Stock material or miscellaneous articles – Composite – Of carbohydrate
Reexamination Certificate
2001-12-19
2003-12-16
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Composite
Of carbohydrate
C428S328000, C428S330000, C428S324000, C428S143000, C428S153000, C428S219000, C428S489000, C428S491000, C428S203000, C428S341000, C428S342000
Reexamination Certificate
active
06663979
ABSTRACT:
BACKGROUND
The present invention relates to a composition for coating gypsum board panels. More particularly, the present invention relates to a coating that provides a smooth, even and uniformly glossy wall surface across seams and nail spots that have been covered with a joint compound. The coating withstands sanding between coats of joint compound, resulting in a surface that takes paint and other decorative finishes evenly.
This invention concerns a gypsum board, particularly, a coated gypsum board. Gypsum board is a well known building material which has been used for years, primarily as an interior wall and ceiling material, but also to a certain extent as an exterior material. These boards have a gypsum core with pressed paper cover sheets on the back and face of the boards. A slurry of calcium sulfate hemihydrate and water is used to form the core, and is permitted to set by allowing the calcium sulfate hemihydrate to react with sufficient water to convert the hemihydrate into a matrix of interlocking dihydrate crystals. As the crystal matrix forms, the product slurry becomes firm and holds the desired shape. Excess water is then removed from the product by drying.
In the construction of buildings, gypsum wallboard, often known as drywall, is frequently used in the construction of walls and/or ceilings. Walls made from gypsum wallboard are traditionally constructed by affixing the panels to wood studs, metal framing or other substrate, and treating the joints between adjoining panels with a specially prepared adhesive called a joint compound. The side edges of the drywall panels are tapered, thus allowing the joint compound to be applied to the seam, between adjoining panels, in such a way that a monolithic surface is created when finished. This process generally proceeds by placing a taping joint compound within the joint formed by the abutted edges of the wallboards, and embedding a liquid-permeable paper or fiberglass tape within that compound. When dry (or set), a second coating referred to as a topping joint compound is applied over the joint, which can be subsequently lightly sanded upon drying. A third or finish coat is applied, allowed to dry, and lightly sanded to create a smooth monolithic surface that conceals any indication of where the drywall seams were. Another type of joint compound is an all-purpose grade that can be used for both embedding the joint tape and for applying the finish coats. A patterned or textured effect can be given to the finished wall and joint through the use of special application tools.
Walls created by this process may sometimes have uneven texture, take paint unevenly or have flat spots on a glossy surface, resulting in noticeable joints even when the wall has been correctly taped, sanded and painted. The difference in the composition between the gypsum board surface and the joint compound can result in a surface that unevenly takes paint or other decorative finishes applied to it. If the porosity of the two surfaces differs greatly, one surface absorbs more paint than the other, giving it a different appearance and texture. Variations in paint absorption across a wall will also change the way it reflects light, making it appear more glossy in some places than others.
Finishes are specified for construction according to their suitability with various types of lighting and wallcoverings. Level 1 and 2 finishes are used where the finished appearance is of no concern. Level 3 is suitable for walls that are to receive heavy or medium texture finishes or where heavy grade wallcoverings are to be applied. Areas to be painted with flat paints should specify a Level 4 finish. The highest level, Level 5, is the only finish recommended for use with enamel, gloss or semi-gloss paints or with severe lighting conditions. The
Gypsum Construction Handbook,
90
th
Edition published by the United States Gypsum Company (1992) suggests that a Level 5 finish be achieved by a combination of high quality materials applied with certain techniques, that a thin skim coat of joint compound be applied to the entire surface followed by application of a high solids primer. A finish suitable for use with gloss or semi-gloss paint is generally achieved through high labor and material costs.
Further, the face paper used on gypsum boards generally does not maintain the same texture after repeated sanding. Attempts to blend the edges of the joint compound with the board surface during sanding can loosen fibers on the surface of the paper, causing them to rise up from the paper surface. Later, when traditional primer, paint or other decorative coating is applied, the paint can seal the loosened fibers in place, leaving a rough surface. The resulting wall shows the seams by rough patches on the paper near the edges of the joint compound when compared to either the joint compound, which has been sanded smooth, or the face paper toward the center of the panel, which has maintained its original surface because it was never sanded.
When using coatings that are to be applied during the manufacture of the gypsum board, the physical properties of the coating must be considered together with processing steps that it may have to withstand. For example, if a coating is impenetrable, it cannot be applied to the board before the board is dried in a kiln. Kiln drying causes steam to escape through the pores of the gypsum. A coating that cannot allow the steam to escape at the surface blisters or cracks during drying. Porosity of the coating also helps prevent pinholes from appearing in the painted surface due to air trapped within the dry film of the joint compound. If the air cannot diffuse through the coating, it may escape through the paint film, leaving pinholes in the paint surface.
One way to obtain an even surface is to apply a skim coat of thinned joint compound to the entire surface of the wall. After joints have been finished, a thinned joint compound is applied by hand to the entire wall. The wall surface is then immediately wiped as tightly as possible using a trowel or broad knife to remove excess joint compound and allowed to dry. This results in a very smooth surface that is uniform in color, porosity and texture, achieving a Level 5 finish when a primer is applied. This is a labor intensive, time consuming and expensive process.
Coatings have been applied to gypsum boards in the prior art for a variety of reasons. U.S. Pat. No. 3,839,141 to McKinnon teaches coating gypsum boards with an emulsion of wax, vinyl polymer and water. The resulting gypsum boards are particularly useful when used adjacent to concrete surfaces. When this coating is applied during the fabrication of the board, concrete will adhere to the surface of the board after the concrete is set. Johnson, in U.S. Pat. No. 4,057,662, applies a thin coating of polyethylene emulsion to a predecorated, printed paper already attached to a gypsum board. The coating overcomes the tendency of the predecorated boards from sticking to the back paper of adjacent boards when stacked for storage and shipping. Coatings have also been added to impart a waterproof surface to gypsum boards (U.S. Pat. No. 2,894,857 to Uraneck et al), and for thermal or acoustic insulation (U.S. Pat. No. 4,361,616).
In U.S. Pat. No. 3,422,587 to Murray, gypsum board is covered with a plaster coating during the manufacturing process that has a raised portion near the edges of the board. When the panels have been nailed into place, the surface of the panels is sprayed with water. As the water is absorbed, the coating softens. It is then shaped with a trowel to fill in the space between the panels and cover the nails. The raised portion of the coating at the edges provides sufficient plaster to fill in the joints. Although it will result in a uniform surface, this method has many disadvantages. The manufacture of such panels is a complex process. A binder solution must be sprayed onto the gypsum board to hold the coating onto the panel. Smoothing and forming of the coating must include a step to provide a raised portion at the edge of
Deodhar Subhash
Haugeberg Tom
Negri Robert
Greer Burns & Crain Ltd.
Janci, Esq. David F.
Kiliman Leszek
Lorenzen, Esq. John M.
United States Gypsum Company
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