Patent Grant
8580055
Gypsum-based building products are commonly used in construction. A gypsum panel made of such materials can be fire retardant and can be used in the construction of walls of almost any shape. It is used primarily as an interior wall and ceiling product. Gypsum has sound-deadening properties, and is relatively easily patched or replaced if it becomes damaged. There are a variety of decorative finishes that can be applied to a gypsum panel, including paint and wallpaper. Given all of these advantages, it is still a relatively inexpensive building material.
One reason for the reasonable cost of gypsum panels is that they are manufactured by a process that is rapid and efficient. In an exemplary process, a slurry, including calcium sulfate hemihydrate and water, is used to form the core, and is continuously deposited on a paper cover sheet moving beneath a mixer. A second paper cover sheet is applied there over and the resultant assembly is formed into the shape of a panel. Calcium sulfate hemihydrate reacts with a sufficient amount of the water to convert the hemihydrate into a matrix of interlocking calcium sulfate dihydrate crystals, causing it to set and to become firm. The continuous strip thus formed is conveyed on a belt until the calcined gypsum is set, and the strip is thereafter cut to form boards of desired length, which boards are conveyed through a drying kiln to remove excess moisture. Since each of these steps takes only minutes, small changes in any of the process steps can lead to gross inefficiencies in the manufacturing process.
The amount of water added to form the slurry is in excess of that needed to complete the hydration reactions. Some of the water that is added to the gypsum slurry is used to hydrate the calcined gypsum, also known as calcium sulfate hemihydrate, to form an interlocking matrix of calcium sulfate dihydrate crystals. Excess water gives the slurry sufficient fluidity to flow out of the mixer and into the facing material to be shaped to an appropriate width and thickness. While the product is wet, it is very heavy to move and relatively fragile. The excess water is removed from the board by evaporation. If the excess water were allowed to evaporate at room temperature, it would take a great deal of space to stack and store the gypsum panel while it was allowed to air dry or to have a conveyor long enough to provide adequate drying time. Until the board is set and relatively dry, it is somewhat fragile, so it must be protected from being crushed or damaged.
In order to dry the boards in a relatively short period of time, the gypsum panel product is usually dried by evaporating the extra water at elevated temperatures, for example, in an oven or kiln. It is relatively expensive to build and operate the kiln at elevated temperatures, particularly when the cost of fossil fuel rises. A reduction in production costs could be realized by reducing the amount of excess water present in set gypsum boards that is later removed by evaporation. In particular, methods of preparing gypsum wallboard which help to provide a reduced slurry viscosity and thus a reduced water content would enable a reduction in drying time and/or heat, and thus a reduction in the use of energy in manufacture.
Accordingly, there is a need in the art for compositions and methods which reduce energy costs associated with the manufacture of gypsum formulations, as well as a way to maintain and/or reduce energy costs associated with the manufacture of water-resistant gypsum formulations, while maintaining desirable formulation properties.
The present invention relates to additives to improve stucco rheology, resulting in less energy demand for gypsum-based building products, such as gypsum wallboards.
In one embodiment of the present invention, an additive comprising a blend of one or more wetting agents, surfactants and/or dispersants can be used as part of a wax emulsion or independently as a standalone additive to modify the stucco slurry rheology in gypsum construction product manufacture, in order to improve the energy demands of the gypsum construction product manufacturing process. In that wax emulsion, the at least one wax may comprise, but is not limited to, one or more of montan wax, paraffin wax, carnauba wax, a Fischer-Tropsch wax, and derivatives and blends thereof. The wax emulsion can include a paraffinic hydrocarbon, which may be a paraffin wax. The wax emulsion can also include at least one stabilizer, such as polyvinyl alcohol, which may be a hydrolyzed polyvinyl alcohol. Optionally, the wax emulsion can also include saponifying agents such as alkali metal hydroxides. One example of such alkali metal hydroxides is potassium hydroxide. The dispersant can be one which contains sulfur or a sulfur-containing group such as lignosulfonic acid, naphthalene sulfonic acid, and combinations and salts thereof.
In another embodiment, mixtures may be made to be wax-free or modified to form an emulsion. The wax-free mixture comprises water; one or more dispersants; and one or more wetting agents, and/or surfactant. Dispersants in this embodiment may be ones which contain sulfur or a sulfur-containing group such as lignosulfonic acid, naphthalene sulfonic acid, and combinations and salts thereof.
In one embodiment, the non-wax or independent additive comprises about 10 percent to about 50 percent by weight of water; about 1 percent to about 30 percent by weight of one or more wetting agents or surfactants; and about 20 percent to about 75 percent by weight of one or more of a dispersant, wherein the dispersant may be lignosulfonic acid, naphthalene sulfonic acid, and combinations and salts thereof.
