Patent Application
20250215688
The present invention relates to induction welding of roofing membranes onto anchor plates mounted below.
Roofing membranes (such as TPO, EPDM and PVC membranes) have been attached onto building roofs using different methods. In one common approach, the edges of one side of the membranes are attached to the insulation and roof deck underneath using mechanical fasteners. The other edge of the membrane is joined to the next membrane which has been fastened down to form a monolith waterproofing system. This is usually called mechanically fasten roofing system. In other approaches, the entire membrane is attached to the insulation boards below via adhesive. In some cases, in order to further increase the wind uplift resistance, one edge of membranes are fastened down to the insulation board underneath. This is usually called fully adhered roofing system.
In the mechanically fastened roofing system, the entire membrane width is loosely laid on top of the insulation board except the two edges (one edge is fastened down directly to the insulation board below and the other edge is welded to the next membrane whose edge is fastened down). This is in contrast to the fully adhered system in which the entire membrane is attached to the insulation board below. As a result, the wind uplifting performance of the mechanically fastened system is significantly worse than that of the fully adhered system.
To enhance the wind uplifting performance of a mechanically fastened roofing system, additional attachment points to the insulation board underneath can be created via induction welding multiple points of membrane to the anchor plates that fastened down the insulation boards. In this approach, special anchor plates are used with a thin layer of hot-melt adhesive coated on the surface of the anchor plates. The Rhino Bond® system sold by OMG, Inc. of Agawam, MA provides such as system, and is described in detail in U.S. Pat. Nos. 10,925,124 and 8,492,683. The IsoWeld® system sold by SFS Holdings of Heerbrugg, Switzerland also provides a system as described in detail in their U.S. Pat. Nos. 10,474,126 and 9,328,515. In these various induction welding systems, mechanical fasteners (called “anchor plates”) are first attached across the roof in an array formation. Next, a TPO membrane (or other suitable membrane) is laid over the anchor plates. Next, the TPO membrane is induction welded to the anchor plates using a magnetic induction heating system. To locate these anchor plates below the TPO membrane, an operator passes a stand-up induction welding tool over the TPO membrane. This tool has sensor coils that detect the presence of the anchor plates below the membrane. After an anchor plate has been detected, the tool then uses magnetic induction to heat the heat-activated adhesive that covers the top of each anchor plate. When heated, the anchor plate's adhesive then becomes thermally welded to the bottom of the TPO membrane, thereby securing the TPO roofing membrane onto the roof.
It is important to design induction welding systems that cope with the problem of high winds. For example, higher winds will exert greater forces on the roofing membrane, possibly causing it to pull up and separate from the adhesives covering the tops of the anchor plates. In this situation, one solution has been to attempt to make the adhesive on the anchor plate stronger.
Roofing membranes (such as standard TPO roofing membranes) have top and bottom TPO layers that are separated by a middle scrim layer. The scrim layer is necessary to give the membrane its overall strength and toughness on the roof. The middle scrim layer also gives the membrane puncture resistance, and makes the overall membrane stronger in tension. When the membrane is first formed, the bonding between the central scrim and top and bottom layers is rather weak. The adhesion strength between the top and bottom layer mostly comes from the bonding of top and bottom layers together through the holes in the scrim layer itself.
Unfortunately, another problem that also occurs during high winds has been that the roofing membrane itself tends to tear apart. This occurs because the presence of the scrim layer between the top and bottom membrane layers can prevent the top and bottom layers from bonding together. This is because the scrim layer does not have strong adhesion to top and bottom layer and the top and bottom layers are simply melted together through the holes in the scrim layer. When the scrim fibers are spaced far apart such that there are large apertures therebetween, there is more contacting surface area between the top and bottom layers. Conversely, when the scrim fibers are closer together (and take up more of the total surface area between the top and bottom layers), then there is less available contacting surface between the top and bottom layers, and they are not able to be bonded together as strongly. Weak bonding between the top and bottom layers of the membrane can affect the performance of the membrane under high wind loads. Specifically, as stated above, the membrane may fail by the top and bottom layers separating from one another.
Manufacturing a membrane that does not tear apart at the scrim layer will enable the roof to perform acceptably under higher winds, thus increasing the wind rating for the roof. It is therefore desirable to find a membrane solution that provides a sufficiently strong middle scrim layer in the membrane (as is required for proper roof performance), yet does not significantly compromise the connection strength between the top and bottom layers of the membrane when bonded together though the holes in the scrim layer.
