Abstract:
A ceramic-based hardwood floor finishing method resistant to panelization, exhibiting improved durability, and suitable for on-site use. The method is comprised of laying down successive layers of water-based primer, armor coat and top coat. The water-based primer utilizes a low resin content and a low co-solvent concentration to substantially reduce panelization of hardwood boards. The water-based armor coat is comprised of large particulate size ceramic additives which, in combination with a low resin content, allow the formation of a microscopic bead structure on the surface of the finish which provides enhanced durability.

Description:
FIELD OF THE INVENTION 
     The invention relates to water-based hardwood floor finishing products and methods of applying the products on site. 
     BACKGROUND OF THE INVENTION 
     Hardwood flooring has long enjoyed favor with consumers due to the unique richness and elegance that it adds to a home or business setting. Although hardwood flooring is a consumer favorite, inherent physical characteristics of hardwood flooring make it susceptible to damage from ordinary usage and the occasional accident. As such, it has become traditional practice in the flooring industry to protect hardwood floors with some form of coating or finish to preserve aesthetic qualities, and ultimately extend the useful life of the surface. 
     Many protective finishes are known in the flooring industry. Protective finishes in the prior art include varnishes, acrylics, urethanes, and epoxies or combinations thereof. In general, protective finishes are applied to hardwood surfaces in successive layers, with each layer performing a specific purpose. For example, a protective finish normally constitutes primers applied directly to the hardwood surface to bond and seal the porous wood itself and top coat layers applied over the sealing layers to provide sheen and stain resistance. In recent years, water-based finishes (i.e., solutions in which water is the primary solvent) have become popular due to environmental and health concerns. In addition, various layers may also contain additives including co-solvents, defoamers, flow additives and wax emulsions to provide ease of application and improve the overall effectiveness of the protective finish. 
     Although the above-mentioned primers and top coats provide some protection against mechanical damage due to scratching, gouging, scuffing or the like, the hardwood flooring industry has invested much time and effort into identifying further additives for floor finishes in order to improve the overall durability of hardwood floor surfaces. Unfortunately, increasing finish durability often results in a finish with reduced abilities to preserve aesthetic qualities. Thus, the fine balance between durability and preservation of desirable characteristics such as clarity is difficult to attain. Nonetheless, such finishes are extremely desirable. 
     Finished hardwood floors also suffer from a problem termed panelization. Panelization, to be more thoroughly discussed below, results when resins contained in the primer coat invade the gaps between hardwood boards, cross-link, and cause neighboring boards to become rigidly affixed to each other as if glued together. Unfortunately, when hardwood boards contract due to seasonal changes in humidity, large sections of panelized flooring contract to leave unsightly, uneven gaps at the boundaries of the panelized units. Without panelization, the gaps between boards would be evenly distributed, and hence smaller and less noticeable throughout seasonal humidity cycles. A method of finishing hardwood floors that avoids this problem, but provides durability and is aesthetically pleasing, is needed. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention is a hardwood floor finishing method that uses water-based coatings and exhibits improved durability during ordinary usage and against accidental damage. It also substantially reduces or eliminates the above mentioned panelization problem. In general, the finishing method is intended to be carried out on-site in several simple, efficient and safe steps. In its preferred form, the method involves the application of a ceramic-based armor coat over the primer layers in order to improve the durability and wearability of the floor finish. 
     The inventive method disclosed herein is preferably implemented on a new floor by applying successive layers of primer, ceramic armor and top coat to a newly screened, cleaned and tacked hardwood surface. The primer is a water-based primer having a low solid content and low co-solvent concentration in order to reduce or eliminate panelization. As with many conventional primers, the primer contains a mixture of acrylic and polyurethane polymer resin dispersions that are not water-soluble, but are suspended in the water/co-solvent mixture. Alternatively, the primer may be a copolymer substitute for the acrylic and polyurethane mixture. Upon application to the prepared surface, this water-based primer penetrates the pores of the hardwood and acts to thoroughly seal the exposed hardwood surface. Use of a water-based primer to seal a hardwood surface is widely known in the field. However, as mentioned, the method disclosed herein involves applying a water-based primer having an unusually low resin content and low co-solvent concentration. It is believed that the combination of the low resin content and a low co-solvent concentration reduces the flow of resins into the gaps between the hardwood boards during the initial drying process. A second coating of primer is applied after initial drying of the first primer coat. Two coats of primer are needed because the coats are thin. The problem posed by panelization of hardwood floor boards is substantially eliminated by using a thin coating of low solid content/low co-solvent concentration primer, but a sufficient primer build is obtained by using two coats of primer. 