In a further embodiment, the non-wax or independent additive comprises about 15 percent to about 30 percent by weight of water; about 5 percent to about 15 percent by weight of one or more wetting agents or surfactants; and about 50 percent to about 75 percent by weight of one or more dispersants, wherein the dispersant may be lignosulfonic acid, naphthalene sulfonic acid, and combinations and salts thereof. Adjustments to pH can be made with alkali metal hydroxides if needed.
In one embodiment, the wax emulsion noted above comprises about 35 percent to about 80 percent by weight of water; about 15 percent to about 60 percent by weight of a blend of paraffinic hydrocarbon and the at least one wax; about 1.0 percent to about 5.0 percent by weight of the dispersant, wherein the dispersant may be lignosulfonic acid, naphthalene sulfonic acid, and combinations and salts thereof; about 0.1 percent to about 10 percent by weight of one or more wetting agents or surfactants; and about 0 percent to about 5 percent by weight of at least one stabilizer.
In a further embodiment, the wax emulsion comprises about 50 percent to about 65 percent by weight of water; about 20 percent to about 40 percent by weight of the blend of paraffinic hydrocarbon and at least one wax; about 2.0 percent to about 4.0 percent by weight of the dispersant; about 0.25 percent to about 2.5 percent by weight of one or more wetting agents or surfactants; and about 0 to about 10 percent by weight of the at least one stabilizer.
The wetting agents and/or surfactants can be chosen from materials including: fatty alcohols, ethoxylated alcohols, vegetable oil ethoxylates, alkyl phenol ethoxylates, monobasic esters, silicone polyethers, alkylated pyrrolidones, asphaltene dispersants, acetylenic diols, EO/PO block copolymers, polyethylene glycols, polyethylene glycol (PEG) esters, alkylbenzenesulfonic acids, alkylbenzene sulfonate, sodium, potassium and amine salts, sodium alkylated diphenyl oxide disulfonates, amine oxides, amine ethoxylates, alkanolamides, sodium and ammonium aromatic sulfonates, alcohol sulfates, alcohol ether sulfates, ethoxylated alcohol phosphate esters, ethoxylated alcohol sulfates, sodium alkyl sulfonates, sodium alpha sulfo methyl esters, sodium dialkyl sulfosuccinates, and fluoroaliphatic surfactants. The wetting agents and/or surfactants can be used independently or in blends of more than one material. It has been found that anionic wetting agents and surfactants did not provide favorable results, likely due to the nature of the hard water and other ions present in the gypsum wallboard system, and also because anionic surfactants tend to generate excessive foam. Wetting agents and/or surfactants are needed that are foam neutral. Some foaming is necessary but excessive foam can lead to inferior wallboard characteristics.
The silicone polyether compound additive in the above embodiments may be one of the following (commercially available from Siltech Corporation): silicone polyethers (Silsurf™ products); phosphated silicone polyether ethers (Silphos™ products); silicone polyether quaternary compounds (Silquat™ products); silicone polyether alkyl polyethers (Silube™ products); silicone defoamers (Siltech™ products); fluorinated silicones (Fluorosil™ products); or silicone pre-polymers (Silmer™ products). In addition, the additive may be one of the following (commercially available from Momentive Performance Materials): silicone copolymer/polyalkylene oxide blends or polyalkyleneoxide modified polydimethylsiloxanes (Silwet™ products, including Hydrostable™ products). The additive may also be an alternative modified polysiloxane (Silbyk™ products, commercially available from Byk Additives and Instruments).
The pyrrolidone-based compound additive in the above embodiments may be a 1-octyl-2-pyrrolidone (Surfadone™ LP100, commercially available from International Specialty Products (ISP)) or 1-dodecyl-2-pyrrolidone (Surfadone LP300, commercially available from ISP); other examples are found in U.S. Pat. No. 7,264,885, incorporated by reference herein.
The ethoxylated alcohol compound additive in the above embodiments may be chosen from a range of either EO content and/or alkyl chain length. The alcohol component can range from C8 to C18 and the EO content can range from 1 mole to 50 moles. Selections such as a one-mol EO C12-13 alcohol (such as Tomadol™ 23-1, commercially available from Air Products and Chemicals, Inc.) or a thirteen-mol EO C14-15 alcohol (such as Tomadol 45-13, commercially available from Air Products and Chemicals, Inc.) provide interesting results. It should be noted that the former has a hydrophile-lipophile balance (HLB) value of 3.7 and the later has a HLB value of 14.4. The gypsum wallboard systems do not follow traditional wetting agent and/or surfactant guidelines of using HLB values to determine system viability. In fact, surfactants with HLB values ranging from about 3 to 16 can be used in combination with the dispersant and stabilizer.