The present invention provides a method of induction welding a roofing membrane onto a roof deck, comprising: (a) placing an insulation layer onto a roof deck; (b) securing roofing anchor plates onto the insulation layer, wherein the roofing plates are covered with a thin layer of hot-melt adhesive; (c) placing a roofing membrane over the roofing anchor plates, wherein the roofing membrane comprises: a top layer, a bottom layer, and a low to medium density scrim between the top and bottom layers; and then (d) applying induction heating to the anchor plates so as to cause the metal plate to heat up to melt the hot-melt adhesive such that the adhesive secures the bottom layer to the anchor plate. Magnetic weights may be used to hold the membrane to the plate until the adhesive cools and solidifies.
In preferred aspects, a low to medium density scrim is used in the present system. As defined herein, a low density scrim has five or less strands per inch; a medium density scrim has five to eight strands per inch and a high density scrim has more than nine strands per inch. As scrims commonly have different numbers of strands per inch in their machine and cross directions, a density of “X number of strands per inch” as used herein refers to a scrim having a density of X strands per inch averaged between its machine and cross direction densities.
There are different types of scrim used in the single ply roofing membrane for reinforcement. One type is produced via weft insertion warp knit machine. Weft refers to cross machine direction while warp refers to machine direction. The weft and warp yarns are knitted together with tie yarns. There are different knit patterns available for this type of scrim. Not to be restricted by the illustrations.
The present inventors have experimentally determined that the above ranges of low to medium scrim fiber density offer surprising benefits as the density is high enough for the membrane to perform acceptably on the roof (in terms of strength, toughness and puncture resistance), yet low enough such that the top and bottom layers of the membrane have a large enough contact surface to bond together through the openings in the scrim layer.
In preferred aspects, the warp and weft yarns have yarn weight of 1,000 to 2,500 deniers. Yarn denier is a measure of the linear mass of the fibers in scrim. Denier is a unit used for the weight of 9,000 meters of filament yarn. Typically, 1,000 or 1,300 denier yarns are used as warp or weft yarns in the scrim for the roof applications. It is possible that when low to medium scrim fiber density is used, a higher denier yarns may need to achieve acceptable performance (in terms of strength, toughness and puncture resistance). In most preferred aspects, the warp and weft yarns have yarn weight of 1,300 to 2,000 deniers.
In preferred aspects, the scrim layer is made of PET (polyethylene terephthalate), and the top and bottom layers of the membrane are made of one of: TPO (thermoplastic polyolefin), EPDM (ethylene propylene diene monomer) or PVC (polyvinyl chloride). It is to be understood that other suitable materials may be used as well for the scrim and membrane layers, all keeping within the scope of the present invention.
In most preferred aspects, the low to medium density scrim has a knit pattern where the tie yarn does not knit two warp yarns to tie together with weft yarns. Instead, the tie yarn knit along one warp yarn and tie together with weft yarns in a knit pattern called I-knit or pillar-knit. Both knit and laid scrim, knit scrims of different fiber density, and knit scrims of different knit patterns have been experimentally determined by the present inventors to have sufficiently large apertures to provide a large enough contact surface to bond together through the opening in the scrim layer to provide good wind uplifting performance.
In other preferred aspects, the present invention provides a roofing membrane suitable for induction welding, comprising: a top layer; a bottom layer; and a low to medium density scrim layer between the top and bottom layers, wherein the scrim has a fiber density of 8 or less strands per inch, such as between 3×3 and 8×8 strands of yarn per inch, or most preferably about 4.5×4.5 to 8×6 strands of yarn per inch. In one preferred embodiment, a 6×6 scrim can be used. The preferred yarn weight is 1,000 to 2,500 denier. In various aspects, the most preferred is 1,300 to 2,000 denier. In one preferred embodiment, 1,500 denier yarns can be used.
Instead, a system is desired in which strong mechanical fastening systems can be used. An example of such a system is seen in
After the TPO membrane 10 has been unrolled and spread over the array of anchor plates 44, an operator-controlled standing induction welding machine 100 is passed over the top of TPO membrane 10. This induction welding machine 100 has sensor coils in it that detect when it is positioned directly over each anchor plate 44. When machine 100 is in its correct position over an anchor plate 44, a magnetic induction field is applied to the anchor plate. This magnetic induction field heats the anchor plate and thus causes the adhesive on the top surface of the anchor plate to melt and bond to the bottom surface of TPO membrane 10. Heavy magnets can then be temporarily placed on top of the induction welding locations to hold TPO membrane 10 onto anchor plate 44 as the adhesive solidifies. As such, induction welding is similar to normal in-seam mechanical fastening, but with the added advantage of more anchoring points in the middle of the TPO membrane. This helps the TPO membrane better withstand high wind loading.
