Compositions: coating or plastic – Coating or plastic compositions – Inorganic settable ingredient containing
Reexamination Certificate
2001-06-01
2004-01-13
Green, Anthony J. (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Inorganic settable ingredient containing
C106S773000, C106S661000, C106S665000, C106S504000, C106S822000, C524S004000, C524S005000
Reexamination Certificate
active
06676746
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to wall repair compounds which can be sanded to a smooth finish, such as drywall joint compounds, used to repair imperfections in walls or fill joints between adjacent wallboard panels. More particularly, the present invention relates to such a wall repair compound that includes an additive which reduces the quantity of airborne dust generated when the fully dried and hardened compound is sanded, but nevertheless has properties comparable to those of conventional joint compounds.
BACKGROUND OF THE INVENTION
Interior walls of residential and commercial buildings are often constructed using gypsum wallboard panels, often referred to simply as “wallboard” or “drywall.” The wallboard panels are attached to studs using nails or other fasteners, and the joints between adjacent wallboard panels are filled using a specially formulated adhesive composition called joint compound to conceal the joints. The procedure for concealing the joint between adjacent wallboards, and thereby producing a smooth seamless wall surface, typically includes applying soft wet joint compound within the joint or seam formed by the abutting edges of adjacent wallboard panels using a trowel or the like. A fiberglass, cloth, or paper reinforcing tape material is then embedded within the wet joint compound, and the compound is allowed to dry and harden. After the joint compound has hardened, a second layer of joint compound is applied over the joint and tape to completely fill the joint and provide a smooth surface. This layer is also allowed to harden. Upon hardening, the joint compound is sanded smooth to eliminate surface irregularities. Paint or a wall covering, such as wall paper, can then be applied over the joint compound so that the joint and the drywall compound are imperceptible under the paint or wall covering. The same joint compound can also be used to conceal defects caused by the nails or screws used to affix the wallboard panels to the studs, or to repair other imperfections in the wallboard panels, so as to impart a continuously smooth appearance to the wall surface.
Various drywall joint compounds are known for concealing joints between adjacent wallboard panels. Conventional joint compounds typically include a filler material and a binder. Conventional fillers are calcium carbonate and calcium sulfate dihydrate (gypsum), which are used in “ready mixed” joint compounds, and calcium sulfate hemihydrate (CaSO
4
-½ H
2
O; also referred to as plaster of Paris or calcined gypsum), which is used in “setting type” joint compounds. Ready mixed joint compounds, which are also referred to as pre-mixed or drying type joint compounds, are pre-mixed with water during manufacturing and require little or no addition of water at the job site. Such joint compounds harden when the water evaporates and the compound dries. Setting type joint compounds, on the other hand, harden upon being mixed with water, thereby causing dihydrate crystals to form and interlock. Setting type joint compounds are therefore typically supplied to the job site in the form of a dry powder to which the user then adds a sufficient amount of water to give the compound a suitable consistency.
In an effort to reduce the dust generation and cleanup problems associated with the sanding of conventional joint compounds, various attempts have been made to develop specialized dustless drywall sanders. The Matechuk U.S. Pat. No. 4,782,632, for example, discloses a drywall sander including a sanding head designed to minimize the release of dust and further discloses attaching a vacuum cleaner to the sanding head to collect the dust. The Krumholz U.S. Pat. No. 4,955,748 discloses a dustless drywall finisher which uses a wet sponge to prevent the formation of airborne dust.
Dust remains a problem, however, when conventional power sanders or hand sanders are used to sand conventional joint compounds. A need therefore exists for a joint compound that can be sanded using conventional sanders without producing a large quantity of fine particles capable of becoming suspended in air but whose properties are nevertheless comparable to those of conventional drywall compounds.
It would therefore be desirable to provide a wall repair compound composition that can be sanded without producing a large quantity of airborne dust. It would be desirable to provide an additive that could be mixed with commercially available joint compounds to inhibit the formation of airborne particles during the sanding procedure without otherwise interfering with the properties of the joint compound. More particularly, it would be desirable to provide a low dust wall repair compound composition including a dust reducing additive that does not bleed into porous materials to which it is applied, and further provide such a wall repair compound that adheres well to a variety of surfaces including conventional wallboard, metal, and plastics such as polyvinyl chloride (PVC).
SUMMARY OF THE INVENTION
The present invention provides a wall repair compound, such as a drywall joint compound which, when allowed to fully dry or harden and is then sanded, generates less airborne dust than conventional joint compounds. More specifically, the present invention provides admixing a dust reducing additive to a sandable compound to reduce the quantity of dust generated when the compound is sanded.
The dust reducing additive is typically pre-mixed with the wet joint compound prior to application to the wall surface. Generally, the dust reducing additive reduces the quantity of airborne dust particles having a size of less than or equal to 10 microns to less than 50% of the quantity that would be generated without the additive when the quantity of dust generated is measured using either of the test procedures described below. In certain embodiments, the quantity of airborne dust particles is reduced by at least 75% compared to a mixture without the additive. Most preferably, the level of airborne dust is reduced by more than 90%.
In one embodiment, the average quantity of airborne particles generated by sanding the hardened wall repair compound of the present invention is less than 50 mg/m
3
when sanded according to the test procedures described in this specification. In certain other embodiments, the quantity of dust generated is less than about 15 mg/m
3
, more preferably less than about 10 mg/m
3
, and most preferably less than about 5 mg/m
3
.
In one aspect, the present invention provides a sandable wall repair compound composition comprising filler material, binder material, and dust reducing additive means for reducing the quantity of dust generated by the compound when the compound is sanded.
Suitable dust reducing additives include oils, such as mineral oils, vegetable oils and animal oils, surfactants, oleoresinous mixtures, pitch, solvents, paraffins, waxes, including natural and synthetic wax, glycols, and other petroleum derivatives. Other materials which do not fit within the above categories, such as molasses, may also effectively reduce the quantity of dust generated by a wall repair compound.
The wall repair compound formulations include a conventional filler material and a binder material, such as a resin. The wall repair compound may also include a surfactant and a thickening agent. Prior to hardening, the wall repair compound preferably includes a sufficient amount of water to form a mud-like spreadable material which can be applied to the wall surface. The present invention also provides a dust reducing additive which can be admixed with conventional joint compounds to reduce the quantity of dust generated by the conventional compounds during sanding. The dust reducing additive can be used with both drying type (i.e. ready mixed) or setting type joint compounds.
The present invention also provides a joint compound having good tensile strength, sandability, trowelability, plasticity, water retention, cohesiveness, viscosity stability, good hardening properties, good adhesion to metal and PVC, good paint adhesion,
3M Innovative Properties Company
Green Anthony J.
Patchett David B.
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