Bonding agents for polymeric planks and methods of adjoining polymeric planks

A surface covering system is described where two or more polymeric planks are connected to each other by a bonding agent which contains at least one solvent capable of at least bonding the edges of the polymeric portion of the planks wherein the bonding agent is present on at least one edge of at least one plank and/or is present on a connector, like a spline, if one is used, in joining the planks. Also described is a method to connect two or more polymeric planks which involves applying the bonding agent to at least one plank edge and/or spline, if present, prior to or after connecting the second or more planks together.

EXAMPLES 
 Example 1 A series of thermoplastic planks were connected together to create a flooring system. The planks had a groove on two opposite edges. A spline (e.g., tongue portion) was used to join edges together of two planks. The two remaining edges of the plank had no groove. In addition, a comparison was made with using no bonding agent and a flooring system using a bonding agent. The bonding agent, tetrahydrofuran (THF) was applied to all sides of the plank including the spline and grooves once the planks with spline were pre-assembled. When no THF was applied to the spline area, the bonding strength was an average of 1.73 pounds using the Instron Universal Tester pulling the bond apart with tension using the following parameters: 50 pound full scale load, jaw speed 0.5 inch/min, three-inch jaw separation at start of test, 1″×5″ sample with 0.156 inch spline thickness. When the same type of extrusion plank had THF applied to the spline area, after 4 hours of setting, the bonding strength of the spline area was an average of 18.1 pounds and after 24 hours curing, the bonding strength of the spline area was 39.1 pounds. When the test was repeated with a 152 mil spline with THF, using the INSTRON test, after a 24 hour cure, the bonding strength was an average of 45.37 pounds. The ends of the extrusion plank were tested for bonding strength wherein the ends have no spline attachment and simply butted against each other. There was no bonding strength when no THF was present since there is nothing holding the edges of each plank together. When THF was applied to the edges after 4 hours cure, the bonding strength was over 100 pounds using a 100 pound scale, and after a 24 hour cure, the bonding strength was over 100 pounds using a 100 pound scale. Although the butt ends are not joined by a spline, the effective contact area is large and the bond strengths were over 100 pounds as described. The variation of the bonding strength can be influenced by such factors as 1) vertical groove opening, 2) thickness of the spline, 3) effective contact areas with surfaces close enough to allow the bonding agent to join them. A rolling load test was then used to determine the strength of the bond with respect to a heavy flexing load. In this test, a 20×30 inch panel was used wherein half of the panel was held by the spline and also THF-bonded and allowed to dry and set for 24 hours. The other half of the panel had only splines holding the panels together. This panel was then placed on a carpet and a 165 pound weight supported by one hard rubber wheel 1.25 inches wide was allowed to roll repeatedly over the bonded joint. This resulted in a severe flexing motion on the joint. The product joined simply by the spline system with a 156-mil thick spline separated after 20 cycles. The other half of the product, which was held by the spline and also bonded with THF, did not separate after 150 cycles. This was impressive considering the panel was not glued down to any surface. A second panel with bonded joint was then made and placed on a reinforced cementitious board (Sterling Board). The joint was shimmed with a piece of felt 0.026 inches thick placed under the plank on one side of the seam. This created a differential height with the purpose of applying a shearing load on the bonded joint. The rolling load test resulted in no separation or breaking of the joint bond. Preparing a joint between the flat end surfaces of the thermoplastic plank tested the water- sealing capability of the bonded joint. This bonded joint was prepared by placing the ends in flush proximity and applying the THF on top of the joint and allowing it to penetrate into the joint. The bond was allowed to dry and set. Next, a three-inch ID pipe was placed over the joint and sealed at the base with silicon caulk. Floor-rinsing solution in water was placed in a twelve-inch high pipe. If the joint is not well sealed, solution placed in the pipe will force its way into the joint and flow through the joint and out of the tube. This will dampen the paper towel placed beneath the joint. After ten minutes, minimal leakage had occurred through the bonded joint. However, significant leakage was evident through the unbonded joint. In view of the above testing, these examples show that the addition of THF as a bonding agent provides significant strength advantages to the overall surface covering systems and also prevents water penetration to the subfloor especially at the plank ends where there is no spline system used. 
