Patent Publication Number: US-2003224122-A1

Title: Method of using a roll coater and method of modifying the same

Description:
FIELD OF THE INVENTION  
       [0001] The invention relates, in general, to roll coating, and, in particular, to roll coating wood substrates for fire-retardant treatment.  
       BACKGROUND OF THE INVENTION  
       [0002] Building codes and public safety concerns in metropolitan areas such as large cities are requiring non-structural, permanently installed wood products such as cabinets, doors, moldings, etc. to have fire-retardant properties. The basic components of many of these wood products include a wood substrate, an adhesive layer, and a veneer or laminae.  
       [0003] Weyerhaeuser Company of Federal Way, Wash. manufactures fire-retardant particle board sold under the tradename Duraflake FR that may be used as the substrate for wood products such as wood panels for cabinets (Duraflake FR was previously sold by Willamette Industries, Inc. of Albany, Oreg. before an acquisition of Willamette Industries, Inc. by Weyerhaeuser Company). Duraflake FR is a manufactured Class  1  fire-rated particle board, wherein a fire retardant is added to the slurry of wood fibers/particles and glue during manufacture of the particle board.  
       [0004] Problems with the Duraflake FR product include that it is expensive, and it does not solve the problem of fire retarding other types of particle board not manufactured to be fire retardant. In regard to the expense of the Duraflake FR product, not only is the product manufactured by a more complicated process than particle board that is not fire-retardant, adding to the expense, but the product is only manufactured in two locations: 1) the East coast, and 2) the West coast. Thus, expense layers of warehousing, trucking, and distribution of the Duraflake FR product adds to the cost of the product.  
       [0005] To fire retard particle board that was not manufactured to be fire retardant, the particle board must be separately chemically treated with a fire retardant at a treatment facility. This may involve shipping the particle board to a chemical treatment facility for fire retardant treatment and, from there, to a wood distributor. The particle board may then be shipped to a laminator where an adhesive and a laminate or veneer (e.g., wood layer, plastic layer) may be applied to make, for example, the basic components of a cabinet, door, molding, etc. The extensive shipping process of the particle board and the additional fire retarding process performed by a separate treatment facility adds cost to the fire-retarded particle board purchased by the laminator.  
       SUMMARY OF THE INVENTION  
       [0006] The inventor of the present invention recognized that many laminators (approximately 4,000 in the United States) use a machine that applies an adhesive for lamination that, with slight modifications, may be used for applying a fire-retardant chemical to wood substrates such as particle board as well as a fire-retardant adhesive. As a result, laminators can fire retard particle board at their facility with the equipment they already have and are familiar with instead of having to buy expensive particle board manufactured for fire retardancy, or expensive particle board that was separately chemically treated for fire retardancy.  
       [0007] Another aspect of the invention involves a method of fire-retarding a wood substrate having an upper surface and a lower surface. The method includes providing a roll coater for applying a fire-retardant coating to the wood substrate, the roll coater including a roller assembly that draws the wood substrate therethrough and a variable-speed mechanism that varies the speed of the roller assembly, the roller assembly including upper rolls that apply a fire-retardant coating to the upper surface of the wood substrate, and one or more lower fluid emitting devices that directly apply a fire-retardant coating to the lower surface of the wood substrate; using the variable-speed mechanism to operate the roller assembly at a speed slower than the speed of the roller assembly without the variable-speed mechanism; feeding the wood substrate into the roll coater; applying the fire-retardant coating to the upper surface of the wood substrate with the upper rolls of the roller assembly; applying the fire-retardant coating directly to the lower surface of the wood substrate with the one or more lower fluid emitting devices; removing the fire-retarded wood substrate with fire-retardant coating from the roll coater; and drying the wood substrate.  
       [0008] A further aspect of the invention involves a method of fire-retarding a wood substrate having an upper surface and a lower surface. The method includes providing a wood substrate; providing a roll coater for applying a fire-retardant layer to the wood substrate, the roll coater including one or more rollers; drawing the wood substrate through the roll coater; applying a fire-retardant layer on at least the upper surface of the wood substrate with one or more rollers; and removing the wood substrate from the roll coater.  