In short,
The important advantage of the present system as compared to traditional IsoWeld® or RhinoBond® induction plate welding systems is that the present system specifically includes a unique and newly designed low to medium density scrim layer 22 for use in its proprietary TPO membrane 10. The Applicant has experimentally determined that this newly devised low to medium density scrim layer 22 offers surprising and unexpected benefits when working with anchor plate induction welding systems.
Specifically, a higher-density scrim layer has been typically used in the industry in the TPO membrane to provide a membrane having sufficient strength and toughness suitable for roofing applications. The present inventors have instead experimentally determined that having a scrim layer with larger apertures (i.e.: a much lower fiber density) provides a greater contact area between the top and bottom layers of the membrane for bonding these layers together. By providing a membrane with stronger bonding between its top and bottom layers, the present TPO membrane 10 is far less likely to separate (i.e. be pulled apart with its top and bottom layers separating) at high wind loading. Simply put, the present inventors have (in one aspect of the present invention) found a preferred low to medium density range of scrim fibers that is high enough to provide sufficient strength, yet low enough to provide strong bonding between the top and bottom layers of the membrane. The specific range of scrim density described and claimed herein thus offers unexpected benefits and performance.
Currently most of the reinforcing scrims in the roofing membrane industry are 9×9 1000×1000 denier, 9×8, 1000×1300 denier or 9×9 1300×1300 denier (9×9 scrim represents 9 ends of PET fiber per inch). Unfortunately, the Applicant has experimentally determined that this density of scrim construction significantly blocks the interaction of the top and bottom layers 22 and 24 of the roofing membrane. In the present system, it was discovered that the induction welding performance can be significantly increased when the openings in the scrim layer 22 are increased in size. For example, by changing from the industry standard 9×9 density scrim to a lower density, e.g. a 4.5×4.5 scrim (or 6×6 scrim), the wind uplift rating can be increased. There are wind uplifting ratings that are desired for each of: seam welded roofing systems, induction welded roofing systems, and fully adhered roofing systems. In each type of system, the weakest point and failure modes are all different. The present system of opening up (i.e.: providing larger) scrim holes makes the weakest link in the induction welding roof system stronger, thereby achieving a better wind uplifting rating.
When the Applicant performed the induction welding wind uplift testing, a sample of TPO membrane was placed on top of the wind uplift testing table with dimensions of 12′ by 24′. These membrane dimensions can vary depending on the specific test, but typically the membrane seams can run lengthwise (24′) or widthwise (12′) on the table. During these tests, RhinoBond® plates were attached to the underside of the membrane through induction welding and can be organized in a grid layout or in rows depending on the desired outputs, specifically, attachment pattern of 5′×18″ were used, i.e. row spacing of 5 feet (60 inches) are used with fastener spacing of 18 inches on center. The plate and fasteners were secured to the insulation and existing roof assembly. The testing started at a pressure of 30 psf and the pressure was held constant for one minute. If there is no failure within that minute, the pressure was then increased in 15 psf increments, with each consecutive pressure held for a minute each. The last pressure level the membrane passes for a minute without failing was designated as the wind uplift rating.
Table 1 below set forth partial details of the experiments performed by the present inventors. It can be seen that the low to medium density scrims (4.5×4.5 and 4.5×6) avoided ply to ply delamination (i.e.: separation of the top and bottom layers under wind loading):
In preferred aspects, the present system provides a low to medium density scrim layer between the top and bottom layers, wherein the scrim has a low fiber density of five or less strands per inch or a medium fiber density of five to eight strands per inch. In some optional aspects, the present system uses a fiber density of between 3×3 and 8×8 strands of yarn per inch, and more preferably, a fiber density of 4.5×4.5 to 8×6 strands of yarn per inch. Stated another way, in preferred aspects, the low density scrim covers less than 40% and more preferably less than 35% of the contact area between the top and bottom layers. In preferred aspects, the present system can achieve a wind uplift rating of 1-105 and above when high yarn weight is used in combination with a low or medium fiber density scrim.
The present application claims priority to U.S. Provisional Patent Application Ser. No. 63/615,050, of same title, filed Dec. 27, 2023; the entire disclosure of which is incorporated herein by reference in its entirety for all purposes.
| Number | Date | Country | |
|---|---|---|---|
| 63615050 | Dec 2023 | US |
