Abstract:
A building element having pressure-sensitive adhesive coating layer having a low initial bond strength, to permit a substrate to be repositioned without destroying the integrity of the adhesive, and a long term bond strength, which occurs after the building element is mechanically fastened to another building element. This allows wood deck components, flooring planks, roofing tiles, and other building material components to be fastened together conveniently while securing a waterproofing and/or sound-deadening effect.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to devices and methods for fastening two or more building materials together, and more particularly to structural building elements having a pre-attached pressure-sensitive layer.  
       BACKGROUND OF THE INVENTION  
       [0002]     Adhesives are available for achieving improved structural integrity and bonding between common building materials, such as those used in subfloor installations. Heavy-duty adhesives sold by ICI Paints under the tradename LIQUID NAILS® are sold, for example, to increase the structural integrity of walls and subfloor systems. These liquid adhesives can be used with plywood, foamboard, particle board, lumber and treated lumber, waferboard, and OSB. Such a construction adhesive provides for “quiet” floor assemblies in that the adhesive is said to eliminate squeaking between boards and between the boards and nails.  
         [0003]     Unfortunately, the decking, flooring, or other component must be attached within fairly short time, such as twenty minutes. Otherwise, a skin will begin to form on the adhesive that can impede the formation of a strong adhesive bond between the building materials. In addition, the liquid adhesive must be applied using a caulking gun so that the liquid adhesive can be squeezed out of a plastic nozzle at the end of a cardboard tube. The application of the adhesive over relatively large surface areas may thus become tiring, inconvenient, and time-consuming.  
         [0004]     In view of the foregoing disadvantages, novel articles and and methods are needed for fastening building materials together in a quick and convenient manner that achieves noise reduction and enhances structural integrity.  
       SUMMARY OF THE INVENTION  
       [0005]     In surmounting the disadvantages of the prior art, the present invention provides a building element, such as an I-beam, joist, stud, roof joist, or floor joist on which one or more surfaces thereof have a pre-formed, pressure-sensitive adhesive layer. The adhesive layer is characterized by having an initial low (or no) bond strength, which permits a second building element to be easily placed and re-positioned against it without initially disrupting the integrity of the adhesive. Further, the adhesive layer has a long-term bond strength. This long-term bond strength is measured in terms of shear-strength at 28 days after the building element is mechanically fastened to another building element such that the adhesive is compressed between them. Preferably, the adhesive layer is a hot melt extruded onto the building element surface and protected by a release sheet liner which is removed at the construction site.  
         [0006]     The present invention is suitable for building applications in which beams, studs, joists, and other building elements are used for supporting flooring, walls, roofing, tiles, panels, boards, and the like. The invention thus provides articles and methods for attaching building elements together in a convenient, safe, and economic manner.  
         [0007]     For decking and flooring applications in particular, it is helpful to have a low initial bond strength such that decking and flooring materials can easily be repositioned without destroying the integrity or continuity of the adhesive layer. It is also helpful to have a long term bond strength after building elements are nailed or screwed together, because building elements become loose over time as a result of fatigue (due to repetitive foot traffic), differential thermal expansion, and differential moisture absorption, and when they become loose they can cause squeaking.  
         [0008]     Thus, it is possible mechanically to fasten together two or more building elements to sandwich the pressure-sensitive adhesive layer, and to re-position a building element without disrupting destroying the adhesive layer integrity, and thereafter to achieve a long term bond strength by mechanically fastening building elements together (e.g., using nails or screws) to compress the adhesive between the building elements and thus prevent unwanted noise or movement at a later time and provide for additional structural integrity over mechanical fastening alone.  
         [0009]     An exemplary building element of the invention therefore comprises a three-dimensional body having at least four major faces, at least one of said at least four major faces having attached thereon a pre-formed, pressure-sensitive adhesive layer comprising a polyolefin resin, or a rubber adhesive having a minimum of 50% filler by total weight; the pressure-sensitive adhesive layer having an average thickness no less than 5 mils and no greater than 100 mils, and, at an ambient temperature of 72° C., having the following properties: (A) an initial bond strength of zero to 1.0 pound per lineal inch (and more preferably at least 0.0025 pli), as determined by a 180 degree angle peel test on an Instron machine whereby a two-inch strip of polyethylene film is attached to a 20 mil thick layer of the adhesive that has been coated onto a 1.5 inch wide wood sample, fifteen minutes after being compressed four times repeatedly using a 30 pound roller; and (B) a long term bond strength of 25-500 pounds per square inch, as determined by measuring shear-strength of an adhesive joint comprising plywood, a 20 mil thick adhesive layer, and spruce wood at a time 28 days after mechanically fastening together the adhesive coated spruce to the plywood (with fastener removed to permit shear-strength testing).  