Powerful wetting agents such as acetylenic diols (such as Surfynol™ 104, commercially available from Air Products and Chemicals, Inc.) are also useful, however these are also powerful defoamers. Defoaming agents can cause severe issues in the gypsum wallboard manufacturing process by coalescing the intentional air bubbles created in the wallboard to reduce weight. When these air bubbles are coalesced, they can form blisters on the surface of the wallboard during manufacture or even cause the paper or other scrim to debond from the gypsum core.
The present invention also includes a settable gypsum composition suitable for forming a gypsum product. The settable gypsum composition comprises: a) a gypsum slurry and b) an additive comprising a blend of one or more wetting agents and/or surfactants, wherein a ratio of the wetting agent/surfactant blend to gypsum in the gypsum slurry is about 0.001:100 to about 10.0:100 by weight. The settable gypsum composition may further comprise a dispersant.
In another embodiment, the settable gypsum composition comprises: a) a gypsum slurry and b) a mixture comprising water, a dispersant, and an additive comprising a blend of one or more wetting agents and/or surfactants, wherein a ratio of the wetting agent/surfactant blend to gypsum in the gypsum slurry is about 0.001:100 to about 10.0:100 by weight. The mixture for the settable gypsum composition can be a wax emulsion comprising at least one wax, a dispersant and an additive comprising a blend of one or more wetting agents and/or surfactants provided in the ratios mentioned above. The gypsum product formed with the settable gypsum composition that includes the wax emulsion is water-resistant.
The present invention also includes an improved method for making gypsum wallboards. The method comprises preparing a gypsum slurry, and adding a mixture to the gypsum slurry comprising water, a dispersant, and an additive comprising a blend of one or more wetting agents and/or surfactants, whereby the viscosity of the gypsum slurry is lowered to a desired level that minimizes the use of water to control the viscosity, using the gypsum slurry to form a structure and drying the structure to form a gypsum wallboard. In other words, the addition of the mixture in the gypsum slurry results in a gypsum slurry that has the same viscosity with lower water content, when compared to the conventional gypsum slurry formulation. Thus, the interim structures formed with such gypsum slurry will have lower water content, and thus less water to be removed during the subsequent drying process to form the final gypsum-based product. In another embodiment, the mixture added to the gypsum slurry can be a wax emulsion comprising at least one wax, water, a dispersant, a blend of one or more wetting agents and/or surfactants, and the resulting gypsum wallboard is water-resistant.
A further improvement includes a method of making gypsum wallboard, wherein the method comprises preparing a gypsum slurry, using the gypsum slurry to form a structure and drying the structure to form a gypsum wallboard, and providing to the gypsum slurry an additive comprising the wetting agents and/or surfactants noted above. In one embodiment, this improvement further comprises providing a dispersant to the slurry.
The provision of the additive comprising a blend of one or more wetting agents and/or surfactants according to the present invention results in an improved manufacturing process for gypsum-based building products. The additive acts as a surfactant for the gypsum crystals in the gypsum slurry and lowers the water content of the gypsum slurry, while maintaining the desired viscosity conventionally achieved with higher water content in the gypsum slurry. This reduces the amount of water which needs to be removed during the subsequent drying process in forming the final gypsum-based building product, and thus reduces the amount of energy required during the manufacturing process. This translates into cost savings for the manufacturer of the building products.
Thus, the provision of the additive provides an improved, more energy efficient manufacturing method for the manufacture of gypsum-based building products, such as gypsum wallboards.
Described herein are various wax emulsions and mixtures which may be made to be wax-free or modified to form wax emulsions, methods for using such emulsions and mixtures, building product formulations including such emulsions and mixtures, improvements to the manufacture of such products using such emulsions and mixtures, gypsum slurry compositions and methods using such compositions. The emulsions, mixtures and compositions described herein are able to reduce energy costs and provide manufacturing cost savings by providing improved gypsum slurry viscosity, which reduces water content in the gypsum slurry generally so that the amount of heat required during the drying process is reduced. In addition, for water-resistant building products using the wax emulsions and mixtures described herein, the emulsions and mixtures are able to provide equivalent percentage water absorption while allowing for energy reduction in the manufacture of such building products by reducing drying times and/or by reducing heat.
