Compositions: coating or plastic – Coating or plastic compositions – Inorganic settable ingredient containing
Reexamination Certificate
2000-11-22
2002-06-18
Wood, Elizabeth D. (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Inorganic settable ingredient containing
C106S698000, C106S772000, C106S775000, C106S776000, C106S782000, C106S814000
Reexamination Certificate
active
06406537
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates generally to gypsum-related compositions and products. More particularly, the invention relates to a composition comprising calcined gypsum that is capable of setting on a substrate, and which is useful as a joint compound.
BACKGROUND OF THE INVENTION
Joint compounds are well-known materials that are used commonly to fill and smooth the joints between abutting edges of two adjacent gypsum boards. Typically, such joint compounds are plaster materials that include water, calcined gypsum and other components such as, for example, fillers, thickeners, set control additives, binders, and the like, as desired to form a workable viscous slurry. The joint compound typically is applied to the joint between two adjacent wallboards, often over a tape or mesh support. As the joint compound is applied, it is typically smoothed over the joint between the two wallboards and it is feathered over at least a portion of each of the two pieces of wallboard to hide the joint and present to the eye a uniform one-piece appearance. Quite often, several applications of the joint compound are required to achieve the desired effect.
The joint compound is allowed to set and dry after each coat. During the setting and drying process, the calcined gypsum reacts with the water to form a matrix of hydrated gypsum or calcium sulfate dehydrate crystals. It is the desired hydration of the calcined gypsum that enables the formation of an interlocking matrix of set gypsum crystals, thereby imparting strength to the gypsum structure in the applied joint compound. After the joint compound is set and dried, the composite surface structure is typically decorated so as to create the appearance of a uniform continuous wall surface.
There is a continuing need for a joint compound with enhanced strength, both its “green ” strength and “final ” strength. Green strength refers to the strength of the joint compound after setting but while it is still wet, while final strength refers to the strength of the joint compound after it has set and dried. For example, there is an increasing demand in the marketplace for homes manufactured on an assembly line in a factory and transported to its final destination. There is a need for joint compounds used to join adjacent pieces of wallboard used in the manufacture of the walls, ceilings and even flooring of such homes that exhibit sufficient strength to withstand flexing and other stresses encountered on the manufacturing line during handling after manufacture. In addition, the final strength of the joint compound is particularly important as the manufactured home is transported to the homesite, where it is subjected to various stresses, such as lifting in order to place the home in its final location. Final strength of the joint compound also is important during the use-life of the final wall product, for example, to avoid cracking.
However, providing a joint compound with enhanced green strength or final strength, while also maintaining sufficient plasticity, has proven to be difficult. In this respect, plasticity is the property of plaster that permits permanent and continuous deformation in any direction. As opposed to low viscosity materials, joint compounds require a measurable force to initiate flow. A material of low plasticity is usually described as being “poor” or hardworking; high plasticity is described in terms of being “rich” or easy working. Previous attempts to provide a joint compound with enhanced strength have not been fully satisfactory because, as strength is enhanced, the plasticity or workability of the joint compound generally is diminished such that the joint compound is not as easily applied to the desired substrate.
Accordingly, it will be appreciated from the foregoing that there is a need in the art for a joint compound that exhibits enhanced green and/or final strength, while also maintaining sufficient workability for application to a substrate, such as the joint between two wallboards.
BRIEF SUMMARY OF THE INVENTION
The present invention provides a composition which, after it is set but still wet, exhibits enhanced green strength and/or after setting and drying exhibits enhanced final strength. The composition of the invention comprises calcined gypsum, trimetaphosphate ion, and a water-soluble linear polymer formed by the addition reaction of ethylene oxide and/or alkoxy-substituted ethylene oxide with water. The composition may include water or it may be dry as formed and then mixed with water to form a slurry of desired consistency and workability prior to application. The composition has a pH of about 9 or less upon the addition of water thereto. When water is added, the composition of the invention has a water to calcined gypsum ratio of from about 100:100 to about 18.6:100. Calcium sulfate alpha hemihydrate has been found to be particularly useful in the practice of the invention. The composition also can include additives such as thickeners, binders, set control additives, and the like so long as the composition has a pH of about 9 or less.
Advantageously, the composition of the invention exhibits enhanced strength, particularly green strength and/or final strength. At the same time, the composition of the invention displays sufficient plasticity and workability such that the composition can be applied with relative ease to a substrate, such as the joint between two wallboards, as well as to the wallboards themselves. As such, the composition and joint compound of the invention can be used to fill and smooth the joints between two wallboards. The invention is useful in any type of building construction and it is particularly useful for homes built in a factory on an assembly line and transported to a homesite. In particular, the composition displays significant green strength to withstand various stresses found in assembly line manufacture of homes and in the handling and transport of pre-fabricated walls, ceilings and flooring. The composition also demonstrates significant final strength to withstand stresses encountered during the construction process at the final building site, independent of the type of construction process or building, and during the use-life of the set composition, for example, so as to minimize cracking.
These and other advantages of the present invention, as well as additional inventive features, will be apparent from the description of the invention. The invention may best be understood with reference to the following detailed description of the preferred embodiments.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention provides a calcined gypsum-containing composition which, after it has set but is still wet, exhibits enhanced green strength and/or after setting and drying exhibits enhanced final strength. The composition also exhibits desirable qualities such as plasticity and workability to facilitate its application. Thus, the composition is particularly useful as a joint compound. It will be appreciated that the composition requires water in use in order to allow it to be applied to a substrate such as to a joint between two abutting pieces of wallboard, ceiling tile, flooring, or the like. Thus, it is contemplated that the composition of the present invention can be provided dry, that is, essentially free of water, or wet, that is, with water included in the composition as formed. The composition of the present invention comprises calcined gypsum, trimetaphosphate ion, and a water-soluble linear polymer formed by the addition reaction of ethylene oxide and/or alkoxy-substituted ethylene oxide with water. Whether water is included in the composition as made, or whether water is added to the dry form of the composition of the invention in order to facilitate application of the composition, sufficient water is included to form a viscous and workable slurry. In accordance with the present invention, the components of the composition of the invention are selected so the composition in conjunction with water has a pH of about 9 or less.
Janci David F.
Leydig Voit & Mayer Ltd
Lorenzen John M.
United States Gypsum Company
Wood Elizabeth D.
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