methods include extrusion coating and calendaring. The embossing rolls useful herein are known in the art and/or modified as described herein.
The single ply roll membranes typically have a width of about 1 to 5 meters (3 to 15 feet), while the length of the membranes may be about 15 meters (50 feet) or more.
The single ply roofing membranes are used with an appropriate adhesive which is painted or sprayed on the unfolded membrane prior to the installation; or can be mechanically attached using techniques well known to those skilled in the art. In both systems, the membranes are rolled out prior to the installation. Blocking tests were conducted on the embossed membranes of the present invention in roll forms, and on unembossed membranes of the prior art in roll forms as control based on ASTM D-751 method. The control samples showed 100% blocking while the membranes of the present invention showed about 25% blocking.
The invention has been described with reference to certain preferred embodiments thereof, however, it is to be understood that variations and modifications can be effected within the spirit and scope of the invention.
