Colorless edge sealant for wood-based panels

Details Colorless edge sealant for wood-based panels Colorless edge sealant for wood-based panels

2001-08-01

2003-08-05

Thomas, Alexander S. (Department: 1772)

Stock material or miscellaneous articles

Structurally defined web or sheet

Edge feature

C428S195100, C428S537100, C428S690000

Reexamination Certificate

active

06602582

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an edge sealant for wood-based panels and, more particularly, to a colorless edge sealant that fluoresces when illuminated by ultraviolet light.
BACKGROUND OF THE INVENTION
Wooden panels, such as oriented strandboard (OSB) or plywood, are commonly used as subfloor sheathing in residential homes. These panels are installed directly on top of floor joists prior to installation of the walls and roof of the structure. Thus, the subfloor is exposed to external environmental conditions for a period of time during the general process of building a house. It is common for the subfloor panels to be subjected to rain during this process. Sill plates, which vertically protrude from the perimeter of the floor, can literally convert the floor into a basin. An uncovered subfloor can accumulate as much as two inches of water during a rainstorm. In some cases the accumulated water will be left to absorb into the subfloor panels for several days during the home-building process.
Subfloors comprised of plywood generally undergo relatively little dimensional change when subjected to rain. Unfortunately, most OSB panels undergo irreversible thickness swell when exposed to rain. OSB flooring panels, which are manufactured at a thickness of 720 mils (0.720 inch), can actually swell to edge thickness values in excess of 1000 mils. Upon drying, these same OSB panels can have an edge thickness of 900 mils. Thus, much of the edge thickness swelling action is not reversible. The worst aspect of this swelling behavior is that OSB panels swell to a greater extent on the edge of the panel than they do in regions towards the center of the panels.
When edge swell occurs during residential home construction, it manifests itself as ridges along the seams in the subfloor. Builders are often required to sand the seams in the subfloor in order to remove these ridges and create a flat, smooth subfloor. Obviously, the practice of sanding the subfloor is costly, time-consuming and frustrating to the builder.
In order to inhibit edge swell, virtually all OSB manufacturers in North America apply a liquid, paint-like, aqueous, sealant formulation onto the edge of their panels. These edge sealant formulations are commercially supplied in North America by companies such as Associated Chemists Incorporated [Portland, Oreg.] and the Willamette Valley Company [Eugene, Oreg.]. Typically, the sealant is applied to the edge of OSB panels and dried to form a coating, which retards the absorption of water and helps to dimensionally stabilize the OSB in wet environments. The edge sealant also provides the function of visually differentiating distinct OSB panels in the marketplace. This is accomplished by incorporating colored pigments into the edge sealant formulation. Thus, the specific color of the edge sealant is commonly used as an identifying marker that allows a customer to easily determine the manufacturer of a given panel. An intensely colored edge sealant also makes it obvious to the consumer that the manufacturer has treated the panel edges. Builders (customers) have learned to associate an intensely colored panel edge with the presence of edge sealant and improved dimensional stability. Thus, one of the most important functions of an edge sealant is its obvious visibility subsequent to application and drying.
In North America, aqueous edge sealant formulations for OSB are generally comprised of latex, emulsified wax, and colorants. The most intense colorants are based on water-insoluble organic compounds. Incorporating these colorants into an aqueous matrix requires the use of additional surfactants in order to stabilize the total sealant formulation. Unfortunately, these same surfactants remain in the sealant formulation as it dries, and they severely detract from the ability of the applied edge sealant to repel water. Thus, a colorless edge sealant should be more water repellant than a colored one. The ability of colored and colorless edge sealant formulations to dimensionally stabilize wooden panels in a wet environment has been evaluated and it has been found that colorless edge sealant formulations perform significantly better than do the colored ones.
The application of colorless edge sealant formulations to aspen and poplar-based OSB panels results in a coating that is essentially colorless and transparent. Thus, the edge of the sealed OSB panel generally appears to be non-treated. Since most builders are accustomed to seeing the colored edge sealant, and they associate the color of it with the attribute of improved dimensional stability, an ironic dilemma arises in which the actual dimensional stability of the panel has been improved, but the builder perceives it as being inferior and might be unwilling to buy it. A second problem associated with the use of colorless edge sealant formulations occurs when the technology is applied to pine-based OSB as described below.
Application of several different colorless edge sealant formulations from three different suppliers were applied to the edge of a pine-based OSB panel. In each of these cases the edge of the treated panel spontaneously became yellow in color within about 5-15 minutes of sealant application. The intensity of the yellow color did seem to be correlated with particular colorless edge sealant formulations. In contrast, when colorless edge sealant was applied to aspen or poplar-based OSB, the edge of the panel retained the off-white color of the aspen wood. Thus, the colorless edge sealant could visually differentiate panels as a function of the wood species. This effect might be undesirable in certain circumstances. For instance, a company that is applying colorless edge sealant at several OSB mills, which use different wood species as furnish, might be required to sell OSB in the marketplace that is generally similar, but different in color as a function of the wood species in the OSB. This company might then be perceived as having poor standardization in the marketplace. Also, other companies in the industry might already be selling an OSB panel with a yellow-colored edge. This would make it more difficult to distinguish between the different brands of OSB. In some cases another company might have even trademarked a yellow colored OSB.
Discoloration of various decorative materials, which are applied to wooden objects, has been reported in the past. For instance, coatings and white plastic coverings are known to become yellow in color subsequent to application on elm wood [see Fracheboud, M.; et al., (1968) “New sesquiterpenes from yellow wood of slippery elm”,
Forest Prod. J.:
18(2), p 37-40]. Vinyl flooring can become discolored over a period of time when applied to various wooden flooring products (see, for example, Anderson, T. (1994) “Barrier layer for floor and wall coverings”, U.S. Pat. No. 5,308,694; Shih, K. S.; et al. (1999) “Stain-blocking barrier layer”, U.S. Pat. No. 5,891,294; and Winterowd, J. G.; et al., (1999) “Stain blocking treatments for wood based panels”, U.S. Pat. No. 5,993,534). The application of many alkaline aqueous colorless solutions to pine species of wood results in yellow discoloration of the wood.
Methods involving the application of primers to wood in order to prevent it from discoloring latex paint are well known. Some of these primer technologies are described in, for example, Gilman, W. S.; et al. (1977) “Aqueous latex emulsions containing basic aluminum compounds of wood stain reducing agents”, U.S. Pat. No. 4,021,398; Meyer, V. E.; et al. (1980) “Pigment for blocking tannin migration”, U.S. Pat. No. 4,218,516; McNeel, T. E.; et al. (1994) “Method for the reduction or prevention of tannin-staining on a surface susceptible to tannin-staining through the use of a complexing agent for a transition metal ion and compositions containing such a complexing agent”, U.S. Pat. No. 5,320,872; Van Rheenen, P. R.; et al. (1994) “Cationic latex coatings”, U.S. Pat. No. 5,312,863; Thomassen, I. P. (1995) “Stain-blocking and mildewcide resista

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