The present invention includes both a wax emulsion for use in manufacturing gypsum-based building products that can provide water-resistance to gypsum-based building products, and a mixture which may optionally be modified to be emulsions, such that waxes and other wax-related additives are optional for such mixtures. In either case, the use of the wax emulsion and the mixture lowers the water content of the gypsum slurry while maintaining the desired viscosity, thus resulting in a more energy efficient manufacturing process.
As used herein, an “emulsion” means an emulsified formulation of components, preferably including at least one wax. A “mixture,” as that term is used herein, includes any combination of components in a formulation, whether in solution, dispersion, suspension or other liquefied form of combined ingredients. Mixtures herein may be modified with emulsification components and made into emulsions.
In a wax-based emulsion, according to a preferred embodiment, is an aqueous emulsion which includes water, at least one wax, a dispersant, and a blend of one or more wetting agents and/or surfactants. The water for use in the emulsion may be any water suitable for forming wax emulsions for building products, and can be standard tap water, distilled water, or the like. Generally, the water content of the aqueous emulsion suitable for gypsum-based building products such as gypsum wall boards is about 35% to about 80%, preferably about 50% to about 65%, by weight, of the emulsion. For any given application, however, the water content may vary depending on the desired end properties.
The wax-based emulsions preferably include a paraffinic hydrocarbon, which is most preferably a paraffin wax. Such a paraffin wax may be any suitable paraffin-based wax that functions compatibly with other waxes and components in the resulting wax emulsion, and further preferably has a melting point of about 40° C. to about 80° C., which properties are favorable for water-resistant wallboard manufacture. Other paraffinic hydrocarbons or paraffinic waxes may be used as well.
As defined herein, the at least one wax may include paraffin wax as well as other waxes known in the art, or to be developed for use in water-resistant wallboard and various wax substitute components used in such a gypsum wallboard formulation. That is, one skilled in the art would understand that the at least one wax component may include materials that substitute functionally for or otherwise satisfy the function of the wax material in the wax emulsions. Some examples of such substitute materials are synthetic polymers, fatty acid derivatives and the like that are modified to perform as waxes in such a formulation, specific siloxanes (e.g., polymethylhydrosiloxane (PMHS)), any other wax substitute known or to be developed in the art, and derivatives and combinations of such materials.
Examples of waxes which may be used herein include natural montan wax, bleached or refined montan wax, carnauba wax, bees wax, scale wax, slack wax, petroleum waxes, polyethylene wax, soybean wax, corn wax, cottonseed wax, rapeseed wax, canola wax, sunflower wax, palm wax, palm kernel wax, coconut wax, cranberry wax, linseed wax and peanut wax. Other waxes which may be used include synthetic waxes, such as Fischer-Tropsch wax and mixtures of synthetic wax acids and synthetic wax esters. It should also be understood that derivatized versions of such waxes, to include various COOH or OH groups for performance, oxidized waxes, or combinations of such waxes (whether by blend or by polymerized functionalizing of the base polymer, as in a modified Fischer-Tropsch wax) can also be used. In one preferred embodiment, blends of saponifiable and non-saponifiable waxes, such as blends of paraffin wax with montan, carnauba and/or Fischer-Tropsch waxes are used.
It should be understood that while certain waxes as described herein are preferred, such as montan, carnauba and Fischer-Tropsch waxes, if the benefits of the additives herein are otherwise achieved within a wax-substituted product or other wax combination useful for water-resistant wallboard, the wax combination is contemplated as being within the scope of the invention herein, and the wax selections should not be seen as limiting the scope of the invention. For example, siloxanes (with and without catalytic or other additives) are known for use as water-resistant wax formulation substitutes for preparing water-resistant gypsum wallboard as described in U.S. Patent Publication No. 2006-0035112-A1, incorporated herein in relevant part with respect to the use of various siloxane formulations in preparing gypsum wallboard.
The at least one wax in the wax emulsion should preferably make up about 15 percent to about 60 weight percent of the wax emulsion, and more preferably about 20 percent to about 40 percent by weight. If a blend of a paraffinic hydrocarbon, such as a paraffin wax and another wax or waxes is used, it is preferred that the blend include about 99:1 to about 1:99 paraffin to the other wax(es) in the blend, more preferably about 80:20 to about 20:80, still more preferably about 70:30 to about 30:70, and most preferably 60:40 to 40:60. Further, the wax(es) (including substitutes) are most preferably included in such an emulsion in a total amount of about 1 part to about 200 parts, preferably about 1 part to about 50 parts, by weight, per 100 parts of the paraffinic hydrocarbon. Most preferred blends in the above-noted compositional ranges include paraffin wax and montan wax.