         [0010]     The invention also relates to methods for fastening building structures together which involves extruding onto the surface of a building element the pressure-sensitive adhesive as mentioned above.  
         [0011]     Further advantages and features are described herein and after.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     The following detailed description of exemplary embodiments may be more readily comprehended when considered in conjunction with the drawings, wherein  
         [0013]      FIG. 1  is a cross-sectional illustration of an exemplary building element of the present invention having a pressure-sensitive adhesive layer;  
         [0014]      FIG. 2  is a cross-sectional illustration of another exemplary building element of the present invention having a pressure-sensitive adhesive layer; and  
         [0015]      FIG. 3  is an illustration of a shear-strength test using two wood blocks that are fastened together with a layer of adhesive. 
     
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
       [0016]     As shown in  FIG. 1 , an exemplary building element  10  of the present invention has a three-dimensional body  12  with at least four major faces  14 ,  15 ,  16 ,  17 . Exemplary building materials are preferably selected from the group consisting of wood, plywood, oriented strand board, gypsum, concrete, mortar, brick, or tile. Such materials can be shaped in the form of a wall stud, floor joist, beam (e.g., rectangular or “I” shaped cross-section profile), a rafter (e.g., a beam for supporting roofing panels), floor decking, wall sheathing, gypsum board, and the like. Most preferred building elements  10  will have a beam shape, as shown in the cross-sectional profile illustration of  FIG. 1 , or an I-beam shape, as shown in  FIG. 2 .  
         [0017]     At least one face  14  of said at least four major faces has attached thereon a pre-formed, pressure-sensitive adhesive layer  20  comprising a polyolefin resin or a rubber adhesive having a minimum of 50% filler by total weight. The adhesive layer  20  has an average thickness of 5-100 mils, and is preferably applied as a hot melt onto the surface  14  of the building element  10  by extrusion, or it may be coated by applying the adhesive as an emulsion and allowing the emulsion to dry, or as a solution and allowing the solution to dry.  
         [0018]     The pressure-sensitive adhesive layer  20  is protected by a removable release sheet liner  22 , such as a waxed or siliconized paper, or a plastic film, which serves to protect the adhesive from damage and which is to be removed at the construction site.  
         [0019]     An exemplary building element  10  of the invention, as illustrated in  FIGS. 1 and 2 , comprises a three-dimensional body with at least four major faces, at least one of said at least four major faces having, attached thereupon, a pre-formed, pressure-sensitive adhesive layer  20  comprising a polyolefin resin, or a rubber adhesive having a minimum of 50% filler by total weight; the pressure-sensitive adhesive layer  20  having an average thickness no less than 5 mils and no greater than 100 mils; the pressure-sensitive adhesive layer having, at an ambient temperature of 72° C., the following properties: (A) an initial bond strength of zero to 1.0 pound per lineal inch (pli) (and more preferably at least 0.0025 pli), as determined by a 180 degree angle peel test on an Instron machine whereby a two-inch strip of polyethylene film is attached to a 20 mil thick layer of the adhesive that has been coated on to a 1.5 inch wide a wood sample, fifteen minutes after being compressed four times repeatedly using a 30 pound roller; and (B) a long term bond strength of 25 to 500 pounds per square inch, as determined by measuring shear-strength of an adhesive joint comprising plywood, a 20 mil thick adhesive layer, and spruce wood at a time 28 days after mechanically fastening together the adhesive coated spruce to the plywood (with fastener removed to permit shear-strength testing).  
         [0020]     The “long term bond strength test” draws upon ASTM D3498(-03) (“Standard Specification For Adhesives for Field-Gluing Plywood to Lumber Framing for Floor Systems”) described below. The initial bond strength test is also described. Preferably, the adhesive is manufactured for shipment in 55 gallon drums, melted at the application site, and pumped using a heated-platten drum melter to a 1.5 inch slot die from which the hot melt is placed onto the wood, lumber, or composite building element substrate as desired.  
         [0021]     For “initial bond strength” testing, all samples are conditioned at 75° F. for 24 hours before sample preparation, and the samples are tested at 75° F. A 20 mil thick layer of the pressure-sensitive adhesive is coated onto wood lumber pieces and then covered with a 16″×2″×0.003″ sample of polyethylene film. It is preferable to place the film over the adhesive coated lumber specimen with one end of the film flush with the end of the lumber piece. A polyethylene film which is suitable for purposes of the present invention, and which has a surface treated by corona discharge (to improve its polar properties), is commercially available under the trade name VALERON). The film/adhesive assembly is then rolled, using a 30 pound roller, in four 1 second passes. After the specimens have aged for 15 minutes, 2 inches of the film are peeled back from one end of the sample by hand to expose part of the adhesive coated wood. The exposed end of the specimen is then placed in the grip of a mechanical testing device (e.g., Instron mechanical tester) with the long axis of the sample aligned in the direction of film peeling. The film is then peeled off from the sample at an angle of 180 degrees at a cross-head speed of 2 inches per minute. The initial bond strength is reported in terms of average peel force. In preferred embodiments of the invention, the maximum peel strength is less than one (1) pound per linear inch (pli), more preferably less than 0.5 pli, and most preferably less than 0.25 pli.  