       [0009] A still further aspect of the invention involves a method of modifying a roll coater for applying a fire-retardant coating to a wood substrate including an upper surface and a lower surface. The method includes providing a roll coater including a roller assembly that draws the wood substrate therethrough, the roller assembly including upper rolls to apply a fire-retardant coating to the upper surface of the wood substrate; adding one or more lower fluid emitting devices to the roll coater to directly apply a fire-retardant coating to the lower surface of the wood substrate so that the wood substrate is coated on both the upper surface and the lower surface; and providing a variable-speed mechanism to vary the speed of the roller assembly.  
       [0010] A yet further aspect of the invention involves a method of creating a fire-rated panel assembly. The method includes providing a wood panel, providing a fire-retardant coating on the wood panel; providing a fire-retardant adhesive on the wood panel; and providing a fire-retardant laminae on the wood panel over the adhesive. In an implementation of the invention, the steps of providing a fire-retardant coating on the wood panel and providing a fire-retardant adhesive on the wood panel is performed using a roll coater.  
       [0011] Further objects and advantages will be apparent to those skilled in the art after a review of the drawings and the detailed description of the preferred embodiments set forth below. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0012]FIG. 1 is a perspective view of an embodiment of a roll coater and fluid supply and delivery system that may be used to apply a fire-retardant chemical and/or a fire-retardant adhesive to a wood substrate such as particle board.  
     [0013]FIG. 2 is a side view of the roll coater and fluid supply and delivery system illustrated in FIG. 1.  
     [0014]FIG. 3 is a simplified schematic of the rollers of the roll coater in FIG. 1 shown receiving a wood substrate. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
     [0015] With reference to FIGS.  1 - 3 , an embodiment of an adhesive spreader and roll coater  10  (hereinafter described as a “roll coater”) that may be used to apply a fire-retardant coating and/or a fire-retardant adhesive to a wood substrate such as particle board will now be described. As used herein, “wood substrate” includes any generally flat, wood-related product. Examples of wood substrates include, but not by way of limitation, particle board, medium-density fiberboard, modified density overlay, plywood, chip board, and oriented strand board. Although the roll coater  10  will be described as being used to apply a fire-retardant coating and a fire-retardant adhesive to a wood substrate, the roll coater  10  may also be used to apply either a fire-retardant coating or a fire-retardant adhesive to a wood substrate.  
     [0016] The roll coater  10  shown and described herein is a  775  Hot Melt Spreader sold by Black Bros. Co. of Mendota, Ill. However, other types of roll coaters may be used. The roll coater  10  generally includes a stand  20 , a collection tray  30 , a frame  40 , a control unit  50 , a roll adjustment handwheel  60 , machine guards  70 , and a roller assembly  80  having multiple rollers rotatably coupled to a motor  82 . The roll coater  10  includes a front  90  and a rear  100 .  
     [0017] A wood substrate  110  includes an upper surface  112  and a lower surface  114 . In the embodiment of the wood substrate  110  shown, the wood substrate  110  is a particle board panel that is 4 ft. by 8 ft. and has a thickness of ¾ in.  
     [0018] The wood substrate  110  is received by a roller assembly  80 , which includes upper rolls  120  and lower rolls  130 . The upper rolls  120  include a main roll  140  and a secondary roll  150 . The lower rolls  130  include a main roll  160  and a secondary roll  170 .  
     [0019] A fluid supply and delivery system  200  may be used to supply one or more different types of fluids to the roll coater  10 . The system  200  generally includes one or more fluid reservoirs  210 , rear supply line  220 , front supply line  222 , rear return line  230 , front return line  232 , and a pump  240  for pumping fluid to and from the roll coater  10 .  