The wax emulsion can also include at least one stabilizer. The stabilizer(s) may be any stabilizer known to be used or to be developed for such use in water-resistant wax emulsion formulations. A preferred stabilizer herein is polyvinyl alcohol; preferably one that is prepared by hydrolysis of polyvinyl acetate and that is preferably a substantially completely or fully hydrolyzed polyvinyl alcohol. Most preferably it is at least about 90% hydrolyzed polyvinyl alcohol, and more preferably 97-98 to 100% hydrolyzed polyvinyl alcohol. Such polyvinyl alcohols are preferably used so as to be soluble in water at elevated temperatures of about 60° C. to about 95° C., but are insoluble in cold water. Stabilizer(s) are optional and, if used, can comprise from 0 up to about 30 percent by weight of the wax emulsion and preferably make up about 1 percent to about 30 percent by weight of the wax emulsion. In other embodiments, the stabilizers may be present in an amount of about 0 percent to about 20 percent by weight of the wax-based emulsion, more preferably about 0 to about 10 percent by weight and most preferably about 0.01 percent to about 8 percent by weight thereof. If polyvinyl alcohol is used as the stabilizer in combination with a wax blend based on a paraffin wax, it may be present in an amount of about 0 to about 50 parts, preferably about 1 part to about 20 parts, by weight, per 100 parts of the paraffinic wax. The polyvinyl alcohol can provide adhesive characteristics, as well as enhancing the water resistance.
In other embodiments, saponifiers or saponifying agents also can be used in the wax emulsions herein. Suitable saponifiers include any of a variety of alkali metal hydroxides and similar materials such as potassium hydroxide, ammonium hydroxide, sodium hydroxide, magnesium sulfate and the like. Saponifiers may be present in an amount of no greater than about 5 weight percent of the emulsion, preferably no greater than about 2 weight percent and most preferably about 0.01 weight percent to about 1 weight percent.
Dispersants are also used in the wax emulsion or the mixture formulations and are preferred for use in combination with a blend of one or more wetting agents and/or surfactant additives herein. Preferred dispersants include, but are not limited to those having a sulfur or a sulfur-containing group(s) in the compound such as sulfonic acids (R—S(═O)2—OH) and their salts, wherein the R groups may be otherwise functionalized with hydroxyl, carboxyl or other useful bonding groups. Preferred are higher molecular weight sulfonic acid compounds such as lignosulfonic acid, naphthalene sulfonic acid, the sulfonate salts of these acids and derivatized or functionalized versions of these materials. In addition, other dispersants known in the art for use in wax emulsions, such as magnesium sulfate; ammonium hepta molybdate/starch combinations; non-ionic surfactants, anionic surfactants, zwitterionic surfactants and mixtures thereof; and alkyl quaternary ammonium montmorillonite clay as well as other known dispersants may be used. Dispersants are preferably present in an amount of about 1.0 percent by weight to about 5.0 percent by weight of the wax emulsion, and preferably about 2.0 percent to about 4.0 percent by weight of the wax emulsion.
The silicone polyether compound additive in the above embodiments may be one of the following (commercially available from Siltech Corporation): silicone polyethers (Silsurf™ products); phosphated silicone polyether ethers (Silphos™ products); silicone polyether quaternary compounds (Silquat™ products); silicone polyether alkyl polyethers (Silube™ products); silicone defoamers (Siltech™ products); fluorinated silicones (Fluorosil™ products); or silicone pre-polymers (Silmer™ products).
In addition, the additive may be one of the following (commercially available from Momentive Performance Materials): silicone copolymer/polyalkylene oxide blends or polyalkyleneoxide modified polydimethylsiloxanes (Silwet™ products, including Hydrostable™ products). The additive may also be an alternative modified polysiloxane (Silbyk™ products, commercially available from Byk Additives and Instruments).
The pyrrolidone-based compound additive in the above embodiments may be a 1-octyl-2-pyrrolidone (Surfadone™ LP100, commercially available from International Specialty Products (ISP)) or 1-dodecyl-2-pyrrolidone (Surfadone LP300, commercially available from ISP); other examples are found in U.S. Pat. No. 7,264,885, incorporated by reference herein.
The ethoxylated alcohol compound additive in the above embodiments may be chosen from a range of either EO content and/or alkyl chain length. Selections such as a one-mol EO C12-13 alcohol (such as Tomadol™ 23-1, commercially available from Air Products and Chemicals, Inc.) or a thirteen-mol EO C14-15 alcohol (such as Tomadol 45-13, commercially available from Air Products and Chemicals, Inc.) provide interesting results. It should be noted that the former has an HLB value of 3.7 and the latter has an HLB value of 14.4. The gypsum wallboard systems do not follow traditional wetting agent guidelines of using HLB values to determine system viability.