     It has been found that panelization results from the use of primers having a high solid content of polymers or copolymer resins and a high concentration of co-solvent. This combination promotes not only the flow of uncrosslinked polymer or copolymer resins into the existing gap between new hardwood boards but also the subsequent solvation step necessary to cross link the resins. However, the polymer or copolymer resins remain uncrosslinked when in a solution having a high water content. Only when water is removed as by evaporation, are the polymer or copolymer resins solved into the increasing concentration of co-solvent. Once solved, the polymer or copolymer resin crosslink into a rigid composition potentially resulting in a group of boards being joined or glued together to form a panel-like unit. It should be noted that hardwood normally contracts in a direction across the grain, and therefore the width of the boards normally shrinks when the hardwood boards respond to seasonal changes in humidity. The unfortunate result of this phenomenon on a panelized floor is that gap width is consequently spread unevenly across the floor surface. Instead of small gaps of uniform width existing between each new hardwood board, a panelized group of boards will have essentially no gaps on its interior, but much larger and noticeable gaps will surround the panel. The gaps due to panelization are especially evident during the winter when humidity is relatively low. These noticeable gaps in the hardwood surface are obviously undesirable. 
     The low concentration of acrylic and polyurethane polymer resins or copolymer resins in the primer effectively reduces the concentration of uncrosslinked resin in the gap area when the primer is first applied. Subsequently, the concentration of the crosslinked resins in the gap area remains relatively low for an extended time period because the water within the gaps takes longer to evaporate than on the hardwood boards&#39; exposed surfaces. Thus, if a second layer of primer is applied within a certain amount of time (e.g. about 45 minutes), the gap area between hardwood boards remains relatively free of cured resins. 
     After the primer layers are dry, the floor is then screened, vacuumed and tacked with a dampened cloth to remove all dust particles. Then, within about two to three hours of applying the second primer coat, the armor coat is applied to the floor. The armor coat effectively seals over the gap which should at this time still contains the primer solution with a relatively high concentration of water. The primer solution in the gap area is consequently left undried. In this manner, the resins in the armor coat are not allowed to reside deep within the gaps. Rather, as the armor coating dries, it forms a relatively thin bridge across the gap between the boards. Within twenty-four hours, the top coat should be applied over the armor coat. When the top coat and the armor coat continue to dry and cure over time, the coats shrink and the thin bridging across the gaps cracks easily. Also, the high content of water contained within the sealed off gap area is slowly absorbed into the porous walls of the neighboring hardwood boards. Left behind is a small amount of crosslinked resin which does not act as glue between hardwood boards. The gap area will ultimately be completely open and each hardwood board may expand and contract independently of their neighbor. In sum, individual hardwood boards do not become rigidly attached to each other and the unsightly effects of panelization are greatly reduced or eliminated totally. 
     The preceding paragraphs discuss the method for finishing newly constructed hardwood floors. However, when finishing older hardwood floors, panelization, if it is going to occur, will have probably already occurred. Thus, there is no advantage in applying a primer layer with panelization-inhibiting abilities to older hardwood floors that have previously been finished. Thus, the preferred method of finishing an older hardwood surface involves buffing the old finish and applying the armor coat and top coat directly on the buffed surface. Alternatively, the existing finish can be removed by sanding and a traditional high solid content primer can be applied in order to provide a sufficient build on the surface. High solid content primers, as noted previously, are widely known in the field. 