     [0020] The rear supply line  220  includes one or more tubes, lines, couplings, or other connectors for delivering fluid to lower fluid emitting devices or nozzles  260 . The lower nozzles  260  may be used to spray fluid directly on the lower surface  114  of the wood substrate  110 . One or more support frames, brackets, or other supporting structures  270  may be used to support the lower nozzles  260  and/or rear support line  220 . At one or more points in the rear supply line  220 , one or more valves  262  may be used to control the amount of flow delivered.  
     [0021] The front supply line  222  includes one or more tubes, lines, couplings, or other connectors for delivering fluid to lower fluid emitting devices or nozzles  264  (FIG. 3) and upper fluid emitting devices or nozzles  250 . The lower nozzles  264  supply fluid to the lower rollers  130  for roll coating the lower surface  114  of the wood substrate  110 .  
     [0022] The upper nozzles  250  supply fluid to the upper rollers  120  for roll coating the upper surface  112  of the wood substrate  110 . One or more support frames, brackets, or other supporting structures may be used to support the nozzles  250 ,  264  and/or front support line  222 . At one or more points in the front supply line  222 , one or more valves  266  may be used to control the amount of flow delivered.  
     [0023] A pump inlet line  267  is used to deliver fluid from the reservoir  210  to the pump  240 . A delivery line  268  is used to deliver fluid from the pump  240  to the supply lines  220 ,  222 . A connector line  269  may branch off of the delivery line  260 . The connector line  269  connects the system  200  with a tote (not shown) of coating solution, usually 200 gallons of coating solution. The connector line  269  may include a valve  271  for controlling the amount of fluid transferred between the tote and the system  200 .  
     [0024] The rear return line  230  and the front return line  232  are connected to the collection tray  30  for delivering fluid in the collection tray  30  to the reservoir  210 .  
     [0025] Inside the reservoir  210 , a float ball  272  may be used to prevent fluid overflow in the reservoir  210 . A shaft  273  extending from the float ball  272  may be pivotally connected to an overflow mechanism  274 . The overflow mechanism  274  is electrically connected to the pump  240  via a wire  276  for shutting off the pump  240  when the float ball  272  rises to a certain fluid level.  
     [0026] A variable-speed mechanism known as an electrical vari-drive  278  provides variable-speed control of the roller assembly  80 . Variable-speed control of the roller assembly  80  is important for operating the roller assembly  80  at a slower speed during application of the lower-viscosity fire-retardant coating solution and for operating the roller assembly  80  at a faster speed during application of the higher-viscosity fire-retardant adhesive solution.  
     [0027] The roll coater  10  may be easily converted to a roll coater suitable for applying a fire-retardant coating solution to a wood substrate by simply adding the fluid supply and delivery system  200  and wiring the electrical vari-drive  278  between the control panel  50  and the motor  82 .  
     [0028] A method of using the roll coater  10  to apply a fire-retardant coating and/or a fire-retardant adhesive to the wood substrate  110  will now be described.  
     [0029] A fire-retardant coating solution is added to the reservoir  210 . This may be done, for example, by connecting a tote of fire-retardant coating solution to the connector line  269  and operating the pump  240  or by pouring or pumping the fire-retardant coating solution directly into the reservoir  210 .  
     [0030] The motor  82  of the roll coater  10  is actuated and controlled through the control unit  50  and the electrical vari-drive  278 . Actuation of the motor  82  causes the upper rolls  120  and the lower rolls  130  of the roller assembly  80  to rotate in the manner shown in FIG. 3. The electrical vari-drive  278  is used to control the speed of the motor  82  and, hence, the speed of the roller assembly  80 . The roller assembly  80  is operated at a speed less than the normal operational speed of the roller assembly without the electrical vari-drive during application of the fire-retardant coating solution to the wood substrate  110 . It is important to slow the roller assembly  80  down when applying the fire-retardant coating because the low-viscosity nature of the fire-retardant coating.  