Powerful wetting agents such as acetylenic diols (such as Surfynol™ 104, commercially available from Air Products and Chemicals, Inc.) are also useful, however these are also powerful defoamers. Defoaming agents can cause severe issues in the gypsum wallboard manufacturing process by coalescing the intentional air bubbles created in the wallboard to reduce weight. When these air bubbles are coalesced, they can form blisters on the surface of the wallboard during manufacturer or even cause the paper or other scrim to debond from the gypsum core.
The blend of one or more wetting agents and/or surfactants preferably is present in the formulation in an amount of about 0.1 weight percent to about 10 weight percent or more of the formulation, and more preferably about 0.25 percent by weight to about 2.5 percent by weight of the wax emulsion formulation.
In one method of manufacture of an aqueous wax emulsion herein, the wax or waxes are each heated to a molten state, and if more than one wax is present, the waxes are then blended together. A hot aqueous solution of the other components, such as stabilizers, for example, polyvinyl alcohol, optional saponifiers, the dispersant(s), the additive and any other components used in the emulsion may then be passed with the hot blend of the waxes through a colloid mill and the resulting emulsion allowed to cool.
Alternatively, a homogenizer may be used instead of a colloid mill. Such homogenizers may be the same general type of equipment used to homogenize milk and other products. In such a method, a mixture of the wax component and the emulsifying components are fed under high pressure (typically about 1500 psi to about 3500 psi) to emulsify the wax(es) and create a smaller particle size than is typically associated with use of a colloid mill. It will be understood to one skilled in the art based upon this disclosure that other manufacturing methods and types of equipment and procedures for preparing the emulsion can be used, as are known or which may be developed in the art. The emulsion of the invention may also readily be reformed by agitation, in the event that emulsified components of the emulsion separate on storage.
Also within the scope of the invention as previously noted are mixtures, in which the at least one wax as defined herein is optional. Such mixtures can be prepared to be “wax-free,” but can optionally be modified and prepared and provided with wax-based materials (or wax substitutes or other water-resistant gypsum additives such as siloxanes as described elsewhere herein) such as to be formed into emulsions. Such mixtures include water, dispersant(s) and at least one of the wetting agents and/or surfactants described hereinabove. Optionally, such mixtures also include one or more stabilizer(s). The water component, dispersant(s), wetting agents and/or surfactants, as well as any stabilizer(s) are the same materials noted above for use in the wax-based emulsions. Optional saponifiers, such as those mentioned hereinabove, may also be used, however, if the mixture is wax-free, such saponifiers would not necessarily function to saponify, but may be useful for adjustment of pH of the mixture.
In one preferred embodiment, such a mixture is prepared including about 10 percent by weight to about 80 percent by weight, more preferably about 15 percent to about 40 percent by weight water; about 5 percent by weight to about 80 percent by weight, more preferably about 40 percent by weight to about 70 percent by weight of dispersant(s) (preferably a lignosulfonic acid or naphthalene sulfonic acid, or salt thereof, combinations of these materials or other known dispersants); about 1.0 percent by weight to about 25 percent by weight or more, more preferably 5.0 percent by weight to about 15.0 percent by weight of a blend of one or more wetting agents and/or surfactants, and optionally about 0 to about 30 percent, more preferably about 0 percent by weight to about 20 percent by weight, most preferably about 0 percent by weight to about 10 percent by weight of a stabilizer(s) (preferably polyvinyl alcohol as described herein). Optionally, other components such as the saponifier(s), pH adjustment additives or various other additives (including waxes) may be added to modify the mixture.
The mixtures in this embodiment, if prepared to be wax-free, may be made by simply combining the components as in the second step of preparing the non-wax phase of the wax-based emulsion using, for example, a colloid mill, homogenizer or a similar mixing mechanism or other method known by those in the art to mix the components.
The present invention also includes settable gypsum formulations which may include any of the wax emulsions or mixtures noted hereinabove or prepared directly using various components of such mixtures as described below. In preparing a gypsum wallboard using the wax emulsions, mixtures and components herein, an aqueous slurry of the gypsum material is prepared in any suitable manner known in the art or to be developed. In an embodiment of the invention, an aqueous wax emulsion or mixture according to the invention is then added to the slurry and mixed with the slurry in proportions to provide about 0.5 part to about 20 parts by weight of solids per 100 parts of gypsum. Alternatively, a gypsum slurry may be formed and a blend of one or more wetting agents and/or surfactants used to modify the stucco slurry viscosity are provided directly to the gypsum slurry without first being mixed with other components. Preferably a dispersant such as those described herein is also added. The amount of dispersant may vary but preferably has a ratio with respect to a blend of one or more wetting agents and/or surfactants used to modify the stucco slurry viscosity to that which is used and described herein if these components are first used in an aqueous mixture and then added.
