Stock material or miscellaneous articles – Structurally defined web or sheet – Weight per unit area specified
Reexamination Certificate
1998-12-23
2002-06-18
Lam, Cathy (Department: 1775)
Stock material or miscellaneous articles
Structurally defined web or sheet
Weight per unit area specified
C428S311110, C156S071000
Reexamination Certificate
active
06406779
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to a paperless gypsum/fiber board with improved surface characteristics, to a process for making such a gypsum/fiber board, and to a primer for use on such gypsum/fiber board to provide improved surface characteristics. More particularly, the present invention relates to a primer to improve the surface characteristics of fiber-reinforced gypsum panels.
Conventional gypsum wallboard or panel is typically manufactured from a plaster slurry wherein a wet slurry of calcium sulfate hemihydrate, generally referred to as calcined gypsum, is placed between two layers of paper and the slurry is allowed a certain amount of time to set. The set gypsum is a hard and rigid product obtained when the calcined gypsum reacts with water to form calcium sulfate dihydrate. Calcined gypsum is either calcium sulfate hemihydrate (CaSO
4
.{fraction (1/2+L )} H
2
O) or calcium sulfate anhydrite (CaSO
4
). When calcium sulfate dihydrate is heated sufficiently, in a process called calcining, the water of hydration is driven off and there can be formed either calcium sulfate hemihydrate, calcium sulfate anhydrite, or both, depending on the temperature and duration of exposure. When water is added to the calcined gypsum to cause the gypsum to set, in essence, the calcined gypsum reacts with water, and the calcined gypsum is rehydrated.
In typical gypsum wallboard, the two layers of paper contain the slurry and provide the strength required in installation and use. The wallboard is cut into discrete lengths to accommodate subsequent handling and then dried in heated dryers until the board is completely dry. The bending strength of the wallboard depends largely on the tensile strength of the paper. The gypsum serves as the core and accounts for fire resistance and moisture absorbing and moisture releasing activities. The paper determines the nature of the joint filler system and the surface treatment that may be used on the board.
Although paper-covered wallboard has many uses and has been a popular building material for many years, the prior art has recognized that for certain applications it would be advantageous to provide gypsum panel that did not rely on paper surface sheets for strength and other properties. Several prior art fiber-reinforced gypsum panels are as follows:
U.S. Pat. No. 5,320,677 to Baig, which is incorporated by reference herein in its entirety, describes a composite product and a process for producing the product in which a dilute slurry of gypsum particles and cellulosic fibers are heated under pressure to convert the gypsum to calcium sulfate alpha hemihydrate. The cellulosic fibers have pores or voids on the surface and the alpha hemihydrate crystals form within, on and around the voids and pores of the cellulosic fibers. The heated slurry is then dewatered to form a mat, preferably using equipment similar to paper making equipment, and before the slurry cools enough to rehydrate the hemihydrate to gypsum, the mat is pressed into a board of the desired configuration. The pressed mat is cooled and the hemihydrate rehydrates to gypsum to form a dimensionally stable, strong and useful building board. The board is thereafter trimmed and dried. The process described in Patent No. 5,320,677 is distinguishable from the earlier processes in that the calcination of the gypsum takes place in the presence of the cellulosic fibers, while the gypsum is in the form of a dilute slurry, so that the slurry wets out the cellulosic fibers, carrying dissolved gypsum into the voids of the fibers, and the calcining forms acicular calcium sulfate alpha-hemihydrate crystals in situ in and about the voids.
U.S. Pat. No. 5,135,805 to Sellers et al, describes a water resistant gypsum product that may be a “faceless” product, i.e. it may not include a facing sheet of paper, fiberglass mat or similar material. The gypsum products described by U.S. Pat. No. 5,135,805 typically contain reinforcing fibers, for example, cellulosic fibers, such as wood or paper fibers, glass fibers or other mineral fibers and polypropylene or other synthetic resinous fibers. The reinforcing fibers can be about to about 20 wt. % of the dry composition from which the set gypsum product is made. The density of such a product is typically within the range of about 50 to about 80 pounds per cubic foot.
U.S. Pat. No. 5,342,566 to Schafer et al, which is incorporated by reference herein in its entirety, refers to a method of producing fiber gypsum board comprising the steps of mixing in a preliminary mixing step predetermined amounts of fibers and water respectively, to form a mixture of wetted, loose fibers; mixing in a mixing step the wetted fibers with a predetermined amount of dry calcined gypsum; premixing an accelerator with one of the components of dry calcined gypsum, fiber and water; promptly laying the mixed composition into a mat; immediately degassing the mat in a first compression step, adding a predetermined amount of water onto the resultant mat; and immediately compressing the mat to form a board composed of bonded fibers and gypsum. This process produces a homogeneous board which is preferably a gypsum board reinforced by fiber, such as paper fiber, wherein several layers of board forming materials are placed on each other before the board is fully formed, pressed, and dried and wherein each of the layers is identical in composition.
U.S. Pat. No. 5,637,362 to Chase et al, which is incorporated by reference herein in its entirety, describes a thin, sealant-coated, fiber-reinforced gypsum panel. This patent describes a wax-free, water-resistant “sealant” which is applied to the board after the board has been dried. The sealant, which preferably is a siliconate mixture, reduces the absorption of water, glue or adhesives into the panel.
Carbo et al Provisional Application Serial No. 60/073,503, which is incorporated by reference herein in its entirety, describes a paperless gypsum/fiber board with improved surface characteristics, a process for making such a gypsum/fiber board, and a primer for use on such gypsum/fiber board to provide improved surface characteristics.
The term “paperless” gypsum/fiber board, as used herein, is intended to distinguish the fiber-reinforced gypsum panels to which the present invention applies from conventional prior art gypsum panels, which are referred to as “wall board” or “dry wall” which have at least one surface comprised of paper, including “wall board” or “dry wall” having some additional form of fiber-reinforcement in the core.
The prior art paperless fiber-reinforced gypsum panels have surface characteristics which differ from the conventional paper-covered wallboard and the difference in the surface characteristics creates an array of problems for the tradesmen who use or install such panels. For example, some of the prior art fiber reinforced gypsum panels tend to absorb water quickly. As a consequence, joint compound applied to such panels does not have sufficient “working time”, i.e. the joint compound dries out before it can be finished properly. Similar problems are encountered in the application of adhesives and paints to the fiber reinforced gypsum panels. Another problem occurs when paints and coatings applied to the fiber reinforced gypsum panels for decorative purposes do not consistently flow over and wet the surface of the panels. This causes major problems in decorating the panels.
However, some coatings or sealants, such as the siliconate sealant described in U.S. Pat. No. 5,632,362 to Chase et al, produce a seal that is too complete, that is they seal the surface so effectively that the “suction” of the surface of the board is reduced which results in deteriorated joint compound performance, and increased drying time for paint.
It is the objective of the present invention to provide a primer system that overcomes these problems in paperless fiber-reinforced gypsum panels.
It is a further objective of the present invention to provide a primer system for paperless fiber-reinforced gypsum panels having
Attard Peter M.
Carbo Adelaida L.
Egan Donald E.
Janci David F.
Lam Cathy
Lorenzen John M.
United State Gypsum Company
LandOfFree
Gypsum/fiber board with improved surface characteristics does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Gypsum/fiber board with improved surface characteristics, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Gypsum/fiber board with improved surface characteristics will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2964642