Patent Publication Number: US-2020299967-A1

Title: Method of reroofing

Description:
This application claims the benefit of U.S. Provisional Application Ser. No. 62/313,239, filed on Mar. 25, 2016, which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     Embodiments of the invention are directed toward methods of reroofing wherein a membrane carrying a factory-applied adhesive is applied directly to an existing membrane and/or additional substrates that are installed on the roof as part of the roofing event such as coverboards. 
     BACKGROUND OF THE INVENTION 
     Large, flexible polymeric sheets, which are often referred to as membranes or panels, are used in the construction industry to cover flat or low-sloped roofs. These membranes provide protection to the roof from the environment, particularly in the form of a waterproof barrier. As is known in the art, commercially popular membranes include thermoset membranes such as those including cured EPDM (i.e., ethylene-propylene-diene terpolymer rubber) or thermoplastics such as TPO (i.e., thermoplastic olefins). 
     These membranes are typically delivered to a construction site in a bundled roll, transferred to the roof, and then unrolled and positioned. The sheets are then affixed to the building structure by employing varying techniques such as mechanical fastening, ballasting, and/or adhesively adhering the membrane to the roof. The roof substrate to which the membrane is secured may be one of a variety of materials depending on the installation site and structural concerns. For example, the surface may be a concrete, metal, or wood deck, it may include insulation or recover board, and/or it may include an existing membrane. 
     In addition to securing the membrane to the roof—which mode of attachment primarily seeks to prevent wind uplift—the individual membrane panels, together with flashing and other accessories, are positioned and adjoined to achieve a waterproof barrier on the roof. Typically, the edges of adjoining panels are overlapped, and these overlapping portions are adjoined to one another through a number of methods depending upon the membrane materials and exterior conditions. One approach involves providing adhesives or adhesive tapes between the overlapping portions, thereby creating a water resistant seal. 
     With respect to the former mode of attachment, which involves securing the membrane to the roof, the use of adhesives allow for the formation of a fully-adhered roofing system. In other words, a majority, if not all, of the membrane panel is secured to the roof substrate, as opposed to mechanical attachment methods that can only achieve direct attachment in those locations where a mechanical fastener actually affixes the membrane. 
     When adhesively securing a membrane to a roof, such as in the formation of a fully-adhered system, there are a few common methods employed. The first is known as contact bonding whereby technicians coat both the membrane and the substrate with an adhesive, and then mate the membrane to the substrate while the adhesive is only partially set. Because the volatile components (e.g. solvent) of the adhesives are flashed off prior to mating, good early (green) bond strength is developed. 
     Another mode of attachment is through the use of a pre-applied adhesive to the bottom surface of the membrane. In other words, prior to delivery of the membrane to the job site, an adhesive is applied to the bottom surface of the membrane. In order to allow the membrane to be rolled and shipped, a release film or member is applied to the surface of the adhesive. During installation of the membrane, the release member is removed, thereby exposing the pressure-sensitive adhesive, and the membrane can then be secured to the roofing surface without the need for the application of additional adhesives. 
     As is known in the art, the pre-applied adhesive can be applied to the surface of the membrane in the form of a hot-melt adhesive. For example, U.S. Publication No. 2004/0191508, which teaches peel and stick thermoplastic membranes, employs pressure-sensitive adhesive compositions comprising styrene-ethylene-butylene-styrene (SEGS), tackifying endblock resins such as cumarone-indene resin and tackifying midblock resins such as terpene resins. This publication also suggests other hot-melt adhesives such as butyl-based adhesives, EPDM-based adhesives, acrylic adhesives, styrene-butadiene adhesives, polyisobutylene adhesives, and ethylene vinyl acetate adhesives. 
     In view of the nature of the adhesives, peel and stick membranes have inherent limitations. For example, there are temperature windows that limit the minimum temperature at which the membranes can be installed on a roof surface. Also, there are maximum temperature limits on the roof surface that the adhesive can withstand while maintaining wind-uplift integrity. With respect to the latter, where the surface temperature on the roof nears the glass transition temperature of the adhesive, the adhesive strength offered by the pressure-sensitive adhesive is not maintained. As a result, peel-and-stick membranes have not gained wide acceptance in the industry. Moreover, the use of peel-and-stick membranes has been limited to use in conjunction with white membranes (e.g., white thermoplastic membranes) because the surface temperature of these membranes remains cooler when exposed to solar energy. 
