Compositions: coating or plastic – Coating or plastic compositions – Inorganic settable ingredient containing
Reexamination Certificate
2000-04-12
2002-01-22
Green, Anthony (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Inorganic settable ingredient containing
C106S677000, C106S680000, C106S698000, C106S778000, C156S039000, C156S045000, C156S346000, C428S449000, C428S537700, C524S423000, C524S444000
Reexamination Certificate
active
06340388
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to new “drywall” compositions and methods for making the same that are useful in the manufacture of wallboard for covering walls and ceilings in construction applications. More particularly, this invention is directed to a novel wallboard composition comprising a unique combination of synthetic binders selected for their ability to establish a strengthened permanent bond in the final dry state, in combination with gypsum and an expanded mineral such as Perlite. Utilizing such synthetic binders provides an increased strength to the wallboard core, enabling lighter-weight Perlite to replace at least a portion of the heavier gypsum traditionally used in wallboard compositions. Moreover, the synthetic binders disclosed herein uniquely cross-link with the expanded mineral to form a much stronger bond between the constituent components of the wallboard core material than that which has been available in previously utilized or known wallboard products. In a preferred embodiment, the lightweight, strengthened wallboard of the present invention also comprises a covering veneer that is applied to the top ply of the face paper to provide increased strength, moisture resistance, and fire retardency, and the back paper top ply is treated to provide increased flexural strength. Additionally, this invention relates to the unique manufacturing process to produce the wallboard composition of the present invention in order to create a lightweight, strengthened, moisture resistant, and fire retardant wallboard used to cover walls and ceilings in construction applications.
2. Description of the Background
Perlite (expanded) can be graded by density in pounds per cubic foot, and classified by product number or trade name for producer and user identification. The expanded product can weigh as little as 2 pounds per cubic foot, but the most widely used bulk-density grade range is from 7 to 15 pounds per cubic foot. The range of expanded Perlite utilized in the wallboard composite core of the present invention is 4 to 10 pounds per cubic foot, but preferably Perlite weighing 4 pounds per cubic foot is utilized in the formulation of the present invention. It has been found that the more friable cryogenic grades in the 3 to 4 pound range are favorable over the heavier grades ranging from 5 to 10 pounds per cubic foot. Grades typical to this range include concrete, plaster, and cavity fill or masonry. The particle size ranges from 100 to 2,000 microns, and preferably from 200 to 1000 microns. Preferably, the expanded Perlite will have a particle size ranging from no larger than 10 mesh sieve size and no smaller than 200 mesh sieve size measured on standard screen scale with 25% measuring 30 minus and the remaining 75% measuring 30 plus on a sieve analysis. The particle size of the preferred expanded Perlite is directly related to the strength of the wallboard core in the aspect of fusion. Particles that are too large tend to space gypsum crystal growth too far apart, and particles that are too small don't allow enough area for the gypsum crystal to fuse onto.
DESCRIPTION OF THE PRIOR ART
The use of calcium sulfate hemihydrate C
A
SO
4
.2H
2
O in the manufacture of gypsum wallboard and its related products has predominately been unchanged for over half a century. It has long been a conventional practice to finish the interiors and exteriors of buildings with gypsum core construction materials such as wallboard, lath, or sheathing. In general, these boards comprise essentially a core of set interlaced gypsum crystals disposed between fibrous, especially paper, liner sheets. After the gypsum slurry has set (i.e., reacted with the water from the aqueous slurry) and dried, the sheet is cut into standard wallboard sizes. Methods for the production of gypsum drywall are described, for example, in the Kirk-Othmer Encyclopedia of Chemical Technology, Second Edition, 1970, Vol. 21, pages 621-24, the disclosure of which is hereby incorporate herein by reference.
It has been known to incorporate certain additional agents in the core of gypsum wallboard. These have included, for example, foam aggregate wherein a foam has been shredded to a rough consistency and then incorporated into the gypsum slurry prior to forming and setting thereof. Also, expanded mineral fillers such as perlite and/or vermiculite have been incorporated into the gypsum slurry in small amounts from 0.5 to 10 percent, in addition to organic adhesives such as starch or dextrin, or other fibers. Other agents have also been added, including simple chemicals which react within the gypsum slurry to form gasses. For example, carbonates are added to yield CO
2
within the slurry; likewise, other air entraining agents, such as soap foams, may be employed to enable whipping air into the gypsum slurry during mixing.
Unfortunately, however, the amount of air or gas cells, or voids, which can be incorporated is limited, because the strength of the composite wallboard core is reduced when the amount of air cells is increased beyond a certain point. Likewise, the ability of the board to withstand a nail pull through the board is adversely effected by excessive air entraining. Additionally, historically expanded minerals were not added in gypsum wallboard beyond 2 to 3 percent because strength tests were significantly reduced, in both nail pull and flexural break tests, according to ASTM C
36
and ASTM C
473
. While it has been an intention of individual inventors and major manufacturers to produce a lightweight, strengthened, and essentially improved wallboard product over current formulations, the problem of providing a wallboard product with increased strength while reducing its weight at a relative low cost has not been practically realized, either in re-engineering the wallboard itself or the manufacturing process thereof. Many combinations and compositions have been tried and tested in the past, but many remain unutilized due to impractical applications and/or significant increases in production costs. Reduced weight and density boards should meet or exceed industry standards and have strengths equal to or greater than their heavier counterparts according to ASTM standards. Such lightweight wallboard compositions should be able to be manufactured using conventional high-speed manufacturing apparatus and not suffer from other negative side effects of a completely different manufacturing process.
The addition of synthetic binders has very recently been attempted as disclosed in U.S. Pat. No. 5,879,825 to Burke et al.; however, the engineering and chemical research in various combinations of complex chemical formulations and combinations thereof has been quite limited. Additionally, Burke et al. fails to address the environmental concerns of noxious fumes under fire engineering standard ASTM testing E
119
, and cost considerations limited the amount of acrylic polymer to 1 to 2 percent, such that a polymer having a minimal cross-linking performance resulted. Further, while the use of Perlite as an antidessicant to prevent the dehydration of gypsum crystals formed during setting of the core composition is disclosed, no consideration is given to introducing an expanded mineral, such as perlite, as a substitute for gypsum as one of the structural foundations of the wallboard core, nor the specific need for a synthetic binder composition for establishing a complete crosslinking between the constituent elements of the wallboard core in order to create a molecular change within the strengthening agent, which molecular change is in turn required to completely bond a reduced amount of gypsum with the other components of the wallboard core. Moreover, the chemical properties of the polyvinyl acetate emulsion of the instant invention, containing block copolymers of partially hydrolyzed polyvinyl alcohol, and the stabilized polyvinyl acetate particles in aqueous solution of the instant invention are very chemically different from the disclosed components of Burke et al. The polyvinyl ace
Advanced Construction Materials Corp.
Green Anthony
Stone, Esq. Gregory M.
Whiteford Taylor & Preston
LandOfFree
Strengthened, light weight wallboard and method and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Strengthened, light weight wallboard and method and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Strengthened, light weight wallboard and method and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2860338