     [0031] In addition to controlling the amount of fluid or fluid flow rate delivered to the wood substrate  110  by controlling the speed of the roller assembly  80  through the electrical vari-drive  278 , the amount of fluid or fluid flow rate delivered to the wood substrate  110  may be controlled through the one or more valves  262 ,  266  or any other valves in the system  200 . The valves may be opened, closed, or partially opened to control flow therethrough. The amount of fluid or fluid flow rate delivered to the wood substrate  110  may also be controlled through the roll adjustment handwheel  60 . The roll adjustment handwheel  60  may be rotated to vary the distance between the rolls  140 ,  150 , which, in turn, varies the amount of fluid or fluid flow rate delivered to the wood substrate  110 .  
     [0032] The wood substrate  110  is advanced into the roller assembly  80  from the rear  100  of the roll coater  10  until the main rolls  140 ,  160  catch and draw the wood substrate  110  therethrough.  
     [0033] The pump  240  is activated to supply fire-retardant coating solution to the nozzles  250 ,  260 ,  264  through the supply lines  220 ,  222 . Instead of, or in addition to, the pump  240 , the fire-retardant solution may be supplied by one or more raised reservoirs  210  so that the force of gravity on the fluids causes fluid delivery to the roll coater  10 .  
     [0034] The fire-retardant coating solution will now be described in more detail. The fire-retardant coating solution is a stable, non-corrosive preservative composition that imparts fire, insect, and fungus resistance qualities to the wood substrate. The fire-retardant coating solution is an aqueous solution of a boron-source composition selected from the group consisting of boric acid and the water-soluble salts thereof, a melamine binder resin, and a urea casein activator resin. The amount of the boron source composition, melamine binder resin, and urea casein activator resin are adjusted so that the resultant preservative composition has a weight ration of boron source to melamine ranging from 1.30:1 to 9.6:1, preferably about 8:1, and a weight ration of urea casein activator resin to melamine binder resin ranging from 1:20 to 1:4, preferably about 5.5:1.  
     [0035] The boron-source composition can be boric acid or the water-soluble salts of boric acid, including sodium tetraborate decahydrate, sodium tetraborate pentahydrate, sodium octaborate tetrahydrate, sodium metaborates, sodium perborate hydrates,  1  potassium tetraborate, sodium pentaborate, ammonium pentaborate hydrate, and hydrasodium tetraborate, potassium metaborate, any alkali metal borate salt, or combinations of these compounds. Preferably, the boron source composition is disodium octaborate tetrahydrate, which is commercially available from IMC Chemical, Overland Park, Kans. or U.S. Borax, Inc., Valencia, Calif. The boron-source compound is a primary fire retardant, as well as an insecticidal and fungicidal agent.  
     [0036] The melamine binder resin can be any amino resin made from melamine (2,4,6-triamino symtriazine) and formaldehyde, typically used for marine graded plywood, or as a nitrogen source in binders used to make pipe insulation. The melamine binder resin is characterized by a viscosity (@ 78° F.) ranging from 600-1000, a pH ranging from 8.6-9.7, a free formaldehyde concentration less than 0.5% by weight, a specific gravity of about 1.2, and a degree of polymerization of about 2.1. The melamine-binder resin acts as a nitrogen-liberating compound, releasing nitrogen in the presence of a flame. The melamine binder resin includes modified melamine-formaldehyde resins such as GP® 482T23 Thermal Insulation Binder Resin or GP® 476T19 Melamine Insulation Resin, both commercially available from Georgia-Pacific Resins, Inc, Dekatur, Ga., or MB 46-50 Liquid Melamine Adhesive commercially available from National Casein or Cytek, located in Santa Ana, Calif., and Jersey City, N.J., respectively. Preferably, the melamine binder resin is a liquid.  
     [0037] The urea casein activator resin can be any liquid urea formaldehyde resin typically used for marine or N graded plywood. The casein resin activator is characterized by a viscosity (@ 78° F.) of about 550 cp, solids percentage of 63%-67%, a pH of about 7.5, a specific gravity ranging from 1.20-1.38, and a formaldehyde concentration less than 1.5%. The urea casein activator resin is also nitrogen-liberating compound, which releases nitrogen in the presence of a flame. Preferably, the urea casein activator resin is #750 Urea Resin Adhesive or GP® 1967, commercially available from National Casein, Santa Ana, Calif. and Ga. Pacific Resins, Decatur, Ga., respectively.  