     Reroofing an existing roof generally includes the application of a newly fabricated membrane over the existing membrane. Reroofing presents challenges, especially where there is a desire to fully adhere the new membrane to an existing membrane, because the existing roof surface can provide an undesirable substrate for adhesive attachment. For example, the roof surface can be environmentally damaged, covered with debris, and/or can be relatively uneven. 
     SUMMARY OF THE INVENTION 
     Embodiments of the present invention provide a method of reroofing, the method comprising of applying to an existing roof surface a membrane composite including a pre-applied adhesive layer by mating the adhesive layer to the existing membrane. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-section perspective view of a membrane composite according to embodiments of the invention. 
         FIG. 2  is a flow chart describing a process for making membrane composite according to embodiments of the present invention. 
         FIG. 3  is a schematic of a continuous process for making membrane composite according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     Embodiments of the invention are based, at least in part, on the discovery of reroofing technique that includes the application of membrane having a pre-applied (e.g. factory-applied) pressure-sensitive adhesive that is at least partially cured directly to an existing membrane secured to the roof being reroofed. In one or more embodiments, the pre-applied adhesive is applied as a hot-melt adhesive and subsequently cured. It has unexpectedly been discovered that the nature of the pre-applied adhesive, including its initial tack and high-temperature strength, allows the membrane composite to be directly attached to the existing membrane. 
     Membrane Construction 
     Practice of the present invention does not necessarily change the overall construction of the membranes of the present invention. As the skilled person understands, membranes that carry an adhesive for application by peel-and-stick methods are generally known as disclosed in U.S. Publication No. 2004/0191508, which is incorporated herein by reference. 
     For example, a membrane  11 , which may be referred to as a membrane composite  11 , is shown in  FIG. 1 . Membrane composite  11  includes polymeric panel  13 , pressure-sensitive adhesive layer  15 , and release member  17  removably attached to layer  15 . 
     Membrane Panel 
     In one or more embodiments, the membrane may be a thermoset material. In other embodiments the membrane may be a thermoformable material. In one or more embodiments, the membrane may be EPDM based. In other embodiments, the membrane may be TPO based. In these or other embodiments, the membrane may be flexible and capable of being rolled up for shipment. In these or other embodiments, the membrane may include fiber reinforcement, such as a scrim. In one or more embodiments, the membrane includes EPDM membranes including those that meet the specifications of the ASTM D-4637. In other embodiments, the membrane includes thermoplastic membranes including those that meet the specifications of ASTM D-6878-03. Still other membranes may include PVC, TPV, CSPE, and asphalt-based membranes. 
     In one or more embodiments, the roofing membrane panels are characterized by conventional dimensions. For example, in one or more embodiments, the membrane panels may have a thickness of from about 500 μm to about 3 mm, in other embodiments from about 1,000 μm to about 2.5 mm, and in other embodiments from about 1,500 μm to about 2 mm. In these or other embodiments, the membrane panels of the present invention are characterized by a width of about 1 m to about 20 m, in other embodiments from about 2 m to about 18 m, and in other embodiments from about 3 m to about 15 m. 
     Hot-Melt Curable Adhesives 
     In one or more embodiments, the pressure-sensitive adhesive layer (e.g. layer  23 ) is a cured pressure-sensitive adhesive. In sub-embodiments thereof, this cured pressure-sensitive adhesive layer is formed from a curable hot-melt adhesive. In other words, and as will be described in greater detail below, an uncured adhesive composition is applied to the membrane as a hot-melt composition (i.e. the composition is heated and applied as a flowable composition in the absence or appreciable absence of solvent), and then the composition is subsequently crosslinked (i.e. cured) to form the cured pressure-sensitive layer. 
     In one or more embodiments, the cured pressure-sensitive adhesive layer may be an acrylic-based hot-melt adhesive. In one or more embodiments, the adhesive is a polyacrylate such as a polyacrylate elastomer. In one or more embodiments, useful polyacrylates include one or more units defined by the formula: 
     
       
         
         
             
             
         
       
     
     where each R 1  is individually hydrogen or a hydrocarbyl group and each R 2  is individually a hydrocarbyl group. In the case of a homopolymer, each R 1  and R 2 , respectively, throughout the polymer are same in each unit. In the case of a copolymer, at least two different R 1  and/or two different R 2  are present in the polymer chain. 