 Example 2 Using the planks or tiles wherein the core is made from polyvinyl chloride as described in U.S. patent application Ser. No. 09/460,928, the planks were made wherein a spline having two tongue portions was inserted into a groove of one plank and then the other tongue section was inserted into the groove of a second plank in order to join two planks together. The solvents set forth in Table 1 (at a 100% concentration) were applied over the entire joining sections of the spline and grooves of the two planks and then the planks with splines were joined together. After 48 hours, the bonding strength, using ASTM D-638 (modified) tensile strength measurement (run at 0.5 inch cross-head speed), was determined based on the parameters set forth in the footnote of the Table. As can be seen, there were a number of solvents which significantly increased the bonding strength as compared to the control, where no solvents were used. 1 TABLE 1 Measurement *(lbs) Solvent &num;1 &num;2 &num;3 Avg. No Solvent 3.2 7.1 5.7 5.3 THF 39.8 33.2 37.3 36.8 Cyclohexanone 7.6 7.6 8.7 8.0 Methylene Chloride 12.6 10.7 12.6 12.0 N-Methyl Pyrrolidone 14.4 11.1 13.8 13.1 Methyl Isobutyl Ketone 12.1 16.7 17.5 15.4 Dimethyl Formamide 10.2 11.2 9.6 10.3 Dipropyl Ketone 16.1 12.6 21.5 16.7 Isophorone 16.5 25.3 24.0 21.9 Methyl Amyl Ketone 32.1 34.5 21.0 28.9 Methyl Ethyl Ketone 50.6 48.3 54.8 51.2 Nitrobenzene 22.4 33.8 28.7 28.3 Methyl Cyclohexanone 23.2 21.5 29.5 24.7 Acetonyl Acetone 12.0 13.2 12.4 12.5 *Instron test parameters: .5 in/min; 100 lb scale; 3″ jaw distance 
 Example 3 In this example, commercially available Wilsonart Pro FX planks (ABS plank) with a tongue and groove design were tested. In this example, various solvents were tested on two Wilsonart Pro FX planks to determine the bonding strength achieved using the solvents of the present invention. As can be seen in Table 2, when the solvent (at 100% concentration) was applied to the tongue and groove sections of two planks and the planks joined together, after 48 hours, a significant increase in bonding strength was achieved using the various solvents of the present invention. Again, the bonding strength was determined based on the INSTRON test parameters (as set forth in the footnote of the table) following ASTM procedure D-638 (modified to 0.5 inch/min cross-head speed) to determine the tensile strength measurement. The numbers indicated in Tables 1 and 2 reflect bonding strength in pounds per inch. These numbers indicate the force required to separate two one-inch wide samples bonded at the tongue and the groove joint. The bond was allowed to dry and set for 48 hours before the test. 2 TABLE 2 Measurement (lbs/inch) Solvent &num;1 &num;2 &num;3 Avg. No Solvent 0.0 0.0 0.0 0.0 THF 131.2 131.2 131.2 131.2 Cyclohexanone 76.8 66.4 72.6 71.9 Methylene Chloride 131.2 131.2 131.2 131.2 Dimethyl Formamide 96.8 98.1 94.7 96.5 Toluene 131.2 131.2 131.2 131.2 Acetone 126.2 117.4 131.2 124.9 Ethylene Dichloride 128.9 121.2 94.8 115.0 Methyl Ethyl Ketone 131.2 131.2 131.2 131.2 
 Example 4 In this example, blends of various solvents were prepared in the formation of the bonding agent of the present invention. The table sets forth the various blends and the amount of each component in the blend. Table 3 sets forth the bonding strengths of the polymeric planks connected together. The bonding strength was measured in the same manner as in Example 1. Further, a six hour leak test was also conducted on the joined planks wherein an amount of water was poured on top of the joined planks to determine if any leakage between the joints of the planks occurred. In each instance, no significant leakage was detected. The results of this example are set forth in Table 3. Three blends were used: (1) 50 (THF) 50 (MEK); (2) 75 (THF) 25 (MEK) (3) 90 (THF) 10 (MEK), each number reflecting % by weight of composition. 3 TABLE 3 Sample No. THF/MEK 50/50 THF/MEK 75/25 THF/MEK 90/10 1 106.6 92.4 74.6 Bonding 2 118.4 105.9 85.1 Strengths 3 146.3 71 111 (PSI) 4 69.5 142 81.4 5 104.5 109.6 112.6 6 114.6 111 98.1 7 82.6 110.7 AVG. 109.9833 102.0714 96.21429 6 Hr. Pass Pass Pass Leak Test Other embodiments of the present invention will be apparent to those skilled in the art from consideration of the specification and practice of the present invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with the true scope and spirit of the present invention be indicated by the following claims and equivalents thereof.