Compositions: coating or plastic – Coating or plastic compositions – Inorganic settable ingredient containing
Reexamination Certificate
2001-04-19
2002-08-20
Marcantoni, Paul (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Inorganic settable ingredient containing
C106S794000, C106S817000, C106SDIG003
Reexamination Certificate
active
06436185
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention generally relates to the production of cementitious compositions and, more specifically, the invention relates to the production of compounds for use in filling and coating joints between adjacent gypsum wallboard sheets, for repairing other imperfections in building materials, and for texturizing.
2. Brief Description of Related Technology
A common manner of constructing interior walls includes the use of inorganic wallboard panels or sheets such as gypsum wallboard, often referred to simply as “wallboard” or “drywall.” Wallboard is typically produced by enclosing a core of an aqueous slurry of gypsum and other additives between two large sheets of paper. After the gypsum slurry has set and dried, the sheet is cut into standard sizes.
A wall is generally made by securing, e.g., with screws and/or nails, the wallboard to a support structure, for example vertically or horizontally-oriented pieces of wood. Because wallboard is typically supplied in standard-sized sheets or panels, when forming a wall from the sheets there will generally be a number of joints between adjacent sheets. In most wallboard construction, it is necessary to conceal these joints between adjacent panels so that the wall will have a smooth, monolithic finish similar to that obtained with conventional wet plaster methods. It is also typically necessary to conceal the screws and/or nails used to secure the wallboard panels to framing, the indentations caused by the screws and/or nails, imperfections in the wallboard panels, and other materials (e.g., corner beads) used to form the wall.
A number of joint compound compositions (sometimes referred to by applicators as “mud”) that can be used to conceal the joints between adjacent sheets of wallboard, other imperfections in the wallboard, and other construction points (e.g., corner beads) are known.
To conceal the joints between wallboard panels, a joint compound is typically applied in several layers or coats. A first coat of joint compound is placed in the joint between the wallboards with a wallboard knife, blade, or trowel. The first coat is primarily for the purpose of filling the space between the adjacent wallboards. Joint tape (for example, made of paper) can then be embedded into the first coat of joint compound. The joint compound may be applied in several, e.g., three, coats or layers in order to obtain a smooth finish. Each coat of joint compound must be allowed to dry or set prior to the placement of the next coat of joint compound. (If the prior coat is not allowed to dry or set, problems such as excess shrinkage and/or cracking can occur.) Once dry or set, the treated area is sanded before applying the next finishing coat of joint compound.
Joint compounds can be used for other purposes, for example, to repair imperfections in various building materials and for adding texture to walls and ceilings.
There are many different types of joint compounds. Joint compounds can be supplied in a dry powder form or in a mill-mixed, ready-mix form. They can also be of a “drying” type or a “setting” type.
The joint compound can be supplied in the form of a dry powder, to which an amount of water is added at the work site by the applicators to give the joint compound a suitable consistency. Other joint compounds, often referred to as “ready-mix” or “ready-mixed” joint compounds, are pre-mixed with water and other additives during manufacturing the product. These joint compounds are generally packaged and sold in a corrugated box or plastic pail in a form that is suitable for use with little or no addition of water at the job site.
Among the prior art joint compound compositions, it is generally known to use a filler (e.g., calcium carbonate, calcium sulfate hemihydrate, or calcium sulfate dihydrate), thickener, preservative, and a binder, as well as various other additives to produce a joint compound, as disclosed in U.S. Pat. No. 5,653,797 (Aug. 5, 1997), the disclosure of which is hereby incorporated herein by reference.
Many joint compounds are of the “drying” or “setting report” type. Drying-type joint compounds contain calcium carbonate (CaCO
3
; i.e., limestone) and/or calcium sulfate dihydrate (CaSO
4
.2H
2
O) and/or talc (Mg
3
Si
4
O
10
(OH)
2
or 3MgO.4SiO
2
.H
2
O). Prior to use (generally during manufacturing), these components and a binder (along with several other ingredients) are mixed for a specific time with water. The drying-type joint compound thus produced has a high ionic content and basic pH. After application, when the compound dries (i.e., water evaporates), a dry, relatively hard cementitious material remains. The calcium sulfate dihydrate and calcium carbonate may comprise a substantial portion of what is sometimes referred to as the filler component.
Many conventional drying-type joint compounds undergo shrinkage upon drying, which makes it difficult to achieve a smooth wall surface. Shrinkage can be particularly troublesome when a second coat of compound is applied over a previous coat that is not completely dried.
General ranges of ingredients used in an all purpose, conventional-weight, drying-type joint compound include the ingredients shown in Table 1, below.
TABLE 1
CONVENTIONAL WEIGHT JOINT COMPOUND
Weight
Ingredient
Percentage
Water
20-37
Preservatives
0.02-1.0
Calcium Carbonate
10-100
Mica (Filler)
0.5-5.0
Attapulgite Clay (non-leveling agent)
0.5-5.0
Cellulose Thickener
0.12-1.0
Latex (Binder)
1.0-4.0
To avoid various disadvantages of the drying-type of joint compound, compounds of the “setting type” have been developed. A setting-type joint compound generally includes calcium sulfate hemihydrate (CaSO
4
.½H
2
O, also referred to as calcined gypsum). (See U.S. Pat. No. 5,653,797.) To produce calcined gypsum, calcium sulfate dihydrate is converted from raw gypsum to the hemihydrate state via a suitable calcination process. A gypsum calcination process removes one and one-half molecules of water from each calcium sulfate dihydrate gypsum molecule. The hemihydrate form of calcium sulfate is substantially more soluble in water than the dihydrate form of calcium sulfate. The calcium sulfate hemihydrate may comprise a substantial portion of what is sometimes referred to as the filler component in a setting-type joint compound.
During use in a setting-type joint compound, the calcium sulfate hemihydrate is rehydrated to the dihydrate state via the addition of water. This rehydration process normally takes place over a fairly short period of time. Accordingly, it has been extremely difficult to produce a setting-type joint compound comprising hemihydrate gypsum pre-mixed with water, because the product would set in its storage container. Thus, joint compounds of the setting-type have generally had to be supplied in the powder form.
Ready-mixed, setting-type joint compounds are also known. For example, Jakacki et al. U.S. Pat. No. 4,661,161 (Apr. 28, 1987) discloses a setting-type joint compound comprising an aqueous slurry of calcium sulfate hemihydrate and a set retarding agent formed of two ingredients: an organic, proteinaceous retarder and a chelating agent, e.g., selected from diethylene triamine pentaacetic acid, ethylene diamine tetraacetic acid, and salts thereof. This patent discloses that the compound has an adequately long shelf life for commercialization, and that when mixed with an accelerator that the joint compound hydrates after a period of time to form a set material having acceptable joint compound properties. However, it is believed that joint compounds of the setting, ready-mix type have not been successfully commercially employed due to the need to find a suitable retarding agent and a suitable accelerator to overcome the retarding agent.
Setting-type joint compounds have the advantage of having generally quicker finishing times (setting time) than drying-typejoint compounds. This is advantageous for the reasons stated above. Further, because setting joint compounds form a crystalline network upon setting (as opposed to
Ayambem Amba
Sethuraman Gopalakrishnan
Smith Richard E.
Howrey Simon Arnold & White , LLP
Marcantoni Paul
National Gypsum Properties LLC
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