     In one or more embodiments, hydrocarbyl groups include, for example, alkyl, cycloalkyl, substituted cycloalkyl, alkenyl, cycloalkenyl, substituted cycloalkenyl, aryl, substituted aryl, aralkyl, alkaryl, allyl, and alkynyl groups, with each group containing in the range of from 1 carbon atom, or the appropriate minimum number of carbon atoms to form the group, up to about 20 carbon atoms. These hydrocarbyl groups may contain heteroatoms including, but not limited to, nitrogen, oxygen, boron, silicon, sulfur, and phosphorus atoms. In particular embodiments, each R 2  is an alkyl group having at least 4 carbon atoms. In particular embodiments, R 1  is hydrogen and R 2  is selected from the group consisting of butyl, 2-ethylhexyl, and mixtures thereof. 
     In one or more embodiments, the polyacrylate elastomers that are useful as adhesives in the practice of this invention may be characterized by a glass transition temperature (Tg) of less than 0° C., in other embodiments less than −20° C., in other embodiments less than −30° C. In these or other embodiments, useful polyacrylates may be characterized by a Tg of from about −70 to about 0° C., in other embodiments from about −50 to about −10° C., and in other embodiments from about −40 to about −20° C. 
     In one or more embodiments, the polyacrylate elastomers that are useful as adhesives in the practice of this invention may be characterized by a number average molecular weight of from about 90 to about 800 kg/mole, in other embodiments from about 100 to about 350 kg/mole, in other embodiments from about 100 to about 700 kg/mole, in other embodiments from about 150 to about 270 kg/mole, in other embodiments from about 120 to about 600 kg/mole, and in other embodiments from about 180 to about 250 kg/mole. 
     In one or more embodiments, the polyacrylate elastomers that are useful as adhesives in the practice of this invention may be characterized by a Brookfield viscosity at 150° C. of from about 10,000 to about 200,000 cps, in other embodiments from about 30,000 to about 60,000 cps, in other embodiments from about 30,000 to about 170,000 cps, in other embodiments from about 25,000 to about 150,000 cps, in other embodiments from about 30,000 to about 60,000 cps, and in other embodiments from about 40,000 to about 50,000 cps. 
     Specific examples of polyacrylate elastomers that are useful as adhesives in the practice of the present invention include poly(butylacrylate), and poly(2-ethylhexylacrylate). These polyacrylate elastomers may be formulated with photoinitiators, solvents, plasticizers, and resins such as natural and hydrocarbon resins. The skilled person can readily formulate a desirable adhesive composition. Useful adhesive compositions are disclosed, for example, in U.S. Pat. Nos. 6,720,399, 6,753,079, 6,831,114, 6,881,442, and 6,887,917, which are incorporated herein by reference. 
     In other embodiments, the polyacrylate elastomers may include polymerized units that serve as photoinitiators. These units may derive from copolymerizable photoinitiators including acetophenone or benzophenone derivatives. These polyacrylate elastomers and the adhesive compositions formed therefrom are known as disclosed in U.S. Pat. Nos. 7,304,119 and 7,358,319, which are incorporated herein by reference. 
     Useful adhesive compositions are commercially available in the art. For example, useful adhesives include those available under the tradename acResin (BASF), those available under the tradename AroCure (Ashland Chemical), and NovaMeltRC (NovaMelt). In one or more embodiments, these hot-melt adhesives may be cured (i.e., crosslinked) by UV light. 
     In one or more embodiments, the hot-melt adhesive is at least partially cured after being applied to the membrane, as will be discussed in greater detail below. In one or more embodiments, the adhesive is cured to an extent that it is not thermally processable in the form it was prior to cure. In these or other embodiments, the cured adhesive is characterized by a cross-linked infinite polymer network. While at least partially cured, the adhesive layer of one or more embodiments is essentially free of curative residue such as sulfur or sulfur crosslinks and/or phenolic compounds or phenolic-residue crosslinks. 
