Patent Application
20090100775
Single ply membrane roofing utilizes a polymeric sheet as the exterior surface of a roof structure. The sheets, which can be 7-50 feet in width, are positioned on the roof. In order to cover the entire roof, multiple sheets are positioned side by side, and the overlapped edges are adhered together to form a seam. This forms a continuous membrane, covering the entire roof.
The membrane can be attached to the roof in a variety of different ways. Adhesive can be used, as well as ballast, i.e., gravel, as well as various types of mechanical fastening systems. The obvious purpose of the membrane is to prevent water from entering the building. If the membrane is damaged, and a tear forms through the membrane, water can leak into the building. Therefore, such tears must be repaired.
The present invention is based on the concept that damage to a roofing membrane can be repaired in-situ by the incorporation of a water swellable polymer layer in the membrane structure. The water swellable polymer, or, super absorbent polymer forms a hydrogel when in contact with water. If a tear in the membrane forms, and water enters through the tear, and is absorbed by the water swellable polymer forming a hydrogel which expands and seals the tear, preventing water from entering the building.
The water swellable layer can be formed between two layers of the membrane sheeting, or, it can be adhered to the bottom surface of the membrane sheeting, as well as other locations, as long as it is not exposed to weather absent a tear in the membrane.
The objects and advantages of the present invention will be further appreciated in light of the following detailed description and drawings in which
A self repairing membrane roofing material 10, as shown in
Membrane 12 can be any polymeric membrane typically used on a membrane roof. Typical membrane roofs are formed from, for example, ethylene propylene diene monomer rubber (EPDM), polyvinyl chloride (PVC), thermoplastic olefins (TPO), modified bitumen membranes, epichlorohydrin, as well as other polymers. Typically, when such membranes are formed, two plies of polymer are formed and laminated together to form the membrane 12. This minimizes the possibility that a membrane will be formed with a perforation. For purposes of the present invention, the membrane 12 will preferably be a clean sheet. In other words, the surface 17 of membrane 12 will not include any talc or any other release agent. Thermoplastic sheeting is normally formed without talc or release agents. Thermoset sheeting such as EPDM is usually formed with talc. A method of forming the clean EPDM sheet is disclosed, for example, in Venable U.S. Pat. No. 5,643,399, the disclosure of which is hereby incorporated by reference.
Water swellable polymers are not typically adhesive in nature. Therefore, the layer 14 may incorporate additional structure to bind the water swellable polymer. The water swellable polymer layer can incorporate a thermoplastic adhesive layer to bind the water swellable polymer particles to the surface of a thermoset membrane. If the membrane is a thermoplastic, such as PVC or TPO, water swellable polymer particles can be pressed into the molten surface of the thermoplastic membrane as it is being manufactured. Alternately, a layer of a nonwoven web, or other fabric material, that physically incorporates the water swellable polymer can be adhesively bonded to the roofing membrane.
Typically, the water swellable polymers are polyacrylates, polyacrylamides, polyvinyl alcohols, copolymers of polyacrylate and polyacrylamide, hydrolyzed starch, poly(acrylonitrile), sodium carboxymethylcellulose, sodium alginate, copolymers of polyacrylate and polyvinyl alcohol, copolymers of polyacryamide and polyvinyl alcohol, and combinations thereof. These are partially cross-linked so that they are not water soluble, but merely water absorbent, forming a hydrogel when combined with water.
The method of forming the water swellable polymer-impregnated fabrics, as well as the method of forming adhesive coatings incorporating the water swellable polymers, are well known and are disclosed, for example, in Anton et al. U.S. Pat. No. 4,837,077; Fairgrieve U.S. Pat. No. 5,925,461; Fairgrieve U.S. Pat. No. 6,348,236; Bahlmann et al. U.S. Pat. No. 6,899,776; and Gruhn et al. U.S. Pat. No. 6,284,267, the disclosures of which are hereby incorporated by reference.
According to the preferred embodiment of the present invention, the layer 14 is a nonwoven web impregnated with the water swellable polymer. Such a material can be obtained from Neptco, Inc. This layer is adhered to surface 17 of membrane 12 with, for example, an adhesive layer 16. A polyethylene thermoplastic adhesive is suitable. If the membrane is a thermoplastic, a separate adhesive layer may not be required.
The amount of water swellable polymer loaded onto the surface will determine the amount of hydrogel formed and, thereby, determine the size of the tear that can be repaired with the hydrogel. Generally, the loading of the dry polymer onto the substrate will be from about 10 to about 50 g/m2.
To form a roof, the membrane sheeting 10 is applied over a roof structure 20, as indicated, with the water swellable polymer layer 14, adjacent the roof surface 20 protected by water by the membrane 12. The roof surface may be metal, wood, concrete, or insulation. The membrane 10 can be attached to the roof structure 20 by a variety of well known application methods, such as ballast, mechanical fasteners or an adhesive layer 18, as shown in
As will be explained below, if the membrane 10 is damaged, water will pass through layer 12 and be absorbed by the water swellable polymer in layer 14. The water swellable polymer will expand, sealing or closing the tear and preventing further water from passing though the damaged area. Even after drying, the polymer in layer 14 will maintain its ability to absorb water and expand, thus providing a long term repair.
An alternate embodiment of the present invention is shown in
A third embodiment of the present invention, as shown in
The present invention can also be incorporated into a built-up roof. As shown in
The present invention will be further appreciated in light of the following detailed example.