The base gypsum compositions may be varied in accordance with conventional gypsum formulation requirements in the art of gypsum manufacture. Other ingredients such as foaming agents, other dispersants and set accelerators may be included in the slurry. In addition, it is noted that in preferred embodiments of settable gypsum slurry formulations using the mixtures or emulsions described herein, or direct addition of a blend of one or more wetting agents and/or surfactants, a ratio of about 0.001:100 to about 10.0:100, more preferably about 0.01:100 to about 2.0:100, and most preferred about 0.1:100 to about 1.0:100 by weight, preferably exists between a blend of one or more wetting agents and/or surfactants and the gypsum in the slurry. While this is not required, it contributes to preferred slurry viscosity properties.
In preparing wallboards from such a settable gypsum formulation, the mixture of gypsum slurry and the mixtures, wax emulsions and a blend of one or more wetting agents and/or surfactants or other compounds described herein can be applied to a first sheet of wallboard liner to form a layer of the gypsum mixture thereon. A second sheet of liner is then disposed on top of the deposited layer to form a wallboard assembly or structure in which the first and second sheets are in opposed, facing relationship and have the layer of the gypsum mixture there between.
Alternatively, the gypsum slurry may be prepared directly into a liner-less wallboard structure using manufacturing methods involving press-in-place molding and similar techniques, such that reference to gypsum wallboard herein is not restricted to liner-covered wallboard. However, it should be understood that any manufacturing technique for making wallboard including a settable gypsum formulation is within the scope of the invention described herein, such as for example, wallboard manufactured with glass mats on the exterior surfaces instead of standard liners.
The resulting structure or assembly may then be dried, such as by oven drying to remove excess water not needed for hydration of the gypsum, to leave finished gypsum wallboard. If liners are used, they may be formed of paper or may comprise fiberglass or organic fiber mats as well. Use of the emulsions and mixtures of the invention and/or providing the wetting agents and/or surfactant additives herein to a slurry help to reduce drying time and/or heat, thereby contributing to energy savings in the manufacture of such gypsum wallboards. In forming water-resistant gypsum wallboard, wax-based emulsions herein are preferably used, and for standard wallboard, either the wax-free mixtures or wax-based emulsions may be used.
The invention provides an improvement to prior methods of preparing gypsum wallboard, in that the emulsions and mixtures herein, when prepared and added to the gypsum slurry, or when directly providing to the gypsum slurry a blend of one or more wetting agents and/or surfactants (preferably with a dispersant), help to provide a reduced slurry viscosity and thus reduced water content, and enable a reduction in drying time and/or heat and thus a reduction in the use of energy in manufacture. This method is also an improvement when using wax-based formulations herein in water-resistant gypsum wallboard. Thus, the invention further includes a method to reduce energy use in the manufacture of building products, such as gypsum wallboard, by providing to the formulations used for forming such building products, prior to any drying step(s) in the manufacturing process of these building products, an emulsion or mixture according to the invention as described herein, or the direct addition of one or more wetting agents and/or surfactants, with a preferred dispersant. If a water-resistant gypsum wallboard is being formed, a wax-based emulsion as described herein is preferably used.
The invention will now be described with respect to the following non-limiting examples, below.
Samples 1-70 and 71-114 (below) all were mixed with 31.5 wt % solid lignosulfonate and the remainder was warm water (180-200° F.). All samples were mixed with a lab scale Cowles disperser. Patty size was the resulting measurement of a slump test. The slump test was conducted by mixing the additive blend with 100 g water; 100 g of stucco obtained from a local gypsum wallboard manufacturing plant was added to the water/additive mixture, allowed to soak for 10 seconds and then mixed on a milkshake mixer for 15 seconds. The stucco slurry was then immediately poured into a brass pipe measuring 2 inch diameter by 2 inch tall that was positioned vertically on a piece of Plexiglas®. As soon as the pipe was filled, it was lifted and the resulting slurry patty was measured.
Varying the concentration of the wetting agents and/or surfactants can also lead to changes in performance as shown in Examples 71-94.
Adjusting the ratios of two nonionic wetting agents and/or surfactants can lead to changes in performance as shown in Examples 95-114.