         [0022]     The “long term bond strength test, as previously mentioned above, is a modification of ASTM D 3498-03. To accomplish this, one should prepare three wood-adhesive composite test assemblies, as follows. A 20 mil layer of adhesive is coated, using hot metal extrusion onto a factory-produced 1.5 inch face of a 15 inch×1.5 inch×2.5 inch sample of spruce wood. Samples of plywood are used having 5.5 inch by 15.75 inch by ⅝ inch dimensions. The adhesive-coated spruce and plywood samples are conditioned for 48 hours at 65° F. at a relative humidity no greater than 40%. Next, the sample of plywood is centered over the adhesive-coated spruce so that plywood and adhesive are in face-to-face contact, and the long axis of the plywood is parallel to the long axis of adhesive coated spruce. Three nails are driven through plywood first, then through the adhesive and into the spruce wood. The nails are 6-penny (2 in. or 51 mm in length) scaffold nails. Two nails are positioned one inch from both ends of the specimen, with the third nail positioned between these two. One should be careful, when driving the nails into the samples, to make sure that the top of the lower head of each scaffold nail is flush with the surface of the plywood. After 28 days, the nails should be removed. Eight block-shear specimens should then be cut, using a sharp saw.  
         [0023]      FIG. 3  illustrates an exemplary block shear assembly. The block shear assembly  30  comprises plywood  31 , spruce  32 , and the adhesive layer  33 . Plywood and spruce width  35  is 1.5 inches. Plywood and spruce height  36  is 1 inch. The plywood and spruce samples are staggered by a distance (designated at  37 ) of 0.25 inches.  
         [0024]     Shear strength testing on the block specimens is then done in accordance with Sections 11.1 and 11.2 of ASTM D3498-03 at an elapsed time of 28 days after the pieces ( 31  and  32 ) were glued and mechanically fastened together. The specimens are tested for shear strength by compression-shear loading in a testing machine, using a loading rate of 0.2 in/min. Although a shearing tool described in Test Method D 905 is recommended for these tests, other equipment may be used, including loading devices that apply compression loads in tension testing machines.  
         [0025]     In other exemplary building elements of the invention, the pressure-sensitive adhesive layer  20  preferably has a penetration hardness of at least 15 dmm (150 g. 5 sec., 70.degree. F.) according to ASTM D 5-73.  
         [0026]     If a polyolefin resin is used for making the pressure-sensitive adhesive layer  20 , it may be selected from the group consisting of an amorphous propylene homopolymer, amorphous propylene-ethylene copolymer, amorphous polypropylene/propylene-ethylene copolymer mixtures, polyethylene wax, polypropylene wax, polyvinyl acetate, copolymer of ethylene and vinyl acetate, and copolymer of ethylene and ethyl acrylate. The foregoing polyolefin resins may be modified with a plasticizer, tackifier, wax, particulate filler material, or mixture thereof, to achieve the above-described initial bond strength and long-term bond strength characteristics.  
         [0027]     Preferred pressure-sensitive adhesive layers of the invention have a Brookfield Thermosel Viscosity (ASTM D3236, @ 190° C.) for 200-25,000 megaPascals, and most preferably 200-5,000 megapascals.  
         [0028]     Such a range would be suitable for use with resins such as amorphous polyolefins including polypropylene homopolymers, amorphous polypropylene/polypropylene-ethylene copolymers, and amorphous polypropylene-ethylene copolymers (e.g., such as available from Eastman under the trade name EASTOFLEX); such as polyolefin waxes including polyethylene wax, polypropylene wax, and maleic anhydride modified polypropylene wax (e.g., such as available from Eastman under the tradename EPOLENE); and such as polyolefin plastomer resins (e.g., such as available from Dow under the tradename AFFINITY GA). The foregoing polyolefin resins may be modified with a plasticizer, tackifier, wax, particulate filler material, or mixture thereof, to achieve the above-described initial bond strength and long term bond strength characteristics.  