     [0038] After application to the treated wood products, the urea casein activator resin initiates a polymerization reaction involving the melamine binder resin. The resulting melamine polymer creates a substantially impervious barrier to atmospheric moisture and also binds or encapsulates the wood preservative composition to the treated wood product to prevent leaching of the boron source composition from the treated wood product through solubalization by atmospheric moisture. The melamine polymer acts as a nitrogen-liberating compound, which releases nitrogen in the presence of a flame.  
     [0039] The fire-retardant coating solution may be prepared by mixing one or more of the boron source compositions, the melamine binder resin, and the urea casein activator resin in an aqueous solution. The boron source compositions may first be dissolved in water and then mixed with the melamine binder resin and the urea casein activator resin, in that order. The melamine binder resin and urea casein activator resin may be each individually mixed in water before addition to the other ingredients of the preservative composition. This allows the proper buffering effect to occur. Generally, the urea casein activator resin is added last. The preservative composition may also be formed by first combining the melamine binder resin and the urea casein activator resin with water to form an aqueous solution. The aqueous solution of the melamine binder urea casein resin activator may then be added to an aqueous solution of the boron source composition. Alternatively, the preservative composition may be formed in a step process within the wood products themselves by first applying the boron-source composition and then applying an aqueous solution comprising the melamine binder resin and the urea casein activator resin.  
     [0040] Further information on the preferred fire-retardant coating solution used with the roll coater and method of making the same is described in U.S. application Ser. No. 09/615,259, entitled “FIRE RETARDANT COMPOSITIONS AND METHODS FOR PRESERVING WOOD PRODUCTS”, filed Jul. 13, 2002, which is incorporated by reference herein as though set forth in full.  
     [0041] The upper nozzles  250  and lower nozzles  264  supply fire-retardant coating solution to the upper rolls  120  and lower rolls  130 , respectively, which in turn apply the fire-retardant coating solution to the upper surface  112  and the lower surface  114  of the wood substrate  110 .  
     [0042] When applying the fire-retardant coating solution to the wood substrate  110 , the lower nozzles  260  are used to spray the fire-retardant coating directly on the lower surface  114  of the wood substrate  110  in addition to or instead of using the lower nozzles  264  to apply the fire-retardant coating on the lower surface  114  of the wood substrate  110 . In a preferred embodiment, the lower nozzles  260  are used instead of the lower nozzles  264  to apply the fire-retardant coating to the lower surface  114  of the wood substrate  110 . If the lower nozzles  260  are used instead of the lower nozzles  264 , one or more valves controlling flow to the lower nozzles  264  may be closed. The inventor determined that applying the fire-retardant coating to the lower surface  114  of the wood substrate  110  using the lower rolls  130  alone does not sufficiently coat the lower surface  114  due to the low-viscosity of the fire-retardant coating.  
     [0043] After the wood substrate  110  is coated with the fire-retardant coating, the wood substrate  110  is removed from the roll coater  10  and dried in any well-known manner (e.g., drying kiln, air dried, microwave dried).  
     [0044] The collection tray  30  collects any fire-retardant coating solution that is not applied and retained by the wood substrate  110 . The fire-retardant coating solution flows from the collection tray  30 , through the return lines  230 ,  232 , and back into the reservoir  210 , for recirculation.  
     [0045] The float ball  272  is used to prevent fluid overflow in the reservoir  210 . If the fluid level in the reservoir  210  gets too high, the float ball will rise to a level that, through the shaft  273 , causes the overflow mechanism  274  to shut off the pump  240 , preventing additional fire-retardant coating solution from being added to the reservoir  210 .  
