Compositions: coating or plastic – Coating or plastic compositions – Inorganic settable ingredient containing
Reexamination Certificate
2002-09-11
2004-08-31
Brunsman, David (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Inorganic settable ingredient containing
C106S779000, C428S219000, C428S312400, C428S535000
Reexamination Certificate
active
06783587
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the field of wall board, or “drywall” compositions containing natural polymers, and methods for their preparation. More particularly, this invention is directed towards methods of preparation of a wallboard composition that is lightweight and retains its strength, while at the same time maintaining a cost comparable to conventional wallboard. Starch is an inexpensive, widely available natural polymer suitable for use in the present invention. Additionally, this invention relates to the manufacturing processes used to produce the wallboard composition of the present invention.
BACKGROUND OF THE INVENTION
Conventional gypsum wallboard, or “drywall”, has been used for over fifty years in the construction industry, specifically in the construction of residential and commercial building interior walls and ceilings. The use of calcium sulfate hemihydrate (CaSO
4
.½H
2
O) as the main ingredient in standard wallboard formulations has remained predominantly unchanged. Typically, such wallboard has consisted of essentially a gypsum core covered with paper bonded to this core. The manufacture of gypsum wallboard is an expensive, tightly controlled manufacturing process, oftentimes entailing elaborate steps with significant environmental concerns and repercussions.
Conventional gypsum wallboard has many advantages, such as its low cost and easy workability in many construction applications. However, a major drawback of conventional wallboard is its weight. Typical gypsum wallboard is approximately ½ inch thick and has a weight of between about 1650 to 1800 pounds per 1,000 square feet of material, or pounds MSF (“MSF”, material square feet, is a standard abbreviation in the art for a thousand square feet. It is an area measurement for boxes, corrugated media and wallboard). This heavy weight, coupled with size of typical sheets (4′×8′ to 16′) and no handholds makes the conventional wallboard both cumbersome and awkward to carry and manipulate. This is especially evident when gypsum wallboard is used in ceiling applications, since the individual sheets must be supported over the installer's head by hand or by some appropriate mechanical means until nails (or other appropriate fasteners) can be employed to secure the wallboard. Not surprisingly, it has been shown that handling massive and bulky wallboard sheets exposes workers to potential hazards and injuries which increases their risk of occupational injury (Pan, C. S., et al.,
Int. J. Industrial Ergonomics
25: 621-631, 2000; Pan, C. S.; Chiou, S. S.,
Int. J Industrial Ergonomics
23: 505-511, 1999; Pan, C. S., et al.
Int. J Industrial Ergonomics
25: 29-37, 1999).
Issued patents and the technical literature are replete with attempts to formulate lightweight wallboard compositions to provide a lightness in density and weight without sacrificing an undue or unacceptable amount of strength. An industry measure for acceptable strength of wallboard is the pounds of nail pull, or the amount of force required for the board to be pulled over the head of a nail. However, these earlier efforts have often resulted in the addition of substantial manufacturing and/or material costs to the finished products, or lacked the necessary strength for use in wall and ceiling applications. For example, attempts have been made to use a small percentage of synthetic binder in the wallboard formulation to increase strength and lighten the wallboard. However, the amounts of binder required in order to increase or maintain strength has not been cost effective. Other attempts which have included the use of foam as a filler suffered from problems with proper hydration and premature setting of the gypsum when performed on a process scale.
Other reported attempts at preparing lightweight wallboard have proposed the use of adhesive compositions which bind cellulose and other porous materials. U.S. Pat. No. 3,720,633 suggests a polyvinyl alcohol-based adhesive composition for use in paper board compositions. However, no mention or suggestion is made of the need for a specific composition which can bind with gypsum to create a wallboard with a reduced weight over compositions previously described while maintaining the necessary strength characteristics.
U.S. Pat. No. 4,265,964 states that the entrainment of air pockets or bubbles will not produce a lightweight wallboard with the desired strength characteristics. In order to achieve a lightweight wallboard, a cementitious material such as gypsum is mixed with lightweight thermoplastic particles, a soap surfactant, starch to aid in binding, and water in order to produce a mixture which is lightweight and exhibits appropriate strength. However, the use of such particles or beads is expensive and results in a process which is cost-prohibitive in the competitive wallboard marketplace.
A different approach to the preparation of a lightweight wallboard has been proposed in U.S. Pat. No. 4,502,901, wherein by-product gypsum from a flue-gas desulfurization process (FGD gypsum) is used to form a wallboard. Through the use of FGD gypsum, the particle size of the gypsum has been reported to be more easily controlled, allowing for more cost-effective manufacturing processes and a potentially lightweight wallboard with the same strength characteristics as standard wallboard.
U.S. Pat. No. 5,879,825 suggests a method of preparation of high-strength wallboard, as well as core compositions which are suitable for use within such wallboard. The core composition includes a slurry of calcium sulfate hemihydrate, water, and an acrylic polymer which acts as the strengthening agent. The use of a foam within the core slurry controls the density, allowing for the production of a wallboard which has a reduced weight while still providing beneficial strength characteristics.
Alternative solutions for producing lightweight wallboard have been proposed using a perlite filler, such as in U.S. Pat. No. 5,922,447. As suggested therein, a lightweight gypsum board can be prepared by mixing a slurry of gypsum, perlite and a minor amount of starch which acts as a binder for the perlite spheres. However, the nail pull values reported for the wallboard of this invention are in the range of 55-80 pounds, which just meets or falls below the ASTM requirement for gypsum wallboard, which specifies an 77 pound nail pull for a ½-inch board. Such a lightweight board as suggested by this method does not offer the increased strength necessary for commercial use.
U.S. Pat. No. 6,171,38 suggests that a lightweight wallboard can be prepared using a mixture of gypsum, one or more naturally occurring or synthetic latex polymers, and one or more nonionic surfactants in excess. The preferred latex polymer is preferably derived from styrene and acrylic acid monomers, and the nonionic surfactant consists of an alcohol ethoxylate. The use of excess surfactant is suggested to aid in the distribution of the latex, and to help improve the strength characteristics of the resultant wallboard. The amount of nonionic surfactant added is suggested to be crucial to the success of the invention. However, in using such specialized polymers and reagents in the formulation, the cost-effectiveness of this method has yet to be realized.
U.S. Pat. No. 6,403,688 suggests a novel lightweight, strengthened, wallboard comprised of synthetic binders and perlite, as well as methods and apparatus for making such wallboard. The binders bond to the perlite in a manner that creates a strengthened bond and reduces the amount of gypsum need to formulate the composition. Also suggested is a veneer covering which adds to the wallboard's strength while simultaneously increasing the moisture resistance and fire retardency.
Despite these advances and potential solutions, there still exists a need for a high strength, lightweight wallboard product which has the structural integrity to withstand the structural and industrial requirements of traditional, heavyweight wallboard products. Such
Metz Lambert J.
Sethuraman Gopalakrishnan
Stav Elisha
Brunsman David
Ice Miller
National Gypsum Properties LLC
Nimmo Anthony
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