Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-11-28
2003-04-08
Yoon, Tae H. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S158000, C524S423000, C524S425000, C524S493000, C106S602000
Reexamination Certificate
active
06545066
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a composition for a joint compound for use in filling and coating the joints between adjacent panels of gypsum wallboard. More specifically, it relates to a composition for lightweight joint compound of the drying type that reduces applicator fatigue, job completion time, and reduces shipping costs of the packaged product.
In the construction of buildings, one of the most common elements is gypsum wallboard, often known as drywall, used in the construction of walls and/or ceilings. Walls made from gypsum wallboard are traditionally constructed by affixing the panels to wood studs or metal framing, 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 may 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 may be used for both embedding the joint tape and for applying the finish coats. A patterned or textured effect may be given to the finished wall and joint through the use of special application tools.
There are several categories of joint compounds. Drying type compounds cure through the evaporation of water, whereas setting type joint compounds chemically react with water during the curing process. Setting type joint compounds typically use calcium sulfate hemihydrate, also known as stucco or plaster of Paris, as a base. When water is added to the setting type powder, it reacts with the calcium sulfate hemihydrate via a hydration reaction to form an interlocking matrix of calcium sulfate dihydrate crystals. The interlocking crystal matrix gives the compound increased strength. The benefit of a setting type joint compound over a drying type is the overall strength of the finished joint, resulting in less shrinking and cracking, as well as an independence from having to wait for the joint compound to be completely dry prior to further finishing. Drying type joint compounds have the advantage of ease of use, as they typically come in a ready mixed form, with water being added and mixed by the manufacturer. A third type of joint compound combines the setting action of a calcium sulfate hemihydrate based compound with the ease of use of a ready mixed compound. The properties of a ready mixed setting type joint compound are taught in U.S. Pat. No. 5,746,822, incorporated herein by reference.
Lightweight joint compounds are known in the art, such as U.S. Pat. No. 4,454,267 to Williams and U.S. Pat. No. 4,657,594 to Struss. Perlite, which is a form of glassy rock similar to obsidian, is ground, heat expanded, and immediately surface treated with a silicone-based compound to provide lightweight filler for use in a joint compound. The special treatment renders the expanded perlite water-insensitive so that it does not soak up water due to capillary action. Despite the water-insensitivity of coated perlite, it still requires a certain amount of available water to wet out and disperse. Use of large amounts of perlite negatively impacts the overall water demand, drying time, strength, bond, viscosity and surface absorption characteristics of the joint compound. The expanded perlite is also susceptible to breakdown during mixing that may further degrade the physical properties of the joint compound.
U.S. Pat. No. 4,824,879 to Montgomery, et al. teaches the addition of expanded perlite or hollow glass microspheres to reduce density and shrinkage in a joint compound. As recited above, there is a limit as to the amount of perlite that may be used in a joint compound without deterioration of certain physical properties. Glass microspheres may be used, however, they are prone to breakage. When microspheres break open, they greatly increase the density of the resultant joint compound due to the filling of the void left behind by the broken sphere with water and other additives. The glass then tends to settle, and is difficult to disperse thereby leading to an unfavorable change in rheological properties. Whenever breakage occurs, more microspheres must be added to make up for the increase in density, in turn, increasing the cost of the formulation. Glass and perlite are also disadvantageous because of the dust that can be produced. Glass microspheres are limited in size and density. These limitations require a greater amount be added to the formulation in order to lower the overall density.
The use of polyacrylate microspheres in a setting type joint compound is taught in U.S. Pat. No. 5,494,947 to Kaplan. This reference is directed to a joint compound to be used in prefabricated walls and ceilings that remain flexible after set, thereby minimizing cracking during transportation and final assembly of the prefabricated unit. The surface chemistry of these polyacrylate resins is such that it tends to stick to itself rather than disperse readily in water, making it difficult to disperse in an aqueous medium typically resulting in the formation of unacceptable clumps.
It is, therefore, an object of this invention to provide an improved lightweight joint compound with a final use density less than the density of water.
It is also an object of this invention to provide an improved lightweight joint compound that provides a smooth finished surface.
It is yet another object of this invention to provide an improved lightweight joint compound utilizing microspheres which are minimally susceptible to breakage during manufacture and end use.
It is still another object of this invention to provide an improved lightweight joint compound utilizing microspheres that readily disperse in an aqueous medium.
BRIEF DESCRIPTION OF THE INVENTION
The above-listed objects are met or exceeded by the present invention that features hollow resin microspheres as filler in lightweight joint compound. Densities less than that of water are obtainable using the formulation of the present invention. Use of the resin microspheres at the same weight percentage as glass microspheres provides a greater change in density due to the much lower density of the resin versus the glass. Resin microspheres also avoid a reported adverse interaction when glass microspheres are used with polyvinyl alcohol, that causes the joint compound to stiffen or gel.
More specifically, the joint compound of the present invention comprises at least one binder and one or more fillers, with at least one filler including hollow resin microspheres with a mean particle size less than 75 microns and exhibiting no more than 1.5% increase in density under high shear testing. Use of hollow resin microspheres as lightweight filler provides for a formulation of an extremely light joint compound with a density less than water, and that does not exhibit a grainy surface when applied over drywall, while improving the application properties. The microspheres blend easily with other ingredients, particularly when added in a pre-wet form, also known as a cake.
Resin microspheres have a density much lower than that of glass microspheres. Because of this lower density, fewer resin microspheres are required to get the same change in resultant volume compared to glass microspheres. This allows preparation of very lightweight joint compounds without adversely affecting other properties of the joint compound.
DETAILED DESCRIPTION OF THE INVENTION
In the following discussion, all percentages indicated are calculated as the weight of all sol
Cimaglio Scott A.
Immordino, Jr. Salvatore C.
Miller Charles J.
Pickles David
Greer Burns & Crain Ltd.
Janci David F.
Lorenzen John M.
United States Gypsum Company
Yoon Tae H.
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