     [0046] In addition to the fire-retardant coating, or as an alternative to the fire-retardant coating, a fire-retardant adhesive may be applied to the upper surface  112  and/or lower surface  114  of the wood substrate  110 . The method of applying the fire-retardant adhesive to the wood substrate  110  is generally the same as the method described above, so only the general differences from the method described above will be described for the method of applying the fire-retardant adhesive. The main differences with the method of applying the fire-retardant adhesive are: 1) the speed of the roller assembly  80  is increased with the electrical-vari drive  278  because the viscosity of the fire-retardant adhesive solution is higher than that of the fire-retardant coating solution, 2) the lower nozzles  260  are not used to directly apply the adhesive to the lower surface  114  of the wood substrate  110 , and 3) the lower nozzles  264  may not be used to apply the adhesive to the lower surface  114  of the wood substrate  110  via the lower rolls  130  if lamination is only going to occur on the upper surface  112 .  
     [0047] Before applying the fire-retardant adhesive, if the fire-retardant coating was previously applied using the roll coater  10 , any extra fire-retardant coating may be pumped from the reservoir  210 , through the connector line  269 , and into a fire-retardant coating solution tote. A separate tote including fire-retardant adhesive solution may be hooked up to the connector line  269  and transferred into the reservoir  210 . The fire-retardant adhesive solution may also be poured into the reservoir  210 .  
     [0048] In a preferred embodiment, the main difference between the fire-retardant coating solution and the fire-retardant adhesive solution is that the amount of water used in the fire-retardant adhesive solution is 60-90% less than the amount of water used in the fire-retardant coating solution. In a more preferred embodiment, the amount of water used in the fire-retardant adhesive solution is approximately 80% less than the amount of water used in the fire-retardant coating solution. Accordingly, the fire-retardant adhesive is more viscous and has a higher specific gravity than the fire-retardant coating solution.  
     [0049] After the wood substrate  110  is coated with the fire-retardant adhesive, a laminae or veneer is applied to the wood substrate  110  over the fire-retardant adhesive.  
     [0050] This new use of a roll coater to apply a fire-retardant coating to a wood substrate allows laminators to fire-retard wood substrates such as particle board with a machine many laminators already have, eliminating the need to purchase expensive particle board that is manufactured to be fire retardant (e.g., Duraflake FR) or particle board that must be separately treated for fire retardancy by a separate treatment facility. The resulting savings may be passed onto customers (e.g., cabinet makers, door makers, molding manufacturers) and/or laminators may realize an additional layer of profitability because the laminators fire retard the panels, not the panel manufacturer and not a separate treatment facility. It is estimated that the laminator&#39;s cost per panel for a standard Duraflake FR panel (4 ft. by 8 ft. % in. thick), which is manufactured to be fire retardant, is presently estimated at approximately $30-35. Because the Duraflake FR panel is only being manufactured by one company at two locations, one on the East coast and one on the West coast, much of the expense of the Duraflake FR panel is from the additional cost layers of warehousing, trucking, and distribution. In contrast, the process of the present invention may be performed at the laminator&#39;s facility, where the necessary equipment (i.e., roll coater) already exists. As a result, the cost to the laminator per panel for a fire-rated panel using the process of the present invention is presently estimated at approximately $20-25, resulting in a significant cost savings to the laminator for fire-rated panels.  
     [0051] Because of the relatively small size of roll coaters such as the roll coater  10  described herein, the process of the present invention may be performed at locations other than a lamination facility. For example, but not by way of limitation, the process may be performed at a distributor, at a manufacturer of the wood substrate, and at a job site.  
     [0052] The present invention also allows the laminator to produce a fire-retardant panel assembly because the wood substrate is fire retarded by the laminator, the adhesive added by the laminator is fire-retardant, and the laminae or veneer may be plastic or another fire-retardant material.  
     [0053] It will be readily apparent to those skilled in the art that still further changes and modifications in the actual concepts described herein can readily be made without departing from the spirit and scope of the invention as defined by the following claims.