Compositions: coating or plastic – Coating or plastic compositions – Carbohydrate or derivative containing
Reexamination Certificate
2001-05-21
2004-03-30
Brunsman, David (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Carbohydrate or derivative containing
C106S194200, C106S197010, C106S198100
Reexamination Certificate
active
06712897
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention generally relates to pre-blend compositions useful in the production of cementitious compositions and, more specifically, the invention relates to the production of cementitious compounds using a pre-blend composition containing water, a cellulose ether thickener, and a salt.
1. 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 of 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, and 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. Typical thickeners include hydroxyethylcellulose (HEC) and hydroxypropylmethylcellulose (HPMC).
Many joint compounds are of the “drying” or “setting” type. Drying-type joint compounds can 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 (e.g., water evaporates), a dry, relatively hard cementitious material remains. The calcium sulfate dihydrate and calcium carbonate can comprise a substantial portion of what is sometimes referred to as the filler component.
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
preservative
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
One of the factors limiting the rate of joint compound manufacture is the relatively long time necessary to completely disperse and dissolve a water soluble polymer thickener, typically a cellulose ether thickener, in a joint compound mixture. The thickener is treated to reduce the rate of dissolution (“surface treated”) by cross-linking hydroxyl groups on a cellulose ether chain. An aqueous solution of the treated thickener is added to the remaining joint compound ingredients, and thoroughly mixed. As these crosslinked groups are hydrolyzed, the cellulose ether dissolves. Thus, the rate of thickening is controlled by the amount of surface treatment. If the cellulose ether thickener has no surface treatment, it would dissolve immediately upon introduction into the water, and would form lumps or “fish eyes” that are very difficult to break up and disperse. Thus, in the typical process, the thickener is surface treated to achieve a rate of dissolution of about 10 to 15 minutes, so that it is well dispersed prior to thickening.
Likewise, if the thickener is one of the first components added to water in a joint compound manufacturing process, followed by fillers, binders, etc., then it also takes a substantially long time to fully disperse the ingredients to a homogeneous mixture (e.g., at least 30 minutes), and the process requires a substantially higher mechanical energy input because of the high torque required to mix the viscous, thickened mixture.
A mixture of a cellulose ether thickener and water also presents other problems. Cellulose ether solutions in water may be prepared only up to relatively low concentrations (e.g., about 2 wt. % to about 4 wt. %), thus creating a physical problem in storing and transporting relatively large quantities of liquid. As discussed above, cellulose ether solutions have a viscous, adhesive consistency, especially within the upper concentration range, and this property causes the solution to adhere to the walls of containers, to tubes and to pumps, and necessitates a troublesome cleaning of such equipment.
It is also known to use organic solvents to dissolve or suspend cellulose ethers. However, when cellulose ethers are to be used in mortar, concrete, and joint compound mixtures, organic solvents are unsuitable, because they frequently affect the setting characteristics of these mixtures in an undesirable manner.
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 st
Ayambem Amba
Smith Richard E.
Taravella Salvatore
Brunsman David
Howrey Simon Arnold & White , LLP
National Gypsum Properties, LLC.
Nimmo Anthony
LandOfFree
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