     In addition to offering a remedy for panelization problems, the preferred embodiment of the invention also provides an approach to improving the durability of the hardwood floor coating. The use of ceramic additives (e.g. aluminum oxide) to provide abrasion resistance and durability in floor finishes has been widely discussed in the prior art. Normally, the aluminum oxide particles are relatively small and embedded into the cured resin. In the preferred embodiment of the invention, however, relatively large-sized ceramic particles are mixed into the water-based armor coat. Also, the armor coat has a low resin content. This provides the fully cured finish with a unique microscopic bead structure on its surface. Standard abrasion resistance testing has shown that the microscopic bead structure provides a finished hardwood floor with extremely high durability. 
     More specifically, the diameter of the large particles of ceramic additive (e.g., aluminum oxide) are preferably in the range of 15 to 35 microns. When the armor coat is applied over the panelization-reducing primer layer(s), a large percentage of the non-ceramic components (i.e. water and co-solvent) in-the armor coat evaporate completely. The components left behind, namely the crosslinked acrylic and polyurethane polymers (or copolymers), produce a thin layer of hardened resin in which the larger ceramic particles remain protruding above. These protrusions are termed microbeads. The microbeads on the surface of top coat layer remain even after subsequent applications of a water-based top coat layer over the heterogeneous armor coat layer. An incidental benefit of the microbeaded top coat surface is the anti-slip characteristics bestowed on the surface due to the increased frictional coefficient of the microbeaded top coat layer. 
     It should be apparent to those skilled in the art that the invention provides a practical and simple hardwood floor finishing method that yields a finish resistant to the problems of panelization. In another aspect, it should also be apparent that the finish is convenient to apply on-site and also provides exceptional durability. The finishing method is easy to apply on-site to both newly constructed hardwood floors and old hardwood floors in need of refinishing. In addition, the invention provides an environmentally safe method that generates no noxious fumes and contains no caustic agents. It is safe for both the people that work with the system and the environment in general. 
    
    
     Various other features, objects, and advantages of the invention will be made apparent from the following detailed description and the drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a flowchart illustrating the preferred process for the finishing method for a newly constructed hardwood floor surface in accordance with the invention. 
     FIGS. 2 a  through  2   e  are schematic views of the specific layers formed during the process described in FIG.  1 . 
     FIG. 3 is a flowchart illustrating the preferred process for refinishing an older hardwood surface in accordance with the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In general, the inventive method involves successive application of a water-based primer to form a primer layer, a water-based armor coat to form an armor coat layer, and a water-based top coat to form a top coat layer. The preferred process for a newly constructed hardwood floor surface is different than the preferred process for an old floor being refinished. 
     FIG. 1 is a flowchart illustrating the preferred steps of the inventive finishing process  10  as applied to a newly constructed hardwood surface. Prior to applying the first primer coat, block  14 , the hardwood surface is screened, block  12 . For neutral or stained floors, the screening should be to a final 80-100 grit. For unstained, natural floors, the final screening should be to a 120-150 grit. Initial screening provides a relatively smooth surface for subsequent application of the finish layers, and also removes irregularities on the hardwood surface which can create breaks in the hardened finish. Following screening, the hardwood surface is thoroughly vacuumed to remove particulate matter. As a final preparatory step, the hardwood surface is tacked with a water dampened cloth to remove any remaining particulate matter and to provide a water-dampened surface to promote the subsequent successful application of a water-based primer, block  14 . 
     A first coat of water-based primer is applied to the prepared hardwood surface, block  16 . The water-based primer is a panelization-inhibiting primer characterized by a low solid content and a low co-solvent concentration. The panelization inhibiting primer is applied directly to the hardwood surface and preferably contains a mixture of self cross-linking acrylic/polyurethane dispersions (or a suitable copolymer), a co-solvent, a flow additive, and a wax emulsion. The preferred panelization-inhibiting primer may be comprised of about 15 percent up to about 20 percent by weight of a mixture of acrylic and polyurethane polymers and about 0.2 percent up to about 1.5 percent by weight of at least one co-solvent. The preferred embodiment of the water-based primer contains 16 percent by weight of a mixture of acrylic and polyurethane polymers and 1 percent by weight of co-solvent. 