     As indicated above, the pressure-sensitive adhesive, in its cured stated, provides sufficient tack to allow the membrane composites of this invention to be used in roofing systems that meet industry standards for wind uplift resistance. In one or more embodiments, this tack may be quantified based upon the peel strength when adhered to another membrane in accordance with ASTM D-1876-08. In one or more embodiments, the cured pressure-sensitive adhesive of the present invention is characterized by a peel strength, according to ASTM D-1876-08, of at least 1.8 lbf/in, in other embodiments at least 3.6 lbf/in, in other embodiments at least 8.0 lbf/in, in other embodiments at least 15 lbf/in, and in other embodiments at least 20 lbf/in. 
     Similarly, the tack of the pressure-sensitive adhesive, in its cured state, may be quantified based upon the peel strength when adhered to a construction board (e.g. insulation board) having a kraft paper facer in accordance with ASTM D-903-98 (2010). In one or more embodiments, the cured pressure-sensitive adhesive of the present invention is characterized by a peel strength, according to ASTM D-903-98 (2010) using an insulation board with kraft paper facer, of at least 1.5 lbf/in, in other embodiments at least 2.0 lbf/in, in other embodiments at least 2.5 lbf/in, in other embodiments at least 3.0 lbf/in, and in other embodiments at least 3.5 lbf/in. 
     Release Member 
     In one or more embodiments, release member 17 may include a polymeric film or extrudate, or in other embodiments it may include a cellulosic substrate. Where the polymeric film and/or cellulosic substrate cannot be readily removed after being attached to the asphaltic component, the polymeric film and/or cellulosic substrate can carry a coating or layer that allows the polymeric film and/or cellulosic substrate to be readily removed from the asphaltic component after attachment. This polymeric film or extrudate may include a single polymeric layer or may include two or more polymeric layers laminated or coextruded to one another. 
     Suitable materials for forming a release member that is a polymeric film or extrudate include polypropylene, polyester, high-density polyethylene, medium-density polyethylene, low-density polyethylene, polystyrene or high-impact polystyrene. The coating or layer applied to the film and/or cellulosic substrate may include a silicon-containing or fluorine-containing coating. For example, a silicone oil or polysiloxane may be applied as a coating. In other embodiments, hydrocarbon waxes may be applied as a coating. As the skilled person will appreciate, the coating, which may be referred to as a release coating, can be applied to both planar surfaces of the film and/or cellulosic substrate. In other embodiments, the release coating need only be applied to the planar surface of the film and/or cellulosic substrate that is ultimately removably mated with the asphaltic component. 
     In one or more embodiments, the release member is characterized by a thickness of from about 15 to about 80, in other embodiments from about 18 to about 75, and in other embodiments from about 20 to about 50 μm. 
     Preparation of Membrane Composite 
     The membrane panels employed in the membrane composites of the present invention may be prepared by conventional techniques. For example, thermoplastic membrane panels may be formed by the extrusion of thermoplastic compositions into one or more layers that can be laminated into a membrane panel. Thermoset membranes can be formed using known calendering and curing techniques. Alternatively, thermoset membranes can be made by continuous process such as those disclosed in WO 2013/142562, which is incorporated herein by reference. Once the membrane is formed, the curable hot-melt adhesive can be extruded onto the membrane by using known apparatus such as adhesive coaters. The adhesive can then subsequently be cured by using, for example, UV radiation. The release film can be applied to the adhesive layer, and the membrane can then be subsequently rolled for storage and/or shipment. Advantageously, where the membrane panel is made by using continuous techniques, the process can be supplemented with continuous techniques for applying and curing the adhesive coatings according to embodiments of the present invention to thereby prepare usable membrane composites within a single continuous process. 
     As generally shown in  FIG. 2 , process  30  for preparing a composite membrane according to the present invention generally begins with a step of heating  32 , wherein a pressure-sensitive adhesive is heated to a sufficient temperature to allow the adhesive to be applied as a coating within a coating step  34 . Within coating step  34 , the adhesive is applied to the membrane to form a coating layer. Following formation of the coating, the coating is subjected to a UV-curing step  36  where sufficient UV energy is applied to the coating to thereby effect a desirable curing or crosslinking of the adhesive. Once the adhesive has been sufficiently cured by exposure to UV curing step  36 , a release member can be applied to the cured coating in a member application step  38 . Following application of a member, the composite is wound into a roll at winding step  40 . 