         [0029]     Preferred pressure-sensitive adhesive layers of the invention, comprising ethylene-acrylic copolymers, have a melt index of 10 g/10 min. to 1000 g/10 min. as determined under ASTM 1238, 190° C./2.16 kg., g/10 min.  
         [0030]     This melt index range is particularly suitable for resins such as ethylene ethyl acrylate resins, and ethylenelacrylate copolymer resins, which are available from Dow Chemical under the tradename AMPLIFY and from DuPont under the tradename ELVALOY.  
         [0031]     If a rubber adhesive is used for making the pressure-sensitive adhesive layer  20 , it may be selected from the group consisting of styrene-isoprene-styrene (SIS), styrene-butadiene-styrene (SBS), styrene-ethylene-butadiene-styrene (SEBS), natural rubber, butadiene rubber, butyl rubber, an acrylic, neoprene, silicone, and isoprene. Preferably, the rubber adhesive comprises a block copolymer comprising SIS, SBS, SEBS, or mixture thereof. The foregoing adhesives may be modified with a plasticizer, tackifier, wax, particulate filler material, or mixture thereof, to achieve the above-described initial bond strength and long term bond strength characteristics. For example, a block copolymer-based adhesive may comprise 100 parts block copolymer, 20-150 parts tackifier, and 20-100 parts plasticizer. The rubber-based adhesive also comprises a particulate filler. The minimum level of particulate filler is 50%, by weight, on total formulation.  
         [0032]     An exemplary adhesive composition comprises 100 parts amorphous polyolefin, 0-100 parts plasticizer, and 0-100 parts tackifier. Preferred plasticizers include liquid polybutenes (such as those sold under the tradename INDOPOL), paraffinic oils, and naphthenic oils. A preferred tackifier is a hydrocarbon resin.  
         [0033]     Another exemplary adhesive composition comprises 100 parts polyolefin wax, 0-100 parts plasticizer, and 0-100 parts tackifier. Preferred plasticizers include liquid polybutenes (such as those sold under the tradename INDOPOL), paraffinic oils, and naphthenic oils. A preferred tackifier is a hydrocarbon resin.  
         [0034]     In still further exemplary embodiments, the pressure-sensitive adhesive layer may comprise a polyvinyl acetate or copolymers of ethylene and vinyl acetate. Suitable polymers are available from DuPont under the tradename ELVAX. Vinyl acetate and ethylene vinyl acetate resins may further comprise a plasticizer, tackifier, wax, particulate filler material, or mixture thereof to achieve the above-described initial bond strength and long-term bond strength characteristics.  
         [0035]     Rubber adhesive layers  20  should preferably be filled, between 50-90% by weight, of a filler material such as particulate filler materials or fibrous materials. The rubber adhesives may also be modified using one or more tackifiers, plasticizers, waxes, partriculate filler material, or mixture thereof to achieve the above-described initial bond strength and long-term bond strength characteristics.  
         [0036]     Exemplary particulate materials which can be used to fill any of the adhesive systems described above include calcium carbonate, sand, silicate sand, cement, talc, titanium dioxide, carbon black, slate dust, granite dust, clay, diatomaceous earth, limestone, clay, shale, fly ash, silica fume, blast furnace slag, alkali or alkaline earth metal nitrite or nitrate, halide, sulfate, carboxylate, aluminum oxide trihydrate, or mixture thereof. Particle size may vary according to preference.  
         [0037]     Exemplary methods of the invention for fastening two or more building elements together, comprising: providing a first building element having a three-dimensional body with at least four major faces, at least one of said at least four major faces having attached thereon a pre-formed, pressure-sensitive adhesive layer comprising a polyolefin resin, or a rubber adhesive having a minimum of 50% filler by total weight; said pressure-sensitive adhesive layer having an average thickness no less than 5 mils and no greater than 100 mils; and said pressure-sensitive adhesive layer having at an ambient temperature of 72° C. the initial bond strength and long term bond strength properties as discussed above.  
         [0038]     Preferably, the pressure-sensitive adhesive layer is melt extruded onto one or more surfaces of the building element, as previously described, or it may be coated using an emulsion process. For example, an acrylic resin, such as commercially available from BASF under the tradename ACRONAL, can be used. It is preferably for purposes of the invention to fill such acrylic resin emulsions with a particulate filler material (e.g., calcium carbonate) to a level up to 90% by weight on a dry solids basis.  
         [0039]     The invention also pertains to building structures that are formed of the above-discussed building materials, such as roof truss assemblies, wood deck assemblies, stud wall assemblies, and other structures formed by joining together two or more building structures using the pressure-sensitive adhesive layer having the afore-mentioned initial bond strength and long term bond strength characteristics.  
         [0040]     The foregoing embodiments are provided for illustrative purposes are not intended to limit the scope of the invention.