     The preferred acrylic dispersion is a pure acrylic dispersion or a styrene acrylic dispersion. The preferred polyurethane dispersion is based on aliphatic or aromatic polyisocyanates. The mixture is preferably 1 to 1½ parts acrylic to 1 part polyurethane (by weight), although pure polyurethane may be used if desired. The preferred co-solvent is N-methylpyrrolidone. Traditional water-based primers/sealants regularly contain between 3 and 10 percent by weight co-solvent. The reduction in co-solvent concentration to 1 percent by weight provides a substantial increase in the ability of the finish to resist panelization. The preferred embodiment also includes a polyalkylene wax emulsion, namely, a polyethylene wax emulsion. 
     In this embodiment, it is desirable to repeat the application of the panelization-inhibiting primer such that two successive primer layers are formed, block  20 . After allowing 45 minutes for the first primer layer to dry, block  18 , the panelization-inhibiting primer is again applied to create a second primer layer, block  22 . After 2-3 hours drying time, block  24 , the surface of the second primer layer is screened, vacuumed and tacked, block  26 , to prepare for the application of the water-based armor coat, block  28 . 
     A water-based armor coat is applied over the screened primer layer, block  30 , and allowed 2-3 hours to dry, block  32 . The water-based armor coat has a low resin content and is comprised of only 15 percent up to about 25 percent by weight of a mixture of acrylic and polyurethane polymers (or suitable copolymer). 
     The preferred polymer mixture is the same as described above with respect to the primer. However, a concentration of 17 percent by weight is preferred in the armor coat. The armor coat includes a low concentration of co-solvent in the range of 5 percent up to about 12 percent by weight with a concentration of 5.8 percent by weight being preferred. The armor coat also comprises about 25 percent up to about 35 percent by weight of at least one ceramic additive having an average particle size (diameter) in the range of about 15 microns to about 35 microns, about 0.2 percent up to about 2.0 percent by weight of a fumed silica, and about 1 percent up to about 2 percent by weight of a non-polyethylene wax emulsion. The armor coat may also comprise at least one flow additive. The preferred ceramic additive is aluminum oxide with a particle size (diameter) in the range of about 28 to about 32 microns. The preferred amount of ceramic additive is about 20-30 percent by weight. It should be noted that the surface of the armor coat layer is not screened before a top coat is applied, block  34 . 
     A water-based top coat, block  34 , is applied over the armor coat layer, block  28 , to form a top coat layer. The water-based top coat, block  36 , is preferably a mixture of acrylic and polyurethane polymer (or suitable copolymer), a co-solvent, a flow additive, a polyethylene wax emulsion and a UV stabilizer. The preferred polymer mixture is the same as described above with respect to the primer and the armor coat. However, the concentration of the polymer mixture should be in a range from about 34 to about 42 percent by weight with 39 percent by weight being preferred. The top coat is also characterized by a high content of co-solvent in the range of about 5 percent to about 12 percent with 6.2 percent by weight being preferred. This high concentration of co-solvent promotes even spreading and drying of the top coat. The top coat layer is allowed 2-3 hours to dry, block  38 . Although the finish will be dry to the touch at this time, four days should be allowed for the finish to cure completely and perform with full durability, block  40 . 
     FIGS. 2 a  through  2   e  depict cross-sectional views of two hardwood boards  42 , a gap  46  existing between the adjacent hardwood boards  42 , and successive layers of coatings formed by the method described above to produce a hardwood floor finish  48 - 54 . FIGS. 2 a - 2   c  represent conditions immediately prior to application of subsequent coats. FIG. 2 d  represents the condition after all coats have been applied, and dried for 2-3 hours. FIG. 2 e  represents the condition of the finish after full curing and seasonal contractions/expansions have occurred. 