     In one or more embodiments, heating step  32  heats the adhesive to a temperature of from about 120 to about 160° C., in other embodiments from about 125 to about 155° C., and in other embodiments from about 130 to about 150° C. 
     In one or more embodiments, coating step  34  applies an adhesive to the surface of a membrane to form a coating layer of adhesive that has a thickness of at least 51 μm (2 mil), in other embodiments at least 102 μm (4 mil), in other embodiments at least 127 μm (5 mil), and in other embodiments at least 152 μm (6 mil). In one or more embodiments, coating step  34  applies an adhesive to the surface of a membrane to form a coating layer of adhesive that has a thickness of from about 51 to about 381 μm (about 2 to about 15 mil), in other embodiments from about 102 to about 305 μm (about 4 to about 12 mil), and in other embodiments from about 127 to about 254 μm (about 5 to about 10 mil). In one or more embodiments, the coating has a uniform thickness such that the thickness of the coating at any given point on the surface of the membrane does not vary by more than 51 μm (2 mil), in other embodiments by more than 38 μm (1.5 mil), and in other embodiments by more than 25 μm (1 mil). 
     In one or more embodiments, UV curing step  36  subjects the adhesive coating to a UV dosage of from about 30 to about 380 millijoule/cm 2 , in other embodiments from about 35 to about 300 millijoule/cm 2 , in other embodiments from about 40 to about 280 millijoule/cm 2 , in other embodiments from about 45 to about 240 millijoule/cm 2 , and in other embodiments from about 48 to about 235 millijoule/cm 2 . It has advantageously been discovered that the required dosage of energy can be exceeded without having a deleterious impact on the adhesives of the present invention. For example, up to ten times, in other embodiments up to five times, and in other embodiments up to three times the required dosage can be applied to the coating composition without having a deleterious impact on the coating composition and/or its use in the present invention. 
     In one or more embodiments, UV curing step  36  subjects the adhesive coating to a UV intensity, which may also be referred to as UV irradiance, of at least 150, in other embodiments at least 200, and in other embodiments at least 250 milliWatts/cm 2 . In these or other embodiments, UV curing step 36 subjects the adhesive coating to a UV intensity of from about 150 to about 500 milliWatts/cm 2 , in other embodiments from about 200 to about 400 milliWatts/cm 2 , and in other embodiments from about 250 to about 350 milliWatts/cm 2 . It has advantageously been discovered that the ability to appropriately cure the coating compositions of the present invention, and thereby provide a useful pressure-sensitive adhesive for the roofing applications disclosed herein, critically relies on the UV intensity applied to the coating. It is believed that the thickness of the coatings (and therefore the thickness of the pressure-sensitive adhesive layer) employed in the present invention necessitates the application of greater UV intensity. 
     In one or more embodiments, the energy supplied to the coating layer within UV radiation step  36  is in the form of UV-C electromagnetic radiation, which can be characterized by a wave length of from about 250 to about 260 nm. In one or more embodiments, the UV dosage applied during UV curing step  36  is regulated based upon a UV measuring and control system that operates in conjunction with UV curing step  36 . According to this system, UV measurements are taken proximate to the surface of the adhesive coating layer using known equipment such as a UV radiometer. The data from these measurements can be automatically inputted into a central processing system that can process the information relative to desired dosage and/or cure states and automatically send signal to various variable-control systems that can manipulate one or more process parameters. For example, the power supplied to the UV lamps and/or the height at which the UV lamps are positioned above the coating layer can be manipulated automatically based upon electronic signal from the central processing unit. In other words, the UV intensity, and therefore the UV dosage, can be adjusted in real time during the manufacturing process. 
     In one or more embodiments, an exemplary process for preparing the membrane composites of the present invention can be described with reference to  FIG. 3 . Continuous process  50  includes a heating step  52  where UV curable hot-melt adhesive  51  is heated to a desired temperature within a heated tank  53 . Adhesive  51  is fed into an extrusion device, such as a coater  55 , which may include a pump, such as a gear pump  57 , and a slot die  59 . Within coating step  54 , coater  55  extrudes adhesive  51 , which is in its molten, liquid or flowable state, and deposits a coating layer  61  of adhesive  51  onto a planar surface  63  of membrane  65 . 
