Joint compound additive for reduction of cracking, cratering...

Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...

Reexamination Certificate

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C524S156000, C524S157000, C524S158000, C524S161000, C524S166000

Reexamination Certificate




This invention relates to a composition for a joint compound for use in filling and coating the joints between adjacent panels of gypsum wallboard. More specifically, it relates to a joint compound composition including a surfactant additive that reduces shrinkage, increases crack resistance and increases crater resistance in a joint compound, without destroying the ability of the joint compound to bond with substrates or decorative applications such as paint.
In the construction of buildings, one of the most common elements is gypsum wallboard, often known as drywall, used in the construction of walls and/or ceilings. Walls made from gypsum wallboard are conventionally constructed by affixing the panels to studs or joists, and then filling and coating the joints between panels with a specially prepared composition called a joint compound. This process generally proceeds by placing a taping grade joint compound within the joint formed by the abutted edges of the wallboards and embedding a liquid-permeable tape within the taping compound. When dry (or set), a second coating comprising a topping grade joint compound is applied over the joint. This is sanded lightly, then a third coat applied and conventionally finished. Another grade of joint compound is an all-purpose grade that is used both for embedding the tape and for applying the finish coats. A patterned effect may be given to the finished wall and joint with the all-purpose joint compound to provide a textured finish.
There are two general types of joint compound, setting type and drying type. Joint compound of the setting type sets up and becomes firm when hydration reactions convert calcium sulfate hemihydrate and water into an interlocking matrix of calcium sulfate dihydrate crystals. Excess water evaporates. Drying type compound becomes firm upon the loss of water by evaporation.
Common problems with joint compounds include cracking, shrinkage and cratering. Cracking and shrinkage occur during the drying process, while craters or surface defects occur during application. Cracking is most likely under harsh environmental conditions or when large amounts of joint compound are applied at once, rather than being applied in several thin layers. Shrinkage and cracking are generally less of a problem with setting type base joint compounds, because some of the water is being absorbed by hydration reactions instead of being driven off by evaporation and because in setting type compounds, the matrix of gypsum crystals formed before drying provides strength to resist shrinkage during drying. Craters are pock marks noticeable on the otherwise smooth surface of the joint compound. It is believed that the factors involved with cratering include rheology, air management and surface tension of the compound.
It is generally known that drywall contractors, in applying joint compounds, sometimes add liquid soap to joint compound immediately before application to improve the finished surface of the joint compound. A soap, or detergent, is a complex mixture of ingredients including, but not limited to acids, bases, antimicrobal agents, antiredeposition agents, colorants, fragrances, defoamers, foamers, hydrotropes, moisturizers, preservatives, solvents, thickeners and surfactants, selected from many possible functional groups. However, soap or detergent addition has also been known to cause a number of problems. Some multicomponent soaps lose effectiveness if they are added at the time of manufacture of the joint compound, making it necessary to measure, add and mix in the soap or detergent immediately before use. It is inconvenient to carry the joint compound, the soap or detergent, a measuring device and a mixer, all to a job site, particularly if it is in a remote location. Use of soaps or detergents also contributes to paint flashing whereby poor paint coverage is obtained.
Two references to O'Connell et al, U.S. Pat. Nos. 4,463,039 and 4,504,602, teach the use of sodium sulfonates as additives to a sprayable acoustical composition to promote foaming. The composition contains mineral wool fillers containing polyolefin fibers. This reference is directed to a sprayable, textured coating and is not useful as a joint compound.
U.S. Pat. No. 4,252,568, to Bounini, discloses the addition of an aqueous solution of ligno sulfonates to make healed stucco for use in gypsum slurries to produce gypsum board. Addition of the ligno sulfate increases the flowability of the stucco and reduces the power required to grind it. There is no claim, teaching or example that such a compound is useful in a joint compound.
It is, therefore, an object of this invention to provide an improved joint compound composition that reduces shrinkage and cracking in drying type joint compounds.
It is another object of this invention to provide an improved joint compound whose additives are all included at the time of manufacture.
It is yet another object of this invention to provide an improved joint compound composition with fewer surface craters.
The above-listed objects are met or exceeded by the present invention that features a joint compound composition that exhibits reduced shrinkage and increases resistance to cracking and cratering.
More specifically, the invention relates to a composition that includes a joint compound, which includes a binder and a filler, and a surfactant additive. The surfactant additive consists essentially of a hydrocarbon substituted sulfate, sulfonate, sulfuric acid or sulfonic acid. The hydrocarbon substituent group is an aliphatic, olefinic, alicyclic or aromatic group, or combinations thereof. Further, the substituent group has from 12 to 24 carbon atoms. Preferably, the substituent group includes an aromatic ring. When used in a drying type joint compound, this composition produces a better quality surface compared to traditional joint compounds. The composition of this invention exhibits less cracking and cratering than prior art compositions without several of the drawbacks that are associated with multicomponent soap or detergent addition.
The joint compound of the present invention also shrinks less than conventional joint compounds. When there is less shrinkage, there are several benefits. Fewer layers of joint compound need be applied to obtain a smooth, monolithic surface. Less joint compound will be required to complete the job. Time will be saved by less waiting for the layers to be applied and less waiting for the compound to dry between coats.
Addition of the hydrocarbon substituted sulfonates sulfates, sulfuric acids or sulfonic acids of the present invention is completed during the manufacture of the joint compound. This eliminates the need to separately carry the additive and a measuring device to a remote job site. Use of the instant additive also minimizes paint flashing.
Another benefit of this composition is a decrease in density when used in a lightweight joint compound. All other properties being equal, lightweight joint compounds are preferred over heavier products. Contractors who apply these compounds in large quantity become fatigued less quickly when handling light products. Low density products are also less expensive to ship than their traditional counterparts. The composition of the present invention also produces a reduction in density in lightweight joint compounds, making it easier to apply and less costly to ship.
The composition of the present invention is a blend of a joint compound with a surfactant additive. The surfactant additive includes a hydrocarbon substituted sulfate, sulfonate, sulfuric acid or sulfonic acid. When the sulfate or sulfonate salt is used, potassium or sodium is the preferred cationic component. In the preferred embodiment, the surfactant is blended with a ready-mix, drying-type joint compound. The surfactant additive preferably is added to a joint compound when it is manufactured.
The first component of the present invention is the surfactant additive, which is a hydrocarbon


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