     Referring to FIG. 2 a , a small gap  46  is inherently created between hardwood boards  42  in the construction of hardwood floors. The first primer layer  48  is formed directly over the hardwood board surfaces  44  by application of the panelization-inhibiting primer. Panelization-inhibiting primer in the gap area  43  remains uncrosslinked due to the reduced evaporative characteristics of the gap area  46 . Referring to FIG. 2 b , a second primer layer  50  is applied over the top of the first primer layer  48 . An armor coat layer  52  is then subsequently formed over the top of the second primer layer  50  by the application of the water-based armor coat (See FIG. 2 c ). FIG. 2 c  reflects the thinness of the layer created by the non-ceramic components of the water-based armor coat after drying has occurred. The large size of the ceramic additive particles  56  allows the ceramic additive particles to protrude significantly above the dried non-ceramic components. The exposed ceramic additive particle surfaces create microbeads  57  in the surface of the armor coat layer  52 . 
     FIG. 2 d  depicts a top coat layer  54  formed over the armor coat layer  52  by the addition of a water-based top coat. The top coat layer  54  covers the microbeads  57  in the armor coat layer  52  but, upon drying, the surface of the top coat layer  58  also contains microbead characteristics due to the underlying microbeads  57 . 
     FIG. 2 e  depicts the condition of the gap area after neighboring hardwood boards have undergone seasonal expansion/contractions due to changed humidity levels. The weak bridge  53 , FIG. 2 d  originally formed by application of the armor coat and top coat has broken, reference number  59 , leaving the gap area  46  no longer sealed. Also, the water content of the panelization-inhibiting, primer in the gap area  43  slowly absorbs into the neighboring hardwood boards  42  leaving behind only a small amount of resins  61 . Thus, the gap area  46  is substantially free of resins that act to rigidly affix the neighboring boards  42  to one another. 
     The durability of the finished floor resulting from the method disclosed herein is due to the concentration and particle size of the ceramic additives  56  in the armor coat layer  52 . One can appreciate from FIGS. 2 d  and  e  that eventual wear of the top coat layer  54  will result in direct contact with the microscopic beads  57  comprised of the ceramic additives  56 . Consequently, before wear can continue through the armor coat layer  52  and into the primer layers  48  and  50 , the large ceramic additives  56  must be entirely worn through. This microscopic bead structure exhibits an extremely high degree of hardness and resistance to wear as shown by results of industry recognized abrasion resistance tests. 
     Referring to FIG. 3, a method of refinishing older previously-finished hardwood floors  70  is shown. A previously finished hardwood surface is first sanded to remove substantially all preexisting finishes, block  72 . The sanded surface is then thoroughly vacuumed and wiped down with a water dampened towel. A primer layer is then formed over the prepared hardwood surface, block  74 . The preferred embodiment requires that only a single primer layer be applied to older hardwood surfaces, block  76 . In contrast to the panelization-inhibiting primer previously described for newly constructed hardwood floors, the primer applied to older hardwood floors should be a conventional high solid content/high co-solvent concentration primer. This change in primer composition is due to the fact that any panelization problems will have already occurred with the hardwood flooring surface, and the application of panelization-inhibiting primers would have little or no beneficial effect on an older hardwood surface. After sufficient drying, block  78 , the high solid content/high co-solvent concentration primer layer is then screened, vacuumed and tacked, block  80 , in a similar fashion as that previously described for a newly constructed hardwood surface (see FIG.  1  and description thereof). Following screening, the finishing process continues in the same manner as that described for the newly constructed hardwood surface (i.e. steps depicted by blocks  84 - 94  in FIG. 3 or the same as steps depicted by blocks  30 - 40  in FIG.  1 ). As an alternative to sanding the previously finished floor to completely remove the old finish, it may be desirable in some circumstances to merely buff or screen the old finish. In such cases, it would not be necessary to apply primer. 
     It is recognized that other equivalents, alternatives, and modifications aside from those expressly stated, are possible and within the scope of the appended claims.