     As shown in  FIG. 3 , coating step  54  can include a roll-coating operation, where adhesive  51  is applied to membrane  65  while membrane  65  is at least partially wound around a coating mandrel  67 . Membrane  65  carrying coating layer  61  is fed to a crosslinking step  56 , where coating layer  61  of adhesive  51  is subjected to a desired dosage of UV radiation  69 , which may be supplied by one or more UV lamps  71 . UV lamps  71  may include, for example, mercury-type UV lamps or LED UV lamps. As the skilled person appreciates, the desired dosage of UV energy can be supplied to coating  61  by adjusting the UV intensity and exposure time. The intensity can be manipulated by the power supplied to the respective lamps and the height (H) that the lamps are placed above the surface of coating  61  of adhesive  51 . Exposure time can be manipulated based upon the line speed (i.e., the speed at which membrane  65  carrying coating layer  61  is passed through UV curing step  56 ). 
     Following UV curing step  56 , release paper  73  may be applied to upper surface  75  of coating layer  61  within release paper application step  58 . As shown in  FIG. 3 , release paper  73  may be supplied from a mandrel  77  and removably mated to upper surface  75  through pressure supplied by nip rolls  79 . After application of release paper  73 , the composite product may be wound within winding step  60  to provide wound rolls  81  of composite products  83 . 
     Characteristics of Composite Membrane 
     In one or more embodiments, the bond between the layer of crosslinked pressure-sensitive adhesive disposed on a surface of the membrane and the membrane of an existing membrane surface according to the present invention may be characterized by an advantageous peel strength. In one or more embodiments, the peel strength of the bond between the layer of crosslinked pressure-sensitive adhesive disposed on the membranes and the existing membrane may be characterized by a peel strength, as determined according to Pressure Sensitive Tape Council (PSTC) 101, of at least 3.0, in other embodiments at least 3.5, and in other embodiments at least 4.0 pounds per linear inch (pli). In these or other embodiments, the peel strength may be from about 3.0 to about 25 in other embodiments from about 3.5 to about 20, and in other embodiments from about 4.0 to about 18 pli. 
     In one or more embodiments, the bond between the layer of crosslinked pressure-sensitive adhesive disposed on a surface of the membrane and the existing membrane may be characterized by an advantageous dead load shear. In one or more embodiments, the dead load shear of the bond between the layer of crosslinked pressure-sensitive adhesive disposed on the membranes of the present invention and the existing membrane may be characterized by a dead load shear, as determined according to PSTC 107, of at least 0.5 hour (time of failure), in other embodiments at least 1.0 hour, and in other embodiments at least 1.5. In these or other embodiments, the dead load shear may be from about 2.0 to about 2.5 hours. 
     Method of Reroofing 
     In one or more embodiments, the method of reroofing includes providing the membrane composite, optionally preparing the roof surface, positioning the membrane composite over the roof surface, removing the release member, and mating the adhesive layer to the existing membrane. 
     In one or more embodiments, the roof surface may be prepared by removing debris from the surface of the existing membrane. This may include using conventional means such as sweeping or blowing (e.g. with the use of power blower) to remove debris from the membrane surface. In addition thereto or in lieu thereof, water may be employed to assist in the removal of debris. This may include the use of a high-pressured water spray (e.g. power washer). In particular embodiments, the existing membranes can be washed using cleaning products such as those available from Firestone Building Products, LLC under the tradename Membrane PreWash. 
     Once the roof surface has been optionally prepared, the membrane composites of the present invention can be secured to the existing roof membrane by using standard peel-and-stick techniques, which include positioning the membrane, removing the release member, and mating the adhesive layer to the roof surface (i.e. to the existing membrane). 
     Roof System 
     In one or more embodiments, practice of the present invention provides roof surface that includes an existing membrane secured to the roof deck, and a second membrane secured to the first membrane through the factory-applied adhesive layer described herein. 
     Various modifications and alterations that do not depart from the scope and spirit of this invention will become apparent to those skilled in the art. This invention is not to be duly limited to the illustrative embodiments set forth herein.