Samples of various grades of water swellable polymer (WSP) impregnated on a nonwoven fabric were obtained from Neptco, Inc. Laboratory samples (about 0.060-0.070 inches) were prepared by placing the WSP impregnated nonwoven fabric between two pieces of uncured EPDM rubber, as shown in
Samples were prepared by attaching the WSP impregnated nonwoven fabric to the bottom of a standard 0.045-inch EPDM membrane using a polyethylene hot melt adhesive (see
Samples were damaged by cutting a 1-inch gash through the entire sample. The test assembly was prepared as previously described. Samples were tested by dripping 125 ml of water over a 10-minute period. Results were recorded every 15 minutes for one hour, and then after an additional hour. The results of the experiment are shown in Table 1.
The control leaked about 89% of the water introduced in the system within the first 15 minutes, and 85% of the remaining water over the following 15 minutes. In one case, the experimental sample leaked only 1 ml of water (0.8%) before the system self-repaired. In the other two cases, self-repairing was somewhat slower, but the process was completed within 45 minutes. It should be noted that the samples were not supported, and the water applied did wick through the WSP material.
The performance of this system as compared to the system where the sample was fabricated with the WSP nonwoven between two cured layers was significantly improved.
Samples were prepared by attaching the WSP nonwoven to the bottom of a membrane as previously described (see
Water was introduced to the system via a burette at the rate of 125 ml (volume of about 1.75 in) over a 15-minute period to simulate a heavy rainstorm. Results were recorded every 15 minutes for one hour, and then after an additional hour. The results of the experiment are shown in Table 2.
As can be seen from the results, two of the three experimental samples exhibited excellent self-repairing characteristics. Although leakage was observed in the third sample, it significantly outperformed the control. (It should be noted that the third sample was tested immediately after preparation.) In the case of the first two samples, they were allowed to sit overnight before testing was commenced. This behavior could be a result of an interaction between the WSP material and residual solvents from the bonding adhesive and has been observed with other samples tested immediately after preparation.
In order to examine the reversibility of the system, the samples were placed in an oven at 100° C. to dry overnight and retested the next day. The testing procedure was identical to that described above. The results of the experiment are shown in Table 3.
The results demonstrate the reversibility of the system. Additionally, the self repairing ability of the third sample improved dramatically. The results suggest that if there is an interaction between residual solvent from the bonding adhesive and the WSP material, it does not permanently affect the self repairing characteristics of the system after the system has completely dried.
In order to test the ability of the system to repair a cut in the membrane, a 2-inch cut was made to the membrane system. The test assembly was prepared and tested as previously described. The results of the simulated cut damage are reported in Table 4.
As the results indicate, the system is capable of self-repair when subjected to damage of this type. The reversibility of the system was also investigated. The samples were dried as before, and tested the next day. The results are shown in Table 5.
One experimental sample exhibited minor leakage. Initial leakage within the first few minutes is expected when the rate of water flowing into the system is greater than the rate of the WSP particles absorbing water and swelling to fill and repair the membrane damage. As can be seen from the results, the volume of water through the system decreased over time. The other two samples were observed to completely self-repair.
In order to determine the effects of heat aging on the ability to self-repair, samples were prepared and attached to insulation as previously described. The samples were aged for 14 days at 70° C. After 14 days the samples were damaged using the simulated tear technique, and then tested. After testing, the samples were returned to the 70° C. oven and tested weekly. The results of this study are summarized in Table 6 and Table 6A.
The results clearly indicate that heat aging at modest temperatures does not impact the ability of the system to self-repair (attempts to age the samples at higher temperatures resulted in a degradation of the polyisocyanurate insulation and bonding adhesive). Additionally, the results also demonstrate the reversibility of the system. In this case, five cycles of swelling/drying/swelling were demonstrated.
Aging studies were also performed on samples with a simulated cut. Samples were aged, assembled and tested as described above. The results of this study are shown in Table 7. As with the simulated tear aging tests, the results indicate that aging has no effect on the ability of the system to self-repair and regenerate after drying.
To study the effect of ponding water on the system, an experimental sample was prepared with a simulated tear as described above. Water (about 150 ml, 2 inches volume) was introduced into the system, and the membrane was allowed to self-repair. The test was checked daily for any signs of leakage. Water was periodically added to the system in order to replace that lost to evaporation. The system held 2 inches of water without leakage for a period of three weeks. Theoretically, the sample should only leak when the hydrostatic pressure of the water above the damage is sufficient enough to force the WSP particles from the damaged area. Preliminary results indicate the simulated cut system can hold in excess of 12 inches of water without leaking.
Ruptures in roofing material can occur during the installation of heavy equipment on a rooftop. In order to investigate the ability of the system to repair damage of this type, a membrane rupture was simulated by the use of a dynamic puncture device as described in ASTM D 5635. A 3,000 g weight was used to create an impact energy of 15 J. The test assembly was prepared as previously described. The samples were aged for 14 days at 70° C. before being subjected to damage. The samples were tested as previously described. The amount of water that leaked through the system was recorded after two hours. The samples were dried at 70° C. overnight and retested. This cycle was repeated for 12 testing periods in order to demonstrate the reversibility of the system. The results of the simulated rupture are reported in Table 8.
As shown in the above examples, the present invention provides a self repairing roofing membrane that provides long term repairs of minor tears in a membrane structure. This will substantially reduce the risk of water damage caused by such tears and reduce and/or eliminate the need for repair of the tear. Further, many of the tears should be visible. This will allow for a secondary repair or patch over the tear.
This has been a description of the present invention along with the preferred method of practicing the invention. However, the invention itself should only be defined by the appended claims, wherein we claim:
