Compositions: coating or plastic – Coating or plastic compositions – Inorganic settable ingredient containing
Reexamination Certificate
2002-10-01
2004-09-14
Marcantoni, Paul (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Inorganic settable ingredient containing
C106S817000, C106SDIG002, C524S426000
Reexamination Certificate
active
06790277
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to joint compound compositions suitable for use in wallboard applications.
BACKGROUND OF THE INVENTION
Interior walls of commercial and residential buildings are often constructed using gypsum wallboards, sometimes referred to as “drywall”. The wallboards are affixed to a support structure such as wooden frames. In order to attach the wallboards, screws or nails are often used. The gaps formed between adjacent wallboards are typically called “joints”.
In order to achieve a smooth, visually appealing surface, the joints between boards, cracks, screw holes, and/or nail holes must be concealed. Wallboard joint compound is commonly used to cover and finish gypsum wallboard joints, cornerbead, and screw or nail holes. Joint compound can be spread over mesh or tape used to connect wallboards. It may also be used to patch and texture interior walls.
Joint compounds are typically applied in thin layers using a trowel or other straight edged tool. Multiple layers may be applied in order to obtain a smooth, attractive finished wall. Each layer is allowed to dry prior to application of the next layer.
Joint compounds are commercially available as dry or wet mixes. Dry mixes require the addition of water and mixing to afford a smooth product.
An array of joint compounds have been sold commercially, described in printed publications, and have been the subject of patent applications. It is common 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. An example of such a joint compound is suggested in U.S. Pat. No. 5,653,797.
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
4
SiO
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.
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 suggests 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 indicates 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-type joint compounds. This is advantageous for the reasons stated above. Further, because setting joint compounds form a crystalline network upon setting (as opposed to merely drying), these compounds typically provide a strong, more durable bond between adjacent wallboard sheets than do drying-type joint compounds. However, because these compounds provide a strong crystalline network upon setting, the joint compound is often harder to sand to a smooth finish.
A calcium sulfate hemihydrate-based, setting-type joint compound can be combined with a calcium carbonate-based, drying-type joint compound to produce a joint compound having advantages of each individual type of compound. Such a hybrid joint compound can be used in applications typical of conventional drying-type and setting-type joint compounds.
One problem with this practice is that calcium carbonate acts as a calcium sulfate hemihydrate set accelerator. Thus, when a calcium sulfate hemihydrate-based, setting-type joint compound would, on its own, set in a time frame of about 210 minutes, its set time after having been mixed with a limestone-based drying-type joint compound (⅔ of hybrid joint compound by volume) is substantially reduced, to about 60 minutes. This drastic reduction in set time narrows in an unacceptable manner the working time window for finishers in the field to apply the compound.
One solution would seem to be the addition of a conventional set retarder to the drying-type joint compound. Others have disclosed retarding agents for use in certain other applications. However, although various types of retarders have been suggested, the purpose of the retarders, the final product, and the conditions under which the product is used (e.g., in wallboard manufacturing or cementing of pipes and casings of oil and gas wells) have differed substantially from the purpose, production conditions, and working conditions of joint compounds, particularly calcium carbonate-based, drying-type joint compounds.
For example, although wallboard manufacturers have used certain types of retarding agents, the purpose in that application is to prevent the immediate absorption of water and stiffening of the slurry during production, as well as to facilitate control of the slurry. In wallboard production, retarding agents are added to stabilize a stucco slurry for only a matter of seconds. It is understood that retarding agents are typically used in wallboard production at an extremely low rate, for example at about 0.0007 weight percent (e.g., in a 1400 pound batch, about 30 grams of retarder could typically be added).
When left in an aqueous, high ionic content, basic pH slurry system made up of such fillers as calcium carbonate and talc, conventional retarders completely lose their retarding potency towards calcium sulfate hemihydrate fairly rapidly, for example in as short as one day.
U.S. Pat. No. 6,436,185 discloses joint treatment formul
Marcantoni Paul
Miller Ice
National Gypsum Properties LLC
Nimmo Anthony
LandOfFree
Lightweight joint treatment formulation does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Lightweight joint treatment formulation, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Lightweight joint treatment formulation will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3264784