Additional formulations, with particular weight percents of components contained therein, are found in the following examples prepared with the same method as examples 1-114.
The emulsions were formed into patties of about 15 cm in diameter and were evaluated for slurry viscosity, which was tested by pouring the slurry into a Number 4 Ford cup. The elapsed time for the slurry to empty out of the cup was recorded, as well as the resulting patty formed 12 cm under the Ford cup on a glass or Plexiglas surface. The patty was measured after the cup had completely emptied, with the larger the patty, the lower the slurry viscosity.
Further testing is found below (examples 151-358). The preparation and testing for these examples was identical to that found in examples 1-114.
A variety of wax formulations (examples 359-372) were prepared for evaluating wax formulations including the wetting agents and/or surfactants herein. The wax emulsions were prepared by mixing water, a dispersant, potassium hydroxide, and polyvinyl alcohol over a hot plate using an overhead mixer until the polyvinyl alcohol was melted and well dispersed (about 15 minutes with a hot plate set at 135° C. to 145° C.). In a separate container, paraffin and montan wax were melted over a hot plate until both were completely melted. After both the water mixture and the wax mixture were ready, the water mixture was placed into a mixing bowl and a mill was started. After the mill was up to full speed, the hot wax blend was added slowly. The resulting combined components were mixed at high speed for 60 seconds. At the end of 60 seconds, the liquid was transferred to a chilled metal vessel, which was immediately placed in an ice bath while mixing at low speed with an overhead mixer until the resulting emulsion was at room temperature. Samples 359-369 contained 0.41 wt % KOH, 2.36 wt % PVOH, 33.3 wt % paraffin wax, 2.1 wt % montan wax and the additive blend, and the remainder was hot water (180-200° F.) unless otherwise noted. Slumps were tested in the same fashion as examples 1-114 and examples 156-342, except 100 g water, 100 g of stucco and 2.2 g of the wax emulsion (samples 359-369) were used to make the slumps.
While some samples performed somewhat better in terms of water absorption, based on varied component amounts, generally it can be seen that the additives tested provided properties that were comparable, and in many cases better than the control having the comparable wax base component composition, particularly as the water content of the wallboard was decreased. In addition to providing the potential for good water absorption for manufacturing water-resistant gypsum wallboard, the inventive formulations assist in reducing slurry viscosity (increasing patty size) to minimize use of water and help reduce energy use by requiring less energy for drying. This results in overall energy efficiency improvements and cost savings to the manufacturers making water resistant gypsum products.
Not to be bound to a single theory, it is anticipated that to efficiently modify stucco slurry rheology in a gypsum wallboard manufacturing process, an additive blend should contain components that not only provide wetting for the system components, but act in a synergistic fashion with the dispersant(s) to ensure that the gypsum and other additives or components of the wallboard formula are properly and efficiently dispersed in the mixture; i.e., the ability of some wetting agents and/or surfactants to sterically interact with the dispersing agent results in facilitating the stable suspension of the gypsum mixture. In support of this hypothesis, some components such as the ethoxylated alcohols also appear to have a dependence on carbon chain length, with C8-C18 chain lengths performing well depending on the degree of ethoxylation.
Use of the HLB system to differentiate wetting agent and/or surfactant performance does not apply to dispersing gypsum. Surfactants with HLB values ranging between about 3 and 16 can be effective.
A low viscosity additive blend also appears to be beneficial to efficient wetting in the system. As those who are familiar with the art of manufacturing gypsum based construction products would appreciate, any additive blend that is introduced to the wallboard manufacturing process should be compatible with all of the components in that system. For example, any new additives introduced to the system should not include defoamers, otherwise the gypsum wallboard density will be adversely affected and failures such as blisters and blows may form during the manufacturing process. However, some additive blends of wetting agents and/or surfactants may slightly coalesce the foaming system used in the gypsum wallboard manufacturing process, resulting in larger bubbles than expected. This increased “activity” of the foaming system may result in higher mechanical properties of the formed gypsum system. It is interesting to note that when using some wetting agents and/or surfactants that are primarily used to decrease the slurry viscosity, some blends can advantageously modify the foam structure, other blends do not impact the foam structure in any manner, and many blends of wetting agents and/or surfactants modify the foam structure in a negative fashion. Thus, care needs to be taken to utilize additive blends that provide slurry viscosity benefits without adversely affecting foam structure.
It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.
This application claims priority to U.S. provisional application Nos. 61/147,296, filed Jan. 26, 2009, and 61/179,048, filed May 18, 2009.
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