Compositions: coating or plastic – Coating or plastic compositions – Inorganic settable ingredient containing
Reexamination Certificate
2000-04-25
2002-06-25
Marcantoni, Paul (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Inorganic settable ingredient containing
C106S776000
Reexamination Certificate
active
06409824
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates generally to gypsum compositions. More particularly, the invention relates to set gypsum compositions that exhibit enhanced resistance to permanent deformation.
BACKGROUND OF THE INVENTION
Set gypsum (calcium sulfate dihydrate) is a well-known material that is included commonly in many types of products. By way of example, set gypsum is a major component of end products created by the use of traditional plasters (e.g., plaster-surfaced internal building walls) and also in paper-faced gypsum boards employed in typical drywall construction of interior walls and ceilings of buildings. In addition, set gypsum is the major component of gypsum/cellulose fiber composite boards and products, and also is included in products that fill and smooth the joints between edges of gypsum boards. Also, many specialty materials, such as materials useful for modeling and mold-making that are precisely machined, produce products that contain major amounts of set gypsum.
Typically, such gypsum-containing products are prepared by forming a mixture of calcined gypsum (calcium sulfate hemihydrate and/or calcium sulfate anhydrite) and water (and other components, as appropriate). The mixture is cast into a desired shape or onto a surface, and then allowed to harden to form set (i.e., rehydrated) gypsum by reaction of the calcined gypsum with the water to form a matrix of crystalline hydrated gypsum (calcium sulfate dihydrate). It is the desired hydration of the calcined gypsum that enables the formation of an interlocking matrix of set gypsum crystals, thus imparting strength to the gypsum structure in the gypsum-containing product. Mild heating is utilized to drive off the remaining free (i.e., unreacted) water to yield a dry product.
One problem with such gypsum-containing products is that they often are subject to permanent deformation (e.g., sag), especially under conditions of high humidity, temperature, or load. For example, the possibility of sag is particularly problematic where gypsum-containing boards and tiles are stored or employed in a manner in which they are positioned horizontally. In this respect, if the set gypsum matrix in these products is not sufficiently resistant to permanent deformation, the products may start to sag in areas between the points to which they are fastened, or supported by, an underlying structure. This can be unsightly and can cause difficulties during use of the products. Furthermore, in many applications, gypsum-containing products must be able to carry loads, e.g., insulation or condensation loads, without perceptible sag.
Another problem with such set gypsum-containing products is that dimensional stability can be compromised during their manufacture, processing, and commercial application. For example, in the preparation of set gypsum products, there is usually a significant amount of free (i.e., unreacted) water left in the matrix after the gypsum has set. Upon drying of the set gypsum in order to drive off the excess water, the interlocking set gypsum crystals in the matrix tend to move closer together as the water evaporates. In this respect, as the water leaves the crystal interstices of the gypsum matrix, the matrix tends to shrink from natural forces of the set gypsum that were resisting capillary pressure applied by the water on the gypsum crystals. As the amount of water in the aqueous calcined gypsum mixture increases, lack of dimensional stability becomes more of a problem.
Dimensional stability is also of concern even after the final dried product is realized, especially under conditions of changing temperature and humidity where set gypsum is susceptible to, for example, expansion and shrinkage. For example, moisture taken up in crystal interstices of a gypsum matrix of a gypsum board or tile exposed to high humidity and temperature can aggravate a sagging problem by causing the humidified board to expand.
If such dimensional instability could be avoided or minimized, various benefits would result. For example, existing gypsum board production methods would yield more product if the boards did not shrink during drying, and gypsum-containing products desired to be relied upon to hold a precise shape and dimensional proportions (e.g., for use in modeling and mold making) would serve their purposes better.
Accordingly, it will be appreciated from the foregoing that there is a need in the art for a set gypsum composition exhibiting enhanced resistance to permanent deformation (e.g., sag) and enhanced dimensional stability. The invention provides such a set gypsum composition satisfying at least one of these needs. These and other advantages of the present invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.
BRIEF SUMMARY OF THE INVENTION
The present invention provides a set gypsum composition that demonstrates enhanced resistance to permanent deformation (e.g., sag) and/or enhanced dimensional stability.
In one aspect, the present invention provides a set gypsum-containing composition comprising an interlocking matrix of set gypsum formed from, i.e., using, at least calcined gypsum, water, and an enhancing material comprising (i) an organic polyphosphonic compound, or a mixture of such compounds; (ii) a borate selected from ulexite, colemanite, or a mixture of ulexite and colemanite; or a mixture of one or more organic polyphosphonic compounds and one or more borates. In some embodiments, the present invention provides for the introduction of borate enhancing material into the set gypsum-containing composition by means other than its direct addition to the aforesaid aqueous composition. For example, the borate may be carried on an accelerator material. In this respect, the borate may be introduced into the aqueous composition in the form of a milled mixture of borate and an accelerator material, particularly, calcium sulfate dihydrate (e.g., gypsum seeds).
In another aspect, the present invention provides a set gypsum-containing composition comprising an interlocking matrix of set gypsum formed from, i.e., using, at least calcined gypsum, water, and an enhancing material comprising (i) a polycarboxylic compound or a mixture of polycarboxylic compounds; and (ii) a polyphosphate compound or a mixture of polyphosphate compounds. In a further aspect of the invention, the polycarboxylic compounds or polyphosphate compounds, alone or in combination, can be used with the organic polyphosphonic compounds or the borates described above, or both.
In yet another aspect, the present invention provides a set gypsum-containing composition comprising set gypsum (e.g., an interlocking set gypsum matrix). The set gypsum is treated in a post-set treatment process with an enhancing material which can be selected from (i) an organic phosphonic compound or a mixture of such compounds; (ii) a borate selected from ulexite, colemanite, or a mixture of ulexite and colemanite; (iii) a carboxylic compound or a mixture of such compounds; or a mixture of (i), (ii) and/or (iii). The set gypsum product need not be dry when post-set treated, although it can be. In the post-set treatment aspect of the present invention, an inorganic phosphate compound also can be used in combination with one or more of the other aforementioned enhancing materials.
In still another aspect, the present invention provides an accelerator for an aqueous calcined gypsum composition comprising a borate and an accelerator material.
The invention may best be understood with reference to the following detailed description of the preferred embodiments.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a set gypsum-containing composition that exhibits enhanced resistance to permanent deformation (e.g., sag) and/or enhanced dimensional stability. By way of example, the set gypsum-containing composition can be in the form of gypsum board.
The set gypsum-containing composition comprises an interlocking set gypsum matrix and is prepared from a mixture (e.g., slur
Shake Michael P.
Veeramasuneni Srinivas
Yu Qiang
Janci David F.
Leydig , Voit & Mayer, Ltd.
Lorenzen John M.
Marcantoni Paul
United States Gypsum Company
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